Automatic power factor Correction using statcom

INTRODUCTIONIn an electric power system, a load with a low power factor draws more current than a load with a high power factor for the same amount of useful power transferred. The higher currents increase the energy lost in the distribution An automatic power factor correction unit consists of a number of capacitors that are switched by means of STATCOM. These contactors are controlled by a regulator that measures power factor in an electrical network. Depending on the load and power factor of the network, the power factor controller will vary the firing angle of the thyristor. This will vary the net value of the capacitance connected to the supply on system, and require larger wires and other equipment.

statcomA Static synchronous compensator operated as a shunt connected VAR generator whose capacitive and inductive output current can be controlled independent of the ac systemStatcom can control real and reactive powerIts main function is to control the voltage, and there by to improve transient stabilityIt absorbs or generate reactive power.

Line diagram of statcom

CHARACTERISTICS OF STATCOM A STATCOM has both turn off and turn on control capabilityIt generates an output ac voltage from a dc voltageThe ac voltage is controllable both in magnitude and phase angleA statcom is also capable to exchange active power with the power system by adding an energy source in the dc sideLike svc, the main function of a statcom is to absorb or generate reactive power

Current-voltage characteristics

BLOCK DIAGRAM

CT AND PTWhen we need to measure the voltage we will step down the normal 230v ac supply to 12v ac signal using the pt. From the pt the voltage signal is given to the peak detector section. When we need to measure the current we will use a current transformer to decrease the magnitude of the current.The output of the ct is flown through a resistor. Now the voltage across this resistor depends on the current of the load. So if we measure the voltage across this resistor this will represent the current flowing to the load with suitable multiplying factor.The voltage from this resistor is given to the peak detector section.

POWER SUPPLYDifferent stages in the power supply are:step down transformer: used to convert the high voltage 230v ac into 12v ac.Bridge Rectifier: used to convert ac into dc.Capacitor filter: This is used to remove the ripples in the output dc voltage from the rectifier.Voltage regulator: used to convert the variable dc into constant 5v dc.

Zero crossing detectorWhen we need to compare two analog signals we will use zero crossing detector.We are using opamp as a zero crossing detector . The opamp ic used in our application is LM324.LM324 has four opamps internally.Comparator has two inputs:

Non inverting input and Inverting input.

Opto couplersOptocouplers use a beam of light to transmit the signals or data across an electrical barrier, and achieve excellent isolation.Optocouplers typically come in a small 6-pin or 8-pin IC package, but are essentially a combination of two distinct devices: an optical transmitter, typically a gallium arsenide LED (light-emitting diode) and an optical receiver such as a phototransistor or light-triggered diac. The two are separated by a transparent barrier which blocks any electrical current flow between the two, but does allow the passage of light.

Symbol of Opto coupler

TRAIC Glass passivated, sensitive gate triacs in a plastic envelope, intended for use in general purpose bidirectional switching and phase control applications, where high voltages sensitivity is required in all four quadrants.

MICRO CONTROLLERWe are using AT89s52 micro controller in our application.This is an updated version of 8052 micro controller seires.Some of the features of the micro controller are:4 ports of 8 bits each8 kb flash memory256 x 8 bits internal RAM.One serial port.Three timers or counters.

LIQUID CRYSTAL DISPLAY:In this project we have used a 16x2 alpha numeric LCD to display the status of the motor. This lcd is connected to the microcontroller through the port 1. This lcd contains a port named RS which makes the lcd to know whether the code send by the microcontroller is data or the instruction. The port RW of the lcd will make the lcd to know whether we are writing the data to the lcd or reading the data. As in this circuit we are only writing the data to the lcd we connected this pin directly to the gnd.

Liquid crystal display