PSM1700 PsimetriQ user manual
16-6
16.5 Interwinding capacitance
The interwinding capacitance of a transformer is computed
from the complex ratio of CH1 (voltage across the
transformer) divided by CH2 (current through the
transformer) using DFT analysis at the fundamental
frequency (refer to the chapter on gain/phase analysis for
the formulae for DFT analysis).
CH2 is forced to be external shunt input – enter the value
of the external shunt as the source resistance via the
SETUP menu.
To manually connect a transformer for interwinding
capacitance measurement, connect an appropriate source
resistance in series with one winding and connect the
PsimetriQ output across the transformer from the series
resistance to another winding. Connect the CH1 input
across the transformer from one winding to the other to
measure the voltage across the windings, and CH2 across
the series resistance (note that the polarity of external
shunt input is the opposite of that for voltage).
When using the transformer analyser fixture, the
connections for interwinding capacitance are made
automatically by relays.
When measuring small capacitance it may be necessary to
zero out stray effects by disconnecting the transformer
and pressing ZERO – the message ‘ZERO SET’ will be
displayed. The transformer analyser fixture TAF01, has a
stray capacitance of around 60pF that can be zeroed out
this way. To remove the effect of the zero press ‘ZERO’
followed ‘DELETE’ within 1.5s and the message ‘ZERO
CLEARED’ will be displayed.
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