Introduction

It is known for all of us that we associate electricity and energy with kilowatts (kW). In fact, kW only makes up a part of the overall energy usage in a home, commercial building or an industrial manufacturing plant. In the world of ‘AC power', there are actually three types of power:

1. Real Power (measured in Watts): Real power is the power that actually powers the equipment and performs useful work. It is also called Actual Power or Active Power.

2. Reactive Power (measured in VARs): It is the power that magnetic equipment (transformer, motor and relay) needs to produce the magnetizing flux.

3. Apparent Power (measured in Volt-Amps): It is the “vector sum” of KVAR and KW.

 

Power factor is defines as the ratio of Working Power (useful power) to Apparent Power.

Power Factor = kW/kVA = cos

 

Thus, for a given KVA:

1. Higher the percentage of KVAR, lower the ratio of KW to KVA. Thus, the lower your power factor.

2. Lower the percentage of KVAR, higher the ratio of KW to KVA. In fact, as KVAR approaches zero, your power factor approaches 1.0.

 

So, In order to have an “efficient” system, the power factor should be as close to 1.0 as possible. Hence, Power factor is the measure of how effectively our electrical equipment converts electric power (supplied by your power utility) into useful power output. The main causes for low power factor are inductive loads. Inductive loads include:

# Transformers

# Induction motors (p.f. = 0.1 / 0.5 / 0.7 / 0.8 / 0.85)

# Induction generators (wind mill generators)

# Electric discharge lamps / Vapour lamps

# Arc lamps

# Industrial heating furnaces

 

Reactive power (KVAR) required by inductive loads increases the amount of apparent power (KVA) required. This increase in reactive and apparent power results in a larger angle φ (measured between KW and KVA). Recall that, as φ increases, cosφ (or power factor) decreases.

 

Effects of Low Power Factor

1. The ratings of the generators, transformers, switchgear, etc., will increase to deliver same power demand at low power factor.

2. More copper will be used for making higher rating equipments. Hence, making the equipments larger and expensive.

3. The large current at low p.f.  causes more I²R loss in all the elements of the supply system. This result in poor efficiency.

4. The voltage regulation is poor because of more voltage drop. Hence extra regulating equipment is required to keep the voltage level within a permissible limit.

5. Penalty from electric power supply company on low power factor.

6. For same kW power, operating the power system at low power factor means overloading the equipments at the time of full load.