GE 469 Instruction Manual page 57

Motor management relay
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469
Electrical Installation
Motor Management Relay
The 469 correctly measures 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 to ensure the appropriate interposing CT is installed in the unit. The
chosen CTs must be capable of driving the 469 phase CT burden (see Specifications
on page 2–5 for ratings).
Verify that the 469 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
CAUTION
phase CTs is critical for Negative Sequence Unbalance calculation, power
measurement, and residual ground current detection (if used).
See Two-Phase CT Configuration on page 8–1 for 2-phase CT information.
b) Ground Current Input
The 469 has a dual primary isolating transformer for ground CT connection. There
are no internal ground connections on the ground current inputs. The ground CT
circuits are shorted by automatic mechanisms on the 469 case if the unit is
withdrawn. The 1 A / 5 A tap is used either for zero-sequence / core balance
applications or residual ground connections where the summation of the three
phase current CTs is passed through the ground current input (see the figure
below). The maximum ground CT primary current is 5000 A for the 1 A / 5 A tap.
Alternatively, the 50:0.025 ground CT input has been designed for sensitive ground
current detection on high resistance grounded systems where the GE Multilin
50:0.025 core-balance CT is to be used. For example, in mining applications where
earth leakage current must be measured for personnel safety, primary ground
current as low as 0.25 A may be detected with the GE Multilin 50:0.025 CT. Only
one ground CT input tap should be used on a given unit.
FIGURE 3–14: Residual Ground CT Connection
The 469 measures up to 5 A secondary current if the 1 A / 5 A tap is used. Since the
conversion range is relatively small, the 1 A or 5 A option is field programmable.
Proper selection of this setpoint ensures proper reading of primary ground current.
The 1 A / 5 A ground CT chosen must be capable of driving the 469 ground CT
burden (see Specifications on page 2–5). The 469 measures up to 25 A of primary
ground current if this tap is used in conjunction with the GE Multilin core balance CT.
GE Multilin
3–11
http://www.GEindustrial.com/multilin

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