ABB Relion 620 Series - Page 790

Figure 414: Example of double-Y-connected shunt capacitor bank unbalance
protection
Connect the phase current analog input I_A and unbalance current
I_UNB to the IED for the CUBPTOC function to start working.
Steps to measure natural unbalance current
1. The setting Natural Comp Enable must be set to “TRUE”.
2. The capacitor bank must be energized.
3. The capacitor bank compensated unbalance current I_COM_AMPL is observed
from Monitored data.
4. The command
Record unbalance must be activated by selecting the
value “Record” which stores the unbalance reference for future unbalance
calculations.
5. The compensated unbalance current ( I_COM_AMPL) is re-checked to be
approximately zero.
The natural unbalance recording should be made only during the steady-
state condition and when all the capacitor bank elements are assumed to
be in service.
Protection functions 1MRS757644 H
790 620 series
Technical Manual