Sel 2414 - Page 91

5.23
Date Code 20130214 Instruction Manual SEL-2414 Transformer Monitor
Metering and Monitoring
Monitoring
Cooling Stage MVA Rating (MVAxCSy)
Range: 1.00–1000.00 MVA, in 0.1 MVA steps
The MVA rating for all types of transformers (ETHERM = 1, 3, or W) is taken as
the nameplate MVA (MVA) rating.
When ETHERM = 1, the ratings of the transformer at different cooling stages are
set using MVA1CS[y]. These ratings are used when calculating the per unit load
of the transformer, reported as T1LOAD, as shown in Equation 5.15.
Equation 5.15
When ETHERM = 3, the ratings of the windings are set using MVA1CS[y],
MVA2CS[y], and MVA3CS[y]. These ratings are used when calculating the per
unit load of the transformer, reported as T1LOAD, T2LOAD, and T3LOAD, as
shown in Equation 5.16, Equation 5.17, and Equation 5.18.
Equation 5.16
Equation 5.17
Equation 5.18
For 3 winding transformers, (ETHERM = W) the ratings of the primary winding
are set using MVA1CS[y], the ratings of the secondary winding are set using
MVA2CS[y], and the ratings of the tertiary winding are set using MVA3CS[y].
These ratings are used when calculating the per unit load of each winding,
reported as W1LOAD, W2LOAD, and W3LOAD. The rating of the transformer,
as a whole that is used when calculating per unit load T1LOAD, is calculated
using Equation 5.19. In this setup, the current going into and out of the
transformer is being measured, so the total current must be divided by 2.
Equation 5.19
Table 5.13 Examples of Cooling Stages and MVA Ratings
ETHERM = 1
Cooling Stage MVA Rating
CS1 (natural oil and air cooled ONAN) MVA1CS1 = 100
CS2 (forced air cooled ONAF) MVA1CS2 = 140
CS3 (forced-oil and air cooled OFAF) MVA1CS3 = 170
ETHERM = 3
Cooling System MVA Rating
Transformer 1 Transformer 2 Transformer 3
CS1
(natural oil and air cooled ONAN)
MVA1CS1 = 100 MVA2CS1 = 100 MVA3CS1 = 100
NOTE: x designates the transformer
and y designates the cooling stage.
T1LOAD
3 largest of IA IB IC,,()TMWNOM• ()
MVA1CS y[] 1000•
-----------------------------------------------------------------------------------------------------------=
T1LOAD
3IA TMWNOM• ()
MVA1CS y[] 1000•
--------------------------------------------------------=
T2LOAD
3 IB TMWNOM2• ()
MVA2CS y[] 1000•
-----------------------------------------------------------=
T3LOAD
3 IC TMWNOM3• ()
MVA3CS y[] 1000•
-----------------------------------------------------------=
T1LOAD
3
IA TMWNOM IB TMWNOM2 IC TMWNOM3• +• +• ()
2
----------------------------------------------------------------------------------------------------------------------------------------------------------
MVA1CS y[] 1000•
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