PSM1700 PsimetriQ user manual
16-7
16.6 Magnetising current
The magnetising current is the current drawn by the
primary, energised under normal operating conditions but
without any secondary load. It is typically measured on
power transformers rather than signal transformers so
although the transformer analyser fixture, TAF01, will
select appropriate relays to make the measurement it is
more common that a manual connection or a custom
fixture would be used.
The magnetising current is measured as the true rms
value (refer to the chapter on the rms voltmeter for the
formulae for rms analysis) so it will include all distortion
components.
To manually connect a transformer for magnetising current
measurement, connect an appropriate shunt in series with
the primary. When selecting the shunt, bear in mind the
current that it must pass, the resulting voltage drop across
it, and the power that will be dissipated in it. Connect CH1
directly across the primary winding, and CH2 across the
series resistance (note that the polarity of external shunt
input is the opposite of that for voltage). Ensure that all
connections and the series resistance are appropriate for
the voltage, the current and the frequency of operation.
Energise the primary so that the voltage seen at the
primary after the series resistance, is the normal operating
voltage.
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