The power factor (PF) in any electrical system can be defined as; the ratio of the real power to the apparent power. Here, real power is measured in kW (kilowatts) and apparent power is measured in kVA (kilovolt amperes). So, the power factor is the measure of how efficiently the power is utilized within an electrical system. A low power factor (LPF) means that the electrical system is not completely using the power so that system efficiency can be reduced and electricity costs can be increased. A high power factor means the electrical system uses the power effectively. In DC circuits, there is no power factor involved because of zero frequency whereas, in AC circuits, the power factor value always ranges between 0 & 1. This article discusses an overview of the low power factor – causes and improvements.
What is Low Power Factor?
A low power factor can be defined as when the electrical load not completely uses the available power and increase the electricity costs & reduces system efficiency. So low power factor indicates inefficient utilisation of electrical power. In general, the electricity drawn by the electrical system includes both the useful energy and the reactive energy. Useful energy is the energy consumed by an electrical system or a device to perform useful work, such a provide light, operating machinery or powering electronics devices whereas reactive energy is the energy that is stored and released by the inductive and capacitive loads, which can cause the voltage and current to become out of phase. This energy does not contribute to the useful work done by the electrical system and therefore, it is wasteful. This reactive energy contributes to the Low Power factor.
An LPF decreases the distribution capacity of an electrical system by increasing the flow of current. So, having a low power factor (LPF) is expensive & inefficient.
Low Power Factor Effects
The LPF effects or some of the disadvantages of a low power factor are discussed below.
Higher Copper Losses
The copper losses are proportional directly to the square of the line current & the line current is proportional inversely to the power factor (PF) of the circuit. So merging these two relations, we can understand that these losses will be proportional inversely to the square of PF. Whenever the power factor (PF) is low, then the line current will be high & the higher copper losses. So this results in low efficiency of the power system.
High kVA Rating
The rating of Transformers is in kVA, so the main relationship between the PF & the kVA rating of the electrical machine is specified by the following formula.
kVA = kW/ CosФ
So by using this formula, we can identify the PF of the machine is proportional inversely to its kVA rating. When the kVA rating of the equipment is larger, the equipment is heavier in size & costly.
Poor Voltage Regulation
We know that when the power factor is poor then that will result in a larger line current to be drawn through the electric equipment. In the LPF case, the current will be high as a result the voltage drop will be high.
Voltage Drop (V) = IZ.
In addition, voltage regulation (V.R) = (VNL – VFL)/ VFL.
In the LPF case, the larger voltage drop can cause low voltage regulation. So, to maintain voltage drop in the particular limit, we have to use an additional voltage regulator.
Larger Size of Conductor
LPF is not only significant for loads however it also plays a significant role in power transmission. As we discussed, LPF causes high-line currents. When the current carrying conductor capacity is proportional directly to its cross-sectional region, high current will need a larger conductor size. So the transmission conductor size will increase.
In an LPF case, there would be large line losses & large voltage drops and this will cause the equipment or system efficiency very low. For example, because of the LPF, there would be huge line losses; so, the alternator requires high excitation, therefore efficiency generation & efficiency of the transformer would be low.
A Penalty from Electric Companies
Generally, electrical companies impose a fine for power factor (PF) under 0.95 lagging within the Electric power bill. Thus you have to improve the power factor above 0.95.
The reasons for low power factor causes are discussed below.
Transformers and electric motors are known as inductive loads which use reactive power using the system that reduces the PF. Inductive loads can cause the current & voltage to become out of phase which enhances the system’s reactive power component.
The power factor at different loads is;
PF at full load is 0.8 to 0.9
PF at a small load is 0.2 to 0.3
PF at no load is nearly Zero which means the PF in pure inductor load is ‘0’.
Capacitors are capacitive loads that produce reactive power & also improve power factor. But, if the capacitance is very high, then it causes overcompensation & leads to a leading power factor. In a pure capacitive load, the power factor is ‘0’.
The occurrence of harmonic current decreases the power factor within the system.
Because of improper wiring, the difference within the three-phase power occurs which causes LPF.
The Difference in the Power System Loading
The demand for load within the current power system is not stable throughout the day. So during the morning & evening hours, the demand is high and the light throughout the rest of the day. Once the system is lightly loaded, the voltage will increase and the machine’s magnetization current demand can also be increased. So this can cause a poor power factor within the system.
The load varies on a power system, so during the low load periods, the voltage supply is improved, which enhances the magnetizing current & decreases the power factor.
Long Distribution Lines
The voltage drop can occur through long distribution lines & reactive power can be increased within the system, which can reduce the power factor.
Low Power Factor Improvement
The improvement of the LPF eliminates the problems that occurred and also it will make the electrical system economic. There are many solutions to improve the LPF like power factor correction equipment installation, electrical equipment upgrade to decrease losses, and system design optimization to decrease reactive power consumption. So understanding the LPF causes is very essential to identify improvement areas & ensuring cost-effective & very efficient electrical systems operation.
There are many sources for poor power factors like distribution transformers, incandescent lamps, mercury vapor lamps, induction motors, synchronous motors, welding transformers, industrial heating furnaces, solenoid and chocks, arc lamps, broken bearings within motors & not utilizing rated wire size within motor windings, etc.
Low Power Factor Operation of Induction Motor
The induction motor power factor mainly changes with load, normally at full load it is approximately 0.85 or 0.90 and at no load, it is about 0.20. An induction motor at no load draws a large magnetizing current & a small active component to reach the no-load losses. So the induction motor’s power factor on no load condition is low.
What is the Low Power Factor Correction?
LPF correction is a technique used to improve the PF & also the quality of power. The LPF can be corrected with capacitor banks & synchronous condenser.
What will happen if Power Factor is Low?
- If the power factor is low then it reduces the handling capability of all the components within the electric system.
- The LPF will enhance the copper losses within the transformer, load & transmission line.
- The LPF can reduce the efficiency of the circuit & increases the overall operating cost.
What is the Maximum Value of the Power Factor?
The maximum value of the power factor is 1.00, so the power delivered to the electric load is 100% which is the active power changed into functional energy.
How Can I Increase the Load Factor?
The load factor can be increased by increasing production efficiency & reducing demand.
Know more about Transmission Distribution MCQs.
Thus, this is an overview of low power factor – effects, causes, and its improvement. Once the power factor is low, then the line current will be high, and as a result, the copper losses will be high. So this can result in less efficiency of the electric power system. A low-power factor wattmeter instrument is used to measure power within low-power factor-based circuits whose PF is < 0.5. Here is a question for you, what is a power factor?