2.41 ACRT - AC HI-POT Ramp.
Where Used
Hi-Pot Ramp testing (to check for insulation breakdown between windings
or between windings and the screen or core) is often specified for power
line transformers or for switched mode power transformers in applications
where safety is important.
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 target voltage is applied across two groups of
windings with the windings in each group being shorted together. The
voltage and current are monitored throughout the ramp time.
In programming the AT you may select the voltage (from 100V to 5.5kVrms),
the frequency (50Hz / 60Hz at the full voltage, or up to 1kHz at reduced
voltage), the current trip level (10μA to 5mApeak), and the ramp up times
(1 to 30sec), all to suit the specification of the transformer under test.
The purpose is to check the safety isolation between windings, windings
and core, or windings and screens, measuring the voltage at which a user
specified current is exceeded, by ramping to a maximum user specified
voltage at a user specified frequency.
The operation is to ramp up the test voltage while measuring the voltage
across the selected terminals and continually monitor the current to check
it is below the test limit.
If target voltage is reached before and the maximum monitored current is
met the test has "Passed".
If the maximum monitored current is met before the target voltage is
reached the test has "Failed".