Insulation Aging / Loss Of Life Feature - GE 745 TRANSFORMER MANAGEMENT RELAY Instruction Manual

5.6 S4 ELEMENTS 5 SETPOINTS

5.6.14 INSULATION AGING / LOSS OF LIFE FEATURE

a) DESCRIPTION
The 745 Insulation Aging/Loss of Life feature is based on the computational methods presented in IEEE stan-
dards C57.91–1995, IEEE Guide for Loading Mineral-Oil-Immersed Transformers , and C57.96–1989, IEEE
Guide for Loading Dry-Type Distribution and Power Transformers . These standards present a method of com-
puting the top oil temperature, the hottest spot inside the transformer, the aging factor, and the total accumu-
lated loss of life. The computations are based on the loading of the transformer, the ambient temperature, and
the transformer data entered. The computations assume that the transformer cooling system is fully opera-
tional and able to maintain transformer temperatures within the specified limits under normal load conditions.
The computation results are a guide only. The transformer industry has not yet been able to define, with any
degree of precision, the exact end of life of a transformer. Many transformers are still in service today, though
they have long surpassed their theoretical end of life, some of them by a factor of three of four times.
Three protection elements are provided as part of the Loss of Life feature. The first element monitors the hot-
test-spot temperature. The second element monitors the aging factor and the third monitors the total accumu-
lated loss of life. Each element produces an output when the monitored quantity exceeds a set limit.
The Insulation Aging/Loss of Life feature is a field-upgradeable feature. For the feature (and associated ele-
ments) to operate correctly, it must first be enabled under the factory settings using the passcode provided at
purchase. If the feature was ordered when the relay was purchased, then it is already enabled. Note that set-
ting this feature using the 745PC software requires that it be enabled the under File > Properties > Loss of
Life menu. If the computer is communicating with a relay with the feature installed, it is automatically detected.
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For the computations to be performed correctly, it is necessary to enter the transformer data under
S2 SYSTEM SETUP/TRANSFORMER. The transformer load is taken from the winding experiencing the greatest
loading. All transformer and winding setpoints must be correct or the computations will be meaningless.
The preferred approach for ambient temperature is to use an RTD connected to the 745. If this is not feasible,
average values for each month of the year can be entered as settings, under S2 SYSTEM SETUP/AMBIENT TEM-
PERATURE/AMBIENT RTD TYPE and selecting By Monthly Average.
b) HOTTEST-SPOT LIMIT
The Hottest-Spot Limit element provides a means of detecting an abnormal hot spot inside the transformer.
The element operates on the computed hottest-spot value. The Hottest-spot temperature will revert to 0°C for
1 minute if the power supply to the relay is interrupted. The necessary settings required for this element to per-
form correctly are entered under:
S4 ELEMENTS/INSULATION AGING/HOTTEST-SPOT LIMIT
5-72 745 Transformer Management Relay GE Power Management