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2–28 850 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL

ELECTRICAL INSTALLATION CHAPTER 2: INSTALLATION

Ground CT Inputs

There are two dedicated ground inputs referred throughout this manual as the Ground

Current and the Sensitive Ground Current inputs.

Before making ground connections, be aware that the relay automatically calculates the

neutral (residual) current from the sum of the three phase current phasors. The following

figures show three possible ground connections using the ground current input (Terminals

J7 and J8) and three possible sensitive ground connections using the sensitive ground

current input (Terminals K7 and K8).

The ground input (Terminals J7 and J8) is used in conjunction with a Zero Sequence CT as

source, or in the neutral of wye-connected source CTs. The ground current input can be

used to polarize both the neutral and sensitive ground directional elements. When using

the residual connection, set the GROUND

CT PRIMARY setpoint to a value equal to the

PHASE

CT PRIMARY setpoint. The sensitive ground current input is intended for use either

with a CT in a source neutral of a high-impedance grounded system, or on ungrounded

systems. On ungrounded systems it is connected residually with the phase current inputs.

In this case, the SENSTV

GND CT PRIMARY setpoint should be programmed to a value

equal to the PHASE CT PRIMARY setpoint. The sensitive ground current input can be

connected to a Zero Sequence CT for increased sensitivity and accuracy when physically

possible in the system.

Figure 2-31: Ground Inputs

892773A2.cdr

8 Series

J8J7 J8J8 J7

GE 850 User Manual

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