Voltage stability by compensating reactive

power

What this project is about??

• This project will illustrate the basic issues related to voltage instability by considering the characteristics of transmission system and afterwards examining how we can improve voltage stability by using reactive power compensation devices.

• Its about how voltage is being brought back to same(nearby) value by compensating reactive power

PRINCIPAL CAUSES OF VOLTAGE STABILITY PROBLEMS

• High reactive power consumption at heavy loads• Generating stations are too far from load centres.• We have observed this from simulation of a case by increasing the

length of the PI section transmission line.• Source voltages are too low.• Poor coordination between various control and protective systems.

Why only reactive power

Ways of improving voltage stability and control• Reactive power compensation is often most effective way to improve both

power transfer capability and voltage stability. The control of voltage levels is accomplished by controlling the production, absorption and flow of reactive power.• To control voltage throughout the system we have to use addition devices to

compensate reactive power.• The device used for this purpose are:

Shunt capacitorsSeries capacitorsShunt reactorsSynchronous condensersSVC(Static Var compensator)STATCOM(Static Synchronous Compensator)

• In this project we will be discussing two of them namely Shunt compensation (by using capacitor banks)SVC(by using thyristors and PWM blocks)

Shunt Compensation (by using Capacitor)• The primary purpose of transmission system shunt compensation

near load areas is voltage control and load stabilization. In other words, shunt capacitors are used to ensure satisfactory voltage levels during heavy load conditions.• Shunt capacitors are used in power system for power-factor

correction. The objective of power factor correction is to provide reactive power close to point where it is being consumed, rather than supply it from remote sources.

For voltage stability, shunt capacitor banks are very useful on allowing nearby generators to operate near unity power factor.

The Qc that we got here should be added to the reactive power loss at the transmission line and Margin of 8-9% of the load reactive power should be added to get the reference voltage value

• We can also calculate the capacitance that will inject the required power by equations

Advantages & Disadvantages

• AdvantagesMuch lower cost compared to SVCSwitching speeds can be quite fast when compared to other compensation

devices

• DisadvantagesWith the increase in voltages the capacitor value(in turn the size) increases

which is difficult to design themPrecise and rapid control of voltages are not possible.

SVC

SVC(Matlab Implementation)

• In SVC we are comparing the Input voltage(reference voltage) and the voltage at the bus by using a summer and the output is given to the input of PID controller and then it is given to PWM controller (which can be used as feed back )and then the output are taken as control pulses to the both thyristors and then the output is given to injection transformer which will eliminate the unwanted harmonics of the output.

Advantages and disadvantages

• Advantages• The main advantage of SVCs over simple capacitor bank

compensation schemes is their near-instantaneous response to changes in the system voltage• Dynamic compensation can be achieved by SVC• Disadvantages:• However, static VAR compensators are more expensive than

Capacitor banks.

THANK YOU