5-48
745 Transformer Management Relay
GE Power Management
5.6 S4 ELEMENTS
5 SETPOINTS
5
The percent differential setpoints are shown below:
y
PERCENT DIFFERENTL
y
[ENTER] for more
This message indicates the start of the
PERCENT DIFFERENTIAL
section. To
continue with these setpoints press
, or press
to go to the
next section.
PERCENT DIFFERENTIAL
FUNCTION: Enabled
Range: Disabled / Enabled
PERCENT DIFFERENTIAL
TARGET: Latched
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.
PERCENT DIFFERENTIAL
PICKUP: 0.30 x CT
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.
PERCENT DIFFERENTIAL
SLOPE 1: 25%
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.
PERCENT DIFFERENTIAL
KNEEPOINT: 2.0 x CT
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.
PERCENT DIFFERENTIAL
SLOPE 2: 95%
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
, it is not guaranteed that the
differential current is always greater than 100% of the restraint
current. Because of this enhancement, the
PERCENT DIFFERENTIAL
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%
PERCENT DIFFERENTIAL
BLOCK: Disabled
Range: Disabled / Logc Inpt 1 (2-16) /Virt Inpt 1 (2-16) / Output Rly 1 (2-8) /
SelfTest Rly / Virt Outpt 1 (2-5)
E N TE R
M E SSA G E
NOTE
I
restraint
'
max
I
1
I
2
I
3
,
,
(
)
=
Summary of Contents for 745 TRANSFORMER MANAGEMENT RELAY
Page 30: ...2 8 745 Transformer Management Relay GE Power Management 2 3 SECURITY 2 GETTING STARTED 2 ...
Page 210: ...7 36 745 Transformer Management Relay GE Power Management 7 2 BLOCK DIAGRAMS 7 SCHEME LOGIC 7 ...
Page 322: ...9 12 745 Transformer Management Relay GE Power Management 9 3 USING 745PC 9 745 PC SOFTWARE 9 ...
Page 396: ...A 4 745 Transformer Management Relay GE Power Management A 1 FIGURES AND TABLES APPENDIXA A ...
Page 400: ...C 2 745 Transformer Management Relay GE Power Management C 1 WARRANTY INFORMATION APPENDIXC C ...
Page 406: ...vi 745 Transformer Management Relay GE Power Management ...
Page 407: ...GE Power Management 745 Transformer Management Relay NOTES ...