Sel 2414 - Insulation Loss of Life

5.18
SEL-2414 Transformer Monitor Instruction Manual Date Code 20130214
Metering and Monitoring
Monitoring
The device calculates the ultimate hot-spot rise over top-oil temperature at the
given load ΔΘ
H,U
, according to the following.
Equation 5.7
Insulation Loss of Life
Insulation Aging Acceleration Factor
The device thermal element uses the hot-spot temperature to calculate an
insulation aging acceleration factor, F
AA
, which indicates how fast the
transformer insulation is aging.
The device calculates the insulation aging acceleration factor, F
AA
, for each time
interval, Δt, as follows.
Equation 5.8
Daily Rate of Loss of Life
The device calculates daily rate of loss of life (RLOL, percent loss of life per
day) for a 24-hour period as follows.
Equation 5.9
The device stores the RLOL value at midnight each day to provide the user with
trend information on the loss of insulation life. This calculation is done for each
winding that is modeled; so when ETHERM = 1, only T1RLOL is calculated.
When ETHERM = 3, T1RLOL, T2RLOL, and T3RLOL are calculated. When
ETHERM = W, W1RLOL, W2RLOL, and W3RLOL are calculated.
where:
EXPm = winding exponent (set from Table 5.14)
TH
gr
= rated winding hot-spot rise over top-oil at rated load, °C
(set from Table 5.14)
ΔΘ
HU,
K
2EXPm•
TH
gr
• =
where:
F
AA
= insulation aging acceleration factor
BFFA = a design constant, typically 15000, °C (set from
Table 5.14)
Θ
H,R
= winding hot-spot temperature at rated load (95°C if THwr
= 55°C, 110°C if THwr = 65°C)
F
AA
e
BFFA
Θ
HR,
273+()
--------------------------------
BFFA
Θ
H
273+()
--------------------------–
=
where:
RLOL = rate of loss of life in percent per day
TRLIFE = expected normal insulation life in hours (set from
Table 5.14)
RLOL
F
EQA
24•
TRLIFE
--------------------------
100• =