Useful Formulae and Tables
Capacitor requirement for Transformer compensation
In all HT installations, the metering is on the HT side of the Distribution Transformer. Invariably, reactive power compensation is carried out on the LT side of the Transformer. This compensation takes care of various inductive loads in the system. Even when the entire system is on no load, the Transformer alone itself is an inductive load viewed from the HT side. Hence, it is necessary to connect a separate fixed Capacitor to take care of Transformer compensation, as indicated below:
It is useful to note that, in the case of APFC systems, the Current Transformer providing feedback to the APFC system must be located in such a way that it does not measure this Capacitor current.
Capacitor requirement calculation formula
The table of Multiplying factor for calculating the required capacitor rating provided in the following page is based on the following formula:
Capacitance value & current calculation for 3 phase delta connection
The Capacitance value across any two terminals of a delta connected
Capacitor unit is:
Calculation of Average Power Factor
In most installations, what is largely relevant is the Reading of Power Factor recorded in the energy meter installed by the Energy Supply Company. For purpose of Billing, the Average PF is considered. The Average PF between any two times may be arrived at by using the following equation:
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