Ground Ct Inputs; Voltage Inputs - GE 845 Instruction Manual

CHAPTER 2: INSTALLATION

Ground CT Inputs

Voltage Inputs

845 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
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).
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 the neutral. When using the residual connection, set the
GROUND CT PRIMARY setpoint to a value equal to the PHASE CT PRIMARY setpoint.
Figure 2-19: Ground Inputs
The 845 relays have four channels for AC voltage inputs, each with an isolating
transformer. Voltage transformers up to a maximum 5000:1 ratio may be used. The
nominal secondary voltage must be in the 10 to 240 V range. The Bus VT connections most
commonly used, wye and delta (or open delta), are shown in the typical wiring diagram.
The single Auxiliary voltage input is commonly used as the "line voltage". The line VT input
channel, used for the synchrocheck feature, can be connected for phase-neutral voltages
V , V , or V ; or for phase-phase voltages V
an bn cn
ELECTRICAL INSTALLATION
, V , or V as shown.
ab bc ca
2–17