Special interest transportation engineering?

Transportation engineering

The engineering of this roundabout in Bristol, England, attempts to make traffic flow free-moving

Transportation engineering or transport engineering is the application of technology and scientific principles to the planning, functional design, operation and management of facilities for any mode of transportation in order to provide for the safe, efficient, rapid, comfortable, convenient, economical, and environmentally compatible movement of people and goods (transport)[citation needed]. It is a sub-discipline of civil engineering.The importance of transportation engineering within the civil engineering profession can be judged by the number of divisions in ASCE (American Society of Civil Engineers) that are directly related to transportation. There are six such divisions (Aerospace; Air Transportation; Highway; Pipeline; Waterway, Port, Coastal and Ocean; and Urban Transportation) representing one-third of the total 18 technical divisions within the ASCE (1987).

transportation engineering outputs

The planning aspects of transportation engineering relate to elements of urban planning, and involve technical forecasting decisions and political factors. Technical forecasting of passenger travel usually involves an urban transportation planning model, requiring the estimation of trip generation (how many trips for what purpose), trip distribution (destination choice, where is the traveler going), mode choice (what mode is being taken), and route assignment (which streets or routes are being used). More sophisticated forecasting can include other aspects of traveler decisions, including auto ownership, trip chaining (the decision to link individual trips together in a tour) and the choice of residential or business location (known as land use forecasting). Passenger trips are the focus of transportation engineering because they often represent the peak of demand on any transportation system.

A review of descriptions of the scope of various committees indicates that while facility planning and design continue to be the core of the transportation engineering field, such areas as operations planning, logistics, network analysis, financing, and policy analysis are also important to civil engineers, particularly to those working in highway and urban transportation. The National Council of Examiners for Engineering and Surveying (NCEES) list online the safety protocols, geometric design requirements, and signal timing.

Transportation engineering, as practiced by civil engineers, primarily involves planning, design, construction, maintenance, and operation of transportation facilities. The facilities support air, highway, railroad, pipeline, water, and even space transportation. The design aspects of transportation engineering include the sizing of transportation facilities (how many lanes or how much capacity the facility has), determining the materials and thickness used in pavement designing the geometry (vertical and horizontal alignment) of the roadway (or track).

Before any planning occurs the Engineer must take what is known as an inventory of the area or if it is appropriate, the previous system in place. This inventory or database must include information on (1)population, (2)land use, (3)economic activity, (4)transportation facilities and services, (5)travel patterns and volumes, (6)laws and ordinances, (7)regional financial resources, (8)community values and expectations. These inventories help the engineer create business models to complete accurate forecasts of the future conditions of the systemReview.

Operations and management involve traffic engineering, so that vehicles move smoothly on the road or track. Older techniques include signs, signals, markings, and tolling. Newer technologies involve intelligent transportation systems, including advanced traveler information systems (such as variable message signs), advanced traffic control systems (such as ramp meters), and vehicle infrastructure integration. Human factors are an aspect of transportation engineering, particularly concerning driver-vehicle interface and user interface of road signs, signals, and markings.

Contents 

1 Highway engineering

2 Railroad engineering

3 Port and harbor engineering

4 Airport engineering

5 Professional Societies

6 See also

7 References

8 External links

Highway engineering

Engineers in this specialization

Handle the planning, design, construction, and operation of highways, roads, and other vehicular facilities as well as their related bicycle and pedestrian realms.

Estimate the transportation needs of the public and then secure the funding for the project.

Analyze locations of high traffic volumes and high collisions for safety and capacity.

Use civil engineering principles to improve the transportation system.

Utilizes the three design controls which are the drivers, the vehicles, and the roadways themselves.

Railroad engineering

Main article: Railway systems engineering

Railway engineers handle the design, construction, and operation of railroads and mass transit systems that use a fixed guideway (such as light rail or even monorails). Typical tasks would include determining horizontal and vertical alignment design, station location and design, and construction cost estimating. Railroad engineers can also move into the specialized field of train dispatching which focuses on train movement control.

Railway engineers also work to build a cleaner and safer transportation network by reinvesting and revitalizing the rail system to meet future demands. In the United States, railway engineers work with elected officials in Washington, D.C. on rail transportation issues to make sure that the rail system meets the country's transportation needs.

Port and harbor engineering

Port and harbor engineers handle the design, construction, and operation of ports, harbors, canals, and other maritime facilities. This is not to be confused with marine engineering.

Airport engineering

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Airport engineers design and construct airports. Airport engineers must account for the impacts and demands of aircraft in their design of airport facilities. These engineers must use the analysis of predominant wind direction to determine runway orientation, determine the size of runway border and safety areas, different wing tip to wing tip clearances for all gates and must designate the clear zones in the entire port.

Professional societies

Young Professionals in Transportation (YPT) 

Institute of Transportation Engineers (ITE) 

American Society for Highway Engineering (ASHE) 

American Society of Civil Engineers (ASCE) 

The American Association of State Highway and Transportation Officials (AASHTO)

Eastern Asia Society for Transportation Studies (EASTS)

Merits of Management engineering?

Engineering management

Ron Diftler (left), NASA Robonaut manager assisting in a Robonaut familiarization training session in the Space Environment Simulation Laboratory at NASA's Johnson Space Center.

Engineering management is a discipline of management in engineering fields.

Engineering management is a career that brings together the technological problem-solving savvy of engineering and the organizational, administrative, and planning abilities of management in order to oversee complex enterprises from conception to completion. A Master of Engineering Management (MEM) is sometimes compared to a Master of Business Administration (MBA) for professionals seeking a graduate degree as a qualifying credential for a career in engineering management.

Areas

Operations management, operations research, and supply chain management

Operations management is concerned with designing and controlling the process of production and redesigning business operations in the production of goods or services. Operations research deals with quantitative models of complex operations and uses these models to support decision-making in any sector of industry or public services. Supply chain management is the process of planning, implementing and managing the flow of goods, services and related information from the point of origin to the point of consumption.

Management of technology

The Management of Technology (MOT) theme builds on the foundation of management topics in accounting, finance, economics, organizational behavior and organizational design. Courses in this theme deal with operational and organizational issues related to managing innovation and technological change.

New product development and product engineering

New product development (NPD) is the complete process of bringing a new product to market. Product engineering refers to the process of designing and developing a device, assembly, or system such that it be produced as an item for sale through some production manufacturing process. Product engineering usually entails activity dealing with issues of cost, producibility, quality, performance, reliability, serviceability, intended lifespan and user features. Design for manufacturability (also sometimes known as design for manufacturing or DFM) is the general engineering art of designing products in such a way that they are easy to manufacture.

Systems engineering

Systems engineering is an interdisciplinary field of engineering and engineering management that focuses on how to design and manage complex systems over their life cycles.

Education

Engineering management programs typically include instruction in accounting, economics, finance, project management, systems engineering, mathematical modeling and optimization, management information systems, quality control & six sigma, operations management, operations research, human resources management, industrial psychology, safety and health.

There are many options for entering into engineering management, albeit that the foundation requirement is an engineering degree (or other computer science, mathematics or science degree) and a business degree.

Under graduate degrees

Although most engineering management programs are geared for graduate studies, there are a few elite institutions that teach EM at the undergraduate level. Some of the ones that are accredited and/or recognized by ASEM include: West Point (United States Military Academy), Norwich University, New York Institute of Technology, Stevens Institute of Technology, Illinois Institute of Technology, Rensselaer Polytechnic Institute, George Washington University, Arizona State University, Missouri University of Science and Technology. Graduates of these programs regularly command nearly $65,000 their first year out of school.

Outside the USA, Istanbul Technical University Management Engineering Department offers an elite undergraduate degree in Management Engineering, attracting top students. The University of Waterloo offers a 4-year undergraduate degree (5 years including co-op education) in the field of Management Engineering. This is the first program of its kind in Canada. In Peru, Pacifico University offers a 5-year undergraduate degree in this field, the first program in this country.

Graduate degrees

Many universities offer Master of Engineering Management degrees. Missouri S&T is credited with awarding the first Ph.D. in Engineering Management in 1984. The National Institute of Industrial Engineering based in Mumbai has been awarding degrees in the field of Post Graduate Diploma in Industrial Engineering since 1973 and the Fellowship (Doctoral) degrees have been awarded since 2008. Massachusetts Institute of Technology offers a Master in System Design and Management, which is a member of the Consortium of Engineering Management.

Students in the University of Kansas' Engineering Management Program are practicing professionals employed by over 100 businesses, manufacturing, government or consulting firms. There are over 200 actively enrolled students in the program and approximately 500 alumni.

Istanbul Technical University Management Engineering Department offers a graduate degree, and a Ph.D. degree in Management Engineering.

According to the American Society for Engineering Education (ASEE) PRISM Magazine (March 2008) the largest Master's of Engineering Management (MEM) programs (in terms of degrees awarded for 2005 -2006) are shown in the following chart.

Largest MEM Programs.jpg

Consulting

As engineering firms are usually small partnerships, they cannot afford in-house management, therefore giving rise to the need for engineering management consultancy. It involves providing management consulting advice that is specific to engineering. Indifferent from the traditional focus of the, A T Kearney, Boston Consulting Group and McKinsey, science and engineering requires a particularly holistic approach involving art and science. There are many branches of engineering management consultancy (commerce), including law, accounting, human resources, marketing, politics, economics, finance, public affairs, and communication. Commonly, engineering management consultants are also used when firms require special technical knowledge, though many prefer to use engineering educational consultants for such a task, to upgrade organizational knowledge and in able to keep the intellectual property confidential. Though many firms opt to use traditional management consulting firms, many lack the know-how to tailor the traditional theories to accommodate professional engineers and other technical workers.

Engineering management consulting is concerned with the development, improvement, implementation and evaluation of integrated systems of people, money, knowledge, information, equipment, energy, materials and/or processes. Consultants strive to improve upon existing processes, products or systems. Engineering management consulting draws upon the principles and methods of engineering analysis and synthesis, as well as the mathematical, physical and social sciences together with the principles and methods of engineering design to specify, predict, and evaluate the results to be obtained from such systems or processes. Engineering management consulting puts a focus on the social impact of the product, process or system that is being analyzed.

Examples of where engineering management consulting might be used include designing new product development process, or an assembly workstation, strategizing for various operational logistics, consulting as an efficiency expert, developing a new financial algorithm or loan system for a bank, streamlining operation and emergency room location or usage in a hospital, planning complex distribution schemes for materials or products (referred to as Supply Chain Management), and shortening lines (or queues) at a bank, hospital, or a theme park. Management engineering consultants typically use computer simulation (especially discrete event simulation), along with extensive mathematical tools and modeling and computational methods for system analysis, evaluation, and optimization.

Professional organizations

There are a number of societies and organizations dedicated to the field of engineering management. One of the largest societies is a division of IEEE, the Engineering Management Society, which regularly publishes a trade magazine. Another prominent professional organization in the field is the American Society for Engineering Management (ASEM), which was founded in 1979 by a group of 20 engineering managers from industry.[14] ASEM currently certifies engineering managers (two levels) via the Associate Engineering Manager (AEM) or Professional Engineering Manager (PEM) certification exam. The Master of Engineering Management Programs Consortium is a newly formed consortium of prominent universities intended to raise the value and visibility of the MEM degree. Also, engineering management university programs have the possibility of being accredited by ABET, ATMAE, or ASEM. In Canada, the Canadian Society for Engineering Management (CSEM) is a constituent society of the Engineering Institute of Canada (EIC), Canada's oldest learned engineering society.

Electrical network analysis using different methods?

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A network, in the context of electronics, is a collection of interconnected components. Network analysis is the process of finding the voltages across, and the currents through, every component in the network. There are many different techniques for calculating these values. However, for the most part, the applied technique assumes that the components of the network are all linear. The methods described in this article are only applicable to linear network analysis, except where explicitly stated.

Definitions

Component A device with two or more terminals into which, or out of which, current may flow.

Node A point at which terminals of more than two components are joined. A conductor with a substantially zero resistance is considered to be a node for the purpose of analysis.

Branch The component(s) joining two nodes.

Mesh A group of branches within a network joined so as to form a complete loop such that there is no other loop inside it .

Port Two terminals where the current into one is identical to the current out of the other.

Circuit A current from one terminal of a generator, through load component(s) and back into the other terminal. A circuit is, in this sense, a one-port network and is a trivial case to analyse. If there is any connection to any other circuits then a non-trivial network has been formed and at least two ports must exist. Often, "circuit" and "network" are used interchangeably, but many analysts reserve "network" to mean an idealised model consisting of ideal components.

Transfer function The relationship of the currents and/or voltages between two ports. Most often, an input port and an output port are discussed and the transfer function is described as gain or attenuation.

Component transfer function For a two-terminal component (i.e. one-port component), the current and voltage are taken as the input and output and the transfer function will have units of impedance or admittance (it is usually a matter of arbitrary convenience whether voltage or current is considered the input). A three (or more) terminal component effectively has two (or more) ports and the transfer function cannot be expressed as a single impedance. The usual approach is to express the transfer function as a matrix of parameters. These parameters can be impedances, but there is a large number of other approaches (see two-port network).

Equivalent circuits

A useful procedure in network analysis is to simplify the network by reducing the number of components. This can be done by replacing the actual components with other notional components that have the same effect. A particular technique might directly reduce the number of components, for instance by combining impedances in series. On the other hand, it might merely change the form into one in which the components can be reduced in a later operation. For instance, one might transform a voltage generator into a current generator using Norton's theorem in order to be able to later combine the internal resistance of the generator with a parallel impedance load.

equivalent circuits

A resistive circuit is a circuit containing only resistors, ideal current sources, and ideal voltage sources. If the sources are constant (DC) sources, the result is a DC circuit. Analysis of a circuit consists of solving for the voltages and currents present in the circuit. The solution principles outlined here also apply to phasor analysis of AC circuits.

Two circuits are said to be equivalent with respect to a pair of terminals if the voltage across the terminals and current through the terminals for one network have the same relationship as the voltage and current at the terminals of the other network.

Nodal analysis

1. Label all nodes in the circuit. Arbitrarily select any node as reference.

2. Define a voltage variable from every remaining node to the reference. These voltage variables must be defined as voltage rises with respect to the reference node.

3. Write a KCL equation for every node except the reference.

4. Solve the resulting system of equations.

Mesh analysis

Mesh — a loop that does not contain an inner loop.

1. Count the number of “window panes” in the circuit. Assign a mesh current to each window pane.

2. Write a KVL equation for every mesh whose current is unknown.

3. Solve the resulting equations

Superposition

In this method, the effect of each generator in turn is calculated. All the generators other than the one being considered are removed and either short-circuited in the case of voltage generators or open-circuited in the case of current generators. The total current through or the total voltage across a particular branch is then calculated by summing all the individual currents or voltages.

There is an underlying assumption to this method that the total current or voltage is a linear superposition of its parts. Therefore, the method cannot be used if non-linear components are present. Note that mesh analysis and node analysis also implicitly use superposition so these too, are only applicable to linear circuits. Superposition cannot be used to find total power consumed by elements even in linear circuits. Power varies according to the square of total voltage or current and the square of the sum is not generally equal to the sum of the squares.

Choice of method

Choice of method is to some extent a matter of taste. If the network is particularly simple or only a specific current or voltage is required then ad-hoc application of some simple equivalent circuits may yield the answer without recourse to the more systematic methods.

Nodal analysis

 The nuber of voltage variables, and hence simultaneous equations to solve, equals the number of nodes minus one. Every voltage source connected to the reference node reduces the number of unknowns and equations by one.

Mesh analysis

 The number of current variables, and hence simultaneous equations to solve, equals the number of meshes. Every current source in a mesh reduces the number of unknowns by one. Mesh analysis can only be used with networks which can be drawn as a planar network, that is, with no crossing components.

Superposition is possibly the most conceptually simple method but rapidly leads to a large number of equations and messy impedance combinations as the network becomes larger.

Transfer function

A transfer function expresses the relationship between an input and an output of a network. For resistive networks, this will always be a simple real number or an expression which boils down to a real number. Resistive networks are represented by a system of simultaneous algebraic equations. However, in the general case of linear networks, the network is represented by a system of simultaneous linear differential equations. In network analysis, rather than use the differential equations directly, it is usual practice to carry out a Laplace transform on them first and then express the result in terms of the Laplace parameter s, which in general is complex. This is described as working in the s-domain. Working with the equations directly would be described as working in the time (or t) domain because the results would be expressed as time varying quantities. The Laplace transform is the mathematical method of transforming between the s-domain and the t-domain.

This approach is standard in control theory and is useful for determining stability of a system, for instance, in an amplifier with feedback.

Ground verses neutral in a descriptive way?

Ground and neutral

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For uses of the term "grounding" or "earth" in electricity but not in the context of mains wiring, see ground (electricity).

symbols for grounding

As the neutral point of an electrical supply system is often connected to earth ground, ground and neutral are closely related. Under certain conditions, a conductor used to connect to a system neutral is also used for grounding (earthing) of equipment and structures. Current carried on a grounding conductor can result in objectionable or dangerous voltages appearing on equipment enclosures, so the installation of grounding conductors and neutral conductors is carefully defined in electrical regulations. Where a neutral conductor is used also to connect equipment enclosures to earth, care must be taken that the neutral conductor never rises to a high voltage with respect to local ground.

Definitions

Ground or earth in a mains (AC power) electrical wiring system is a conductor that provides a low-impedance path to the earth to prevent hazardous voltages from appearing on equipment. (The terms "ground" and "earth" are used synonymously here. "Ground" is more common in North American English, and "earth" is more common in British English.) Under normal conditions, a grounding conductor does not carry current.

Neutral is a circuit conductor that normally carries current back to the source, and is connected to ground (earth) at the main electrical panel.

In the electrical trade, the conductor of a 2-wire circuit connected to the supply neutral point and earth ground is referred to as the "neutral". 

In a polyphase (usually three-phase) AC system, the neutral conductor is intended to have similar voltages to each of the other circuit conductors, but may carry very little current if the phases are balanced.

The United States' National Electrical Code and Canadian electrical code only define neutral as the grounded, not the polyphase common connection. In North American use, the polyphase definition is used in less formal language but not in official specifications. In the United Kingdom the Institution of Engineering and Technology defines a neutral conductor as one connected to the supply system neutral point, which includes both these uses.

All neutral wires of the same earthed (grounded) electrical system should have the same electrical potential, because they are all connected through the system ground. Neutral conductors are usually insulated for the same voltage as the line conductors, with interesting exceptions.

Circuitry

Neutral wires are usually connected at a neutral bus within panelboards or switchboards, and are "bonded" to earth ground at either the electrical service entrance, or at transformers within the system. For electrical installations with split-phase (three-wire single-phase service), the neutral point of the system is at the center-tap on the secondary side of the service transformer. For larger electrical installations, such as those with polyphase service, the neutral point is usually at the common connection on the secondary side of delta/wye connected transformers. Other arrangements of polyphase transformers may result in no neutral point, and no neutral conductors.

Grounding systems

Main article: Grounding system

The IEC standard (IEC 60364) codifies methods of installing neutral and ground conductors in a building, where these earthing systems are designated with letter symbols. The letter symbols are common in countries using IEC standards, but North American practices rarely refer to the IEC symbols. The differences are that the conductors may be separate over their entire run from equipment to earth ground, or may be combined over all or part of their length. Different systems are used to minimize the voltage difference between neutral and local earth ground. Current flowing in a grounding conductor will produce a voltage drop along the conductor, and grounding systems seek to ensure this voltage does not reach unsafe levels.

In the TN-S system, separate neutral and protective earth conductors are installed between the equipment and the source of supply (generator or electric utility transformer). Normal circuit currents flow only in the neutral, and the protective earth conductor bonds all equipment cases to earth to intercept any leakage current due to insulation failure. The neutral conductor is connected to earth at the building point of supply, but no common path to ground exists for circuit current and the protective conductor.

In the TN-C system, a common conductor provides both the neutral and protective grounding. The neutral conductor is connected to earth ground at the point of supply, and equipment cases are connected to the neutral. The danger exists that a broken neutral connection will allow all the equipment cases to rise to a dangerous voltage if any leakage or insulation fault exists in any equipment. This can be mitigated with special cables but the cost is then higher.

In the TN-C-S system, each piece of electrical equipment has both a protective ground connection to its case, and a neutral connection. These are all brought back to some common point in the building system, and a common connection is then made from that point back to the source of supply and to the earth.

In a TT system, no lengthy common protective ground conductor is used, instead each article of electrical equipment (or building distribution system) has its own connection to earth ground.

Combining neutral with ground

Stray voltages created in grounding (earthing) conductors by currents flowing in the supply utility neutral conductors can be troublesome. For example, special measures may be required in barns used for milking dairy cattle. Very small voltages, not usually perceptible to humans, may cause low milk yield, or even mastitis (inflammation of the udder). So-called "tingle voltage filters" may be required in the electrical distribution system for a milking parlour.

Connecting the neutral to the equipment case provides some protection against faults, but may produce a dangerous voltage on the case if the neutral connection is broken.

Combined neutral and ground conductors are commonly used in electricity supply companies' wiring and occasionally for fixed wiring in buildings and for some specialist applications where there is little alternative, such as railways and trams. Since normal circuit currents in the neutral conductor can lead to objectionable or dangerous differences between local earth potential and the neutral, and to protect against neutral breakages, special precautions such as frequent rodding down to earth (multiple ground rod connections), use of cables where the combined neutral and earth completely surrounds the phase conductor(s), and thicker than normal equipotential bonding must be considered to ensure the system is safe.

Fixed appliances on three-wire circuits

In North America, the cases of some kitchen stoves (ranges, ovens), cook tops, clothes dryers and other specifically listed appliances were grounded through their neutral wires as a measure to conserve copper from copper cables during World War II. This practice was removed from the NEC in the 1996 edition, but existing installations (called "old work") may still allow the cases of such listed appliances to be connected to the neutral conductor for grounding.

This practice arose from the three-wire system used to supply both 120 volt and 240 volt loads. Because these listed appliances often have components that use either 120, or both 120 and 240 volts, there is often some current on the neutral wire. This differs from the protective grounding wire, which only carries current under fault conditions. Using the neutral conductor for grounding the equipment enclosure was considered safe since the devices were permanently wired to the supply and so the neutral was unlikely to be broken without also breaking both supply conductors. Also, the unbalanced current due to lamps and small motors in the appliances was small compared to the rating of the conductors and therefore unlikely to cause a large voltage drop in the neutral conductor.

Portable appliances

In North American and European practice, small portable equipment connected by a cord set is permitted under certain conditions to have merely two conductors in the attachment plug. A polarized plug can be used to maintain the identity of the neutral conductor into the appliance but neutral is never used as a chassis/case ground. The small cords to lamps, etc., often have one or more molded ridges or embedded strings to identify the neutral conductor, or may be identified by colour. Portable appliances never use the neutral conductor for case grounding, and often feature "double-insulated" construction.

In places where the design of the plug and socket cannot ensure that a system neutral conductor is connected to particular terminals of the device ("unpolarized" plugs), portable appliances must be designed on the assumption that either pole of each circuit may reach full voltage with respect to ground.

Technical equipment

In North American practice, equipment connected by a cord set must have three wires, if supplied exclusively by 240 volts, or must have four wires (including neutral and ground), if supplied by 120/240 volts.

There are special provisions in the NEC for so-called technical equipment, mainly professional grade audio and video equipment supplied by so-called "balanced" 120 volt circuits. The center tap of a transformer is connected to ground, and the equipment is supplied by two line wires each 60 volts to ground (and 120 volts between line conductors). The center tap is not distributed to the equipment and no neutral conductor is used. These cases generally use a grounding conductor which is separated from the safety grounding conductor specifically for the purposes of noise and "hum" reduction.

Another specialized distribution system was formerly specified in patient care areas of hospitals. An isolated power system was furnished, from a special isolation transformer, with the intention of minimizing any leakage current that could pass through equipment directly connected to a patient (for example, an electrocardiograph for monitoring the heart). The neutral of the circuit was not connected to ground. The leakage current was due to the distributed capacitance of the wiring and capacitance of the supply transformer.  Such distribution systems were monitored by permanently installed instruments to give an alarm when high leakage current was detected.

Shared neutral

A shared neutral is a connection in which a plurality of circuits use the same neutral connection. This is also known as a common neutral, and the circuits and neutral together are sometimes referred to as an Edison circuit.

Three-phase circuits

In a three-phase circuit, a neutral is shared between all three phases. Commonly the system neutral is connected to the star point on the feeding transformer. This is the reason that the secondary side of most three-phase distribution transformers is wye or star wound. Three-phase transformers and their associated neutrals are usually found in industrial distribution environments.

A system could be made entirely ungrounded. In this case a fault between one phase and ground would not cause any significant current. In fact, this is not a good scheme. Commonly the neutral is grounded (earthed) through a bond between the neutral bar and the earth bar. It is common on larger systems to monitor any current flowing through the neutral-to-earth link and use this as the basis for neutral fault protection.

The connection between neutral and earth allows any phase-to-earth fault to develop enough current flow to "trip" the circuit overcurrent protection device. In some jurisdictions, calculations are required to ensure the fault loop impedance is low enough so that fault current will trip the protection (In Australia, this is referred to in AS3000:2007 Fault loop impedance calculation). This may limit the length of a branch circuit.

In the case of two phases sharing one neutral, the worst-case current draw is one side has zero load and the other has full load, or when both sides have full load. The latter case results in 1 + 1@120deg = 1@60deg, i.e. the magnitude of the current in the neutral equals that of the other two wires.

In a three-phase linear circuit with three identical resistive or reactive loads, the neutral carries no current. The neutral carries current if the loads on each phase are not identical. In some jurisdictions, the neutral is allowed to be reduced in size if no unbalanced current flow is expected. If the neutral is smaller than the phase conductors, it can be overloaded if a large unbalanced load occurs.

The current drawn by non-linear loads, such as fluorescent & HID lighting and electronic equipment containing switching power supplies, often contains harmonics. Triplen harmonic currents (odd multiples of the third harmonic) are additive, resulting in more current in the shared neutral conductor than in any of the phase conductors. In the absolute worst case, the current in the shared neutral conductor can be triple that in each phase conductor. Some jurisdictions prohibit the use of shared neutral conductors when feeding single-phase loads from a three-phase source; others require that the neutral conductor be substantially larger than the phase conductors. It is good practice to use four-pole circuit breakers (as opposed to the standard three-pole) where the fourth pole is the neutral phase, and is hence protected against overcurrent on the neutral conductor.

Split phase

Main article: Split-phase electric power

In split-phase wiring, for example a duplex receptacle in a North American kitchen, devices may be connected with a cable that has three conductors, in addition to ground. The three conductors are usually coloured red, black, and white. The white serves as a common neutral, while the red and black each feed, separately, the top and bottom hot sides of the receptacle. Typically such receptacles are supplied from two circuit breakers in which the handles of two poles are tied together for a common trip. If two large appliances are used at once, current passes through both and the neutral only carries the difference in current. The advantage is that only three wires are required to serve these loads, instead of four. If one kitchen appliance overloads the circuit, the other side of the duplex receptacle will be shut off as well. This is called a multiwire branch circuit. Common trip is required when the connected load uses more than one phase simultaneously. The common trip prevents overloading of the shared neutral if one device draws more than rated current.

Grounding concepts in a comprehensive way?

Ground (electricity)

A typical earthing electrode (left of gray pipe), consisting of a conductive rod driven into the ground, at a home in Australia.

Most electrical codes specify that the insulation on protective earthing conductors must be a distinctive color (or color combination) not used for any other purpose.

In electrical engineering, ground or earth is the reference point in an electrical circuit from which voltages are measured, a common return path for electric current, or a direct physical connection to the Earth.

grounding model

Electrical circuits may be connected to ground (earth) for several reasons. In mains powered equipment, exposed metal parts are connected to ground to prevent user contact with dangerous voltage when electrical insulation fails. In electrical power distribution systems, a protective ground conductor is an essential part of the safety Earthing system. Connection to ground also limits the build-up of static electricity when handling flammable products or electrostatic-sensitive devices. In some telegraph and power transmission circuits, the earth itself can be used as one conductor of the circuit, saving the cost of installing a separate return conductor (see single-wire earth return).

For measurement purposes, the Earth serves as a (reasonably) constant potential reference against which other potentials can be measured. An electrical ground system should have an appropriate current-carrying capability to serve as an adequate zero-voltage reference level. In electronic circuit theory, a "ground" is usually idealized as an infinite source or sink for charge, which can absorb an unlimited amount of current without changing its potential. Where a real ground connection has a significant resistance, the approximation of zero potential is no longer valid. Stray voltages or earth potential rise effects will occur, which may create noise in signals or if large enough will produce an electric shock hazard.

The use of the term ground (or earth) is so common in electrical and electronics applications that circuits in portable electronic devices such as cell phones and media players as well as circuits in vehicles may be spoken of as having a "ground" connection without any actual connection to the Earth, despite "common" being a more appropriate term for such a connection. This is usually a large conductor attached to one side of the power supply (such as the "ground plane" on a printed circuit board) which serves as the common return path for current from many different components in the circuit.

Building wiring installations

Electrical power distribution systems are often connected to ground to limit the voltage that can appear on distribution circuits. A distribution system insulated from ground may attain a high potential due to transient voltages caused by arcing, static electricity, or accidental contact with higher potential circuits. A ground connection of the system dissipates such potentials and limits the rise in voltage of the grounded system.

In a mains electricity (AC power) wiring installation, the term ground conductor typically refers to three different conductors or conductor systems as listed below.

Equipment earthing conductors provide an electrical connection between non-current-carrying metallic parts of equipment and the earth. According to the U.S. National Electrical Code (NEC), the reason for doing this is to limit the voltage imposed by lightning, line surges, and contact with higher voltage lines. The equipment earthing conductor is usually also used as the equipment bonding conductor .

Equipment bonding conductors provide a low impedance path between non-current-carrying metallic parts of equipment and one of the conductors of that electrical system's source, so that if a part becomes energized for any reason, such as a frayed or damaged conductor, a short circuit will occur and operate a circuit breaker or fuse to disconnect the faulted circuit. The earth itself has no role in this fault-clearing process since current must return to its source; however, the sources are very frequently connected to earth. (see Kirchhoff's circuit laws). By bonding (interconnecting) all exposed non-current carrying metal objects together, they should remain near the same potential thus reducing the chance of a shock. This is especially important in bathrooms where one may be in contact with several different metallic systems such as supply and drain pipes and appliance frames. The equipment bonding conductor is usually also used as the equipment earthing conductor.

Metal water pipe used as grounding electrode

A grounding electrode conductor (GEC) connects one leg of an electrical system to one or more earth electrodes. This is called "system grounding" and most systems are required to be grounded. The U.S. NEC and the UK's BS 7671 list systems that are required to be grounded. The grounding electrode conductor connects the leg of the electrical system that is the "neutral wire" to the grounding electrode(s). The grounding electrode conductor is also usually bonded to pipework and structural steel in larger structures. According to the NEC, the purpose of earthing an electrical system is to limit the voltage to earth imposed by lightning events and contact with higher voltage lines, and also to stabilize the voltage to earth during normal operation. In the past, water supply pipes were often used as grounding electrodes, but this was banned where plastic pipes are popular. This type of ground applies to radio antennas and to lightning protection systems.

Permanently installed electrical equipment usually also has permanently connected grounding conductors. Portable electrical devices with metal cases may have them connected to earth ground by a pin in the interconnecting plug (see Domestic AC power plugs and sockets). The size of power ground conductors is usually regulated by local or national wiring regulations.

Earthing systems

In electricity supply systems, an earthing (grounding) system defines the electrical potential of the conductors relative to that of the Earth's conductive surface. The choice of earthing system has implications for the safety and electromagnetic compatibility of the power supply. Regulations for earthing systems vary considerably between different countries.

A functional earth connection serves a purpose other than providing protection against electrical shock. In contrast to a protective earth connection, a functional earth connection may carry a current during the normal operation of a device. Functional earth connections may be required by devices such as surge suppression and electromagnetic-compatibility filters, some types of antennas and various measurement instruments. Generally the protective earth is also used as a functional earth, though this requires care in some situations.

Impedance grounding

Distribution power systems may be solidly grounded, with one circuit conductor directly connected to an earth grounding electrode system. Alternatively, some amount of electrical impedance may be connected between the distribution system and ground, to limit the current that can flow to earth. The impedance may be a resistor, or an inductor (coil). In a high-impedance grounded system, the fault current is limited to a few amperes (exact values depend on the voltage class of the system); a low-impedance grounded system will permit several hundred amperes to flow on a fault. A large solidly grounded distribution system may have thousands of amperes of ground fault current.

In a polyphase AC system, an artificial neutral grounding system may be used. Although no phase conductor is directly connected to ground, a specially constructed transformer (a "zig zag" transformer) blocks the power frequency current from flowing to earth, but allows any leakage or transient current to flow to ground.

Low-resistance grounding systems use a neutral grounding resistor (NGR) to limit the fault current to 25 A or greater. Low resistance grounding systems will have a time rating (say, 10 seconds) that indicates how long the resistor can carry the fault current before overheating. A ground fault protection relay must trip the breaker to protect the circuit before overheating of the resistor occurs.

High-resistance grounding (HRG) systems use an NGR to limit the fault current to 25 A or less. They have a continuous rating, and are designed to operate with a single-ground fault. This means that the system will not immediately trip on the first ground fault. If a second ground fault occurs, a ground fault protection relay must trip the breaker to protect the circuit. On an HRG system, a sensing resistor is used to continuously monitor system continuity. If an open-circuit is detected (e.g., due to a broken weld on the NGR), the monitoring device will sense voltage through the sensing resistor and trip the breaker. Without a sensing resistor, the system could continue to operate without ground protection (since an open circuit condition would mask the ground fault) and transient overvoltages could occur.

Ungrounded systems

Where the danger of electric shock is high, special ungrounded power systems may be used to minimize possible leakage current to ground. Examples of such installations include patient care areas in hospitals, where medical equipment is directly connected to a patient and must not permit any power-line current to pass into the patient's body. Medical systems include monitoring devices to warn of any increase of leakage current. On wet construction sites or in shipyards, isolation transformers may be provided so that a fault in a power tool or its cable does not expose users to shock hazard.

Circuits used to feed sensitive audio/video production equipment or measurement instruments may be fed from an isolated ungrounded technical power system to limit the injection of noise from the power system.

Role of protective relay in electrical engineering?

Introduction and background

In electrical engineering, a protective relay is a relay device designed to trip a circuit breaker when a fault is detected.:4 The first protective relays were electromagnetic devices, relying on coils operating on moving parts to provide detection of abnormal operating conditions such as over-current, over-voltage, reverse power flow, over-frequency, and under-frequency.

relay configuaration

Microprocessor-based digital protection relays now emulate the original devices, as well as providing types of protection and supervision impractical with electromechanical relays. Electromechanical relays provide only rudimentary indications of involved phase and zone targets. In many cases a single microprocessor relay provides functions that would take two or more electromechanical devices. By combining several functions in one case, numerical relays also save capital cost and maintenance cost over electromechanical relays.However, due to their very long life span, tens of thousands of these "silent sentinels" are still protecting transmission lines and electrical apparatus all over the world. Important transmission lines and generators have cubicles dedicated to protection, with many individual electromechanical devices, or one or two microprocessor relays.

The theory and application of these protective devices is an important part of the education of a power engineer who specializes in power systems. The need to act quickly to protect circuits and equipment as well as the general public often requires protective relays to respond and trip a breaker within a few thousandths of a second. In some instances these clearance times are prescribed in legislation or operating rules. A maintenance or testing program is used to determine the performance and availability of protection systems.

Based on the end application and applicable legislature, various standards such as ANSI C37.90, IEC255-4, IEC60255-3, and IAC govern the response time of the relay to the fault conditions that may occur.

Operation principles

Electromechanical protective relays operate by either magnetic attraction, or magnetic induction.:14 Unlike switching type electromechanical relays with fixed and usually ill-defined operating voltage thresholds and operating times, protective relays have well-established, selectable, and adjustable time and current (or other operating parameter) operating characteristics. Protection relays may use arrays of induction disks, shaded-pole,:25 magnets, operating and restraint coils, solenoid-type operators, telephone-relay contacts,and phase-shifting networks.

Protective relays can also be classified by the type of measurement they make.:92 A protective relay may respond to the magnitude of a quantity such as voltage or current. Induction relays can respond to the product of two quantities in two field coils, which could for example represent the power in a circuit.

"It is not practical to make a relay that develops a torque equal to the quotient of two a.c. quantities. This, however is not important; the only significant condition for a relay is its setting and the setting can be made to correspond to a ratio regardless of the component values over a wide range.

Several operating coils can be used to provide "bias" to the relay, allowing the sensitivity of response in one circuit to be controlled by another. Various combinations of "operate torque" and "restraint torque" can be produced in the relay.

By use of a permanent magnet in the magnetic circuit, a relay can be made to respond to current in one direction differently from in another. Such polarized relays are used on direct-current circuits to detect, for example, reverse current into a generator. These relays can be made bistable, maintaining a contact closed with no coil current and requiring reverse current to reset. For AC circuits, the principle is extended with a polarizing winding connected to a reference voltage source.

Lightweight contacts make for sensitive relays that operate quickly, but small contacts can't carry or break heavy currents. Often the measuring relay will trigger auxiliary telephone-type armature relays.

In a large installation of electromechanical relays, it would be difficult to determine which device originated the signal that tripped the circuit. This information is useful to operating personnel to determine the likely cause of the fault and to prevent its re-occurrence. Relays may be fitted with a "target" or "flag" unit, which is released when the relay operates, to display a distinctive colored signal when the relay has tripped.

Types according to construction

Electromechanical

Electromechanical relays can be classified into several different types as follows:

attracted armature

moving coil

induction

motor operated

mechanical

thermal

"Armature"-type relays have a pivoted lever supported on a hinge or knife-edge pivot, which carries a moving contact. These relays may work on either alternating or direct current, but for alternating current, a shading coil on the pole:14 is used to maintain contact force throughout the alternating current cycle. Because the air gap between the fixed coil and the moving armature becomes much smaller when the relay has operated, the current required to maintain the relay closed is much smaller than the current to first operate it. The "returning ratio or "differential" is the measure of how much the current must be reduced to reset the relay.

A variant application of the attraction principle is the plunger-type or solenoid operator. A reed relay is another example of the attraction principle.

"Moving coil" meters use a loop of wire turns in a stationary magnet, similar to a galvanometer but with a contact lever instead of a pointer. These can be made with very high sensitivity. Another type of moving coil suspends the coil from two conductive ligaments, allowing very long travel of the coil.

Induction disc overcurrent relay

"Induction" disk meters work by inducing currents in a disk that is free to rotate; the rotary motion of the disk operates a contact. Induction relays require alternating current; if two or more coils are used, they must be at the same frequency otherwise no net operating force is produced. These electromagnetic relays use the induction principle discovered by Galileo Ferraris in the late 19th century. The magnetic system in induction disc overcurrent relays is designed to detect overcurrents in a power system and operate with a pre-determined time delay when certain overcurrent limits have been reached. In order to operate, the magnetic system in the relays produces torque that acts on a metal disc to make contact, according to the following basic current/torque equation:

The following important conclusions can be drawn from the above equation.

Two alternating fluxes with a phase shift are needed for torque production.

Maximum torque is produced when the two alternating fluxes are 90 degrees apart.

The resultant torque is steady and not a function of time.

The relay's primary winding is supplied from the power systems current transformer via a plug bridge, which is called the plug setting multiplier (psm). Usually seven equally spaced tappings or operating bands determine the relays sensitivity. The primary winding is located on the upper electromagnet. The secondary winding has connections on the upper electromagnet that are energised from the primary winding and connected to the lower electromagnet. Once the upper and lower electromagnets are energised they produce eddy currents that are induced onto the metal disc and flow through the flux paths. This relationship of eddy currents and fluxes creates torque proportional to the input current of the primary winding, due to the two flux paths being out of phase by 90°.

In an overcurrent condition, a value of current will be reached that overcomes the control spring pressure on the spindle and the braking magnet, causing the metal disc to rotate towards the fixed contact. This initial movement of the disc is also held off to a critical positive value of current by small slots that are often cut into the side of the disc. The time taken for rotation to make the contacts is not only dependent on current but also the spindle backstop position, known as the time multiplier (tm). The time multiplier is divided into 10 linear divisions of the full rotation time.

Providing the relay is free from dirt, the metal disc and the spindle with its contact will reach the fixed contact, thus sending a signal to trip and isolate the circuit, within its designed time and current specifications. Drop off current of the relay is much lower than its operating value, and once reached the relay will be reset in a reverse motion by the pressure of the control spring governed by the braking magnet.

Static

Application of electronic amplifiers to protective relays was described as early as 1928, using vacuum tube amplifiers and continued up to 1956. Devices using electron tubes were studied but never applied as commercial products, because of the limitations of vacuum tube amplifiers. A relatively large standby current is required to maintain the tube filament temperature; inconvenient high voltages are required for the circuits, and vacuum tube amplifiers had difficulty with incorrect operation due to noise disturbances.

Static relays have no or few moving parts, and became practical with the introduction of the transistor. Measuring elements of static relays have been successfully and economically built up from diodes, zener diodes, avalanche diodes, unijunction transistors, p-n-p and n-p-n bipolar transistors, field effect transistors or their combinations.6 Static relays offer the advantage of higher sensitivity than purely electromechanical relays, because power to operate output contacts is derived from a separate supply, not from the signal circuits. Static relays eliminated or reduced contact bounce, and could provide fast operation, long life and low maintenance.

Digital

Digital protective relays were in their infancy during the late 1960s. An experimental digital protection system was tested in the lab and in the field in the early 1970s. Unlike the relays mentioned above, digital protective relays have two main parts: hardware and software. The world's first commercially available digital protective relay was introduced to the power industry in 1984,In spite of the developments of complex algorithms for implementing protection functions the microprocessor based-relays marketed in the 1980s did not incorporate them. A microprocessor-based digital protection relay can replace the functions of many discrete electromechanical instruments. These relays convert voltage and currents to digital form and process the resulting measurements using a microprocessor. The digital relay can emulate functions of many discrete electromechanical relays in one device, simplifying protection design and maintenance. Each digital relay can run self-test routines to confirm its readiness and alarm if a fault is detected. Digital relays can also provide functions such as communications (SCADA) interface, monitoring of contact inputs, metering, waveform analysis, and other useful features. Digital relays can, for example, store multiple sets of protection parameters, which allows the behavior of the relay to be changed during maintenance of attached equipment. Digital relays also can provide protection strategies impossible to implement with electromechanical relays. This is particularly so in long distance high voltage or multi-terminal circuits or in lines that are series or shunt compensated.They offer self-testing and communication to supervisory control systems.

A digital (numeric) multifunction protective relay for distribution networks. A single such device can replace many single-function electromechanical relays, and provides self-testing and communication functions.

Numerical

The distinction between digital and numerical protection relay rests on points of fine technical detail, and is rarely found in areas ther than Protection[28]:Ch 7, pp 102. Numerical relays are the product of the advances in technology from digital relays. Generally, there are several different types of numerical protection relays. Each type, however, shares a similar architecture, thus enabling designers to build an entire system solution that is based on a relatively small number of flexible components.They use high speed processors executing appropriate algorithms,

Relays by functions

The various protective functions available on a given relay are denoted by standard ANSI device numbers. For example, a relay including function 51 would be a timed overcurrent protective relay.

Overcurrent relay

An overcurrent relay is a type of protective relay which operates when the load current exceeds a pickup value. The ANSI device number is 50 for an instantaneous over current (IOC) or a Definite Time Overcurrent (DTOC). In a typical application the over current relay is connected to a current transformer and calibrated to operate at or above a specific current level. When the relay operates, one or more contacts will operate and energize to trip (open) a circuit breaker. The Definite Time Overcurrent Relay has been used extensively in the United Kingdom but its inherent issue of operating slower for faults closer to the source led to the development of the IDMT relay.

Inverse Definite Minimum Time

The inverse definite minimum time (IDMT) protective relays were developed to overcome the shortcomings of the Definite Time Overcurrent Relays.

If the source impedance remains constant and the fault current changes appreciably as we move away from the relay then it is advantageous to use IDMT overcurrent protection : to achieve high speed protection on largesection protected circuit.However, if the source impedance is significantly larger than the feeder impedance then the characteristic of the IDMT relay cannot be exploited and DTOC may be utilized.[35]:42 Secondly if the source impedance varies and becomes weaker with less generation during light loads then this leads to slower clearance time hence negating the purpose of the IDMT relay.

While it is more common to use IDMT relays for current protection it is possible to utilize IDMT mode of operation for voltage protection[39]:3. It is possible to program customised curves in some protective relays[40]:pp Ch2-9 and other manufacturers[41]:18 have special curves specific to their relays. Some numerical relays can be used to provide inverse time overvoltage protection[42]:6 or negative sequence overcurrent protection.[43]:915

Distance relay/Impedance relay[edit]

Distance relays differ in principle from other forms of protection in that their performance is not governed by the magnitude of the current or voltage in the protected circuit but rather on the ratio of these two quantities. Distance relays are actually double actuating quantity relays with one coil energized by voltage and other coil by current. The current element produces a positive or pick up torque while the voltage element produces a negative or reset torque. The relay operates only when the V/I ratio falls below a predetermined value(or set value). During a fault on the transmission line the fault current increases and the voltage at the fault point decreases. The V/I [45] ratio is measured at the location of CTs and PTs. The voltage at the PT location depends on the distance between the PT and the fault. If the measured voltage is lesser, that means the fault is nearer and vice versa. Hence the protection called Distance relay. The load flowing through the line appears an impedance to the relay and sufficiently large loads (as impedance is inversely proportional to the load) can lead to a trip of the relay even in the absence of a fault.[46]:467

Current differential protection scheme[edit]

"The differential protection is 100% selective and therefore only responds to faults within its protected zone. The boundary of the protected zone is uniquely defined by the location of the current transformers. Time grading with other protection systems is therefore not required, allowing for tripping without additional delay.

GFCI (ground fault circuit interrupter) circuit breakers combine overcurrent protection and differential protection (non-adjustable) in standard, commonly available modules.

Directional relay

A directional uses an additional polarizing source of voltage or current to determine the direction of a fault. Directional elements respond to the phase shift between a polarizing quantity and an operate quantity. The fault can be located upstream or downstream of the relay's location, allowing appropriate protective devices to be operated inside or outside of the zone of protection.

Synchronism check

A synchronism checking relay provides a contact closure when the frequency and phase of two sources are similar to within some tolerance margin. A "synch check" relay is often applied where two power systems are interconnected, such as at a switchyard connecting two power grids, or at a generator circuit breaker to ensure the generator is synchronized to the system before connecting it.Courtesy of wikipedia...

What is power system operation corporation?

Power System Operation Corporation

Power System Operation Corporation Limited (POSOCO) was a wholly owned subsidiary of Power Grid Corporation of India Limited (PGCIL) till 2nd January 2016. It was formed in March 2010 to handle the power management functions of PGCIL. It is responsible to ensure the integrated operation of the Grid in a reliable,efficient and secure manner. It consists of 5 Regional Load Despatch Centres and a National Load Despatch Centre (NLDC). The subsidiary was eventually made a separate company, leaving the parent firm with only the task of setting up transmission links. The load despatch functions, earlier handled by PGCIL, will now come up to POSOCO. Now POSOCO is fully govt. Company because on 3rd Jan 2017 it was separated from powergrid.

company logo

History

Central Government through Ministry of Power in exercise of the power conferred by sub-section (3) of Sect 26 and sub-section (2) of Section 27 of the Electricity Act, 2003, by notification dt. September 27, 2010 in the Gazette of India notified that the Power System Operation Corporation Ltd (POSOCO), a wholly owned subsidiary of the Power Grid Corporation of India Limited (a Government Company) shall operate National Load Despatch Centre and the five Regional Load Despatch Centers, with effect from October 1, 2010.

The subsidiary was set up on the recommendations of a government committee headed by G.B. Pradhan, additional secretary in the Union ministry of power. To make load despatch centres financially self-reliant and autonomous, the committee recommended independent and sustainable revenue streams. The move to separate the two functions is in keeping with the provisions of the Electricity Act, 2003, which seeks to separate commercial interests from load management functions. The Pradhan committee had recommended setting up a separate representative board structure overseeing the functions of the five regional load despatch centres (RLDCs) run by PGCIL—the northern, eastern, north-eastern, western and southern regions at that time.

The Present Board of directors are as following:

Mr. I.S.Jha, Chairman

Mr. Ravi P. Singh, Director

Mrs. Jyoti Arora, Director (Government nominee)

Mr. Major Singh, Director (Government Nominee)

Mr. Jagdishbhai Ishwarbhai Patel (Independent Director)

Mr. Sushil Kumar Soonee is the Chief Executive Officer of POSOCO and a special invitee in the Board meetings.

The Corporate Centre of POSOCO is at B-9, Qutab Institutional Area, Katwaria Sarai, New Delhi-110016, INDIA

POSOCO mainly comprises -

National Load Despatch Centre (NLDC)

Five Regional Load Despatch Centres

Northern Regional Load Despatch Centre (NRLDC)

Western Regional Load Despatch Centre (WRLDC)

Eastern Regional Load Despatch Centre (ERLDC)

Southern Regional Load Despatch Centre (SRLDC)

North-Eastern Regional Load Despatch Centre (NERLDC)

National Load Despatch Centre[edit]

On 25 February 2009 the National Load Despatch Centre (NLDC) was inaugurated by Sh.Sushilkumar Shinde(Union Minister of Power) and Smt.Shiela Dixit(Chief Minister, Delhi). National Load Despatch Centre (NLDC) has been constituted as per Ministry of Power (MOP) notification, New Delhi dated 2 March 2005 and is the apex body to ensure integrated operation of the national power system.

The main functions assigned to NLDC are:

♦ Supervision Over the Regional Load Despatch Centres.

♦ Scheduling and dispatch of electricity over the inter-regional links in accordance with grid standards specified by the authority and grid code specified by Central Commission in coordination with Regional Load Despatch Centres.

♦ Coordination with Regional Load Despatch Centres for achieving maximum economy and efficiency in the operation of National Grid.

♦ Monitoring of operations and grid security of the National Grid.

♦ Supervision and control over the inter-regional links as may be required for ensuring stability of the power system under its control.

♦ Coordination with Regional Power Committees for regional outage schedule in the national perspective to ensure optimal utilization of power resources.

♦ Coordination with Regional Load Despatch Centres for the energy accounting of inter-regional exchange of power.

♦ Coordination for restoration of synchronous operation of national grid with Regional Load Despatch Centres.

♦ Coordination for trans-national exchange of power.

♦ Providing Operational feedback for national grid planning to the Authority and Central Transmission Utility.

♦ Levy and collection of such fee and charges from the generating companies or licensees involved in the power system, as may be specified by the Central Commission.

♦ Dissemination Of information relating to operations of transmission system in accordance with directions or regulations issued by Central Government from time to time.

Regional Load Despatch centres

The main responsibilities of RLDCs are:

♦ System parameters and security.

♦ To ensure the integrated operation of the power system grid in the respective region.

♦ System studies,planning and contingency analysis.

♦ Daily scheduling and operational planning.

♦ Facilitating bilateral and inter-regional exchanges.

♦ Computation of energy despatch and drawal values using SEMs.

♦ Augmentation of telemetry, computing and communication facilities.

POWERGRID transmission network failure

The Northern Region Grid, which provides power to nine states in northern India including Delhi, experienced a widespread outage due to a grid disturbance that occurred at about 2.35 a.m on 30 July 2012.

Restoration work started immediately under the direction of CEO, POSOCO and POWERGRID’s Chairman & Managing Director. A team of engineers tried to find out a way for restoring the normal supply of power immediately, so that railways, Metro, airports and other power users deemed essential could get immediate restoration of electricity. With the coordinated efforts of the whole team of engineers and constituent state utilities, power supply to the essential services and other essential loads in northern India was restored by about 8.00 a.m. and about 60% of load of the Northern Region was restored by 11:00 a.m. This was possible by gearing up the power supply from hydroelectric sources and also extending power from the Eastern and Western regions for start-up supply for thermal generating units of the Northern Region. Thus the associated problems for want of power supply could be partially overcome by this time. Later, power supply was restored progressively and by 12:30 p.m. power was extended to most of the cities and towns through POWERGRID substations. The Northern Grid was brought back to normalcy to meet the demand of about 30 GW at 7:00 p.m.

On 31 July 2012, the northern grid collapsed for a second time, hours after the power supply was restored in the entire northern region following a disruption on the previous day. The eastern transmission lines also failed, disrupting power supply in Delhi, Uttar Pradesh, Haryana, West Bengal, Assam and Punjab, among other states.

Independent audit of Grids

Power Minister Veerappa Moily said that transmission grids will be independently audited in three months to ensure that the grids are fail-safe.

High voltages concept in electrical engineering?

High voltage description

The term high voltage usually means electrical energy at voltages high enough to inflict harm on living organisms. Equipment and conductors that carry high voltage warrant particular safety requirements and procedures. In certain industries, high voltage means voltage above a particular threshold (see below). High voltage is used in electrical power distribution, in cathode ray tubes, to generate X-rays and particle beams, to demonstrate arcing, for ignition, in photomultiplier tubes, and in high power amplifier vacuum tubes and other industrial and scientific applications.

voltage doubler

Definition

IEC voltage range AC (Vrms) DC (V) Defining risk

High voltage (supply system) > 1000 > 1500 Electrical arcing

Low voltage (supply system) 50–1000 120–1500 Electrical shock

Extra-low voltage (supply system) < 50 < 120 Low risk

The numerical definition of 'high voltage' depends on context. Two factors considered in classifying a voltage as "high voltage" are the possibility of causing a spark in air, and the danger of electric shock by contact or proximity. The definitions may refer to the voltage between two conductors of a system, or between any conductor and ground.

In electric power transmission engineering, high voltage is usually considered any voltage over approximately 35,000 volts. This is a classification based on the design of apparatus and insulation.

The International Electrotechnical Commission and its national counterparts (IET, IEEE, VDE, etc.) define high voltage as above 1000 V for alternating current, and at least 1500 V for direct current—and distinguish it from low voltage (50–1000 V AC or 120–1500 V DC) and extra-low voltage (<50 V AC or <120 V DC) circuits. This is in the context of building wiring and the safety of electrical apparatus.

In the United States 2011 National Electrical Code (NEC) is the standard regulating most electrical installations. There are no definitions relating to high voltage. The NEC® covers voltages 600 volts and less and that over 600 volts. The National Electrical Manufacturer's Association (NEMA) defines high voltage as over 100kV to 230kV. British Standard BS 7671:2008 defines high voltage as any voltage difference between conductors that is higher than 1000 V AC or 1500 V ripple-free DC, or any voltage difference between a conductor and Earth that is higher than 600 V AC or 900 V ripple-free DC.

Electricians may only be licensed for particular voltage classes, in some jurisdictions. For example, an electrical license for a specialized sub-trade such as installation of HVAC systems, fire alarm systems, closed circuit television systems may be authorized to install systems energized up to only 30 volts between conductors, and may not be permitted to work on mains-voltage circuits. The general public may consider household mains circuits (100–250 V AC), which carry the highest voltages they normally encounter, to be high voltage.

Voltages over approximately 50 volts can usually cause dangerous amounts of current to flow through a human being who touches two points of a circuit—so safety standards, in general, are more restrictive around such circuits.The definition of extra high voltage (EHV) again depends on context. In electric power transmission engineering, EHV equipment carries more than 345,000 volts between conductors. In electronics systems, a power supply that provides greater than 275,000 volts is called an EHV Power Supply, and is often used in experiments in physics.

The accelerating voltage for a television cathode ray tube may be described as extra-high voltage or extra-high tension (EHT), compared to other voltage supplies within the equipment. This type of supply ranges from >5 kV to about 50 kV.

In automotive engineering, high voltage is defined as voltage in range 30–1000 Vac or 60–1500 Vdc.

In digital electronics, a high voltage usually refers to that representing a logic 1 in positive logic and a logic 0 in negative logic. It is not used to indicate a hazardous voltage and levels between ICs to TTL/CMOS standards and their modern derivatives are well below hazardous levels. The highest in mainstream use were 15V for original CMOS and 5V for TTL but modern devices use 3.3V, with 1.8V or lower used in many applications.

Safety

International safety symbol "Caution, risk of electric shock" (ISO 3864), also known as high voltage symbol

Voltages greater than 50 V applied across dry unbroken human skin can cause heart fibrillation if they produce electric currents in body tissues that happen to pass through the chest area. The voltage at which there is the danger of electrocution depends on the electrical conductivity of dry human skin. Living human tissue can be protected from damage by the insulating characteristics of dry skin up to around 50 volts. If the same skin becomes wet, if there are wounds, or if the voltage is applied to electrodes that penetrate the skin, then even voltage sources below 40 V can be lethal.

Accidental contact with high voltage supplying sufficient energy may result in severe injury or death. This can occur as a person's body provides a path for current flow, causing tissue damage and heart failure. Other injuries can include burns from the arc generated by the accidental contact. These burns can be especially dangerous if the victim's airways are affected. Injuries may also be suffered as a result of the physical forces experienced by people who fall from a great height or are thrown a considerable distance.

Low-energy exposure to high voltage may be harmless, such as the spark produced in a dry climate when touching a doorknob after walking across a carpeted floor. The voltage can be in the thousand-volt range, but the current (the rate of charge transfer) is low.

Safety equipment used by electrical workers includes insulated rubber gloves and mats. These protect the user from electric shock. Safety equipment is tested regularly to ensure it is still protecting the user. Test regulations vary according to country. Testing companies can test at up 300,000 volts and offer services from glove testing to Elevated Working Platform (or EWP) testing.

Sparks in air

Long exposure photograph of a Tesla coil showing the repeated electric discharges

The dielectric breakdown strength of dry air, at Standard Temperature and Pressure (STP), between spherical electrodes is approximately 33 kV/cm. This is only as a rough guide, since the actual breakdown voltage is highly dependent upon the electrode shape and size. Strong electric fields (from high voltages applied to small or pointed conductors) often produce violet-colored corona discharges in air, as well as visible sparks. Voltages below about 500–700 volts cannot produce easily visible sparks or glows in air at atmospheric pressure, so by this rule these voltages are "low". However, under conditions of low atmospheric pressure (such as in high-altitude aircraft), or in an environment of noble gas such as argon or neon, sparks appear at much lower voltages. 500 to 700 volts is not a fixed minimum for producing spark breakdown, but it is a rule-of-thumb. For air at STP, the minimum sparkover voltage is around 327 volts, as noted by Friedrich Paschen.

While lower voltages do not, in general, jump a gap that is present before the voltage is applied, interrupting an existing current flow with a gap often produces a low-voltage spark or arc. As the contacts are separated, a few small points of contact become the last to separate. The current becomes constricted to these small hot spots, causing them to become incandescent, so that they emit electrons (through thermionic emission). Even a small 9 V battery can spark noticeably by this mechanism in a darkened room. The ionized air and metal vapour (from the contacts) form plasma, which temporarily bridges the widening gap. If the power supply and load allow sufficient current to flow, a self-sustaining arc may form. Once formed, an arc may be extended to a significant length before breaking the circuit. Attempting to open an inductive circuit often forms an arc, since the inductance provides a high-voltage pulse whenever the current is interrupted. AC systems make sustained arcing somewhat less likely, since the current returns to zero twice per cycle. The arc is extinguished every time the current goes through a zero crossing, and must reignite during the next half-cycle to maintain the arc.

Unlike an ohmic conductor, the resistance of an arc decreases as the current increases. This makes unintentional arcs in an electrical apparatus dangerous since even a small arc can grow large enough to damage equipment and start fires if sufficient current is available. Intentionally produced arcs, such as used in lighting or welding, require some element in the circuit to stabilize the arc's current/voltage characteristics.

Electrostatic devices, natural static electricity and similar phenomena

A high voltage is not necessarily dangerous if it cannot deliver substantial current. The common static electric sparks seen under low-humidity conditions always involve voltage well above 700 V. For example, sparks to car doors in winter can involve voltages as high as 20,000 V. Also, physics demonstration devices such as Van de Graaff generators and Wimshurst machines can produce voltages approaching one million volts, yet at worst they deliver a brief sting. That is because the number of electrons involved is not high. These devices have a limited amount of stored energy, so the average current produced is low and usually for a short time, with impulses peaking in the amp range for a nanosecond. During the discharge, these machines apply high voltage to the body for only a millionth of a second or less. So a low-amperage current is applied for a very short time, and the number of electrons involved is very small.

The discharge may involve extremely high voltage over very short periods, but, to produce heart fibrillation, an electric power supply must produce a significant current (amperage) in the heart muscle continuing for many milliseconds, and must deposit a total energy in the range of at least millijoules or higher. A current of relatively high amperage at anything more than about fifty volts can therefore be medically significant and potentially fatal.

Tesla coils are not electrostatic machines and can produce significant currents for a sustained interval. Although their appearance in operation is similar to high voltage static electricity devices, the current supplied to a human body will be relatively constant as long as contact is maintained, and the voltage will be much higher than the break-down voltage of human skin. Used correctly, the output of a Tesla coil of proper design can have useful therapeutic effects.Used incorrectly, the output can be dangerous or even fatal.

Power lines

Power lines with high voltage warning sign.

Electrical transmission and distribution lines for electric power always use voltages significantly higher than 50 volts, so contact with or close approach to the line conductors presents a danger of electrocution. Contact with overhead wires is a frequent cause of injury or death. Metal ladders, farm equipment, boat masts, construction machinery, aerial antennas, and similar objects are frequently involved in fatal contact with overhead wires. Digging into a buried cable can also be dangerous to workers at an excavation site. Digging equipment (either hand tools or machine driven) that contacts a buried cable may energize piping or the ground in the area, resulting in electrocution of nearby workers. A fault in a high-voltage transmission line or substation may result in high currents flowing along the surface of the earth, producing an earth potential rise that also presents a danger of electric shock.

Unauthorized persons climbing on power pylons or electrical apparatus are also frequently the victims of electrocution. At very high transmission voltages even a close approach can be hazardous, since the high voltage may arc across a significant air gap.

For high-voltage and extra-high-voltage transmission lines, specially trained personnel use "live line" techniques to allow hands-on contact with energized equipment. In this case the worker is electrically connected to the high-voltage line but thoroughly insulated from the earth so that he is at the same electrical potential as that of the line. Since training for such operations is lengthy, and still presents a danger to personnel, only very important transmission lines are subject to maintenance while live. Outside these properly engineered situations, insulation from earth does not guarantee that no current flows to earth—as grounding or arcing to ground can occur in unexpected ways, and high-frequency currents can burn even an ungrounded person. Touching a transmitting antenna is dangerous for this reason, and a high-frequency Tesla coil can sustain a spark with only one endpoint.

Protective equipment on high-voltage transmission lines normally prevents formation of an unwanted arc, or ensures that it is quenched within tens of milliseconds. Electrical apparatus that interrupts high-voltage circuits is designed to safely direct the resulting arc so that it dissipates without damage. High voltage circuit breakers often use a blast of high pressure air, a special dielectric gas (such as SF6 under pressure), or immersion in mineral oil to quench the arc when the high voltage circuit is broken.

Arc flash hazard

High voltage testing arrangement with large capacitor and test transformer

Depending on the prospective short circuit current available at a switchgear line-up, a hazard is presented to maintenance and operating personnel due to the possibility of a high-intensity electric arc. Maximum temperature of an arc can exceed 10,000 kelvin, and the radiant heat, expanding hot air, and explosive vaporization of metal and insulation material can cause severe injury to unprotected workers. Such switchgear line-ups and high-energy arc sources are commonly present in electric power utility substations and generating stations, industrial plants and large commercial buildings. In the United States, the National Fire Protection Association, has published a guideline standard NFPA 70E for evaluating and calculating arc flash hazard, and provides standards for the protective clothing required for electrical workers exposed to such hazards in the workplace.

Explosion hazard

Main article: Electrical equipment in hazardous areas

Even voltages insufficient to break down air can be associated with enough energy to ignite atmospheres containing flammable gases or vapours, or suspended dust. For example, hydrogen gas, natural gas, or petrol/gasoline vapor mixed with air can be ignited by sparks produced by electrical apparatus. Examples of industrial facilities with hazardous areas are petrochemical refineries, chemical plants, grain elevators, and coal mines.

Measures taken to prevent such explosions include:

Intrinsic safety by the use of apparatus designed not to accumulate enough stored electrical energy to trigger an explosion

Increased safety, which applies to devices using measures such as oil-filled enclosures to prevent sparks

Explosion-proof (flame-proof) enclosures, which are designed so that an explosion within the enclosure cannot escape and ignite a surrounding explosive atmosphere (this designation does not imply that the apparatus can survive an internal or external explosion)

In recent years, standards for explosion hazard protection have become more uniform between European and North American practice. The "zone" system of classification is now used in modified form in U.S. National Electrical Code and in the Canadian Electrical Code. Intrinsic safety apparatus is now approved for use in North American applications.

Toxic gases

Electrical discharges, including partial discharge and corona, can produce small quantities of toxic gases, which in a confined space can be a serious health hazard. These gases include ozone and various oxides of nitrogen.

Lightning

The largest-scale sparks are those produced naturally by lightning. An average bolt of negative lightning carries a current of 30 to 50 kiloamperes, transfers a charge of 5 coulombs, and dissipates 500 megajoules of energy (120 kg TNT equivalent, or enough to light a 100-watt light bulb for approximately 2 months). However, an average bolt of positive lightning (from the top of a thunderstorm) may carry a current of 300 to 500 kiloamperes, transfer a charge of up to 300 coulombs, have a potential difference up to 1 gigavolt (a billion volts), and may dissipate 300 GJ of energy (72 tons TNT, or enough energy to light a 100-watt light bulb for up to 95 years). A negative lightning strike typically lasts for only tens of microseconds, but multiple strikes are common. A positive lightning stroke is typically a single event. However, the larger peak current may flow for hundreds of milliseconds, making it considerably hotter and more dangerous than negative lightning.

Hazards due to lightning obviously include a direct strike on persons or property. However, lightning can also create dangerous voltage gradients in the earth, as well as an electromagnetic pulse, and can charge extended metal objects such as telephone cables, fences, and pipelines to dangerous voltages that can be carried many miles from the site of the strike. Although many of these objects are not normally conductive, very high voltage can cause the electrical breakdown of such insulators, causing them to act as conductors. These transferred potentials are dangerous to people, livestock, and electronic apparatus. Lightning strikes also start fires and explosions, which result in fatalities, injuries, and property damage. For example, each year in North America, thousands of forest fires are started by lightning strikes.

Measures to control lightning can mitigate the hazard; these include lightning rods, shielding wires, and bonding of electrical and structural parts of buildings to form a continuous enclosure.

High-voltage lightning discharges in the atmosphere of Jupiter are thought to be the source of the planet's powerful radio frequency emissions.