affecting the three-phase motor influences not only the effectiveness of using the energy but also the operating costs. The low power factor wastes energy and overloads the equipment. In a way, for companies to improve the power factor by either capacitor banks or synchronous motors, they will reduce their electricity bills effectively while giving a longer life to the equipment.
What is Power Factor
Power factor is a ratio that indicates how efficiently an electrical device—either a motor or an appliance—uses electrical power. It is defined by the ratio of active and apparent power: Active power is actual power utilized to do work in the motor, while apparent power is the amount of power supplied by the grid, comprising both active and reactive power. Reactive power does not perform actual work but is common in inductive loads, such as motors and transformers, for maintaining the magnetic field in the circuit. The power factor ranges between 0 and 1, where 1 indicates a very efficient system whereby the total incoming power is converted to active power. If this power factor is lower, efficiency will be reduced since a great deal of energy will be wasted on reactive power.
In the industries, motors and other inductive loads consume reactive power, thereby pulling down the power factor. If the power factor is low, it further places undue pressure on the power transmission system. Moreover, it raises the electricity cost for companies as utility firms generally charge users based on lower power factors.
Why Power Factor Matters
The power factor has a direct influence on the energy efficiency and the operation cost for industrial users. When the power factor is low, all equipment needs more current to do a specific task; this increases the load on cables and transformers, thus increasing the electricity bill. Moreover, it may influence the stability of a power system and increase the possibility of voltage fluctuations, making the system operate unstably.
Low power factor causes a number of problems for industrial users, including the following:
A low power factor greatly increases current consumption and, as a result of this, electrical equipment losses. For example, if a motor operates under low power factor conditions, it needs more current to compensate for this, which may heat up cables and transformers, thus reducing equipment life. Also, a poor power factor increases the requirement of reactive power in the grid, and utility companies usually charge consumers extra money so that the losses created in transmission through reactive power are compensated by them. When the power factor of a firm is poor, then it is liable to an increase in its electricity cost up to 10% to 30% every month.
A low PF reduces the supply capacity of the system in cases when this system or grid is under peak load conditions. A low power factor may result in voltage drops, hence unstable operations of the equipment. Such instability is particularly unacceptable in precision equipment, as such may lead to malfunctioning or reduced performance.
Effects on Motor Efficiency
The power factor directly affects the efficiency of three-phase motors. The lower the power factor, the more current the equipment will draw and the greater the energy losses will be. If a motor has to work for extended periods under low power factor conditions, the increased current in the coils raises the temperature, thus influencing its efficiency and operational life.
A motor running at 0.75 power factor needs more current due to a higher reactive power requirement, which increases the internal temperature of the motor and also causes overheating and premature wear in the mechanical parts. For every 10°C rise in the temperature of a motor, its life is reduced to half. Improved power factor will try to reduce the effective heating loss so that the motor works in the most efficient state possible, prolonging its life.
The low power factor further influences voltage fluctuation in the motor, where surges of current at motor start-up increase and consequently result in more wear and tear of the equipment. Voltage fluctuations can thus be reduced and system stability increased when the power factor is improved. This is quite applicable to an industrial setup where variations in loads occur quite often. A high power factor can substantially lower the failure rates of equipment and raise overall system reliability.
Impact on Energy Costs
Low power factor is directly related to the cost of electricity. Utility firms can and may charge for an additional amount due to transmission losses when low power factors cause added loads from such inefficiencies. Companies with generally lower power factors than 0.85 are charged reactive power surcharges, at times even up to 10 or 20 percent of the total bill, depending on regions.
Another factor affecting the cost calculation is the power factor. Some utility companies charge for apparent, rather than active, power. If the power factor is low, then the apparent power will be significantly higher than the active power, resulting in the company paying more for electricity even though actual consumption has not increased.
For example, a factory with a power factor of 0.7 may pay 15-30% more in electricity each month. By correcting it to 0.9, the factory will save a pretty penny for electricity expenses. Especially for those energy-intensive industries, improving the power factor has a pretty obvious economic benefit. It is assumed that in certain factories, electricity used to cost 1,000,000 yuan a month. The yearly saving could amount to tens of thousands of yuan if the power factor was raised from 0.7 to 0.9.
Improving Power Factor
Improving the power factor is based on not overloading the demand for reactive power so that the equipment works in an efficient state. Among the common methods used in the correction of power factor are capacitor banks, synchronous motors, and automatic power factor correction devices.
Capacitor banks are the most used compensators of power factor. In the capacitors, it is possible to make positive reactive power and improve the power factor. Parallel connections are common for power factor improvement in industrial production. A motor may have a power factor of 0.75 and through proper compensation with capacitors, have its power factor elevated to 0.9 with the reduction of the active power demand.
Other methods of improvement of power factor are based on the use of synchronous motors. Because they can supply reactive power from themselves during their operation, they do not need reactive loads; hence, there is no need to have smoothing capacitors either. This method is especially appropriate in cases of power-intensive motor applications. While they represent higher costs at the outset, in most cases they will yield considerable economic benefits in the long run because of their capability for power factor improvement and efficiency augmentation.
Industrial consumers are also increasingly seeking after automatic power factor correction systems. Such a system will automatically adjust the real-time reactive power compensation in line with any change in loads, ensuring operation of the equipment at the optimal power factor. In applications with high load fluctuations, this ensures that there are no fluctuations in power factors, offering more stability and efficiency in the system.
Common Power Factor Issues
During actual operations, the power factor may drop due to many reasons, the most common of which is an excessive number of inductive loads. These include motors and transformers. Inductive loads consume reactive power from the supply grid, and therefore the power factor reduces. If the equipment is not well designed or if the motor is used under low load conditions, the power factor tends to go even lower.
Another cause for declining power factor relates to the failure or aging of capacitor banks. Over time, capacitors may become unable to provide adequate reactive compensations and fail to do so, leading to a power factor that is unacceptably in decline. It, therefore, becomes important that capacitor banks are regularly inspected and maintained to ensure that the power factor does not drift away.
An excessively high power factor is a problem that can arise. While the high power factor does indicate system efficiency, overcompensation can result in voltage increases and even overload in equipment. The correction, therefore, should not stop at the improvement of the power factor but it should also be so designed to require some kind of control against overcompensation.
Benefits of Correction
It is observed that correcting the power factor has several advantages to the business. First, there is a possibility of reducing the cost of electricity especially in utility companies charging for reactive power. Second, increasing the power factor offers numerous advantages such as increased efficiency within equipment, minimization of motor heat, and reduced systems losses to prolong the equipment’s life.
This further leads to the stability of the grid, causing limited voltage fluctuations and, as such, ensuring better quality of power. In large-scale industrial production, stable voltage supply and high power factor are closely linked to equipment operational safety. After the improvement in power factor, besides directly attaining savings on an electricity bill, companies can reduce the load on the power system to promote overall system stability and safety.
Large industrial enterprises are very economical investments and, at the same time, a technical optimization measure for power factor correction.
