Correcting power factor problems is becoming increasingly cost-effective as more power suppliers charge for low power factor.
Power factor is often compared to the weather—everybody talks about it, but nobody does anything about it. However, that is no longer accurate; now you can take steps to control poor power factors.
This article reviews technical considerations and discusses the benefits of power factor correction.
Three important terms relate to power factor: real power (kW), apparent power (kVA), and reactive power (kVAR). The first term, real power or kW, represents the actual work being done by the electrical system. Simplified, the work done (kW) multiplied by the number of hours (h) becomes the kWh or energy charge portion of the bill.
The next term, apparent power or kVA, is the product of volts and amps. This term is often misunderstood. Remember, it is called apparent power for a reason.
It may seem that "real power" should be volts times amps, but it is not (except in the rare case where the power factor is exactly 1.0). In a typical plant, some of the apparent power is used to magnetize electrical devices, known as magnetizing currents. This magnetizing, or reactive (kVAR), power does no work and does not register as kWh on the power meter.
Therefore, you might see a high apparent power (kVA) alongside a low real power (kW) if the magnetizing power is significant. This is where the power factor (PF) comes in. The power factor percentage is real power (kW) divided by apparent power (kVA).
In a system with no magnetizing or reactive current, real and apparent power are equal, and the power factor is 100% (unity power factor). Most real-world systems have a power factor much lower than 100%. This is confusing because magnetizing (reactive, kVAR) power is not simply the difference between apparent and real power. Real and magnetizing currents are at right angles to each other.
In the example above, the magnetizing power is 60 kVAR, more than the difference between the apparent (100 kVA) and real (80 kW) power. (The figure forms a familiar 3-4-5 right triangle.) Other articles and textbooks explain the theory and calculations in depth, so we will proceed to practical implications.
To simplify, remember: real power (kW) is actual work done, apparent power (kVA) is volts times amps, power factor (PF) is real power as a percentage of apparent power, and magnetizing or reactive power (kVAR) is the difference between real and apparent powers (due to the right-angle relationship of real and magnetizing currents).
If you have followed this far, you might wonder why we bother with power factor, magnetizing power, or reactive power since the energy charge is measured on the kilowatt-hour meter and magnetizing current is non-work current that doesn't register on the meter.
Addressing apparent power is essential because many power suppliers charge for low power factors beyond the kilowatt-hour rate. Low power factor loads are more costly to serve than high power factor loads with the same kilowatt-hour consumption.
Costs increase because the power company must generate the apparent power (kVA). Low power factor requires more expensive generating capacity for the same amount of work. Line losses in the transmission and distribution system, which the power company absorbs, are proportional to the line currents squared; extra reactive power means wasteful loss of costly energy.
Low power factor requires larger transformers, increasing initial service costs and future maintenance expenses. Low power factor loads are less energy efficient. Many agricultural sites now pay a premium for energy based on inefficiency. Power factor correction capacitors can improve the power factor and reduce these premiums.
Capacitors use reactive current, 180° out of phase with the magnetizing current. By matching capacitors with the magnetizing current, you can reduce or cancel low power factor causes.
The best location for power factor correction capacitors is at the source of the problem, often electric motors. Section 460 of the 2014 National Electric Code provides guidance on installing capacitors on motors. Wiring capacitors on the motor side of the starter, per NEC 460-8, has three advantages:
Additional capacitors may be needed at the service entrance or branch circuit, requiring protection and disconnect to comply with NEC.
A successful installation depends on a favorable cost/benefit ratio. Compare capacitor costs to the reduction in power premiums to analyze the benefits of using power factor correction capacitors in monetary terms.
Contact our Sales team for more information on these and other RONK quality products: sales@ronkelectrical.com • 1-800-221-7665
