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3.2 TYPICAL WIRING
3 INSTALLATION
3
Figure 3–11: DRY AND WET CONTACT CONNECTIONS
3.2.10 ANALOG INPUT
Terminals A1 (+) and A2 (–) are provided for the input of a current signal, from one of the following: 0-1 mA, 0-
5 mA, 0-20 mA, or 4-20 mA transducer outputs. This current signal can represent any external quantity, such
as temperature, current or voltage. Be sure to observe polarity markings for correct operation. Both terminals
are clamped to within 36 volts of ground with surge protection. As such, common mode voltages should not
exceed this limit. Shielded wire, with only one end of the shield grounded, is recommended to minimize noise
effects. The A2 (–) terminal must be connected to the A5 (ANALOG OUTPUT COM) terminal at the 745.
3.2.11 TAP POSITION INPUT
Terminals A3 (+) and A4 (-) are provided to monitor the position of an Onload Tap Changer from a stepped-
resistance position indicator device. Terminal A3 is connected internally to a 4.3 mA current source. This cur-
rent is used to measure the value of the external resistance. The 745 uses the measured resistance value to
calculate the Tap Position.
3.2.12 RTD DRIVER/SENSOR
Terminals B10 (RTD HOT), B11 (RTD COMP) and B12 (RTD RET) provide for the connection of various types
of RTD devices. This connection may be made using two or three wires to the RTD. Terminal B10 is connected
internally to a 5 mA current source for energizing the RTD. Terminal B11 is connected internally to a 5 mA cur-
rent source for the purpose of cancelling out the resistance of the wires connecting the RTD to the 745. Termi-
nal B12 is the return path for the two current sources.
In the three-wire connection scheme, the connection from terminal B11 to B12 is made at the RTD. The three-
wire connection scheme compensates for the resistance of the wiring between the 745 and the RTD.
In the two-wire connection scheme, the connection from terminal B11 to B12 is made at the terminal block on
the rear of the 745. This connection must not be omitted. The two-wire connection scheme does not compen-
sate for the resistance of the wiring between the 745 and the RTD.
3-10
745 Transformer Management Relay
GE Power Management
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