Secondary Wiring Insulation-Resistance Test; Current-Transformer Ratio And Polarity Tests; Figure 1.3-1 Ct Polarity Test 1 Arrangement - Siemens 7PG2113 Technical Manual

Note. If the current transformers associated with the protection are located in power transformer bushings it may
not be possible to apply test connections between the current transformer and the power transformer windings.
Primary injection is needed, however, to verify the polarity of the CTs. In these circumstances primary current
must be injected through the associated power transformer winding. It may be necessary to short circuit another
winding in order to allow current to flow. During these primary injection tests the injected current is likely to be
small due to the impedance of the transformer.
1.3.3

Secondary wiring insulation-resistance test

This test should not include the pilots, which should be tested separately as described in
connections, earth-links, and supply fuses and links removed, measure the resistance to earth of all the
secondary wiring. Satisfactory values for the various readings depend upon the amount of wiring concerned.
1.3.4

Current-transformer ratio and polarity tests

If testing by single-phase primary injection is not possible, make the alternative tests detailed in Section 2.10.
A
B
C
Remove the trip-links. Connect the test-circuit as shown in Figure 1.3-1 CT Polarity test 1 arrangement and inject
a primary current of 50 per cent or more of the current transformer primary rating in order to obtain a reliable
secondary-current reading. Check that the ratio of current transformer is correct by referring to the readings on
ammeters Y. Also check that the polarity of the current-transformers, is correct by referring to ammeter X, the
readings of which should be negligible compared with those in the individual phases. Repeat the tests for at least
one other phase-to-phase fault condition.
©2010 Siemens Protection Devices Limited

Figure 1.3-1 CT Polarity test 1 arrangement

7PG2113/4/5/6 Commissioning & Maintenance
1.3.5.
Chapter 6 Page 9 of 77
With all earth-