VOLTECH AT3600 USER MANUAL TRANSFORMER TESTS
TESTS AND TEST CONDITIONS VPN 98 - 024 PAGE 7.1.73.
1.45. 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 particular 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.
It is typically performed between all primary windings connected together, and all
secondary windings plus the screen connected together.
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.
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