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Seminar Topic on
Importance of Reactive Power for
Presented by-Devendra Mishra
OUTLINE OF PRESENTATION
IMPORTANCE OF REACTIVE POWER
NESSARY TO CONTROL OF VOLTAGE & REACTIVE
BASIC CONCEPT OF REACTIVE POWER
We 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
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
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
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
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
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
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 current
II. Must raise the voltage higher to push the power through
the inductance of the lines
III. 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 compensations
2. Dynamic compensation
3. 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 other
2. 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.