Sel 2414 - Page 85

5.17
Date Code 20130214 Instruction Manual SEL-2414 Transformer Monitor
Metering and Monitoring
Monitoring
The device calculates the ultimate top-oil rise over ambient temperature, ΔΘ
TO,U
,
according to the following expression.
Equation 5.3
For any EXPn (oil exponent) value and any load value, the device calculates the
thermal top-oil time constant according to the following expression.
Equation 5.4
Calculating Hot-Spot Temperature
The device calculates the winding hot-spot temperature, according to the
following expression.
Equation 5.5
The device calculates winding hot-spot rise over top-oil temperature, ΔΘ
H
,
according to the following.
Equation 5.6
where:
RATL = ratio of load loss at rated load to no-load loss (set from
Table 5.14)
EXPn = oil exponent (set from Table 5.14)
TH
or
= top-oil rise over ambient temperature at rated load, °C
(set from Table 5.14)
K = load expressed in per unit of transformer nameplate rating
according to the cooling system in service (phase current
divided by the nominal current)
where:
OTR = thermal time constant in hours at rated load with initial top-oil
temperature equal to ambient temperature (set from Table 5.14)
ΔΘ
TO U,
K
2
RATL 1+• ()
RATL 1+()
--------------------------------------------
⎝⎠
⎛⎞
EXPn
TH
or
• =
T
o
OTR
ΔΘ
TO U,
TH
or
---------------------
ΔΘ
TO i,
TH
or
-------------------–
ΔΘ
TO U,
TH
or
---------------------
⎝⎠
⎛⎞
1
EXPn
---------------
ΔΘ
TO i,
TH
or
-------------------
⎝⎠
⎛⎞
1
EXPn
---------------
–
------------------------------------------------------------------------------------
⎝⎠
⎜⎟
⎜⎟
⎜⎟
⎜⎟
⎜⎟
⎜⎟
⎛⎞
• =
where:
Θ
H
= winding hot-spot temperature, ° C
Θ
TO
= top-oil temperature, °C
ΔΘ
H
= winding hot-spot rise over top-oil temperature, °C
where:
ΔΘ
H,U
= the ultimate hot-spot rise over top-oil temperature at given
load, °C
ΔΘ
H,i
= initial hot-spot rise over top-oil temperature at the start
time of the interval, °C
T
hs
= thermal time constant of hot spot, in hours (set from
Table 5.14)
Θ
H
Θ
TO
ΔΘ
H
+=
ΔΘ
H
ΔΘ
HU,
ΔΘ
Hi,
–()1e
Δt–
60 T
hs
•
--------------------
–
⎝⎠
⎜⎟
⎜⎟
⎛⎞
ΔΘ
Hi,
+• =