Voltage Inputs; Restricted Ground Fault Inputs - GE 850 Instruction Manual

ELECTRICAL INSTALLATION

Voltage Inputs

CAUTION:

Restricted Ground Fault Inputs

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The 850 relays have four channels for AC voltage inputs, each with an isolating
transformer in each J and K slot. 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. In Main-Tie-
Main bus transfer scheme, the three phase inputs are mostly used for "Bus voltage". 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". For LEA inputs, the "line voltage" connection is line to neutral voltages. 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
Figure 2-33: Line VT Connections
If Delta VTs are used for three-phase voltages, the zero sequence voltage (V0) and
neutral/sensitive ground polarizing voltage (–V0) are zero. Also, with the Delta VT
connection, the phase-neutral voltage cannot be measured and is not displayed.
Restricted Ground Fault protection, (also referred to as Restricted Earth Fault protection,) is
often applied to transformers having grounded Wye windings to provide ground fault
detection for faults near the transformer neutral. Each current bank on the relay has 3
phase current inputs and one ground input. Any of the available inputs on the relay current
banks can be selected as a signal input for an RGF element.
Although the 850 is designed for feeder protection, it can provide Restricted Ground Fault
protection on transformers that do not have dedicated protection.
The phase and ground input CT connections to the relay are shown below:
, V , or V
ab bc
850 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 2: INSTALLATION
as shown.
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