GE Multilin 889, Инструкция по эксплуатации

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CHAPTER 4: SETPOINTS PROTECTION
889 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL 4–115
Figure 4-37: Percent Differential Characteristic
The horizontal axes value of the percent differential characteristic is the Restraining
current (I
r
) and the vertical axes value is the Differential current (I
d
).
Each pair of measured restraining and differential currents represents a point on the
previous figure: Percent Differential Characteristic. If this point is located above the limit
line (area labeled “Operate”), then the differential flag is set (DIF=1). If the point is located
below or on the limit line (area labeled “Block”), then the differential flag is reset (DIF=0).
Setpoints
Path:
Setpoints > Protection > Group 1 > Generator > Percent Differential
FUNCTION
Range: Disabled, Trip, Configurable
Default: Disabled
PICKUP
Range: 0.05 to 1.00 x CT in steps of 0.01
Default: 0.20
This setting defines the minimum differential current required for operation, and is based
on the amount of differential current seen under normal operating conditions. A setting
of 0.1 to 0.3 pu is typically recommended. The CT base of the setting is the reference CT
nominal (the CT with the maximum primary current rating).
SLOPE 1
Range: 1 to 100% in steps of 1
Default: 25%
The setting is applicable for restraint currents from zero to BREAK 1, and defines the
ratio of differential to restraint current above which the element operates. The slope is
set to ensure sensitivity to internal faults at normal operating current levels. The criterion
for setting this slope is to allow for maximum expected CT mismatch error when
operating at the maximum permitted current. This maximum error is generally in the
range of 5 to 10% of CT rating.