Voltage Inputs; Restricted Earth Fault Inputs - GE Multilin 850 Instruction Manual

ELECTRICAL INSTALLATION

Voltage Inputs

CAUTION:

Restricted Earth Fault Inputs

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The 850 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. 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".
The line VT input channel, used for the synchrocheck feature, can be connected for phase-
neutral voltages V , V , or V
an bn
Figure 2-22: 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 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 Earth Fault
protection on transformers that do not have dedicated protection.
The phase and ground input CT connections to the relay are shown below:
; or for phase-phase voltages V
cn
850 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 2: INSTALLATION
, V , or V as shown.
ab bc ca