Acrt - Ac Hi-Pot Ramp - Voltech AT5600 User Manual

C H A P T E R 7 – T E S T S
7.44.

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 AT5600 you may select the voltage (from 100V to 5.5kVrms),
the frequency (50Hz / 60Hz at the full voltage, or up to 1 kHz at reduced voltage),
the current trip level (10A 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 AC voltage.
The operation is to ramp up the test voltage while continually monitoring the
current to check it is below the test limit. If target voltage is reached and the
maximum monitored current is not exceeded the test has "Passed".
If the maximum monitored current is exceeded before the target voltage is
reached the test has "Failed"
Please also see
14.6.40 for specific advice on programming the test, and
10.2.29 for test accuracy specification
AT5600 User Manual 98-119 issue 14
A N D T E S T C O N D I T I O N S
Page 164