Application Guide for High Power resonant Capacitors
(Conduction Cooled Capacitors)
Capacitor selection
The following formula is to be used to determine what capacitance value is required:
KVAr= (V
2
/X
c)
=V
2
x 2πf x C x 10
-6
Where
KVAr= Kilovolt-ampere reactance
V= Applied RMS voltage
X
c
= Capacitive reactance =1/(2πfC)
C= capacitance in μF
f= Operating frequency in kHz
Select a capacitance that is equal to or greater than the calculated value.
Cooling Power Capacitors
High power resonant capacitors are designed to handle large voltages and currents in a
small compact package size. As a result of their small size these capacitors need to be
cooled. Failure to cool the capacitors properly will result in the capacitors failing
prematurely. Proper cooling of high power resonant capacitors is to be done by the use
of water cooled heatsinks or bus bars.
At no time are high power resonant capacitors to have their external surfaces exceed
85°C. When possible the external surfaces of the capacitors should not exceed 45°C
when used at full power.
At temperatures above 45°C the KVAr rating of the capacitors must be de-rated per the
chart shown below. Failure to de-rate the capacitors properly can cause them to fail
prematurely.