GE 745 Instruction Manual page 293

CHAPTER 7: COMMISSIONING
7.5.19.4 Loss of Life Limit
7.5.20 Tap Monitor Failure
745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
Typical settings for the loss-of-life limit element dictate that either the limit be changed or
the initial transformer loss-of-life be changed temporarily. Verification of this function is
recommended by programming an initial loss-of-life above the element threshold. The
element operates instantly as it has no associated time delay.
The tap monitor failure element operates when the sensed resistance is 150% larger than
the programmed values for the monitor circuit.
 Connect a resistance to simulate the tap changer resistance and increase
this resistance until the element operates.
 Calculate that the resistance at which the element operated is 150% of
the resistance that would be present at the maximum tap position.
 Verify all relay, targets and messages for correct operation per
programmed values.
PROTECTION SCHEMES
7–55