GE T60 Instruction Manual page 567
Transformer protection system
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CHAPTER 5: SETTINGS
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 is zero and the flashover element is not
initiated.
The flashover detection resets 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 does not allow the flashover element to pickup prior to the
SPV c
trip.
The flashover detection can be used for external alarm, re-tripping the breaker, or energizing the lockout relay.
Consider the following configuration:
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:
•
52a status = 0
•
VAg, VBg, or VCg is greater than the pickup setting
•
IA, IB, IC = 0; no current flows through the breaker
•
ΔVA is greater than pickup (not applicable in this scheme)
The conditions at flashover detection are:
•
52a status = 0
•
IA, IB, or IC is greater than the pickup current flowing through the breaker
ΔVA is greater than pickup (not applicable in this scheme)
•
Six VT breaker flashover application
The per-phase voltage difference approaches zero when the breaker is closed. This 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
setting, and no current flows through the breaker poles. During breaker flashover, the per-phase
BRK 1 FLSHOVR V PKP
voltages from both sides of the breaker drops below the pickup value defined by the
voltage difference drops below the pickup setting, and flashover current is detected. These flashover conditions initiate
FlexLogic 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
T60 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
BRK 1 FLSHOVR DIFF V PKP
. This applies to either the difference between two live voltages per phase or when the
BRK 1 FLSHOVR PKP DELAY
setting. However, monitoring the breaker contact ensures scheme stability.
,
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.
CONTROL ELEMENTS
, and
BRK 1 FLSHOVR
setting, the
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5
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