Sel 2414 - Thermal Element Calculations

5.16
SEL-2414 Transformer Monitor Instruction Manual Date Code 20130214
Metering and Monitoring
Monitoring
As indicated in Figure 5.13, the active cooling stage is an input into the thermal
model and does not provide direct control output to cooling equipment. Separate
cooling logic may be written to control fans and oil pumps using SEL
OGIC con-
trol equations, but the bits in this section do not provide that functionality. The
device determines the cooling stage for transformer x (where x = 1, 2, or 3) based
on the value of TxCS2 and TxCS3 according to the logic shown in Table 5.12.
TxCS2 and TxCS3 may be set by any number of methods; they may be set, for
example, from digital inputs from another device or from SEL
OGIC control equa-
tions that control the fans from the device. The important thing is that these
Device Word bits represent what is happening on the transformer(s). For exam-
ple, if the first stage of fans on Transformer 1 is on, then T1CS2 should be
asserted, and if the first and second stage of fans are on, then T1CS2 and T1CS3
should both be asserted.
CSALARM will assert if TxCS3 is asserted, but TxCS2 is not asserted, indicating
the device is unable to determine the proper cooling stage for one of the trans-
formers.
Thermal Element Calculations
Calculating Top-Oil Temperature
The device calculates top-oil temperature, Θ
TO
, according to the following.
Equation 5.1
The device calculates top-oil rise over ambient temperature according to the fol-
lowing.
Equation 5.2
Table 5.12 Cooling Stage Determination Logic
TxCS2 TxCS3 Cooling Stage CSALARM
0010
1020
1130
0111
where:
Θ
A
= ambient temperature (measured or default), °C
ΔΘ
TO
= top-oil rise over ambient temperature, °C
where:
ΔΘ
TO,U
= the ultimate top-oil rise over ambient temperature for any
load, °C, and is a function of load and the values in
Table 5.14
ΔΘ
TO,i
= initial top-oil rise over ambient temperature at the start
time of the interval, °C
T
o
= thermal top-oil time constant of transformer, in hours
Δt = one-minute data acquisition interval
Θ
TO
Θ
A
ΔΘ
TO
+=
ΔΘ
TO
ΔΘ
TO U,
ΔΘ
TO i,
–()1e
Δt–
60T
o
------------
–
⎝⎠
⎜⎟
⎛⎞
ΔΘ
TO
i
+• =