Seminar Topic on

Importance of Reactive Power for Power System

Presented by-Devendra Mishra EN-14

1401421020

OUTLINE OF PRESENTATION

INTRODUCTION

IMPORTANCE OF REACTIVE POWER

NESSARY TO CONTROL OF VOLTAGE & REACTIVE POWER

BASIC CONCEPT OF REACTIVE POWER

IntroductionWe always in practice to reduce reactive power to improve

system efficiency .This are acceptable at some level. If system is purely resistively or capacitance it make cause some problem in Electrical system. Alternating systems supply or consume two kind of power: real power and reactive power.

Real power accomplishes useful work while reactive power supports the voltage that must be controlled for system reliability. Reactive power has a profound effect on the security of power systems because it affects voltages throughout the system.

Find important discussion regarding importance about Reactive Power and how it is useful to maintain System voltage healthy

Importance of Reactive Power Voltage control in an electrical power system is important

for proper operation for electrical power equipment to prevent damage such as overheating of generators and motors, to reduce transmission losses and to maintain the ability of the system to withstand and prevent voltage collapse.

Decreasing reactive power causing voltage to fall while increasing it causing voltage to rise. A voltage collapse may be occurs when the system try to serve much more load than the voltage can support.

When reactive power supply lower voltage, as voltage drops current must increase to maintain power supplied, causing system to consume more reactive power and the voltage drops further . If the current increase too much, transmission lines go off line, overloading other lines and potentially causing cascading failures.

If the voltage drops too low, some generators will disconnect automatically to protect themselves. Voltage collapse occurs when an increase in load or less generation or transmission facilities causes dropping voltage, which causes a further reduction in reactive power from capacitor and line charging, and still there further voltage reductions. If voltage reduction continues, these will cause additional elements to trip, leading further reduction in voltage and loss of the load. The result in these entire progressive and uncontrollable declines in voltage is that the system unable to provide the reactive power required supplying the reactive power demands

 Necessary to Control of Voltage and Reactive Power

Voltage control and reactive power management are two aspects of a single activity that both supports reliability and facilitates commercial transactions across transmission networks.

On an alternating current (AC) power system, voltage is controlled by managing production and absorption of reactive power.

There are three reasons why it is necessary to manage reactive power and control voltage

First, both customer and power system equipment are designed to operate within a range of voltages, usually within±5% of the nominal voltage. At low voltages, many types of equipment perform poorly, light bulbs provide less illumination, induction motors can overheat and be damaged, and some electronic equipment will not operate at. High voltages can damage equipment and shorten their lifetimes.

Second, reactive power consumes transmission and generation resources. To maximize the amount of real power that can be transferred across a congested transmission interface, reactive power flows must be minimized. Similarly, reactive power production can limit a generator’s real power capability.

Third, moving reactive power on the transmission system incurs real power losses. Both capacity and energy must be supplied to replace these losses.

Voltage control is complicated by two additional factors.

First, the transmission system itself is a nonlinear consumer of reactive power, depending on system loading. At very light loading the system generates reactive power that must be absorbed, while at heavy loading the system consumes a large amount of reactive power that must be replaced. The system’s reactive power requirements also depend on the generation and transmission configuration.

Consequently, system reactive requirements vary in time as load levels and load and generation patterns change. The bulk power system is composed of many pieces of equipment, any one of which can fail at any time. Therefore, the system is designed to withstand the loss of any single piece of equipment and to continue operating without impacting any customers. That is, the system is designed to withstand a single contingency. The loss of a generator or a major transmission line can have the compounding effect of reducing the reactive supply and, at the same time, reconfiguring flows such that the system is consuming additional reactive power.

At least a portion of the reactive supply must be capable of responding quickly to changing reactive power demands and to maintain acceptable voltages throughout the system. Thus, just as an electrical system requires real power reserves to respond to contingencies, so too it must maintain reactive-power reserves.

Loads can also be both real and reactive. The reactive portion of the load could be served from the transmission system. Reactive loads incur more voltage drop and reactive losses in the transmission system than do similar size (MVA) real loads.

Basic concept of Reactive Power

 Why We Need Reactive Power- Active power is the energy supplied to run a motor, heat a

home, or illuminate an electric light bulb. Reactive power provides the important function of regulating voltage.

If voltage on the system is not high enough, active power cannot be supplied.

Reactive power is used to provide the voltage levels necessary for active power to do useful work.

Reactive power is essential to move active power through the transmission and distribution system to the customer .Reactive power is required to maintain the voltage to deliver active power (watts) through transmission lines.

• Motor loads and other loads require reactive power to convert the flow of electrons into useful work.

• When there is not enough reactive power, the voltage sags down and it is not possible to push the power demanded by loads through the lines.”

Reactive Power is a Byproduct of AC Systems Transformers, Transmission lines, and motors require

reactive power. Electric motors need reactive power to produce magnetic fields for their operation.

Transformers and transmission lines introduce inductance as well as resistance

I. Both oppose the flow of currentII. Must raise the voltage higher to push the power through the

inductance of the linesIII. Unless capacitance is introduced to offset inductance

How Voltages Controlled by Reactive Power:

Voltages are controlled by providing sufficient reactive power control margin to supply needs through

1. Shunt capacitor and reactor compensations2. Dynamic compensation3. Proper voltage schedule of generation.

Voltages are controlled by predicting and correcting reactive power demand from loads

Reactive Power and Power Factor

Reactive power is present when the voltage and current are not in phase

1. One waveform leads the other2. Phase angle not equal to 0°3. Power factor less than unity

Measured in volt-ampere reactive (VAR) Produced when the current waveform leads voltage

waveform (Leading power factor) Vice verse, consumed when the current waveform lags

voltage (lagging power factor)

 Reactive Power Limitations: Reactive power does not travel very far.

Usually necessary to produce it close to the location where it is needed

A supplier/source close to the location of the need is in a much better position to provide reactive power versus one that is located far from the location of the need

Reactive power supplies are closely tied to the ability to deliver real or active power.

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