Percent Differential - GE 745 TRANSFORMER MANAGEMENT RELAY Instruction Manual

5.6 S4 ELEMENTS
The percent differential setpoints are shown below:
S PERCENT DIFFERENTL
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PERCENT DIFFERENTIAL

FUNCTION: Enabled
PERCENT DIFFERENTIAL
TARGET: Latched
PERCENT DIFFERENTIAL
PICKUP: 0.30 x CT
PERCENT DIFFERENTIAL
SLOPE 1: 25%
5
PERCENT DIFFERENTIAL
KNEEPOINT: 2.0 x CT
PERCENT DIFFERENTIAL
SLOPE 2: 95%
PERCENT DIFFERENTIAL
BLOCK: Disabled
5-48
This message indicates the start of the PERCENT DIFFERENTIAL section. To
continue with these setpoints press
next section.
Range: Disabled / Enabled
Range: Self-reset / Latched / None
Select None to inhibit the display of the target message when the element
operates. Thus an element whose "target type" is None never disables the
LED self-test feature since it cannot generate a displayable target message.
Range: 0.05 to 1.00 (steps of 0.01)
Enter the minimum differential current required for operation. This setting is
chosen based on the amount of differential current that might be seen under
normal operating conditions.
Range: 15 to 100 (steps of 1)
Enter the slope 1 percentage (of differential current to restraint current) for
the dual-slope percent differential element. The slope 1 setting is applicable
for restraint currents of zero to the kneepoint, and defines the ratio of
differential to restraint current above which the element will operate. This
slope is set to ensure sensitivity to internal faults at normal operating current
levels. The criteria for setting this slope are: (1) to allow for mismatch when
operating at the limit of the transformer's onload tap-changer range; (2) to
accommodate for CT errors.
Range: 1.0 to 20.0 (steps of 0.1)
Enter the kneepoint for the dual-slope percent differential element. This is
the transition point between slopes 1 and 2, in terms of restraint current, in
units of relay nominal current. Set the kneepoint just above the maximum
operating current level of the transformer between the maximum forced-
cooled rated current and the maximum emergency overload current level.
Range: 50 to 200 (steps of 1)
Enter the slope 2 percentage (of differential current to restraint current) for
the dual-slope percent differential element. This setting is applicable for
restraint currents above the kneepoint and is set to ensure stability under
heavy through fault conditions which could lead to high differential currents
as a result of CT saturation.
Since I =
restraint '
differential current is always greater than 100% of the restraint
current. Because of this enhancement, the PERCENT DIFFERENTIAL
NOTE
SLOPE 2 settings may cause slow operation (in rare cases no
operation) in the following situations:
1. PERCENT DIFFERENTIAL SLOPE 2 is set above 100%.
2. The source is connected to one winding only.
Therefore, the PERCENT DIFFERENTIAL SLOPE 2 value cannot be
greater than 100%. To increase dependability, the slope 2 settings
should be less than 98%
Range: Disabled / Logc Inpt 1 (2-16) /Virt Inpt 1 (2-16) / Output Rly 1 (2-8) /
SelfTest Rly / Virt Outpt 1 (2-5)
745 Transformer Management Relay
, or press
E N TE R
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max I I I , it is not guaranteed that the
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GE Power Management
5 SETPOINTS
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