Definition of Reactive Power

8/13/2019 Definition of Reactive Power

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1. Definition of reactive power

2. How reactive power important to transmit the active power in transmission line?

3. Light load, Induction motor, heating Elements

4. How load are absorbing reactive power?

5. What equipment are absorbing reactive power and what equipment are generates reactive

power?

Solution

1. Reactive power is the electrical power that oscillate between the magnetic field of an inductor and

the electric filed of the capacitor. Reactive Power Cannot Converts to non-electrical power e.g. heat,

light & torque. Instantaneous reactive power equal to the multiplication instantaneous current,

instantaneous voltage and the sinusoidal of phase difference of current & voltage. It only present in ac

power if there is any phase difference between instantaneous current and instantaneous voltage.

During complete cycle average reactive power is zero.

2. 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. 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.

3.(A)Illuminating Load are many types

Filament lamps

Halogen lamps having power factor nearly 1.It is purely Resistive in nature.

Tungsten Lamp having power factor nearly 1.It is purely Resistive in nature.

Discharge lamps

o Sodium Discharge lamps having power factor 0.3 lagging .It is Inductive In nature.

o High pressure sodium discharge lamps having power factor 0.5 lagging .It is Inductive In

nature.

o Florescent lamps having power factor 0.3 lagging with the choke circuit. by improving

capacitor its power factor increased .95 lagging.

o Compact Florescent Lamp having power factor 0.5 lagging .It is Inductive In nature. by

improving capacitor its power factor .95 lagging.

o Light Emitting Diode Lamps having domestic application has power factor 0.7 lagging &

industrial application has power factor 0.9 lagging.


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(B)Induction Motor loads-

Three phase induction Motor having dynamic power factor behavior according to the load. In

squirrel cage induction motor no load power factor is in between 0.1 to0.3 lagging. As in

increase in the load the power factor also increased. the power factor is maximum 0.85 at 80-

85% of full load beyond that load decreasing. Slip ring induction motor ,deep bar inductionmotor & double cage induction are having better power factor in no load condition but loaded

condition the are vey much similar to squirrel cage induction motor.

Single phase induction motor are various types

o Split Phase Single phase induction motor have power factor 0.65 lagging .It is Inductive

In nature

o Capacitor start Single phase induction motor have grater power factor than split phase

and shaded pole induction due to use of starting capacitor .

o Capacitor Start & run Single phase induction motor have highest power factor in single

phase induction motor .It may have two different capacitor or one fixed capacitor

running and starting in both condition.o Shaded pole Single phase induction motor have power factor 0.6 lagging .It is Inductive

In nature.

(C) Electric Heating can be classified into two categories

Power Frequency Electric Heating

Resistance Heating have power factor nearly equal to 1.It is resistive circuit in

nature.

Arc Heating have power factor nearly equal 0.6.This circuit inductive in nature.

High Frequency electric heating-

o Induction Heating have power factor 0.3 to 0.6.It is inductive circuit in nature. Its

power factor improved by capacitor.

o Dielectric Heating have power factor have 0.03.It is due to high frequency wave

generator. It power factor improved by suitable capacitor.

4. Transformers, Transmission lines, and motors require reactive power.

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

drawn by the motor is related to the energy needed to maintain the motor's internal magnetic field. The

current drawn by an inductive winding lags the applied voltage by 90 degrees. The magnitude of current

is dependent on the supply voltage and will not change with load. So if the motor is unloaded the totaleffect is a low active power draw with a relatively high reactive power draw, while if the motor is loaded

the active power is increased while the reactive power is unchanged

Transformers also need reactive power to produce magnetic flux in the core. Which cuts the secondary

winding of the transformer and produce secondary electro-motive force.


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Long loaded transmission lines have high reactance. It is due to the internal and external flux of the line.

When a current flowing through a conductor it produce flux around it. This flux represented in long

transmission line as lumped inductor. this flux of the trans mission of the line also need reactive power.

5.In power System Reactive power absorbs by the inductive load. For example-Industrial & Domestic

motor, electric heating, transformer, loaded transmission line, electromagnet, Solenoid, lamp ballast,

Ignition coil, relay, rectors etc.

In Power system Reactive generates by capacitive loads. It is rare in power system. But to compensate

the reactive power demand in the power system many devices are used. For Example Over Exited

synchronous motor (synchronous Condenser),Capacitor Banks, Static var compensator, STATCOM etc

This is my Assignment of Reactive power control and voltage stability(PSM 205(a)).I will thankful to

Molla Sohail for his upload.

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Definition of Reactive Power