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5.7 CONTROL ELEMENTS
THREE VT BREAKER FLASHOVER APPLICATION
When only one set of VTs is available across the breaker, the
an open breaker condition in this application, the scheme checks if the per-phase voltages were recovered (picked up), the
status of the breaker is open (contact input indicating the breaker status is off), and no flashover current is flowing. A con-
tact showing the breaker status must be provided to the relay. The voltage difference will not be considered as a condition
for open breaker in this part of the logic.
Voltages must be present prior to flashover conditions. If the three VTs are placed after the breaker on the
line (or feeder), and the downstream breaker is open, the measured voltage would be zero and the flash-
NOTE
over element will not be initiated.
The flashover detection will reset if the current drops back to zero, the breaker closes, or the selected FlexLogic™ operand
for supervision changes to high. Using supervision through the
settings is recommended by selecting a trip operand that will not allow the flashover element to pickup prior
FLSHOVR SPV C
to the trip.
The flashover detection can be used for external alarm, re-tripping the breaker, or energizing the lockout relay.
Consider the following configuration:
5
The source 1 (SRC1) phase currents are feeder CTs and phase voltages are bus VTs, and Contact Input 1 is set as Breaker
52a contact. The conditions prior to flashover detection are:
1.
52a status = 0.
2.
VAg, VBg, or VCg is greater than the pickup setting.
3.
IA, IB, IC = 0; no current flows through the breaker.
ΔVA is greater than pickup (not applicable in this scheme).
4.
The conditions at flashover detection are:
1.
52a status = 0.
2.
VAg, VBg, or VCg is lower than the pickup setting.
3.
IA, IB, or IC is greater than the pickup current flowing through the breaker.
ΔVA is greater than pickup (not applicable in this scheme).
4.
SIX VT BREAKER FLASHOVER APPLICATION
The per-phase voltage difference approaches zero when the breaker is closed. The is well below any typical minimum
pickup voltage. Select the level of the
across the breaker when the close or open breaker resistors are left in service. Prior to flashover, the voltage difference is
larger than
BRK 1 FLSHOVR DIFF V PKP
voltage from one side of the breaker has dropped to zero (line de-energized), at least one per-phase voltage is larger than
the
BRK 1 FLSHOVR V PKP
voltages from both sides of the breaker drops below the pickup value defined by the
age difference drops below the pickup setting, and flashover current is detected. These flashover conditions initiate Flex-
Logic™ pickup operands and start the
This application does not require detection of breaker status via a 52a contact, as it uses a voltage difference larger than
the
BRK 1 FLSHOVR DIFF V PKP
5-252
BRK 1 FLSHOVR DIFF V PKP
. This applies to either the difference between two live voltages per phase or when the
setting, and no current flows through the breaker poles. During breaker flashover, the per-phase
BRK 1 FLSHOVR PKP DELAY
setting. However, monitoring the breaker contact will ensure scheme stability.
T60 Transformer Protection System
setting should be "None". To detect
BRK 1 FLSHOVR SIDE 2 SRC
,
BRK 1 FLSHOVR SPV A
BRK 1 FLSHOVR SPV B
setting to be less than the voltage difference measured
BRK 1 FLSHOVR V PKP
timer.
5 SETTINGS
, and
BRK 1
setting, the volt-
GE Multilin
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