Voltech AT360, User Manual

Page: 351 / 470

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When choosing the test conditions, the following potential problems should be
considered:
a) Current Levels
For larger capacitance, 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 capacitance 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.
See the 'Series and Parallel Circuits' and 'Capacitor Measurements' sections
at the end of this chapter.
The tester always uses a parallel equivalent circuit for inter-winding
capacitance measurements. Series and parallel capacitance tests (CS and
CP) are also available.
Use the PC Editor’s ‘Measure’ button (together with a sample part) if you are
unsure of how to choose the test conditions.
Choosing Test Limits
The test limits can be:
% A nominal value together with + and – percentage limits.
>< Minimum and maximum values