Power system,supplies and sources of energy?

Summary of power system

In an ordinary  power system the electric power from generating station via transmission and distribution systems reach the loads of various nature depending upon the usage.This journey takes place from supply to the loads via various other sections.

typical grid station

Sources for power system

Sources for power system may be internal and external depending upon the requirements.The external source is from external side to the power system internal power systems are part of the power system.

Sources of power production

Power is alternating current power or direct current power.Batteries,photo voltaic cell or fuel cells can be used to obtain direct current power.While on the other hand rotor is rotated between magnetic field of a device for the generation of alternating current power.Such a device involving rotor is known as turbo generator.Now how to rotate or spin rotor in a magnetic field, there are some special techniques employed for this purpose.The spinning of rotor can be with steam heating using fossil fuels or falling water or nuclear or wind power.

Some rotors types

1) Squirrel cage rotor

2) wound rotor

3) cylindrical rotor

4) salient pole rotor

Speed and Frequency of power

Generators produce alternating current power and the frequency of this alternating current power is determined by speed of rotor spinning and the number of poles on the generator.If load on the power system increases,the more torque is required for the generator to spin.Ordinarily the fuel or steam is directly related to the quantity of electrical energy supplied.

Phases of power and operation

Alternating current generators can produce variable number of phases.One interesting point about power system operation is that more phase increase the efficiency of the power system.Furthermore for efficient power system the basic structure of the power system increases

Some considerations in power system

One big consideration in power system is the same frequency and phases of multiple  generators and loads that are connected by"grids of electricity".Furthermore considerations are as follows,

starting time of generator

amount of energy that a generator will supply

the mechanism by which generator will start
nature of generator
nature of rotor
speed of turbine and number of poles

Phase nature in power system

Typically three phase at 50 or 60 Hz is employed.In our residences and homes single phase is used.The best example of single phase is "Toaster" draws current from 2 to 10 amp at 110 to 260 volt at power consuming rate of 600 to 1200 watts.

Types

DC power supply
A DC power supply is one that supplies a constant DC voltage to its load. Depending on its design, a DC power supply may be powered from a DC source or from an AC source such as the power mains.
AC-to-DC supply

Schematic of basic AC-to-DC power supply, showing (from L-R) transformer, full-wave bridge rectifier, filter capacitor and resistor load
Some DC power supplies use AC mains electricity as an energy source. Such power supplies will sometimes employ a transformer to convert the input voltage to a higher or lower AC voltage. A rectifier is used to convert the transformer output voltage to a varying DC voltage, which in turn is passed through an electronic filter to convert it to an unregulated DC voltage.

The filter removes most, but not all of the AC voltage variations; the remaining AC voltage is known as ripple. The electric load's tolerance of ripple dictates the minimum amount of filtering that must be provided by a power supply. In some applications, high ripple is tolerated and therefore no filtering is required. For example, in some battery charging applications it is possible to implement a mains-powered DC power supply with nothing more than a transformer and a single rectifier diode, with a resistor in series with the output to limit charging current.

Linear regulator
The function of a linear voltage regulator is to convert a varying DC voltage to a constant, often specific, lower DC voltage. In addition, they often provide a current limiting function to protect the power supply and load from overcurrent (excessive, potentially destructive current).

A constant output voltage is required in many power supply applications, but the voltage provided by many energy sources will vary with changes in load impedance. Furthermore, when an unregulated DC power supply is the energy source, its output voltage will also vary with changing input voltage. To circumvent this, some power supplies use a linear voltage regulator to maintain the output voltage at a steady value, independent of fluctuations in input voltage and load impedance. Linear regulators can also reduce the magnitude of ripple and noise present appearing on the output voltage.

AC power supplies

An AC power supply typically takes the voltage from a wall outlet (mains supply) and lowers it to the desired voltage. Some filtering may take place as well.

In modern use, AC power supplies can be divided into single phase and three phase systems. "The primary difference between single phase and three phase AC power is the constancy of delivery."  AC power Supplies can also be used to change the frequency as well as the voltage, they are often used by manufacturers to check the suitability of their products for use in other countries. 230V 50 Hz or 115 60 Hz or even 400 Hz for avionics testing.

Switched-mode power supply

Main article: Switched-mode power supply
In a switched-mode power supply (SMPS), the AC mains input is directly rectified and then filtered to obtain a DC voltage. The resulting DC voltage is then switched on and off at a high frequency by electronic switching circuitry, thus producing an AC current that will pass through a high-frequency transformer or inductor. Switching occurs at a very high frequency (typically 10 kHz — 1 MHz), thereby enabling the use of transformers and filter capacitors that are much smaller, lighter, and less expensive than those found in linear power supplies operating at mains frequency. After the inductor or transformer secondary, the high frequency AC is rectified and filtered to produce the DC output voltage. If the SMPS uses an adequately insulated high-frequency transformer, the output will be electrically isolated from the mains; this feature is often essential for safety.

Switched-mode power supplies are usually regulated, and to keep the output voltage constant, the power supply employs a feedback controller that monitors current drawn by the load. The switching duty cycle increases as power output requirements increase.

SMPSs often include safety features such as current limiting or a crowbar circuit to help protect the device and the user from harm. In the event that an abnormal high-current power draw is detected, the switched-mode supply can assume this is a direct short and will shut itself down before damage is done. PC power supplies often provide a power good signal to the motherboard; the absence of this signal prevents operation when abnormal supply voltages are present.

Some SMPSs have an absolute limit on their minimum current output. They are only able to output above a certain power level and cannot function below that point. In a no-load condition the frequency of the power slicing circuit increases to great speed, causing the isolated transformer to act as a Tesla coil, causing damage due to the resulting very high voltage power spikes. Switched-mode supplies with protection circuits may briefly turn on but then shut down when no load has been detected. A very small low-power dummy load such as a ceramic power resistor or 10-watt light bulb can be attached to the supply to allow it to run with no primary load attached.

The switch-mode power supplies used in computers have historically had low power factors and have also been significant sources of line interference (due to induced power line harmonics and transients). In simple switch-mode power supplies, the input stage may distort the line voltage waveform, which can adversely affect other loads (and result in poor power quality for other utility customers), and cause unnecessary heating in wires and distribution equipment. Furthermore, customers incur higher electric bills when operating lower power factor loads. To circumvent these problems, some computer switch-mode power supplies perform power factor correction, and may employ input filters or additional switching stages to reduce line interference.Courtesy of wikipedia....