Ac Voltage Input - GE 745 Instruction Manual

TYPICAL WIRING
CAUTION
Note
NOTE
3.2.6

AC Voltage Input

3.2.7 Logic Inputs
CAUTION
3–14
Verify that the relay's nominal current of 1 A or 5 A matches the secondary rating of the
connected 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.
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.
FIGURE 3–13: Zero-sequence (core balance) CT installation
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.
External contacts can be connected to the 16 logic inputs. As shown, these contacts can
be either dry or wet. It is also possible to use a combination of both contact types.
A dry contact has one side connected to terminal D11. This is the +32 V DC voltage rail. The
other side is connected to the required logic input terminal. When a dry contact closes, a
2.2 mA current flows through the associated circuit.
A wet contact has one side connected to the positive terminal of an external DC power
supply. The other side is connected to the required logic input terminal. In addition, the
negative side of the external source must be connected to the relay DC negative rail at
terminal D12. The maximum external source voltage for this arrangement is 300 V DC.
Correct polarity must be observed for all logic input connections or equipment damage
may result.
745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 3: INSTALLATION