ISA T 2000 - Page 27

DOC. MIE11110 Rev. 5
Page
27
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110
Purpose of the test is to measure the actual CT ratio and to verify
its polarity, with a test current higher than the one available from
T 3000. To this purpose, the external current booster option
allows to get up to 4000 A, according to the number of
transformers. Note that with this test it is impossible to measure
the burden, as it is in the former test.
The booster is made of:
. An interposing module type IM2000 (not necessary with one
transformer only);
. A set of transformers, that are fit on the cable that will be
connected to the CT under test. Of these transformers, one has
two connectors, for the voltage supply and for the current
measurement.
Te test is performed applying current to one or more transformers;
the adjustment is performed by the test set adjustment knob (fine
adjustment) and/or by the interposing module (coarse
adjustment), by means of the selection switch marked 1 to 4.
NOTE: the test current generated by the booster is measured as
voltage, connecting the measurement transformer output to the
10 V measurement input; the secondary current is measured
connecting the CT secondary to the current metering input.
From a practical standpoint, consider that the weight of the
transformer plus cable plus clamps is about 20 kg for one
transformer; 30 kg for two transformers, and 50 kg for 4
transformers. As a consequence, let us consider the case of
testing a CT located high:
. With one transformer, it is possible to lift the set using two
isolated rods, and to screw the clamp on the CT terminations;