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Power Factor


What is Power Factor?


Duquesne Light monitors commercial and industrial customers to determine how efficiently they use the electric power that we supply to them. This efficiency element is known as power factor, and it is applied to Duquesne Light’s customers who have:



Note: if you only have single-phase service there is no need for you to read any further. Power factor penalty does not apply to single-phase service.


Power factor is essentially a measure of efficiency. It is the ratio of real, or useful, power (kW) to total power (kVa). The higher the power factor, the more efficiently electrical power is being used. The lower the power factor, the less efficiently electric power is being used and the higher the total power drawn from Duquesne Light’s distribution network.


Ideally, all businesses would be operating at 100 percent efficiency, resulting in a power factor of 1.00. (Ninety percent efficiency would equal a power factor of 0.90; eighty percent efficiency would equal a power factor of 0.80, and so forth.) How efficiently businesses consume electricity varies from company to company and from month to month.


When a business is not using available electricity efficiently, there is a heavier drain on Duquesne Light’s transformers, switches, and conductors. This requires greater transformer and generator capacity at a higher cost. Because Duquesne Light is committed to providing enough electric capacity to handle all of our customers’ needs, we must compensate for the burden placed on our electrical system by a poor power factor. This compensation takes the form of a higher cost which is passed to the customer causing the heavier drain through a power factor multiplier adjustment.


Power factor adjustments are not unique to Duquesne Light; most utilities measure their customers’ use of energy and make billing adjustments on customers who operate electric loads below a given level of efficiency. Duquesne Light imposes this power factor adjustment on you when your power factor dips below the 95 percent efficiency level. Our company views these billing adjustments as an incentive for commercial and industrial customers to increase their efficiency when using the electric energy we supply.



What Causes Poor Power Factor?


Electric equipment consists of capacitive loads, resistive loads, and inductive loads. Capacitive loads mainly include capacitors that are installed to start motors or to control power factor. This will be discussed in greater detail later.


Resistive loads are generated by incandescent lighting, electric resistance heating, and electric ovens and ranges. These operate at nearly 100 percent electrical efficiency and, therefore, have a power factor approaching 1.00. This electrical usage or resistive current is recorded in kilowatts on our standard meter and is referred to as real power (kW). Real power is consumed as this current converts energy into useful work.


Inductive loads include motors, transformers, battery chargers, fluorescent lighting, air conditioning, and induction furnaces. While this equipment is partially powered by a resistive current, a magnetizing current is also required to operate inductive load equipment. The magnetizing current performs no visible work but still draws power from our electric system. This means that for the same kilowatt load, Duquesne Light has to supply more power. This causes a customer’s power factor to decrease, making his or her use of power less efficient.


Since a standard kilowatt-hour (kWh) meter cannot measure inductive power requiring magnetizing current, Duquesne Light installs an additional meter, known as a reactive meter, to measure the inductive power supplied as the magnetizing current. You will notice this second meter next to the demand meter at your facility. The combination of the kWh meter and the reactive meter allows Duquesne Light to determine a power factor multiplier that increases as the power factor decreases.



Power Factor Multiplier


On your bill, rather than listing power factor, you will see a number or equation for Duquesne Light’s power factor multiplier (PFM). The power factor multiplier is the adjustment factor used in determining the customer’s share of the financial burden that he or she has caused for the billing month. If your power factor multiplier exceeds 1.00 and your demand is greater than 30 kW, you will incur a power factor adjustment. The equation reflects the 95 percent efficiency level that Duquesne Light encourages your business to maintain.



Correcting Poor Power Factor


Power factor can be corrected by installing capacitors. This is the easiest way to reduce or “correct” your power factor multiplier to 1.00. Capacitors supply reactive power, reducing the magnetizing current burden on Duquesne Light’s electrical distribution and generation system. They are typically installed after our meters on your main service but may also be installed directly at the inductive load causing the problem, for example, on large motors. If sized properly, capacitors can restore your service’s power factor multiplier to 1.00, which reduces the total power drawn from Duquesne Light’s distribution system and subsequently increases available system capacity.