9440300990 5-1
DECS-250 Voltage and Current Sensing
5 • Voltage and Current Sensing
The DECS-250 senses generator voltage, generator current, and bus voltage through dedicated, isolated
inputs.
Generator Voltage
Three-phase generator sensing voltage is applied to DECS-250 terminals E1, E2, and E3. This sensing
voltage is typically applied through a user-supplied voltage transformer, but may be applied directly.
These terminals accept three-phase, three-wire connections at terminals E1 (A), E2 (B), and E3 (C) or
single-phase connections at E1 (A) and E3 (C).
The generator voltage sensing input accepts a maximum voltage of 600 Vac and has a burden of less
than 1 VA.
The transformer primary and secondary winding voltages are entered in settings that the DECS-250 uses
to interpret the applied sensing voltage and calculate system parameters. The phase rotation of the
generator sensing voltage can be configured as ABC or ACB. Information about configuring the DECS-
250 for the generator sensing voltage is provided in the Configuration chapter of this manual.
Typical generator voltage sensing connections are illustrated in Figure 5-1.
Figure 5-1. Typical Generator Voltage Sensing Connections
Generator Current
Generator current sensing inputs consist of three phase-sensing inputs and a sensing input for cross-
current compensation.
Current transformer (CT) grounding should be applied in accordance
with local codes and conventions.
Phase Sensing
Three-phase generator sensing current is applied to DECS-250 terminals CTA+ and CTA–, CTB+ and
CTB–, and CTC+ and CTC– through user-supplied current transformers (CTs). Single-phase generator
sensing current is applied to DECS-250 terminals CTB+ and CTB–. The DECS-250 is compatible with
CTs having 5 Aac or 1 Aac nominal secondary ratings. The DECS-250 uses this secondary rating, along
with the CT nominal primary ratings to interpret the sensed current and calculate system parameters.
Information about configuring the DECS-250 for the generator sensing voltage is provided in the
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