GE Multilin C70 Capacitor Bank Protection and Control System 8-178 THEORY OF OPERATION 8.1 OVERVIEW8(EQ 8.70)Equation 8.67 becomes:(EQ 8.71)Equation 8.68 becomes:(EQ 8.72)Note that in the ungrounded case, the operating signal is half of that for the grounded case.• With the grounded configuration, the two banks must be nominally identical. With the ungrounded configuration thetwo banks need not be the identical though each should be balanced. In this situation, the base for ΔC(pu) is thecapacitance of the string which has the element failure, so the larger bank will have a lower sensitivity than the smallerbank.ddC A1--------------I OPC A1 C A2+( ) C A1–C A1 C A2+( )2------------------------------------------------I A=C A2I AC A1 C A2+( )2----------------------------------=I A4---- 1C A1----------×≅I OP pu( ) I A4---- C pu( )Δ×=I OP pu( ) I rated4I base---------------- C pu( )Δ×=
