Technical Notes on Discharge Resistors for PFC Capacitors

Technical Notes on the selection and use of discharge resistors for PFC Capacitors installations

Main points to know 

-Discharge resistors MUST be used in all PFC installation within Australia and New Zealand

-Discharge resistors are selected to match each Kvar/Voltage Rating of the capacitor. similar ratings can be used such as 35/40/50kvar can use the same rating. 

-Discharge resistor temperatures can get up to 250 Deg C in service. The exact temperature is affected of the operating voltage of the capacitor. Usually the temperature is less than 200°C.

- DO NOT confuse the discharge resistors with the Contactor Discharge resistors. They are both required.

For Vishay, RTR, Iskra Doo Capacitor Brands, the Discharge Resistors are included. However for ELECTRONICON, the resistors must be ordered separately. 

Be sure to check the condition of existing resistors as they may be in good condition. 

Selection of Discharge Resistors

It is possible to use the same resistor on multiple capacitor ratings. Please see below selection Guide for more information.

Reference is below:

Electronicon Capacitor Selection Guide

Regarding the different colours stand for the respective maximum capacitances and the discharge time:

For example the discharge module 275.100-10180 can be used for the capacitor 15kvar 525V. 

The different colours stand for the respective maximum capacitances and the discharge time:

The numbers in brackets at the top of the table are the "selection code" of the respective discharge module. In this case number 6 stands for the discharge module 275.100-10180, which means that at 525V max. 3x124µF can be discharged in 1min or 3x436µF in 3min.

It means that for a capacitance between 3x74µF and 3x124µF you would have to use this particular resistor. But even for a lower capacitance you can use this resistor.

For further clarification feel free to contact Fastron technical team.