GE 735 Instruction Manual page 37

3 SETUP AND OPERATION
a) PHASE TIME MULTIPLIER SHIFT
Although only 10 discrete curves can be selected for phase time overcurrent using the time multiplier dial, the trip times can
be shifted to effectively create additional curves. This allows for more accurate coordination. To change the curve shift
value, the relay must be drawn out from the captive chassis and the option switches on the side of the relay set according
to the table above.
Use the following procedure to select the correct shift value:
1. Plot the required curve for coordination.
2. Select the closest curve shape
3. Select the appropriate Time Multiplier and Phase Shift overcurrent combination to match the required curve trip times
(refer to the examples below for details).
EXAMPLE 1:
The plotted curves falls on normally inverse curve number 4. In this case, select:
CURVE SHAPE: Normal Inverse
TIME MULTIPLIER: 4
and set the OPTION SWITCHES for a phase overcurrent shift of 1 (switches 1 and 2 both OFF).
EXAMPLE 2:
The plotted curve is approximately halfway in-between Very Inverse curves 5 and 6. In this case, select values for Phase
Time O/C Shift and Time Multiplier that most closely match the required curve so that:
Time Multiplier x Phase Shift = 5.5
To meet this requirement, set Time Multiplier = 7 and Phase Time O/C Shift = 0.8. The selected curve will have an approxi-
mate time multiplier of 7 × 0.8 = 5.6. Select:
CURVE SHAPE: Very Inverse
TIME MULTIPLIER: 7
and set the option switches for a phase overcurrent shift of 0.8 (switch 1 OFF and switch 2 ON).
b) GROUND MULTIPLIER SHIFT
Ground time multiplier shift works exactly the same way as the phase shift time multiplier except that it affects the selected
ground curve.
c) FREQUENCY
Nominal system frequency should be set to determine the sample rate for optimum current measurement.
d) PICKUP/CAUSE OF TRIP RELAYS (737 ONLY)
The 737 has 8 additional output relays fir more complex control schemes or for status signalling to a SCADA system.
These are programmed with option switches 6 and 7 to energize on:
1. PULSED TRIP ONLY: In addition to the two form A common trip output contacts, a separate contact for each protec-
tion element will also activate. This makes the 737 the equivalent of 8 separate protection relays for interfacing to more
complex protective relaying schemes. Relay output contacts for the 50/51 protection element that is causing the trip
operate in the same manner as the common trip output contacts.
2. LATCHED CAUSE OF TRIP ONLY: After a trip, the relay(s) corresponding to the 50/51 element that caused the trip will
be latched until the front panel CLEAR key is pressed or a "reset cause of trip" command is received through the com-
munications port. The output relays energized will be the same as the TRIP indicators on the front panel. This is useful
for interface to a SCADA system to diagnose the cause of trip.
3. PICKUP ONLY: Output relays activate when any phase/ground current is above the pickup setting. Relays automati-
cally reset if the ground/phase current drops below the pickup level. This is useful for interface to a SCADA system to
warn of faults which could lead to a trip if not corrected.
4. PICKUP OR CAUSE OF TRIP: Either pickup or latched cause of trip will energize the relays. This is the same as items
2 and 3 together.
GE Power Management 735/737 Feeder Protection Relay
3.4 SWITCHES
3
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