Basler DECS-250 - Field Protection

9440300990 10-9
DECS-250 Protection
Field Protection
BESTCOMSPlus Navigation Path: Settings Explorer, Protection, Field
HMI Navigation Path: Settings, Protection, Field
Field protection provided by the DECS-250 includes field overvoltage, field overcurrent, an exciter diode
monitor, and power input failure.
Field Overvoltage
A field overvoltage condition occurs when the field voltage exceeds the field overvoltage threshold for the
duration of the field overvoltage 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.
Settings that are related to machine ratings can be set in either actual units of voltage or in per unit
values. When a native unit is edited, BESTCOMSPlus automatically recalculates the per unit value based
on the native unit setting and the rated data parameter (on the System Parameters, Rated Data screen)
associated with it. When a per unit value is edited, BESTCOMSPlus automatically recalculates the native
value based on the per unit setting and the rated data parameter associated with it.
Once all per unit values are assigned, if the rated data parameters are changed, BESTCOMSPlus
automatically recalculates all native unit settings based on the modified rated data parameters.
The Overvoltage pickup has a native unit of Primary Volts and the rated data associated with it is Field
Rated Data, Voltage – Full Load (on the System Parameters, Rated Data screen).
BESTCOMSPlus field overvoltage settings are illustrated in Figure 10-12.
Figure 10-12. Field Overvoltage Protection Settings
Field Overcurrent
A field overcurrent condition is annunciated when the field current exceeds the field overcurrent pickup
level for the duration of the field overcurrent time delay. Depending on the selected timing mode, the time
delay can be fixed or related to an inverse function. Definite timing mode uses a fixed time delay. In
inverse timing mode, the time delay is shortened in relation to the level of field current above the pickup
level. The time dial setting acts as a linear multiplier for the time to an annunciation. This enables the
DECS-250 to approximate the heating characteristic of the generator and generator step-up transformer
during overexcitation. The field current must fall below the dropout ratio (95%) for the function to begin
timing to reset. The following equations are used to calculate the field overcurrent pickup and reset time
delays.


=
 × 
+
√
+  × 
Equation 10-3. Inverse Field Overcurrent Pickup