Tap Changer Failure - GE 845 Instruction Manual

MONITORING

Tap Changer Failure

NOTE:
4–250
The Tap Changer Failure element compares the actual tap changer position with the
maximum and minimum set values. The element picks up when the measured tap position
actual value exceeds by one tap step the value programmed for maximum tap, or when it
is lower by one tap step than the value programmed for minimum tap. The minimum and
maximum taps are set in Max Tap and Min Tap setpoints respectively under
System > Transformer > On-load Tap Changer
selected as a Delay setpoint, the element will operate.
The Tap Changer Failure element will not be able to detect tap failure , if the Min Tap and
Max Tap setpoints Input from the Tap Changer setup menu are set to the minimum and
maximum available values from the range. This applies to any of the three methods used
for tap position detection – BCD, DCmA, and Ohms. To be able to successfully detect Tap
changer failure, the selected Ohms or DCmA at Tap Min must be bigger than the smallest
measured Ohms or DCmA values by a value corresponding to at least one tap step, and
the selected Ohms or DCmA values must be smaller than the highest Ohm or DCmA
measured value by a value corresponding to at least one tap step
If the Tap position is used for compensation of the differential current due to the new
transformation ratio and the tap position is detected below the Minimum, or above the
Maximum tap , the relay may show small differential current. If the percent differential
protection is set to a very sensitive pickup level, this differential current may cause
operation. To avoid such undesired operation, it is wise to de-sensitize the protection until
the tap position is detected back in the range between the minimum and maximum tap.
For this reason either operand TC at Min Tap, or TC at Max Tap from the Tap changer
Setup, or The Tap Changer Fail PKP can be used for setpoint group change, where the
Percent differential protection can be enabled with less sensitive settings.
Path:
Setpoints > Monitoring > Transformer > Tap Changer Failure
FUNCTION
Range: Disabled, Alarm, Latched Alarm, Configurable
Default: Disabled
DELAY
Range: 0.00 to 600.00 s in steps of 0.01 s
Default: 5.00 s
BLOCK
Range: Off, Any FlexLogic operand
Default: Off
OUTPUT RELAYS
Range: Do Not Operate, Operate
Default: Do Not Operate
EVENTS
Range: Enabled, Disabled
Default: Enabled
TARGETS
Range: Disabled, Self-reset, Latched
Default: Latched
. If this condition persists for the time
845 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 4: SETPOINTS
Setpoints >