C H A P T E R 7 – T E S T S A N D T E S T C O N D I T I O N S
AT5600 User Manual 98-119 issue 14 Page 166
7.46. ACVB - AC Voltage Break Down
Where Used
This test may be used to check the action of devices such as metal oxide
varistors (MOV) that are used to protect transformer windings from transient over-
voltages that may be present on the AC supply system.
A varistor is a non-linear semiconductor device that has little effect on the circuit
until a break-down, voltage is reached. When that voltage is reached, the MOV
conducts current and limits the applied voltage to its rated break-down voltage. A
MOV is limited by the energy (Joules) that it can dissipate under break-down
conditions to transient over-voltages only.
Specifying the Measurement
During the test, an AC voltage is ramped up across the protection device (MOV)
under test and the current is monitored.
When the desired current flows, the test stops, and the measured result is the
break-down voltage. If the voltage is within the desired limits, the test is a PASS.
If the voltage is outside the desired limits, or if no breakdown is detected when the
maximum voltage is reached, the test is a FAIL.
The voltage will ramp to the specified maximum plus 50V.
In programming the AT5600 you may select the voltage (from 100V to 5kVrms),
the frequency (50Hz / 60Hz at the full voltage, or up to 1 kHz at reduced voltage),
the current trip level (10A to 5mApeak), and the ramp up times (1 to 30sec), all
to suit the specification of the transformer under test.
Please also see
14.6.42 for specific advice on programming the test, and
10.2.31 for test accuracy specification
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