Transformer Compensation - Arbiter Systems Portable Power Sentinel 933A Operation Manual

9.11

Transformer Compensation

There are two different types of transformer compensation. They are used
to correct for the losses in a transformer when primary-side metering is
used to meter the energy delivered to a customer at the secondary of the
transformer.
Copper compensation is used to correct for the I
former windings due primarily to their (nonzero) resistance. As you would
expect, this effect is primarily active (resistive), although there may be
minor reactive effects, and it is proportional to the current squared. This
factor allows the user to correct for these losses. It is a complex factor,
providing both watts and VARs correction, and is proportional to current
squared; i.e. so many watts and VARs are to be subtracted from the
registered amounts per ampere squared of load current.
Iron losses (also called core losses) are due to magnetizing currents (the
small amount of current required to generate the flux in the core, which is
unrelated to the load current) and eddy current losses in the core material.
These are approximately proportional to the square (watts) or 4th power
(VARs) of the voltage, and the compensation is performed using the same
basic method as described above for copper loss.
9.12 DC Offsets
DC offsets may be present in the signals applied to the input of the
933A, although this is unusual. More commonly, small dc errors in the
measurement circuit result in nonzero average of the samples.
This potential source of error must be corrected to obtain maximum
accuracy, since the 933A makes wideband measurements of power, voltage,
and current. Components at any frequency within the measurement
bandwidth, including dc, will affect the measurement. Therefore, part
of the measurement process is to average the (windowed) data, measuring
the dc component. The effects of dc offsets are then subtracted from the
results.
2
R losses in the trans-
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