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Power Factor Correction Capacitors

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  rev. 2008-11-25        

Existing Conditions

Assuming if local capacitors are recommended, confirm that the chillers do not already have capacitors built in.  Also note that VFD chillers do not contribute to a low power factor so capacitors are not appropriate.

Some types of electrical equipment commonly found in buildings, such as motors, ballasts and transformers are known as inductive loads.  They cause the current of the electricity supplied to “lag” the voltage (In a normal AC circuit, the voltage is applied in a sine wave at 60 cycles per second).  The current is said to “lag” the voltage if the peaks and troughs occur after the peaks and troughs of the voltage.)  Capacitive loads are much less common and have the opposite effect, causing the current to “lead” the voltage.  If the current is either “lagging” or “leading”, the power being delivered by the utility is not being as effectively used as it might be.

The electrical demand meter records the peak monthly power requirements in the facility in kilowatts (kW).  A second meter records the “apparent” peak monthly power requirements, measured in kilo-volt-amps (kVA).  The ratio of these readings (kW / kVA) is called the Power Factor.

The utility will have to generate more power, and deliver a greater current, to a facility with a low or overly high power factor.  A power factor of 1.0 is ideal.  In practice, most buildings have lagging power factors somewhere between 0.8 and 1.0.  It is not common to see a leading power factor (higher than 1.0).

Although a low power factor does not mean that power is being wasted by the facility, it does increase the requirements from the utility. The size of distribution components such as transformers, breakers, wires, etc., is dictated by amperage, not by the end use of power.

Therefore, the utility penalizes customers for power factors that are less than 0.90.  The demand charge on the monthly electrical bill is either the kW reading or 0.90 times the kVA reading, whichever is higher.  It was found that there were numerous months during the year in which the kVA reading was used because of a relatively poor power factor at this facility.

Retrofit Conditions

It is recommended that capacitor banks be installed at the main feed to the building, in order to increase the power factor to a minimum of 0.90 during the worst conditions.  In order to achieve this, static [dynamic] capacitors totalling xxx kVAR are required [with xxx kVAR steps and a minimum capacitance of xxx kVAR].

Further Benefits




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