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3.2 ELECTRICAL
For the correct operation of many relay features, the instrument transformer polarities shown above in Figure 3–9: Typical
Wiring Diagram on page 3–7 must be followed. Note the solid square markings shown with all instrument transformer con-
nections. When the connections adhere to this drawing, the arrow shows the direction of power flow for positive watts and
the positive direction of lagging vars. The phase sequence is user programmable to be either ABC or ACB rotation.
a) DESCRIPTION
The 750/760 relays have five (5) channels for AC current inputs, each with an isolating transformer and an automatic short-
ing mechanism that acts when the relay is withdrawn from its case. There are no internal ground connections on the current
inputs. Current transformers with 1 to 50000 A primaries may be used.
3
Verify that the relay's nominal input 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.
CAUTION
IMPORTANT: The phase and ground current inputs will correctly measure to 20 times the current input's
nominal rating. Time overcurrent curves become horizontal lines for currents above the 20 × CT rating.
This becomes apparent if the pickup level is set above the nominal CT rating.
CAUTION
b) GROUND AND SENSITIVE 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, consider 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 G10 and H10) and three possible sensitive ground connections using the sensi-
tive ground current input (Terminals G3 and H3).
The ground input (Terminals G10 and H10) 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 direc-
tional elements. When using the residual connection set the
setpoint.
PRIMARY
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
sensitive ground current input can be connected to a Zero Sequence CT for increased sensitivity and accuracy when phys-
ically possible in the system.
Units that do not have the Sensitive Ground input (such as older units which have been upgraded with new firm-
ware) use the G3 and H3 terminals as the polarizing input. The G10 and H10 terminals are used for the Ground
NOTE
input. These connections will be shown on the terminal assignment label on the back of the relay's case.
The Sensitive Ground input (G3 and H3 terminals) must only be used on systems where the maximum ground cur-
rent does not exceed 500 A.
NOTE
3-8
Courtesy of NationalSwitchgear.com
3.2.2 PHASE SEQUENCE AND TRANSFORMER POLARITY
GROUND CT PRIMARY
setpoint should be programmed to a value equal to the
750/760 Feeder Management Relay
3 INSTALLATION
3.2.3 CURRENT INPUTS
setpoint to a value equal to the
setpoint. The
PHASE CT PRIMARY
PHASE CT
GE Multilin
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