Megger DELTA4000, Instruction Manual, Page: 60 / 74

M
AVTMDELTA4000-EN Rev 6 April 2018
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Description of Tests
Transformer Overall Tests
Prior to the overall insulation tests, short all high side (H) bushings together and short all
low side (L) bushings together, keeping both windings separated. Remove ground
connections from neutral bushings.
Test 1 - This is a measurement of the insulation between the transformer high voltage
winding and the transformer tank, plus the insulation between the high voltage winding
and the low voltage winding, both measured in parallel. Connect the HV cable to the H
winding and connect the Red lead to the X winding. Test mode is GST-GND.
Test 2 - This is a measurement of the insulation between the transformer high voltage
winding and the transformer tank. Connections are exactly the same as for Test 1. Test
mode is GSTg-RB.
Test 3 - This is a measurement of the insulation between the transformer high voltage
winding and the low voltage winding. Connections are exactly the same as for Test 1
and 2. Test mode is UST-R.
NOTE: Once Tests 1, 2 and 3 are completed, Line 4 will populate with values calculated
by subtracting Test 2 from Test 1. This is applicable for values of capacitance,
current and watts. Line 4 is a calculated comparison to the direct measurements
of Test 3. Values on these two lines should be essentially the same. If they are
not, re-check all connections and verify the proper operation of the test set. If Test
3 and Line 4 vary by more than 2%, the Insulation Rating (IR) will
automatically populate with B (Bad).
Test 5 - This is a measurement of the insulation between the transformer low voltage
winding and the transformer tank, plus the insulation between the low voltage winding
and the high voltage winding, both measured in parallel. Connect the HV cable to the
low side (L) winding and connect the Red lead to the H winding. Test mode is GST-
GND.
Test 6 - This is a measurement of the insulation between the transformer low voltage
winding and the transformer tank. Connections are exactly the same as for Test 5. Test
mode is GSTg-RB.
Test 7 - This is a measurement of the insulation between the transformer low voltage
winding and the high voltage winding. Connections are exactly the same as for Test 5
and 6. Test mode is UST-R.