Basler DECS-250, Instruction Manual

Page: 62 / 352

46 9440300990 Rev J
Protection DECS-250
Underfrequency
An underfrequency condition occurs when the frequency of the generator voltage decreases below the
81U pickup threshold
A
for the duration of the 81U time delay setting
B
. A voltage inhibit setting
C
, expressed
as a percentage of the rated generator voltage, can be implemented to prevent an underfrequency trip
from occurring during startup when the generator voltage is rising toward the nominal level.
Underfrequency protection can be enabled and disabled
D
without altering the pickup, delay, and inhibit
settings. Underfrequency pickup and trip elements in BESTlogic Plus can be used in a logic scheme to
initiate corrective action in response to the condition. BESTCOMS Plus underfrequency settings are
illustrated in Figure 32.
Figure 32. Underfrequency Protection Settings
A
Underfrequency (81U) Pickup (Hz) : Adjustable from 30 to 70 hertz in 0.01 hertz increments.
B
Underfrequency (81U) Time Delay (s) : Adjustable from 0.1 to 300 seconds in 0.1 second increments.
C
Underfrequency (81U) Voltage Inhibit (%) : Adjustable from 50 to 100% in 1% increments.
D
Underfrequency (81U) Mode : Select Disable or Under.
Power Protection
BESTCOMSPlus Navigation Path: Settings Explorer, Protection, Power
HMI Navigation Path: Settings, Protection, Power
Generator power levels are monitored to protect against reverse power flow and loss of excitation.
Reverse Power
Reverse power protection guards against reverse power flow that may result from a loss of prime mover
torque (and lead to generator motoring). A reverse power condition occurs when the flow of reverse
power exceeds the 32R pickup threshold
A
for the duration of the 32R time delay
B
. Reverse power
protection can be enabled and disabled
C
without altering the pickup and time delay settings. Reverse
power pickup and trip elements in BESTlogic Plus can be used in a logic scheme to initiate corrective
action in response to the condition. BESTCOMS Plus reverse power protection settings are illustrated in
Figure 33.