BankGuard PLUS
S&C Electric Company
Control
Proprietary Information
16
Operation
1011-540 5-17-04
continuously for a time greater than the applicable time delay setpoint value, the
appropriate control action is taken. The control will lockout the bank if the “Gross Over
Voltage Level” or the “Lockout Level” setpoint value is exceeded, or issue an alarm if the
“Alarm Level” setpoint value is exceeded. The “Reactor Only” value is generally selected
when the voltage variations between the line phases are expected to be negligible in
comparison to the neutral-to-ground voltage changes resulting from the loss of reactor
turns.
In addition to the neutral-to-ground potential device, three S&C 30-Volt-Ampere Potential
Devices are required to be installed on each line phase when the “Unbalance
Compensation” feature is set to “Reactor/Line”. The control uses the three potential
devices to obtain the sum of the line voltages magnitude and a reference angle. Since the
sum is obtained from all the line voltages, compensation for fixed system imbalances is
provided. During the setup of the unbalance compensation feature, a neutral-to-ground
voltage magnitude sample, a sum of the line voltages sample and the reference angle are
used to calculate and store a magnitude correction value (see Signal Processing below for
an explanation of how the value is calculated. During each control cycle, the stored
magnitude correction factor is subtracted from the real-time neutral-to-ground magnitude
to obtain a compensated neutral to ground voltage magnitude. Reactor-turn failures will
cause the real-time line-to-neutral voltage to change and therefore change the
compensated neutral-to-ground voltage magnitude. The control compares the
compensated neutral-to-ground voltage magnitude to the “Gross Over Voltage Level,”
“Lockout Level,” and “Alarm Level” setpoint values, if enabled. If the compensated
neutral-to-ground voltage magnitude exceeds a setpoint value continuously for a time
greater than the applicable time delay setpoint value, the appropriate control action is
taken. The control will lock out the bank if the “Gross Over Voltage Level or the “Lockout
Level” setpoint values are exceeded. The control will issue an alarm if the “Alarm Level”
setpoint value is exceeded.
