44
9440300990 Rev J
Protection
DECS-250
Generator Overvoltage
An overvoltage pickup condition occurs when the sensed generator terminal voltage increases above the
pickup setting
A
. An overvoltage trip condition occurs if the generator voltage remains above the pickup
threshold for the duration of the time delay setting
B
. Generator overvoltage protection can be enabled and
disabled
C
without altering the pickup and time delay settings. Overvoltage 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
®
generator overvoltage settings are illustrated in Figure 29.
Figure 29. Generator Overvoltage Protection Settings
A
Generator Overvoltage Pickup (V)
: Adjustable from 0 to 600,000 Vac in 1 Vac increments.
B
Generator Overvoltage Time Delay (s)
: Adjustable from 0.1 to 60 seconds in 0.1 second increments.
C
Generator Overvoltage Enable/Disable
: Select Enabled or Disabled.
Loss of Sensing
The generator voltage is monitored for a loss of sensing (LOS) condition. LOS protection settings are
illustrated in Figure 30.
In the DECS-250, a loss of sensing event is calculated using sequence components. A loss of sensing
event occurs when the positive sequence voltage drops below the balanced
A
setting percentage of the
AVR setpoint, or when the negative sequence voltage increases above the unbalanced
B
setting
percentage of the positive sequence voltage. A delay timer
C
is started when the event occurs, delaying
the alarm by a predetermined time.
A LOS condition can be used to initiate a transfer to manual (FCR) control mode
D
. It also can be
configured in BESTlogic
Plus
to initiate other actions. Protection can be enabled and disabled
E
without
altering the individual loss of sensing settings.
LOS protection is automatically disabled when a short circuit exists. A short circuit is detected when the
measured current is greater than twice the rated current for a single-phase CT connection and when the
positive sequence current is greater than twice the rated current for a three-phase CT connection.
Summary of Contents for DECS-250
Page 2: ......
Page 6: ...iv 9440300990 Rev J Revision History DECS 250 ...
Page 16: ...xiv 9440300990 Rev J Contents DECS 250 ...
Page 20: ...4 9440300990 Rev J Introduction DECS 250 ...
Page 28: ...12 9440300990 Rev J Power Stage DECS 250 ...
Page 32: ...16 9440300990 Rev J Voltage and Current Sensing DECS 250 ...
Page 40: ...24 9440300990 Rev J Synchronizer DECS 250 ...
Page 52: ...36 9440300990 Rev J Auxiliary Control DECS 250 ...
Page 56: ...40 9440300990 Rev J Contact Inputs and Outputs DECS 250 ...
Page 84: ...68 9440300990 Rev J Limiters DECS 250 ...
Page 114: ...98 9440300990 Rev J Power System Stabilizer DECS 250 Figure 96 PSS Parameter Settings ...
Page 124: ...108 9440300990 Rev J Stability Tuning DECS 250 ...
Page 126: ...110 9440300990 Rev J Mounting DECS 250 Figure 103 Overall and Projection Mounting Dimensions ...
Page 127: ...9440300990 Rev J 111 DECS 250 Mounting Figure 104 DECS 250 Escutcheon Plate Dimensions ...
Page 198: ...182 9440300990 Rev J Timekeeping DECS 250 ...
Page 210: ...194 9440300990 Rev J CAN Communication DECS 250 ...
Page 304: ...288 9440300990 Rev J Maintenance DECS 250 ...
Page 316: ...300 9440300990 Rev J Specifications DECS 250 ...
Page 334: ...318 9440300990 Rev J Analog Expansion Module DECS 250 ...
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