7PG21 Solkor Rf Commissioning
©2012 Siemens Protection Devices Limited
Chapter 6 Page 5 of 21
Fig 1(b)
Connect the test supply to simulate a yellow earth fault as shown in Fig. 1b. Inject a suitable value of primary
current and check the readings on ammeters X and Y. The reading of ammeter X should equal the reading of the
ammeter Y which is connected in the yellow phase C.T. secondary.
Repeat the tests at the other end of the feeder.
Tabulate the results as shown in Table 1.
Secondary current (A)
Test condition
Primary
current
(amps)
Red
phase
Yellow
phase
Blue
phase
Neutral
phase
Feeder end 1
R-Y
Y-B
Y
only
Feeder end 2
R-Y
Y-B
Y
only
Table 1 - C.T ratio and polarity tests
2.6 Pilot Tests
2.6.1 Insulation-resistance test
The voltage for the insulation-resistance test of the pilots should not exceed the nominal insulation level of the
pilots, and the test should be made as follows:
With the pilots disconnected from the relay at both ends of the feeder, apply the insulation resistance test
between the pilot cores, and between each core and earth. This test should be carried out with an insulation
resistance test set. Compare the readings obtained with the value quoted by the manufacturer of the pilot-cable.
2.6.2 Pilot-loop resistance tests
With the pilots disconnected at both ends of the feeder, join the cores together at one end and measure the pilot-
loop resistance from the other end. If the pilot loop resistance is less than the standard value for the particular
arrangement being used (See Table 2) add padding resistance at each end. If isolating transformers are being
used, choose the secondary tap to suit the measured pilot resistance. Thus for a pilot loop resistance lower than
440 ohms choose tap T1; for a pilot loop resistance between 440 ohms and 880 ohms choose tap T2; For a pilot
loop resistance between 880 ohms and 1760 ohms choose tap F2. This will ensure that pilot capacitance will
have a minimal effect upon the relay fault setting. The padding resistor comprises five series-connected sections,
each section having a short-circuiting link. The values of resistance in the sections are 35 ohms, 65 ohms, 130
