Tettex MIDAS 2881, Operating Instructions Manual

Page: 123 / 164

Applications Guide 113
Hot Collar Test (Collar to Center Conductor)
Due to the caution statement mentioned above, it is important to note that for tap-insulation tests the
applied voltage should not exceed 5 kV for potential taps and 500 V for dissipation factor taps.
For the overall and the center conductor to tap test a convenient voltage at or below the bushing
nameplate rating should be chosen.
The hot collar test should be performed at a test voltage of about 10kV.
14.1.1 Spare Bushings
For testing a spare bushing care must be taken in the method used to hoist the bushing.
The bushing should be mounted in a grounded metal rack with nothing connected to the terminals.
Tests should not be performed with the bushings mounted in wooden crates or lying on a floor.
Otherwise the test results can be affected by the wood or the cement floor.
It is also important to ensure that the bushing centre conductor is not in contact with a foreign material
(sling, rope, etc.).
The overall test for spare bushings,
with or without taps, can be
performed with the GST gA+B
(INPUT A must not be connected).
With this test mode the overall
capacitance is measured
C = C1 || C2.
The main insulation (C1) of
bushings equipped with taps can
be tested separately (INPUT A to
tap). The C1 insulation is
measured using the UST A mode.
With this test connection the tap
insulation capacitance (C2) is not
measured directly but can be
calculated from the GST gA+B and
the UST A mode using following
formula: C2 = (C
 C1) / (C1-C).
Spare Bushing Insulation Test