The electrical energy is generated, transmitted and distributed in the form of alternating current. In alternating current the direction and magnitude of quantity is varied with regularly intervals. It means AC current has phase angle. The lag or lead of current in any electrical circuit from voltage make a angle between voltage and current is called power factor. There are three types of circuit resistive circuit, inductive circuit and capacitive circuit. In resistive circuit current and voltage always in phase. In case of inductive e circuit current lags behind the voltage and in case of capacitive circuit currents lead the voltage. Where current in phase with voltage is called unity power factor. Current lags behind the voltage called zero lagging power factors. Current leads the voltage is called leading power factor. Most of the loads are inductive in nature and hence have low lagging power factor. Low power factor causing increase in current which increase in loss. In this article we will discuss about concept, causes, disadvantages and methods of improvement of power factor.
Concept of Power Factor
Most of loads are inductive loads (such as induction motors). The current taken by inductive motors or inductive circuit consists of two components. One is called magnetizing component active components transformed energy into useful work and magnetizing component which is often termed as idle components. Magnetizing component is called wattles component. Active component being in phase with the voltage accounts for the useful work done and magnetizing component being in quadrature with the voltage does not do any work in circuit and is mainly responsible for the creation of magnetism. More magnetizing current causing low power factor.
What is Power Factor?
The cosine of the angle between voltage and current in an ac circuit is called power factor.
The analysis of power factor can also be made in terms of power drawn by the ac circuit. Draw a triangle which is called power triangle.
OA = VI cosф and represents the active power in watts or KW and denoted by P.
AB = VI sinф and represents the reactive power in VAR or KVAR and it is denoted by θ.
OB = VI and represents the reactive power in VA or KVA. It is denoted by S.
The following points may be noted from the power triangle.
The apparent power consists of two components
Active power and Reactive power
Both are mutually perpendicular to each other.
(Apparent Power)2 = (active power)2 + (reactive power)
From above equation power factor may be defined as it is the ratio of active power to the apparent power.
It is also observed from the power triangle the reactive power is responsible for the low power factor. So, if the reactive power is more low the power factor of the circuit.
The reactive power is neither consumed in the circuit nor it does any useful work. A wattmeter does not measure reactive power.
Causes of low Power Factor
Induction motors are extensively used in industries. Induction motor is used for variety of purposes. At full load 3-phase induction motor operates at a power factor of around 0.8 lagging. At light load the value of power factor is 0.2 to 0.8 which is considered very poor. The power factor of a single phase induction motors is about 0.6 lagging.
Are lamps, electric discharge lamps and industrial heating furnaces operate at low power factor in the system.
The transformers draw a magnetizing current from the supply system. This current is at a power factor of zero lagging.
DISADVANTAGES OF LOW POWER FACTOR
Power consumed by the circuit given by the relation
Low power factor has following disadvantages.
- Large KVA rating of equipments
The electrical machinery is always rated in KVA. The KVA rating of the machine is inversely proportional to the power factor. If the power factor of the load is low the drawn by the machine will be high and vice versa and large KVA rating of the machine is required.
- Greater conductor size
To transmit or distribute a certain amount of power at constant voltage, the conductor will have to carry more current at low power factor.
Large copper losses
If the conductor will carry large current the loss will be also high because the power losses are directly proportional to the square of load current.
Poor voltage regulation
The large current at low power factor causes greater voltage drops in electrical machine (such as alternators, transformer etc.) Which drop the voltage at the supply end which results in poor voltage regulation. In order to keep the supply end voltage with in permissible limits, extra equipment is required.
To Avoid these limitations power factor correction is necessary.
Effects of low Power factor
To meet the load requirement at a low power factor, the capacity of power plant and substation equipment has to be more than that which would be necessary if the load were demanded at unity power factor.
At low power factor machine will draw large current hence higher energy losses.
Law power factor causes the voltage regulation to be poor.
ADVANTAGES OF POWER FACTOR IMPROVEMENT
By improving power factor circuit current is reduced.
Improve the voltage regulation.
By improving power factor copper losses is reduced due to decreasing line current.
Reduction in investment in the system facilities per KW of the load supplied.