9492600990 8-5
DECS-150 Protection
Exciter Field Current Limit
When checked, Shutdown Enable causes the DECS-150 to shut down excitation when the field current is
too high (approximately 23 A), which could result in damage to the regulator. A restart is required to begin
regulating again. The Exciter Field Current Limit screen is illustrated in Figure 8-6.
Figure 8-6. Exciter Field Current Limit Screen
Field Overvoltage
A field overvoltage condition occurs when the field voltage exceeds the pickup level for the duration of the
Time Delay. Field overvoltage protection can be enabled and disabled without altering the Pickup and
Time Delay settings. Field overvoltage pickup and trip elements in BESTlogicPlus can be used in a logic
scheme to initiate corrective action in response to the condition.
The Field Overvoltage screen is illustrated in Figure 8-7.
Figure 8-7. Field Overvoltage Screen
Shutdown Enable
When checked, Shutdown Enable causes the DECS-150 to stop excitation when the field overvoltage
element trips.
Exciter Diode Monitor
The exciter diode monitor (EDM) monitors the condition of a brushless exciter’s power semiconductors by
monitoring the exciter field current. The EDM detects both open and shorted rotating diodes in the exciter
bridge.
All of the EDM setup guidelines presented here assume that the
exciter diodes are not open or shorted at the time of setup and testing.
The EDM estimates the ripple of the exciter field current using root-mean-square (rms). The rms value of
the ripple is calculated and compared to the pickup threshold for open or shorted diode detection. If the
field current ripple exceeds the pickup level for the duration of the Time Delay, the condition is
annunciated. EDM pickup and trip elements in BESTlogicPlus can be used in a logic scheme to initiate
corrective action in response to an open or shorted diode condition.
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