What is electronic component OPTO COUPLER or OPTO ISOLATOR?

Opto-isolator

Schematic diagram of an opto-isolator showing source of light (LED) on the left, dielectric barrier in the center, and sensor (phototransistor) on the right.

In electronics, an opto-isolator, also called an optocoupler, photocoupler, or optical isolator, is a component that transfers electrical signals between two isolated circuits by using light. Opto-isolators prevent high voltages from affecting the system receiving the signal. Commercially available opto-isolators withstand input-to-output voltages up to 10 kV and voltage transients with speeds up to 10 kV/μs.

opto isolator

A common type of opto-isolator consists of an LED and a phototransistor in the same opaque package. Other types of source-sensor combinations include LED-photodiode, LED-LASCR, and lamp-photoresistor pairs. Usually opto-isolators transfer digital (on-off) signals, but some techniques allow them to be used with analog signals.

History

The value of optically coupling a solid state light emitter to a semiconductor detector for the purpose of electrical isolation was recognized in 1963 by Akmenkalns,et al. (US patent 3,417,249). Photoresistor-based opto-isolators were introduced in 1968. They are the slowest, but also the most linear isolators and still retain a niche market in audio and music industry. Commercialization of LED technology in 1968–1970 caused a boom in optoelectronics, and by the end of the 1970s the industry developed all principal types of opto-isolators. The majority of opto-isolators on the market use bipolar silicon phototransistor sensors. They attain medium data transfer speed, sufficient for applications like electroencephalography.The fastest opto-isolators use PIN diodes in photoconductive mode.

Operation

An opto-isolator contains a source (emitter) of light, almost always a near infrared light-emitting diode (LED), that converts electrical input signal into light, a closed optical channel (also called dielectrical channel), and a photosensor, which detects incoming light and either generates electric energy directly, or modulates electric current flowing from an external power supply. The sensor can be a photoresistor, a photodiode, a phototransistor, a silicon-controlled rectifier (SCR) or a triac. Because LEDs can sense light in addition to emitting it, construction of symmetrical, bidirectional opto-isolators is possible. An optocoupled solid state relay contains a photodiode opto-isolator which drives a power switch, usually a complementary pair of MOSFETs. A slotted optical switch contains a source of light and a sensor, but its optical channel is open, allowing modulation of light by external objects obstructing the path of light or reflecting light into the sensor.

Electric isolation

Planar (top) and silicone dome (bottom) layouts - cross-section through a standard dual in-line package. Relative sizes of LED (red) and sensor (green) are exaggerated.

Electronic equipment and signal and power transmission lines can be subjected to voltage surges induced by lightning, electrostatic discharge, radio frequency transmissions, switching pulses (spikes) and perturbations in power supply.[8] Remote lightning strikes can induce surges up to 10 kV, one thousand times more than the voltage limits of many electronic components.A circuit can also incorporate high voltages by design, in which case it needs safe, reliable means of interfacing its high-voltage components with low-voltage ones.

The main function of an opto-isolator is to block such high voltages and voltage transients, so that a surge in one part of the system will not disrupt or destroy the other parts. Historically, this function was delegated to isolation transformers, which use inductive coupling between galvanically isolated input and output sides. Transformers and opto-isolators are the only two classes of electronic devices that offer reinforced protection — they protect both the equipment and the human user operating this equipment. They contain a single physical isolation barrier, but provide protection equivalent to double isolation.[12] Safety, testing and approval of opto-couplers are regulated by national and international standards: IEC 60747-5-2, EN (CENELEC) 60747-5-2, UL 1577, CSA Component Acceptance Notice #5, etc.Opto-isolator specifications published by manufacturers always follow at least one of these regulatory frameworks.

An opto-isolator connects input and output sides with a beam of light modulated by input current. It transforms useful input signal into light, sends it across the dielectric channel, captures light on the output side and transforms it back into electric signal. Unlike transformers, which pass energy in both directions with very low losses, opto-isolators are unidirectional (see exceptions) and they cannot transmit power. Typical opto-isolators can only modulate the flow of energy already present on the output side. Unlike transformers, opto-isolators can pass DC or slow-moving signals and do not require matching impedances between input and output sides.[note 4] Both transformers and opto-isolators are effective in breaking ground loops, common in industrial and stage equipment, caused by high or noisy return currents in ground wires.

The physical layout of an opto-isolator depends primarily on the desired isolation voltage. Devices rated for less than a few kV have planar (or sandwich) construction.The sensor die is mounted directly on the lead frame of its package (usually, a six-pin or a four-pin dual in-line package). The sensor is covered with a sheet of glass or clear plastic, which is topped with the LED die. The LED beam fires downward. To minimize losses of light, the useful absorption spectrum of the sensor must match the output spectrum of the LED, which almost invariably lies in the near infrared. The optical channel is made as thin as possible for a desired breakdown voltage. For example, to be rated for short-term voltages of 3.75 kV and transients of 1 kV/μs, the clear polyimide sheet in the Avago ASSR-300 series is only 0.08 mm thick. Breakdown voltages of planar assemblies depend on the thickness of the transparent sheet and the configuration of bonding wires that connect the dies with external pins. Real in-circuit isolation voltage is further reduced by creepage over the PCB and the surface of the package. Safe design rules require a minimal clearance of 25 mm/kV for bare metal conductors or 8.3 mm/kV for coated conductors.

Opto-isolators rated for 2.5 to 6 kV employ a different layout called silicone dome. Here, the LED and sensor dies are placed on the opposite sides of the package; the LED fires into the sensor horizontally. The LED, the sensor and the gap between them are encapsulated in a blob, or dome, of transparent silicone. The dome acts as a reflector, retaining all stray light and reflecting it onto the surface of the sensor, minimizing losses in a relatively long optical channel. In double mold designs the space between the silicone blob ("inner mold") and the outer shell ("outer mold") is filled with dark dielectric compound with a matched coefficient of thermal expansion.

Types of opto-isolators

Device type Source of light Sensor type Speed Current transfer ratio

Resistive opto-isolator

(Vactrol) Incandescent light bulb CdS or CdSe photoresistor (LDR) Very low <100%[note 6]

Neon lamp Low

GaAs infrared LED Low

Diode opto-isolator GaAs infrared LED Silicon photodiode Highest 0.1–0.2%

Transistor opto-isolator GaAs infrared LED Bipolar silicon phototransistor Medium 2–120%

Darlington phototransistor Medium 100–600%

Opto-isolated SCR GaAs infrared LED Silicon-controlled rectifier Low to medium >100%

Opto-isolated triac GaAs infrared LED TRIAC Low to medium Very high

Solid-state relay Stack of GaAs infrared LEDs Stack of photodiodes driving

a pair of MOSFETs or an IGBT Low to high Practically unlimited

Resistive opto-isolators

The earliest opto-isolators, originally marketed as light cells, emerged in the 1960s. They employed miniature incandescent light bulbs as sources of light, and cadmium sulfide (CdS) or cadmium selenide (CdSe) photoresistors (also called light-dependent resistors, LDRs) as receivers. In applications where control linearity was not important, or where available current was too low for driving an incandescent bulb (as was the case in vacuum tube amplifiers), it was replaced with a neon lamp. These devices (or just their LDR component) were commonly named Vactrols, after a trademark of Vactec, Inc. The trademark has since been genericized, but the original Vactrols are still being manufactured by PerkinElmer.

The turn-on and turn-off lag of an incandescent bulb lies in hundreds of milliseconds range, which makes the bulb an effective low-pass filter and rectifier but limits the practical modulation frequency range to a few Hertz. With the introduction of light-emitting diodes (LEDs) in 1968–1970, the manufacturers replaced incandescent and neon lamps with LEDs and achieved response times of 5 milliseconds and modulation frequencies up to 250 Hz. The name Vactrol was carried over on LED-based devices which are, as of 2010, still produced in small quantities.

Photoresistors used in opto-isolators rely on bulk effects in a uniform film of semiconductor; there are no p-n junctions. Uniquely among photosensors, photoresistors are non-polar devices suited for either AC or DC circuits.Their resistance drops in reverse proportion to the intensity of incoming light, from virtually infinity to a residual floor that may be as low as less than a hundred Ohms. These properties made the original Vactrol a convenient and cheap automatic gain control and compressor for telephone networks. The photoresistors easily withstood voltages up to 400 volts, which made them ideal for driving vacuum fluorescent displays. Other industrial applications included photocopiers, industrial automation, professional light measurement instruments and auto-exposure meters. Most of these applications are now obsolete, but resistive opto-isolators retained a niche in audio, in particular guitar amplifier, markets.

American guitar and organ manufacturers of the 1960s embraced the resistive opto-isolator as a convenient and cheap tremolo modulator. Fender's early tremolo effects used two vacuum tubes; after 1964 one of these tubes was replaced by an optocoupler made of a LDR and a neon lamp.To date, Vactrols activated by pressing the stompbox pedal are ubiquitous in the music industry. Shortages of genuine PerkinElmer Vactrols forced the DIY guitar community to "roll their own" resistive opto-isolators. Guitarists to date prefer opto-isolated effects because their superior separation of audio and control grounds results in "inherently high quality of the sound". However, the distortion introduced by a photoresistor at line level signal is higher than that of a professional electrically-coupled voltage-controlled amplifier.Performance is further compromised by slow fluctuations of resistance owing to light history, a memory effect inherent in cadmium compounds. Such fluctuations take hours to settle and can be only partially offset with feedback in the control circuit.

Photodiode opto-isolators

A fast photodiode opto-isolator with an output-side amplifier circuit.

Diode opto-isolators employ LEDs as sources of light and silicon photodiodes as sensors. When the photodiode is reverse-biased with an external voltage source, incoming light increases the reverse current flowing through the diode. The diode itself does not generate energy; it modulates the flow of energy from an external source. This mode of operation is called photoconductive mode. Alternatively, in the absence of external bias the diode converts the energy of light into electric energy by charging its terminals to a voltage of up to 0.7 V. The rate of charge is proportional to the intensity of incoming light. The energy is harvested by draining the charge through an external high-impedance path; the ratio of current transfer can reach 0.2%. This mode of operation is called photovoltaic mode.

The fastest opto-isolators employ PIN diodes in photoconductive mode. The response times of PIN diodes lie in the subnanosecond range; overall system speed is limited by delays in LED output and in biasing circuitry. To minimize these delays, fast digital opto-isolators contain their own LED drivers and output amplifiers optimized for speed. These devices are called full logic opto-isolators: their LEDs and sensors are fully encapsulated within a digital logic circuit.[34] The Hewlett-Packard 6N137/HPCL2601 family of devices equipped with internal output amplifiers was introduced in the late 1970s and attained 10 MBd data transfer speed. It remained an industry standard until the introduction of the 50 MBd Agilent Technologies 7723/0723 family in 2002. The 7723/0723 series opto-isolators contain CMOS LED drivers and a CMOS buffered amplifiers, which require two independent external power supplies of 5 V each.

Photodiode opto-isolators can be used for interfacing analog signals, although their non-linearity invariably distorts the signal. A special class of analog opto-isolators introduced by Burr-Brown uses two photodiodes and an input-side operational amplifier to compensate for diode non-linearity. One of two identical diodes is wired into the feedback loop of the amplifier, which maintains overall current transfer ratio at a constant level regardless of the non-linearity in the second (output) diode.[38]

A novel idea of a particular optical analog signal isolator was submitted on 3, June 2011. The proposed configuration consist of two different parts. One of them transfers the signal, and the other establishes a negative feedback to ensure that the output signal has the same features as the input signal. This proposed analog isolator is linear over a wide range of input voltage and frequency. However linear opto couplers using this principle have been available for many years, for example the IL300.

Solid-state relays built around MOSFET switches usually employ a photodiode opto-isolator to drive the switch. The gate of a MOSFET requires relatively small total charge to turn on and its leakage current in steady state is very low. A photodiode in photovoltaic mode can generate turn-on charge in a reasonably short time but its output voltage is many times less than the MOSFET's threshold voltage. To reach the required threshold, solid-state relays contain stacks of up to thirty photodiodes wired in series.

Phototransistor opto-isolators

Phototransistors are inherently slower than photodiodes. The earliest and the slowest but still common 4N35 opto-isolator, for example, has rise and fall times of 5 μs into a 100 Ohm load and its bandwidth is limited at around 10 kilohertz - sufficient for applications like electroencephalography or pulse-width motor control. Devices like PC-900 or 6N138 recommended in the original 1983 Musical Instrument Digital Interface specification allow digital data transfer speeds of tens of kiloBauds.Phototransistors must be properly biased and loaded to achieve their maximum speeds, for example, the 4N28 operates at up to 50 kHz with optimum bias and less than 4 kHz without it.

Design with transistor opto-isolators requires generous allowances for wide fluctuations of parameters found in commercially available devices. Such fluctuations may be destructive, for example, when an opto-isolator in the feedback loop of a DC-to-DC converter changes its transfer function and causes spurious oscillations, or when unexpected delays in opto-isolators cause a short circuit through one side of an H-bridge.Manufacturers' datasheets typically list only worst-case values for critical parameters; actual devices surpass these worst-case estimates in an unpredictable fashion. Bob Pease observed that current transfer ratio in a batch of 4N28's can vary from 15% to more than 100%; the datasheet specified only a minimum of 10%. Transistor beta in the same batch can vary from 300 to 3000, resulting in 10:1 variance in bandwidth.

Opto-isolators using field-effect transistors (FETs) as sensors are rare and, like vactrols, can be used as remote-controlled analog potentiometers provided that the voltage across the FET's output terminal does not exceed a few hundred mV.[38] Opto-FETs turn on without injecting switching charge in the output circuit, which is particularly useful in sample and hold circuits.

Bidirectional opto-isolators

All opto-isolators described so far are uni-directional. Optical channel always works one way, from the source (LED) to the sensor. The sensors, be it photoresistors, photodiodes or phototransistors, cannot emit light. But LEDs, like all semiconductor diodes, are capable of detecting incoming light, which makes possible construction of a two-way opto-isolator from a pair of LEDs. The simplest bidirectional opto-isolator is merely a pair of LEDs placed face to face and held together with heat-shrink tubing. If necessary, the gap between two LEDs can be extended with a glass fiber insert.

Visible spectrum LEDs have relatively poor transfer efficiency, thus near infrared spectrum GaAs, GaAs:Si and AlGaAs:Si LEDs are the preferred choice for bidirectional devices. Bidirectional opto-isolators built around pairs of GaAs:Si LEDs have current transfer ratio of around 0.06% in either photovoltaic or photoconductive mode — less than photodiode-based isolators, but sufficiently practical for real-world applications.

Aerospace engineering with extensive concepts?

Aerospace engineering

Aerospace engineering is the primary field of engineering concerned with the development of aircraft and spacecraft. It has two major and overlapping branches: aeronautical engineering and astronautical engineering. Avionics engineering is similar but deals with the electrical side of aerospace engineering.

assembly of equipments

Aeronautical engineering was the original term for the field. As flight technology advanced to include craft operating in outer space (astronautics), the broader term "aerospace engineering" has largely replaced it in common usage. Aerospace engineering, particularly the astronautics branch, is often colloquially referred to as "rocket science".

Overview

Flight vehicles are subjected to demanding conditions such as those produced by changes in atmospheric pressure and temperature, with structural loads applied upon vehicle components. Consequently, they are usually the products of various technological and engineering disciplines including aerodynamics, propulsion, avionics, materials science, structural analysis and manufacturing. The interaction between these technologies is known as aerospace engineering. Because of the complexity and number of disciplines involved, aerospace engineering is carried out by teams of engineers, each having their own specialized area of expertise.

History

Orville and Wilbur Wright flew the Wright Flyer in 1903 at Kitty Hawk, North Carolina.

The origin of aerospace engineering can be traced back to the aviation pioneers around the late 19th to early 20th centuries, although the work of Sir George Cayley dates from the last decade of the 18th to mid-19th century. One of the most important people in the history of aeronautics, Cayley was a pioneer in aeronautical engineering and is credited as the first person to separate the forces of lift and drag, which are in effect on any flight vehicle. Early knowledge of aeronautical engineering was largely empirical with some concepts and skills imported from other branches of engineering. Scientists understood some key elements of aerospace engineering, like fluid dynamics, in the 18th century. Many years later after the successful flights by the Wright brothers, the 1910s saw the development of aeronautical engineering through the design of World War I military aircraft.

The first definition of aerospace engineering appeared in February 1958. The definition considered the Earth's atmosphere and the outer space as a single realm, thereby encompassing both aircraft (aero) and spacecraft (space) under a newly coined word aerospace. In response to the USSR launching the first satellite, Sputnik into space on October 4, 1957, U.S. aerospace engineers launched the first American satellite on January 31, 1958. The National Aeronautics and Space Administration was founded in 1958 as a response to the Cold War.

This section needs expansion with: newer history, including recent events. You can help by adding to it. (November 2009)

Elements

Wernher von Braun, with the F-1 engines of the Saturn V first stage at the US Space and Rocket Center

Soyuz TMA-14M spacecraft engineered for descent by parachute

See also: List of aerospace engineering topics

Some of the elements of aerospace engineering are:

A fighter jet engine undergoing testing. The tunnel behind the engine allows noise and exhaust to escape.

Radar cross-section – the study of vehicle signature apparent to Radar remote sensing.

Fluid mechanics – the study of fluid flow around objects. Specifically aerodynamics concerning the flow of air over bodies such as wings or through objects such as wind tunnels (see also lift and aeronautics).

Astrodynamics – the study of orbital mechanics including prediction of orbital elements when given a select few variables. While few schools in the United States teach this at the undergraduate level, several have graduate programs covering this topic (usually in conjunction with the Physics department of said college or university).

Statics and Dynamics (engineering mechanics) – the study of movement, forces, moments in mechanical systems.

Mathematics – in particular, calculus, differential equations, and linear algebra.

Electrotechnology – the study of electronics within engineering.

Propulsion – the energy to move a vehicle through the air (or in outer space) is provided by internal combustion engines, jet engines and turbomachinery, or rockets (see also propeller and spacecraft propulsion). A more recent addition to this module is electric propulsion and ion propulsion.

Control engineering – the study of mathematical modeling of the dynamic behavior of systems and designing them, usually using feedback signals, so that their dynamic behavior is desirable (stable, without large excursions, with minimum error). This applies to the dynamic behavior of aircraft, spacecraft, propulsion systems, and subsystems that exist on aerospace vehicles.

Aircraft structures – design of the physical configuration of the craft to withstand the forces encountered during flight. Aerospace engineering aims to keep structures lightweight and low-cost, while maintaining structural integrity

Materials science – related to structures, aerospace engineering also studies the materials of which the aerospace structures are to be built. New materials with very specific properties are invented, or existing ones are modified to improve their performance.

Solid mechanics – Closely related to material science is solid mechanics which deals with stress and strain analysis of the components of the vehicle. Nowadays there are several Finite Element programs such as MSC Patran/Nastran which aid engineers in the analytical process.

Aeroelasticity – the interaction of aerodynamic forces and structural flexibility, potentially causing flutter, divergence, etc.

Avionics – the design and programming of computer systems on board an aircraft or spacecraft and the simulation of systems.

Software – the specification, design, development, test, and implementation of computer software for aerospace applications, including flight software, ground control software, test & evaluation software, etc.

Risk and reliability – the study of risk and reliability assessment techniques and the mathematics involved in the quantitative methods.

Noise control – the study of the mechanics of sound transfer.

Aeroacoustics – the study of noise generation via either turbulent fluid motion or aerodynamic forces interacting with surfaces.

Flight test – designing and executing flight test programs in order to gather and analyze performance and handling qualities data in order to determine if an aircraft meets its design and performance goals and certification requirements.

The basis of most of these elements lies in theoretical physics, such as fluid dynamics for aerodynamics or the equations of motion for flight dynamics. There is also a large empirical component. Historically, this empirical component was derived from testing of scale models and prototypes, either in wind tunnels or in the free atmosphere. More recently, advances in computing have enabled the use of computational fluid dynamics to simulate the behavior of fluid, reducing time and expense spent on wind-tunnel testing. Those studying hydrodynamics or Hydroacoustics often obtained degrees in Aerospace Engineering.

Additionally, aerospace engineering addresses the integration of all components that constitute an aerospace vehicle (subsystems including power, aerospace bearings, communications, thermal control, life support, etc.) and its life cycle (design, temperature, pressure, radiation, velocity, lifetime).

Degree programs

Main article: List of aerospace engineering schools

Aerospace engineering may be studied at the advanced diploma, bachelor's, master's, and Ph.D. levels in aerospace engineering departments at many universities, and in mechanical engineering departments at others. A few departments offer degrees in space-focused astronautical engineering. Some institutions differentiate between aeronautical and astronautical engineering. Graduate degrees are offered in advanced or specialty areas for the aerospace industry.

A background in chemistry, physics, computer science and mathematics is important for students pursuing an aerospace engineering degree.

In popular culture

The term "rocket scientist" is sometimes used to describe a person of great intelligence since "rocket science" is seen as a practice requiring great mental ability, especially technical and mathematical ability. The term is used ironically in the expression "It's not rocket science" to indicate that a task is simple. Strictly speaking, the use of "science" in "rocket science" is a misnomer since science is about understanding the origins, nature, and behavior of the universe; engineering is about using scientific and engineering principles to solve problems and develop new technology. However, the media and the public often use "science" and "engineering" as synonyms.

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.