GE C70 Instruction Manual page 389

CHAPTER 5: SETTINGS GROUPED ELEMENTS
The bank phase overvoltage element responds to voltages across the capacitors of the bank. Three stages of definite time
operation, and one stage of inverse time operation are provided. Pickup thresholds of this function are adjustable on a per-
phase basis. The shape of the inverse time curve is user-programmable (via FlexCurves™) with individual pickup levels and
a multiplier common for all three phases. The definite time delays are individually programmable per stage.
The function works with grounded and ungrounded banks. With ungrounded banks, either the neutral point voltage is
measured by the relay and used to derive the true bank voltage based on the bus and neutral-point voltages, or a
simplified method to provide proper voltage protection is used responding to vector differences between the phase-to-
phase voltages.
When fed from wye-connected VTs, the function responds to phase-to-ground voltages. When fed from delta-connected
VTs, it responds to the vector difference between the phase-to-phase voltages.
The function responds to true RMS voltages to account for effects of harmonics (harmonics impacting losses in the
capacitor, harmonics increasing peak values in the voltages compared with the filtered fundamental frequency
magnitudes).
Figure 5-118: Bank overvoltage basic connections
5
For more information, see the Application of Settings chapter.
The following settings are available for each bank phase overvoltage element.
— Indicates the signal source that signifies the bus voltage of the capacitor bank. The function uses
BANK OV 1 BUS SOURCE
this source as reference for per-unit (pu) settings of the pickup thresholds. The VT ratio and secondary nominal voltage are
set under the menu.
SETTINGS  SYSTEM SETUP  AC INPUTS  VOLTAGE BANK
— Indicates the signal source that signifies the neutral-point voltage of the bank. The auxiliary
BANK OV 1 NTRL SOURCE
voltage channel of this source is used, and must be labelled "Vn" under the VT setup menu. The neutral point voltage is
used only when the function is applied to an ungrounded bank, to derive the true voltage drop across the capacitors. The
VT ratio and secondary nominal voltage are set under the
SETTINGS  SYSTEM SETUP  AC INPUTS  VOLTAGE BANK
menu.
C70 CAPACITOR BANK PROTECTION AND CONTROL SYSTEM – INSTRUCTION MANUAL 5-223