MIL-HDBK-1133
Table D-1 in Appendix D lists typical no-load and load
losses for various transformer sizes taken from data contained in
Electric Power Distribution System Engineering, Gnen, 1986. The
load loss given in the table represents operation at full
nameplate capacity, as measured in kVA.
NOTE
Although Table D-1 has value related to losses for older
existing transformers, it is not accurate for transformers
that the Navy has been procuring through NAVFAC guide
specifications such as NFGS-16272, Three Phase Pad-Mounted
Transformers. The no load losses derived from the NFGS are
lower than those in Table D-1. The load losses for larger
transformers derived from the NFGS are lower than those in
Table D-1.
To calculate the total energy loss of the transformers,
both the no-load and load contributions must be accounted for.
The no-load energy consumption is the no-load loss multiplied by
the number of hours in the time period under consideration. The
load loss contribution must include the nature of part-loading on
transformers as well as variations in the load.
2.6.2.1
Peak Load. Because the peak load normally differs from
the transformer capacity given in Table D-1, the actual loss must
be adjusted accordingly. Equation 2 gives the formula for
calculating the demand loss factor (FDLS) used to adjust the
transformer loss during peak loading as opposed to nameplate
capacity operation. Because the load loss is primarily resistive
losses in the windings, this equation is based on the I2R nature
of resistive loss:
2
Peak Load (kW) * div. factor
F DLS =
Nameplate Capacity(kVA)
(2)
where
Peak Load (kW)
= peak billed kilowatts from
utility billing
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