TRANSFORMER TESTS VOLTECH AT3600 USER MANUAL
PAGE 7.1.32. VPN 98 - 024 TESTS AND TEST CONDITIONS
1.16. C2 – CAPACITANCE MATCH
WHERE USED
The interwinding capacitance match test calculates the ratio between two capacitance
measurements on two groups of windings. It is measured by applying a specified ac
voltage between two separate windings and the voltage across and current flow
between the two windings is measured to obtain a complex impedance. This is
performed to the two groups in turn.
This test is suitable for switched mode power supply, audio and telecommunication
transformers. It checks that the windings are installed in the correct positions on the
bobbin.
MEASUREMENT CONDITIONS
When calculating capacitance match the tester performs 2 capacitance measurements.
Firstly the tester applies an ac voltage between first group of windings to be tested,
usually with all taps on each winding shorted together. It then measures the voltage
between the windings, and the resulting current using harmonic analysis. Dividing
the voltage by the current gives the inter-winding impedance, from which the
capacitance may be calculated. This is then repeated for the second winding group.
The capacitance match is the ratio of first to second winding group capacitances.
The test voltage can be in the range of 1mV to 5V at a frequency of 20Hz to 1MHz.
The table below gives the recommended test conditions for different values of
average capacitance:
Average Capacitance
(Geometric Mean)
Preferred test signal
Frequency Voltage
1pF
10pF
100pF
1nF
10nF
→
→
→
→
→
10pF
100pF
1nF
10nF
100nF
100KHz
100KHz
10KHz
1KHz
100Hz
5V
5V
5V
5V
5V
The Test Conditions for Capacitance Match Measurement
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