Controlling System Voltage

Without capacitors, the voltage drop across a system is calculated as::

or

V_{d          =}              voltage drop across system leading to the load

kVA    =          3-phase load kVA

kV       =          phase to phase voltage at load

cos theta    =    cosine of the power factor angle

R         =          resistance of system leading up to the load (ohms)

X         =          inductive reactance of the system leading up to the load (ohms)

The percent voltage rise at a load due to the addition of a capacitor bank is:

V_r        =          % voltage rise at load

kVAR =          3-phase capacitive kilovar

kV       =          phase to phase kilovolts

X         =          inductive reactance of the system

KVA_sc =         3-phase short circuit kVA

The percent voltage rise from primary to secondary of a transformer is:

Where:

Vr        =          the percent voltage rise at the transformer

kVAR =          3-phase kilovar applied

kVA_t   =          3-phase kVA of the transformer

X_t        =          transformer reactance in percent