7PG2113/4/5/6 Commissioning & Maintenance
©2012 Siemens Protection Devices Limited
Chapter 6 Page 9 of 77
For all high current tests it must be ensured that the test equipment has the required rating and stability and that
the relay is not stressed beyond its thermal limit. Requirements of section 1.2.3 should be observed.
1.3.2 Primary Injection Tests
Primary injection tests are essential to check the ratio and polarity of the transformers as well as the secondary
wiring.
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 1.3.5
.
With all earth-
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
Figure 1.3-1 CT Polarity test 1 arrangement
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.