ABB RELION REX640 - 7.3.5.6 Level detector 2; 7.3.6 Application

The total loss of life is the sum of the momentary loss of life and the total loss of life
until time, n-1.
L L DL
n n n
= +
−1
(Equation 337)
The initial loss of life L
0
, is taken from the setting Initial loss of life .
For new transformer installations, the Initial loss of life setting should be
“0”. For previously installed transformers, the Initial loss of life can be set
to the consumed transformer life in months.
The calculated value of the loss of life in years, LOSS_OF_LIFE, is given as an output
in the Monitored data view.
The calculated value of LOSS_OF_LIFE can be reset through the input RESET.
7.3.5.6 Level detector 2
This module compares the ALM_AGE_RATE output with the setting Alarm level Age
Rte .
If the calculated AVG_AGE_RATE over the
Avg Age rate period setting is greater than
Alarm level Age Rte , the module activates the binary output ALM_AGE_RATE.
The binary input RST_AVGAGING can be used to reset the output ALM_AGE_RATE and
also the calculated value of AVG_AGE_RATE.
Once the RST_AVGAGING input is active, the average ageing rate values stored over
the
Avg Age rate period setting is erased and the calculation of AVG_AGE_RATE is
restarted.
If the
Avg Age rate period is set to "YEAR", the output AVG_AGE_RATE is
refreshed once in 30 days starting from the time the relay is installed or
since the last activation of binary input RST_AVGAGING.
The activation of the BLOCK input deactivates the ALM_AGE_RATE output.
7.3.6 Application
The insulation used in transformer windings is paper oil insulation that can
degrade over a period of time. The deterioration of insulation is a time function
of temperature, moisture and oxygen content. With modern oil preservation
systems, the moisture and oxygen contributions to insulation deterioration can be
minimized, leaving insulation temperature as the controlling parameter.
Since, in most of the transformers the temperature distribution is not uniform, the
part that is operating at the highest (hot-spot) temperature normally undergoes
the greatest deterioration. Hot-spot temperature of winding needs to be monitored
continuously in order to not exceed the flashover value of transformer insulation
oil. The first step in monitoring the insulation age is the calculation of hot-spot
temperature of the transformer.
A simplified representation of the variation of temperature inside the transformer is
shown in Figure 790 (IEC 60076-7).
1MRS759142 F
Condition monitoring functions
REX640
Technical Manual
1391