VOLTECH AT3600 USER MANUAL TRANSFORMER TESTS
TESTS AND TEST CONDITIONS VPN 98 - 024 PAGE 7.1.33.
When choosing the test conditions, the following potential problems should be
considered:
A) CURRENT LEVELS
For larger capacitances, particularly at higher frequencies, the current flowing
during the measurement can be very high, and similarly the measured current
could also be very small for small capacitances at lower frequencies and
voltages.
Where possible, you should use the recommended test signal levels in the table
above to ensure that the currents which flow can be measured accurately.
B) NON-LINEAR CAPACITANCE
Normally non-linearities in the stray capacitance of transformers are not a
problem, and therefore capacitance is measured with as large a voltage as
possible.
C) EQUIVALENT CIRCUIT
As with inductance, capacitance is actually measured as a complex impedance,
and therefore the result can be expressed in terms of either a series or a parallel
equivalent circuit.
It was explained in section 1.5. of this chapter, that parallel and series
equivalent inductance do not necessarily have the same values. The same is
true for capacitance; parallel and series equivalents can also be different.
The tester uses a parallel equivalent circuit for capacitance measurements, and
does not give you a choice of a series equivalent.
Generally, this will present no problems, as on the majority of transformers the
difference between the two values is usually negligible, and can be ignored.
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