Schweitzer Engineering SEL-387-0, Instruction Manual

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3.38
SEL-387-0, -5, -6 Relay Instruction Manual Date Code 20170601
Differential, Restricted Earth Fault, Thermal, and Overcurrent Elements
Thermal Element (SEL-387-6 Relay)
The equivalent life at the reference hot-spot temperature (95ºC or 110ºC) that
will be consumed in a given time period for a given temperature cycle is:
Equation 3.27
During 24 hours, the total number of time intervals is:
Equation 3.28
Because the time intervals and the total time period used in the thermal model
will be constant, we can simplify the calculation of F
EQA
to the following:
Equation 3.29
Total Accumulated Loss of Life
The relay estimates the total accumulated loss of insulation life in percentage
of normal insulation life by summing all of the daily RLOL values:
Equation 3.30
The relay stores the TLOL value at midnight each day. You can use the
THE P command to load an initial value of TLOL into the relay.
where:
F
EQA
= equivalent insulation aging factor for a total time period
n = index of the time interval,

t
N = total number of time intervals for the time period
F
AAn
= insulation aging acceleration factor for the time interval,

t
n

t = time interval (fixed at 1 minute)
where:

t

time interval (fixed at 1 minute)
F
EQA
F
AA
n
n 1
=
N


t
n
•

t
n
n 1
=
N

-------------------------------------- =
N
24

t
60
------
 
 
-----------
1440

t
------------ = =
F
EQA
F
AA
n
n 1
=
N

N
-----------------------
(equivalent life in days)
=
where:
TLOL
d
= total accumulated loss of life, TLOL
RLOL
d
= most recent daily calculation
TLOL
d-1
= previous TLOL
TLOL
d
RLOL
d
TLOL
d 1
–
+ =