GE 489 - Manual (Page 96)

4-46 489 Generator Management Relay GE Multilin
4.8 S7 POWER ELEMENTS 4 SETPOINTS
4
4.8.2 REACTIVE POWER
PATH: SETPOINTS ÖØ S7 POWER ELEMENTS Ö 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:
For example, given Rated MVA = 100 MVA and Rated Power Factor = 0.85, we have
(EQ 4.25)
„ REACTIVE POWER
„ [ENTER] for more
BLOCK Mvar ELEMENT
FROM START: 1 s
Range: 0 to 5000 s in steps of 1
REACTIVE POWER
ALARM: Off
Range: Off, Latched, Unlatched
ASSIGN ALARM
RELAYS (2-5): ---5
Range: Any combination of Relays 2 to 5
POSITIVE Mvar ALARM
LEVEL: 0.85 x Rated
Range: 0.02 to 2.01 × Rated in steps of 0.01
NEGATIVE Mvar ALARM
LEVEL: 0.85 x Rated
Range: 0.02 to 2.01 × Rated in steps of 0.01
POSITIVE Mvar ALARM
DELAY: 10.0 s
Range: 0.2 to 120.0 s in steps of 0.1
Note: Lagging vars, overexcited
NEGATIVE Mvar ALARM
DELAY: 1.0 s
Range: 0.2 to 120.0 s in steps of 0.1
Note: Leading vars, underexcited
REACTIVE POWER ALARM
EVENTS: Off
Range: On, Off
REACTIVE POWER
TRIP: Off
Range: Off, Latched, Unlatched
ASSIGN TRIP
RELAYS (1-4): 1---
Range: Any combination of Relays 1 to 4
POSITIVE Mvar TRIP
LEVEL: 0.80 x Rated
Range: 0.02 to 2.01 × Rated in steps of 0.01
NEGATIVE Mvar TRIP
LEVEL: 0.80 x Rated
Range: 0.02 to 2.01 × Rated in steps of 0.01
POSITIVE Mvar TRIP
DELAY: 20.0 s
Range: 0.2 to 120.0 s in steps of 0.1
Note: Lagging vars, overexcited
NEGATIVE Mvar TRIP
DELAY: 20.0 s
Range: 0.2 to 120.0 s in steps of 0.1
Note: Leading vars, underexcited
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Rated Mvars Rated MVA cos
1 – Rated PF ( ) ( ) sin × 100 cos
1 – 0.85 ( ) ( ) sin × 52.67 Mvars = = =