9492600990 8-7
DECS-150 Protection
Where:
G = metered generator angle
B = metered bus angle
A = angle compensation value
When the Gen Freq > Bus Freq box is checked, the 25 status virtual output will not assert unless the
generator frequency is greater than the bus frequency.
The Sync Check screen is illustrated in Figure 8-9.
Figure 8-9. Sync Check Screen
Machine Frequency Less Than 10 Hertz
A Generator/Motor Below 10 Hz condition is annunciated when the machine frequency decreases below
10 Hz or when residual voltage is low at 50/60 Hz. A Generator/Motor Below 10 Hz annunciation is
automatically reset when the machine frequency increases above 10 Hz or the residual voltage increases
above the threshold.
Configurable Protection
BESTCOMSPlus Navigation Path: Settings Explorer, Protection, Configurable Protection
The DECS-150 has eight configurable protection elements which can be used to supplement the
standard DECS-150 protection. To make the protection elements easier to identify, each element can be
given a user-assigned name of up to 16 alphanumeric characters. A protection element is configured by
selecting the parameter to be monitored and then establishing the operating characteristics for the
element.
Protection will always be enabled when Stop mode is not inhibited. When Stop mode is inhibited,
protection can be enabled only when the DECS-150 is enabled and supplying excitation. When protection
is enabled only in Start mode, an arming time delay can be used to delay protection following the start of
excitation.
A hysteresis function holds the protection function active for a user-defined percentage above/below the
pickup threshold. This prevents repeated pickups and dropouts where the monitored parameter is
hovering around the pickup threshold. For example, with a hysteresis setting of 5% on a protection
element configured to pick up at 100 Aac of A-phase machine overcurrent, the protection element would
pick up when the current rises above 100 Aac and remain picked up until the current decreases below 95
Aac.
Each of the eight configurable protection elements has four individually-adjustable thresholds. Each
threshold can be set for pickup when the monitored parameter increases above the pickup setting (Over),
pickup when the monitored parameter decreases below the pickup setting (Under), or no pickup
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