GE 735, Instruction Manual, Page: 44 / 110

3-16 735/737 Feeder Protection Relay GE Power Management
3.6 SETUP EXAMPLE 3 SETUP AND OPERATION
3
3.6 SETUP EXAMPLE 3.6.1 EXAMPLE REQUIREMENTS AND SETTINGS
Refer to Section 3.2: CONTROLS for the corresponding dial settings.
CTs: 600:5
The primary CT current rating (600 A) affects phase and ground pickup and instantaneous dials since these are a percent-
age of CT sensor. Check label on side of drawout chassis to ensure the relay is configured for 5 A CTs.
Phase Time Overcurrent Pickup: 360 A
Set the PHASE PICKUP dial to 60%. Note this is the LO band used in setting the PHASE CURRENT SHAPE dial.
Phase Current Shape: Normal Inverse
Set PHASE CURVE SHAPE to Normal Inverse-LO to match the PHASE PICKUP dial setting on LO band (60% of sensor)
Phase Time Multiplier: 1 second at 4
×
PU
From system co-ordination curves, choose the closest matching curve by overlaying the required curve shape with the
curve figures or reading off a trip time point for a given shape. Assuming an ANSI Normal Inverse curve with a trip time of 1
second at 4
×
PU, this is curve multiplier 2. Set the PHASE TIME MULTIPLIER to 2. Set phase o/c curve shift to 1 (option
switches 2=OFF 1=OFF).
Phase Instantaneous: 6000 A
Set the PHASE INSTANTANEOUS to 10 (
×
CT). This setting is independent of the PHASE PICKUP setting used for time
overcurrent trips.
Ground Sensing: Residual
Wire the ground current input using the phase CTs connected for residual sensing. Use the phase CT primary as the
ground CT value in setting pickup and instantaneous ground settings.
Ground Fault Trip Level: 240 A
Ground current sensing is by residual connection of the phase CTs. If a separate ground CT is used for ground fault detec-
tion, use the primary value for the CT in calculating the GROUND PICKUP dial setting.
The GROUND PICKUP dial is set to 40 (% of CT) which falls on the LO band. Consequently, the selected ground curve
shape must be on the LO band setting.
Ground Time Multiplier: 200 ms delay definite time
A fixed delay of 200 ms after ground fault detection is required for co-ordination so set the curve shape to DEFINITE TIME-
LO. From the definite time curves to get a 200 ms delay, curve 2 is required with a ground time o/c shift of 1. Set GROUND
TIME MULTIPLIER to 2. Set ground time o/c shift option switches 4=OFF, 3=OFF.
Ground Instantaneous Trip: None
Only the 200 ms delayed pickup of 240 A is required so set the GROUND INSTANTANEOUS dial to OFF.
Setting
CT Primary
------------------------------
360
600
----------
60%
= =
Setting
CT Ratio
-----------------------
6000
600
------------- 10 CT
×
= =
Pickup Setting
Sensor CT
--------------------------------------
240
600
----------
40% of CT
= =