Basler Electric DECS-100 - Manual (Page 29)

9287500991 Rev M DECS-100 Functional Description 3-5
Generator Overvoltage
A generator overvoltage condition can be configured (in BESTCOMS) to close the DECS-100 relay
output, disable the DECS-100, initiate both actions, or initiate neither action. When the sensed generator
voltage increases above the adjustable voltage level setpoint for the duration of the adjustable alarm time
delay, the DECS-100 initiates the selected action.
If the DECS-100 is configured to close the relay output, a generator overvoltage condition will light the
front panel and BESTCOMS Generator Overvoltage indicator and close the relay output at terminals AL1
and AL2.
If the DECS-100 is configured for hardware shutdown, a generator overvoltage condition will disable the
DECS-100 after the alarm time delay expires. When the DECS-100 is powered up following a generator
overvoltage shutdown, the Generator Overvoltage indicator will light for five seconds.
The voltage level setpoint is adjustable from 100 to 120 % of the system voltage setting. The alarm time
delay is adjustable from 0 to 10 seconds.
Loss of Sensing Voltage
The DECS-100 monitors the sensed generator output voltage and takes protective action if a loss of
sensing voltage is detected. A loss of sensing voltage is detected during the following conditions.
• The sensed voltage is less than 50 percent of the rated voltage (one-phase or three-phase sensing).
• A total loss of any phase occurs (three-phase sensing).
• The voltage difference between any phase (line-to-line) and the three-phase average exceeds 20
percent of nominal (three-phase sensing).
A time delay of 0 to 25 seconds is adjustable through BESTCOMS software. This delays the protective
action in order to allow field forcing in applications that do not sense B-phase generator current. The
default time delay setting is 10 seconds.
BESTCOMS software allows the selection of one of two protective actions for a loss of sensing. Either a
complete shutdown or a transfer to Manual mode may be selected.
If shutdown is selected and a loss of sensing occurs, the Loss of Generator Sensing indicator on the front
panel and in BESTCOMS lights, the relay output closes, and the DECS-100 shuts down after the
adjustable time delay expires. When the DECS-100 is powered up following a loss of generator sensing
shutdown, the Loss of Generator Sensing indicator will light for five seconds. However, if the loss of
sensing conditions still exists, the DECS-100 will not shut down due to loss of sensing until the soft-start
time delay and the loss of sensing time delay expires.
If transfer to Manual is selected and a loss of sensing occurs, the relay output closes, and the DECS-100
transfers to the Manual mode of operation after the adjustable time delay expires. The DECS-100 will
remain in this mode of operation until switched via BESTCOMS. Prior to selecting transfer to Manual on
loss of sensing, it is necessary to determine an appropriate Manual (FCR) mode setpoint level to be
transferred to. An inappropriate excitation level could result in severe damage to equipment.
This function is disabled when the frequency decreases below 12 hertz or when a generator short circuit
condition is detected. A generator short-circuit is determined when the B-phase CT current exceeds three
times the per unit value. Loss of sensing shutdown or transfer is not active during the soft-start time.
Field Overvoltage (Overexcitation Shutdown)
A field overvoltage condition can be configured (in BESTCOMS) to close the DECS-100 relay output,
disable the DECS-100, initiate both actions, or initiate neither action. When the field voltage increases
above the adjustable voltage level setpoint for the fixed duration of 10 seconds, the DECS-100 initiates
the selected action.
If the DECS-100 is configured to close the relay output, a field overvoltage condition will light the front
panel and BESTCOMS Overexcitation Shutdown indicator and close the relay output at terminals AL1
and AL2.
If the DECS-100 is configured for hardware shutdown, a field overvoltage condition will disable the DECS-
100 after the 10 second time delay expires. When the DECS-100 is powered up following a field
overvoltage shutdown, the Overexcitation Shutdown indicator will light for five seconds.
The voltage level setpoint is adjustable from 0 to 250 Vdc. The field overvoltage time delay is fixed at 10
seconds.