Power Factor Improvement Of An

Induction Motor

Harshit agarwal 22Atul kumar sahu 16Ashish kumar singh 14Ashish pani vimal 15

Under guidance of: Mr. Mohamed Samir

Introduction Of Induction Motor

• Singly Excited A.C machine.• Its stator winding is directly connected to A.C source. Where

as its rotor winding receives its energy by Induction (Transformer Action).

• No load Current in Induction Motor varies from 30 to 50 % of full load current.

• In Induction motor magnetizing current (lagging nearly 90 degree behind the applied voltage) forms a considerable portion of No load current that’s why Induction motor have low power factor at no load.

• The effect of low value of a No load Power Factor is to decrease the Full Load Operating Power Factor of Induction motor.

Introduction Of Power Factor

• Working /Active Power: Normally measured in kilowatts (kW). It does the "work" for the system--providing the motion, torque, heat, or whatever else is required.

• Reactive Power: Normally measured in kilovolt-amperes-reactive (kVAR), doesn't do useful "work." It simply sustains the electromagnetic field.

• Apparent Power: Normally measured in kilovolt-amperes (kVA). Working Power and Reactive Power together make up apparent power.

To understand power factor, visualize a horse pulling a railroad car down a railroad track. Because the railroad ties are uneven, the horse must pull the car from the side of the track. The horse is pulling the railroad car at an angle to the direction of the car’s travel. The power required to move the car down the track is the working (real) power. The effort of the horse is the total (apparent) power. Because of the angle of the horse’s pull, not all of the horse’s effort is used to move the car down the track. The car will not move sideways; therefore, the sideways pull of the horse is wasted effort or nonworking (reactive) power.

Power Factor : A measure of efficiency. The ratio of Active Power (output) to Total Power (input)

A power factor reading close to 1.0 means that electrical power is being utilized effectively, while a low power factor indicates poor utilization of electrical power.

Total Power (kVA)

Active Power (kW)

Power Factor = Active (Real) Power Total Power

= kW kVA

= Cosine (θ) = DISPLACEMENT POWER FACTOR

ReactivePower(KVAR)

Power Factor Fundamental

Why do we care about Power Factor?• Low power factor results in:

– Poor electrical efficiency!– Higher utility bills **– Lower system capacity– On the Supply Side, Generation Capacity & Line Losses

• Good Power Factor results in: Environmental benefit. Reduction of power consumption due to improved

energy efficiency. Reduced power consumption means less greenhouse gas emissions and fossil fuel depletion by power stations.

Reduction of electricity bills. Reduction of I2R losses in transformers and distribution equipment Reduction of voltage drop in long cables. Extended equipment life – Reduced electrical burden on cables and

electrical components.• Power Factor Correction Capacitors (PFCC)

provide an economical means for improving Energy utilization

In this example, demand was reduced to 8250 kVA

from 10000 kVA.

1750KVA Transformer Capacity Release.

The power factor was improved from 80% to 97%

Before After

Why do we install Capacitors?

Power factor correction Of induction motor• Power factor correction is the term given to a technology that

has been used since the turn of the 20th century to restore the power factor to as close to unity as is economically viable.

• This is normally achieved by the addition of capacitors to the electrical network which compensate for the reactive power demand of the inductive load and thus reduce the burden on the supply. There should be no effect on the operation of the equipment.

• To reduce losses in the distribution system, and to reduce the electricity bill, power factor correction, usually in the form of capacitors, is added to neutralize as much of the magnetizing current as possible.

• Capacitors contained in most power factor correction equipment draw current that leads the voltage, thus producing a leading power factor

MOTOR LOAD CHARACTERISTICS

No-load test

1. The motor is allowed to spin freely2. The only load on the motor is the friction and

windage losses, so all Pconv is consumed by mechanical losses

3. The slip is very smallPoc = Voc * Ioc * Cos(@oc) Roc = Voc / Ioc Cos(@oc)Xm = Voc / Ioc Sin(@oc)

Blocked-rotor test

In this test, the rotor is locked or blocked so that it cannot move, a voltage is applied to the motor, and the resulting voltage, current and power are measured.

Rsc = Psc / (Isc * Isc)Zsc = Vsc / IscXsc = Under root( sqr(Zsc) – sqr(Rsc))

Installation Of Static Capacitor

• This method involves the connection of static capacitor across stator terminals Of Induction motor.

• In smaller size motors Controlling the Power factor by static capacitor is a Simplest & most economical method.

• The stator current is I1 & motor operating PF is Cos(@1).

• When Capacitor are connected across stator terminals, The current Ic through the capacitors lead the voltage V1 by 90 degree.

• The Phasor sum of I1 & Ic is I1’ drawn by supply.

• The PF of the combination is improved from Cos(@1) to Cos (@1’) and stator current decreases from I1 to I1’.

Phasor Diagram

Pertaining to IM PF control By Static Capacitor

• The stator current locus to the IM is shifted to the left, this shift being equal to the length of the current phasor Ic.

• This means that the centre of current locus shift from C to C’. Such that the length CC’ = Ic.

• By the fig. it is clear that if full load PF is near to unity the PF at No load & Half load are leading.

Self Excitation Of IM

• Self-excitation occurs when the capacitive reactive current from the capacitor is greater than the magnetizing current of the induction motor. When this occurs, excessive voltages can result on the terminals of the motor. This excessive voltage can cause insulation degradation and ultimately result in motor insulation failure.

Simplified Circuit Diagram for Motor Controller and Power Factor Correction Capacitors (Diagram Shown For Motor Controller in Open Position)

• The rotating magnetic field can be thought of as stored energy.• When the motor is switched off, the stored energy still present in

the air-gap of the motor begins to collapse and produce a current in the rotor winding.

• This rotor current induces a voltage on the stator winding and terminals of the motor which are disconnected (the motor becomes a generator).

• Because the motor has just been disconnected, it is still spinning due to its rotating inertial speed which will decrease in time.

• The decaying speed produces a subsequent voltage (and current flow through the capacitor) at a decaying frequency (starting at a value near 60 hertz).

• When the frequency of the motor terminal voltage equals the resonant frequency of the motor and capacitor reactance combination, high voltage may be produced. This high voltage can lead to insulation failure on the motor.

• To create self-excitation, the capacitive reactance of the capacitor must be less than that of the motor reactance (this occurs when to large of a capacitor is chosen).

• If the capacitive reactance is greater than the motor magnetizing reactance (this occurs for a properly sized capacitor), the resonant frequency is greater than the motor speed (greater than 60 hertz). Under this condition, when the motor is disconnected, the frequency of the decaying terminal voltage will never correspond with the resonant frequency of the motor and capacitor reactance combination. Therefore, a high voltage condition will not occur.

• The figure shows a plot of the capacitor and motor magnetizing voltage verses current waveforms.

• The motor magnetizing curve is sloped over, which is a characteristic of iron.

• The capacitor characteristic is a straight line.

• The curve labeled "B" is sized improperly because its capacitive current is greater than the magnetizing current at 1 per-unit voltage.

• When disconnected, the "B" curve in figure 3 shows a valid operating point at 140% voltage.

• This voltage may occur as the motor slows in speed and passes through its resonant frequency.

• The curve labeled "A" is sized properly because its capacitive current is less than that of the magnetizing current at nominal voltage.

• Request a recommended kvar rating from the motor manufacturer.

• Size the capacitor at 80% of the no-load current rating (magnetizing current) of the motor. In no case should the rating be greater than 90%.

• Utilize recommended capacitor sizing tables induction motors. • Measure the no-load motor current and size the capacitor at

80% of the no-load current rating of the motor.

The following techniques be used when applying capacitors or harmonic filers directly on the terminals of an induction

motor.

Practical Aspects

• Small Induction motor have low Pf than large motor at Low load.• Small induction motor also have low PF at Full load.• Our objective Of project is to improve the Power factor Of small

Induction motor at Low as well as Full Load.

Procedure & Feasibility Of Project

• Perform No Load test & Blocked Rotor test to find out Internal impedance of the Motor.

• Determining The power factor & Efficiency of the Motor.• Making calculations For the size of Capacitor Bank should be

install to Improve the Power factor.• Determining The New improved Power Factor & Efficiency.• Compare the New Power Factor With Previous Power Factor. • Calculation for the Net saving In operating cost Of the Motor.

By the best of our research and Knowledge this project is feasible & worth while to perform.