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CHAPTER 5: SETPOINTS
489 GENERATOR MANAGEMENT RELAY – INSTRUCTION MANUAL
5–61
5.8.2
Reactive Power
PATH: SETPOINTS
ZV
S7 POWER ELEMENTS
Z
REACTIVE POWER
In a motor/generator application, it may be desirable not to trip or alarm on reactive power
until the machine is online and the field has been applied. Therefore, this feature can be
blocked until the machine is online and adequate time has expired during which the field
had been applied. From that point forward, the reactive power trip and alarm elements will
be active. A value of zero for the block time indicates that the reactive power protection is
active as soon as both current and voltage are measured regardless of whether the
generator is online or offline. Once the 3-phase total reactive power exceeds the positive
or negative level, for the specified delay, a trip or alarm will occur indicating a positive or
negative Mvar condition. The level is programmed in per unit of generator rated Mvar
calculated from the rated MVA and rated power factor. The reactive power elements can
be used to detect loss of excitation. If the VT type is selected as “None” or VT fuse loss is
detected, the reactive power protection is disabled. Rated Mvars for the system can be
calculated as follows:
1 REACTIVE
[
Z
]
POWER
BLOCK Mvar ELEMENT
FROM ONLINE: 1 s
Range: 0 to 5000 s in steps of 1
MESSAGE
REACTIVE POWER
ALARM: Off
Range: Off, Latched, Unlatched
MESSAGE
ASSIGN ALARM
RELAYS (2-5): ---5
Range: Any combination of Relays 2 to
5
MESSAGE
POSITIVE Mvar ALARM
LEVEL: 0.85 x Rated
Range: 0.02 to 2.01
×
Rated in steps of
0.01
MESSAGE
NEGATIVE Mvar ALARM
LEVEL: 0.85 x Rated
Range: 0.02 to 2.01
×
Rated in steps of
0.01
MESSAGE
POSITIVE Mvar ALARM
DELAY: 10.0 s
Range: 0.2 to 120.0 s in steps of 0.1
(lagging vars, overexcited)
MESSAGE
NEGATIVE Mvar ALARM
DELAY: 1.0 s
Range: 0.2 to 120.0 s in steps of 0.1
(leading vars, underexcited)
MESSAGE
REACTIVE POWER ALARM
EVENTS: Off
Range: On, Off
MESSAGE
REACTIVE POWER
TRIP: Off
Range: Off, Latched, Unlatched
MESSAGE
ASSIGN TRIP
RELAYS (1-4): 1---
Range: Any combination of Relays 1 to
4
MESSAGE
POSITIVE Mvar TRIP
LEVEL: 0.80 x Rated
Range: 0.02 to 2.01
×
Rated in steps of
0.01
MESSAGE
NEGATIVE Mvar TRIP
LEVEL: 0.80 x Rated
Range: 0.02 to 2.01
×
Rated in steps of
0.01
MESSAGE
POSITIVE Mvar TRIP
DELAY: 20.0 s
Range: 0.2 to 120.0 s in steps of 0.1
(lagging vars, overexcited)
MESSAGE
NEGATIVE Mvar TRIP
DELAY: 20.0 s
Range: 0.2 to 120.0 s in steps of 0.1
(leading vars, underexcited)