9440300990 8-1
DECS-250 Auxiliary Control
8 • Auxiliary Control
BESTCOMSPlus Navigation Path: Settings Explorer, Operating Settings, Auxiliary Inputs
HMI Navigation Path: Settings, Operating Settings, Auxiliary Inputs
The DECS-250 accepts an external analog control signal for auxiliary control of the regulation setpoint.
Auxiliary setpoint control is possible in all regulation modes: AVR, PF, Var, FCR, and FVR. The control
signal can also be used for limiter scaling or power system stabilizer control. Auxiliary control settings are
illustrated in Figure 8-1.
Auxiliary Control Input Type
Either a voltage or current control signal may be used for auxiliary control. Terminals I+ and I– accept a 4
to 20 mAdc signal. Terminals V+ and V– accept a –10 to +10 Vdc signal. An adjacent terminal labeled
GND provides the connection for a recommended cable shield. The input type is selected in
BESTCOMSPlus
®
.
Auxiliary Control Input Function
The analog control input can be used for auxiliary control of the regulation setpoint, as a power system
stabilizer test input, for limiter scaling, or for grid code input.
PSS Test Input
The auxiliary control input can be used for control of the optional power system stabilizer function during
testing and validation. More information is provided in the Power System Stabilizer chapter of this
manual.
Limiter Scaling
When the auxiliary control input is configured for limiter scaling, the stator current limiter (SCL) and
overexcitation limiter (OEL) low-level values can be automatically adjusted. Automatic adjustment of the
SCL and OEL is based on six parameters: signal and scale for three points. The signal value for each
point represents the accessory input voltage. The scale value defines the limiter low level as a
percentage of rated field current for the OEL and rated stator current for the SCL. For accessory input
voltages between two of the three defined points, the low-level limiter setting is linearly adjusted between
the two scale values. Limiter settings and limiter scaling are discussed in detail in the Limiters chapter of
this manual.
Grid Code Input
The grid code input must be selected when it is desired to use the auxiliary input as the adjustment
source for active and reactive power control.
Setpoint Limits
Minimum and maximum setpoint limits are observed when the With Limit box is checked.
Auxiliary Control Gains
When a current input type is selected, the input current is converted internally by the DECS-250 into a
voltage signal in the range of –10 to +10 Vdc. The DECS-250 uses the following equation when
converting the applied current into a voltage.
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