Insulation Aging - GE 745 TRANSFORMER MANAGEMENT RELAY Instruction Manual

10.6 PROTECTION SCHEMES
a) PRELIMINARIES
The three elements under the Insulation Aging feature, Hottest-Spot Limit , Aging Factor Limit and Loss of
Life Limit , must be tested with a valid set of transformer data programmed into the relay. The ambient temper-
ature must also be programmed (obtained from an RTD or programmed as 12-month averages). The tests
consist of simulating transformer loading by applying a current signal to Winding 1 Phase A at the correct fre-
quency.
b) HOTTEST SPOT LIMIT
The hottest-spot temperature value is a function of load, ambient temperature, and transformer rating. Apply a
current to Winding 1 phase A to represent at least a 100% load on the transformer. Use the actual value
ACTUAL VALUES/A2 METERING/LOSS OF LIFE/HOTTEST-SPOT WINDING TEMPERATURE
to observe the hottest spot temperature increases gradually. The simulated load to may be increased for a
faster temperature rise. When the hottest spot temperature reaches the programmed operating level:
SETPOINTS/S4 ELEMENTS/INSULATION AGING/HOTTEST-SPOT LIMIT/HOTTEST-SPOT LIMIT PICKUP
the element should operate. Verify all programmed relay operations as per FlexLogic settings. Verify that all
the targets and messages are as expected and programmed.
The time delay can be verified with a watch as the delay is normally set in minutes.
c) AGING FACTOR LIMIT
The Aging Factor value is also a function of load, ambient temperature, and transformer ratings. Apply a cur-
rent to Winding 1 phase A to represent at least a 100% transformer load. Use the actual value
ACTUAL VALUES/A2 METERING/LOSS OF LIFE/INSULATION AGING FACTOR
to observe that the aging factor increases gradually. You may want to increase the simulated load or the simu-
lated or programmed ambient temperature to cause a faster increase. When the aging factor reaches the pro-
grammed operating level under:
SETPOINTS/S4 ELEMENTS/INSULATION AGING/AGING FACTOR LIMIT/AGING FACTOR LIMIT PICKUP
the element should operate. Verify all programmed relay operations as per FlexLogic settings. Verify that all
the targets and messages are as expected and programmed.
The time delay can be verified with a watch as the delay is normally set in minutes.
d) LOSS-OF-LIFE LIMIT
Typical settings for the Loss-of-Life Limit element dictate that either the limit be changed or the initial trans-
former loss-of-life be changed temporarily. Verification of this function is recommended by programming an ini-
tial 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.
10
10-42 745 Transformer Management Relay
10 COMMISSIONING

10.6.23 INSULATION AGING

10.6.24 TAP MONITOR FAILURE
GE Power Management