5-80
745 Transformer Management Relay
GE Multilin
5.6 S4 ELEMENTS
5 SETPOINTS
5
5.6.13 INSULATION AGING / LOSS OF LIFE
a) MAIN MENU
PATH: SETPOINTS
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S4 ELEMENTS
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INSULATION AGING
The 745 Insulation Aging/Loss of Life feature is based on the computational methods presented in IEEE standards
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 computing the top oil temperature,
the hottest spot inside the transformer, the aging factor, and the total accumulated 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 operational 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 pre-
cision, 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 hottest-spot tem-
perature. The second element monitors the aging factor and the third monitors the total accumulated loss of life. Each ele-
ment produces an output when the monitored quantity exceeds a set limit.
The Insulation Aging/Loss of Life feature is a field-upgradable feature. For the feature (and associated elements) 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 setting 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.
For the computations to be performed correctly, it is necessary to enter the transformer data under
S2 SYSTEM SETUP
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TRANSFORMER
. The transformer load is taken from the winding experiencing the greatest loading. All transformer and wind-
ing 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 val-
ues for each month of the year can be entered as settings, under
S2 SYSTEM SETUP
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AMBIENT TEMPERATURE
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AMBI-
ENT RTD TYPE
and selecting By Monthly Average.
INSULATION AGING
[ENTER] for more
HOTTEST-SPOT LIMIT
[ENTER] for more
See page 5–81.
AGING FACTOR LIMIT
[ENTER] for more
See page 5–82.
LOSS OF LIFE LIMIT
[ENTER] for more
See page 5–83.
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