GE Multilin 489 Instruction Manual page 167

CHAPTER 5: SETPOINTS
489 GENERATOR MANAGEMENT RELAY – INSTRUCTION MANUAL
Courtesy of NationalSwitchgear.com
ZONE #2
MESSAGE
REACH: 15.0 Ωsec
ZONE #2
MESSAGE
ANGLE: 75°
ZONE #2 TRIP
MESSAGE
DELAY: 2.0 s
The distance protection function (ANSI device 21) implements two zones of mho phase-to-
phase distance protection (six elements total) using the conventional phase comparator
approach, with the polarizing voltage derived from the pre-fault positive sequence voltage
of the protected loop. This protection is intended as backup for the primary line protection.
The elements make use of the neutral-end current signals and the generator terminal
voltage signals (see figure below), thus providing some protection for internal and unit
transformer faults. In systems with a delta-wye transformer (DY330°), the appropriate
transformations of voltage and current signals are implemented internally to allow proper
detection of transformer high-side phase-to-phase faults. The reach setting is the positive
sequence impedance to be covered, per phase, expressed in secondary ohms. The same
transformation shown for the Loss of Excitation element can be used to calculate the
desired settings as functions of the primary-side impedances.
The elements have a basic operating time of 150 ms. A VT fuse failure could cause a
maloperation of a distance element unless the element is supervised by the VTFF element.
In order to prevent nuisance tripping the elements require a minimum phase current of
0.05 x CT.
Protection Zone 1
Protection Zone 2
Neutral End CT
489
Relay
FIGURE 5–11: Distance Element Setup
The 489 phase distance element is intended to provide backup protection for phase-to-
phase faults on the electric power system. This element uses the phase-to-phase voltage
measured at the generator terminals and phase currents measured at the neutral side of
the generator. As such this element will provide coverage for the generator step-up
transformer and will also provide a degree of protection for stator phase-to-phase faults.
The element has a offset mho characteristic as shown in FIGURE 5–12: Distance Element
Characteristics on page –59. Offset in the third quadrant is 1/8th of the forward reach to
provide better resistive fault coverage for close-in faults. The element provides a separate
measurement in three loops for AB, BC, and CA faults. There is a setting for specification of
Range: 0.1 to 500.0 Ωsec in steps of 0.1
Range: 50 to 85° in steps of 1
Range: 0.0 to 150.0 s in steps of 0.1
52
Terminal VT
808740A1.CDR
5–57