Basler Electric DECS-400 User Manual
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Generator Voltage
Generator sensing voltage is supplied to DECS-400 terminals A9 (E1), A10 (E2), and A11 (E3) through
external, user-supplied, isolation transformers with a nominal output rating of 120 Vac or 240 Vac. The
DECS-400 automatically selects the proper generator voltage sensing range based on the generator
voltage sensing transformer’s secondary voltage value entered in the DECS-400.
DECS-400 generator voltage sensing inputs consist of an A-phase to B-phase (V
AB
) voltage input, a B-
phase to C-phase voltage input (V
BC
), and a C-phase to A-phase voltage input (V
CA
).
The V
CA
voltage sensing input is used by the DECS-400 to calculate generator frequency. Sensed
voltage is filtered (through a zero-crossing detector) to eliminate multiple zero crossings during one
fundamental period.
Bus Voltage
Bus sensing voltage is supplied to DECS-400 terminals A13 (BUS1) and A14 (BUS3) through external,
user-supplied isolation transformers with a nominal output rating of 120 Vac or 240 Vac. The DECS-400
automatically selects the proper bus voltage sensing range based on the bus voltage sensing
transformer’s secondary voltage value entered in the DECS-400.
The sensed bus voltage is filtered (through a zero-crossing detector) to eliminate multiple zero crossings
during one fundamental period. This input is compared with the generator sensing voltage for the purpose
of voltage matching.
Line Current
The line current sensing inputs consist of an A-phase current input (I
A
), a B-phase current input (I
B
), and
a C-phase current input (I
C
).
Generator sensing current is supplied to DECS-400 terminals A1 and A2 (CTA), A3 and A4 (CTB), and
A5 and A6 (CTC) through external, user-supplied current transformers (CTs) with a secondary rating of 1
Aac (DECS-400 style XX1X) or 5 Aac (DECS-400 style XX5X).
When only one phase of generator current is sensed, the I
B
input (terminals A3 and A4) must be used.
A minimum of two generator current phases must be sensed for PSS applications.
Cross-Current Compensation
This input (CCC) is used when generators are operating in cross-current compensation (reactive
differential) mode.
B-phase generator sensing current is supplied to DECS-400 terminals A7 and A8 through an external,
user-supplied CT with a secondary rating of 1 Aac (DECS-400 style XX1X) or 5 Aac (DECS-400 style
XX5X).
Accessory Input
The accessory input can be configured to receive an external excitation setpoint control signal, the control
signal from an external PSS, or for limiter scaling. (For more information about limiter scaling, see Limiter
Functions, Limiter Scaling later in this chapter.) The accessory input accepts either a –10 Vdc to +10 Vdc
signal at DECS-400 terminals A16 (+) and A17 (–) or a 4 mAdc to 20 mAdc control signal at A19 (+) and
A20 (–).
When a current input type is selected, the input current is converted by the DECS-400 to a voltage signal
in the range of –5 to +5 Vdc. The following equation is used by the DECS-400 when converting the
applied current into a voltage.
V
aux
= 0.625 (I – 12)
where: Vaux = the calculated voltage signal
I = current applied to the accessory input (in milliamperes)
For setpoint control, V
aux
is multiplied by the appropriate accessory gain setting: AVR mode gain, FCR
mode gain, Var mode gain, or Power Factor mode gain. The accessory input can be active in all four
operating modes.
Functional Description
DECS-400