326 User’s Manual TOS93 Series
Appendix
Example of partial discharge test
Applicable model:
This section explains how to perform tests in conformity with EN50
178.
Calculating the setting
Before the test, calculate the test voltage to apply to the EUT, the electric charge for detecting the
discharge extinction voltage, and the limit voltage.
Rated voltage of the partial discharge test
When the EUT is in a steady-state condition, measure the maximum repeating peak voltage of the two
isolated circuits using an oscilloscope or the like. The sum of the maximum repeating peak voltages is the
rated voltage.
Discharge extinction voltage limit
Calculate as follows.
Ve = Vt × 1.25 ÷ ≈ Vt × 0.884 Vrms
Ve: Discharge extinction voltage limit
Vt: Rated voltage of the partial discharge test
Maximum application voltage
Calculate as follows.
Vmax = Vr × 1.875 ÷ ≈ Vr × 1.326 Vrms
Vmax: Maximum application voltage
Vr: Rated isolation voltage of the E
UT
Performing a pre-test inspection
Partial discharge tests according to the EN50178 require the entire test environment to be inspected
before testing.
1
Check that the environment is not too far off from 23 °C and 50 % humidity.
EN50178 recommends that tests be performed in this environment.
9301PD
2
2
In EN50178, this inspection is described as “calibration,” but this document will refer to it as
“inspection.” This is because this inspection can be confused with the periodic calibration of
the instrument or the electric charge calibration performed before testing.
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