- Three-impulse withstand test in which one disruptive discharge on the self-restoring
insulation is tolerated. If this occurs, nine additional impulses are applied during which
no disruptive discharge is tolerated.
- The up-and-down withstand test with seven impulses per level in which disruptive
discharges on self-restoring insulation are tolerated.
- The up-and-down test with one impulse per level, which is recommended only if the
conventional deviation, z, defined in IEC 60-1 is known. The values suggested there,
z = 6 Yo for switching and z = 3 Oh for lightning impulses, shall be used if, and only if, it
is known that ZI 6 % and z 5 3 OX, respectively. Otherwise other methods shall be used.
In all the test procedures described above no disruptive discharge is tolerated on the
non-self-restoring insulation.
No statistical meaning can be given to the three-impulse withstand test in which no
disruptive discharge is tolerated (P, is assumed to be 100 O/.). Its use is limited to cases in
which the non-self-restoring insulation may be damaged by a large number of voltage
applications.
When selecting a test for equipment in which non-self-restoring insulation is in parallel
with self-restoring insulation, serious consideration should be given to the fact that in
some test procedures voltages higher than the rated withstand voltagem ay be applied and
many disruptive discharges may occur.