Load Encroachment - GE 889 Instruction Manual

CHAPTER 4: SETPOINTS

Load Encroachment

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889 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL
The 889 relay is equipped with the Load Encroachment element.
The Load Encroachment element responds to the positive-sequence voltage and current
and applies a characteristic shown in the figure below:
Figure 4-79: Load Encroachment Characteristic
The element operates if the positive-sequence voltage is above a set level, and asserts its
output signal so that it can be used to block selected protection elements such as Phase
Overcurrent.
The settings of this function are applied to the positive sequence voltage and positive
sequence impedance. The Load Encroachment Pickup flag is asserted when the
impedance is inside the Load Encroachment operating area (see the above figure) and the
positive sequence voltage is above the minimum operating value. The Load Encroachment
Trip flag is asserted if the element stays picked up for the time defined by the Pickup time
delay.
Load Encroachment can be inhibited by a blocking input.
Path: Setpoints > Protection > Group 1(6) > Current > Load Encroachment
FUNCTION
Range: Disabled, Enabled
Default: Disabled
MINIMUM VOLTAGE
Range: 0.00 to 1.50 x VT in steps of 0.01 x VT
Default: 0.20 x VT
The setting sets the minimum operating positive-sequence voltage required for
operation of the Load Encroachment element. If this voltage is below the set minimum
threshold, the element does not operate.
If 3-phase VT is delta connected, the true supervision level is internally changed to 1/sqrt(3)
of the user setting since the base of VT here is the phase-phase voltage.
REACH
Range: 0.02 to 250.00 Ω in steps of 0.01 Ω
Default: 5.00 Ω
The setting specifies the resistive reach of the element as shown in the Load
Encroachment characteristic diagram. The setting is entered in secondary ohms and is
calculated as the positive-sequence resistance seen by the relay under maximum load
conditions and unity power factor.
PROTECTION
4–215