Current Inputs - GE Multilin 489 Instruction Manual

CHAPTER 3: INSTALLATION
3.2.4

Current Inputs

489 GENERATOR MANAGEMENT RELAY – INSTRUCTION MANUAL
Courtesy of NationalSwitchgear.com
Ensure applied control voltage and rated voltage on drawout case terminal label match.
For example, the HI power supply will work with any DC voltage from 90 to 300 V, or AC
voltage from 70 to 265 V. The internal fuse may blow if the applied voltage exceeds this
range.
Extensive filtering and transient protection are built into the 489 to ensure proper
operation in harsh industrial environments. Transient energy must be conducted back to
the source through the filter ground terminal. A separate safety ground terminal is
provided for hi-pot testing.
FIGURE 3–12: Control Power Connection
Phase Current
The 489 has six phase current transformer inputs (three output side and three neutral end),
each with an isolating transformer. There are no internal ground connections on the CT
inputs. Each phase CT circuit is shorted by automatic mechanisms on the 489 case if the
unit is withdrawn. The phase CTs should be chosen such that the FLA is no less than 50% of
the rated phase CT primary. Ideally, the phase CT primary should be chosen such that the
FLA is 100% of the phase CT primary or slightly less. This will ensure maximum accuracy
for the current measurements. The maximum phase CT primary current is 50000 A.
The 489 will measure correctly up to 20 times the phase current nominal rating. Since the
conversion range is large, 1 A or 5 A CT secondaries must be specified at the time of order
such that the appropriate interposing CT may be installed in the unit. CTs chosen must be
capable of driving the 489 phase CT burden (see SPECIFICATIONS for ratings).
Verify that the 489 nominal phase current of 1 A or 5 A matches the secondary rating
and connections of the connected CTs. Unmatched CTs may result in equipment
damage or inadequate protection. Polarity of the phase CTs is critical for phase
differential, negative sequence, power measurement, and residual ground current
detection (if used).
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