3-8 745 Transformer Management Relay GE Power Management
3.2 TYPICAL WIRING 3 INSTALLATION
3
3.2.5 PHASE SEQUENCE AND TRANSFORMER POLARITY
For the correct operation of many relay features, the phase sequence and instrument transformer polarities
shown on the typical wiring diagram must be followed. Note the markings shown with all instrument trans-
former connections. When the connections adhere to this drawing, the relay will operate properly.
3.2.6 AC CURRENT TRANSFORMER INPUTS
The 745 has eight or eleven channels for AC current inputs, each with an isolating transformer and an auto-
matic shorting mechanism that acts when the relay is withdrawn from its case. There are no internal ground
connections on the current inputs. Current transformers with 1 to 50 000 A primaries may be used.
Verify that the relay’s nominal current of 1 A or 5 A matches the secondary rating of the con-
nected CTs. Unmatched CTs may result in equipment damage or inadequate protection.
The exact placement of a zero-sequence CT so that ground fault current will be detected is shown below.
Twisted pair cabling on the zero-sequence CT is recommended.
Figure 3–9: ZERO-SEQUENCE (CORE BALANCE) CT INSTALLATION
IMPORTANT: The relay will correctly measure up to 46 times the current input nominal rating.
Time overcurrent curves become horizontal lines for currents above the 46
×
CT rating.
3.2.7 AC VOLTAGE INPUT
The 745 has one voltage divider type input for AC voltages. There are no internal fuses or ground connections.
Voltage transformers up to a maximum 5000:1 ratio may be used. The nominal secondary voltage must be in
the 60 to 120 V range.
CAUTION
NOTE
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