Connection; Secondary Wiring Insulation-Resistance Test - Siemens 7PG21 Solkor Rf Technical Manual

2.4 Connection

Where isolating transformers are used the terminals connected to the pilots should be carefully checked to ensure
that the same tap is used at each end. The protection should normally be connected on the N tapping. The N1
tapping should only be used where very low settings are required (e.g. in non-effectively earthed systems), and
because of its greater sensitivity, care is necessary in the choice of current-transformers. It should be noted that
the N1 tapping is not brought out to a terminal on the relay backplate, and if it is to be used the lead which is
normally connected to the terminal N on top of the summation transformer should be connected to the adjacent
N1 terminal.
Examine the relay giving special attention to the following points:
•
Wipe off any dust from the outside of the relay and remove the cover.
•
See that the armature and contacts move freely and that the flag indicates when the relay is
operated by hand.
•
Record particulars of any damage, repairs or adjustments found necessary.

2.5 Secondary wiring insulation-resistance test

This test should not include the pilots, which should be tested separately as described in "Pilot Tests". 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.
Where considerable multi-core wiring is involved, a reading of 2.5 to 3 megohms is satisfactory. For short lengths
of wiring the readings should be higher. A value of 1 megohm should not normally be considered satisfactory.
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.
Remove the trip-links. Connect the test-circuit as shown in Fig. 1(a) 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.
©2012 Siemens Protection Devices Limited
7PG21 Solkor Rf Commissioning
Fig 1(a)
Chapter 6 Page 4 of 21