7PG21 Solkor Rf Commissioning
©2012 Siemens Protection Devices Limited
Chapter 6 Page 11 of 21
each current transformer by comparing the secondary current in each phase with the corresponding primary
current. Check the polarity of the current transformers; the reading of ammeter X in the neutral circuit should be
negligible compared with the secondary phase-currents. Some current may exist in the neutral circuit due to
unbalance of primary load current and/or secondary burden.
2.11 Check of secondary connections
The purpose of these tests is to establish that the secondary wiring between the current-transformers and the
summation-transformer at each end is in accordance with the particular diagram supplied for the installation.
However, if load-current is to be used it is unlikely that actual setting-values can be obtained in which event it is
considered reasonable if suitable readings can be taken to confirm that the feeder ends behave similarly for the
same fault-condition. Care should be taken that there is a reasonable value of load current available i.e. 25% to
50% of nominal.
Remove the trip-links. Check that the pilots are connected at each of the feeder and that the padding resistors are
correctly set. In order to obtain comparable readings at each end the primary-current should remain constant.
When using load-current this condition can best be approached by taking readings for a given fault-condition at
each end in turn. With this object in view, initially connect the secondary circuit at each end as shown in Fig. 3a
(Solkor Rf without isolating transformers) or Fig. 3b (Solkor Rf with isolating transformers). For a Red-Earth fault-
condition remove the short-circuiting connection from the Red-phase current-transformer at the end of which the
first readings are to be obtained. Measure the current in the operating-coil of the relay at this end, also the primary
and secondary currents, and record the readings. Replace the short-circuiting connection across the Red-phase
current-transformer, and repeat the above procedure at the other end to obtain comparable readings for the Red-
Earth fault-conditions.
In a similar manner, by suitably connecting the current-transformer secondary leads at each end, obtain alternate
readings at each end for the Yellow-Earth and Blue-Earth fault-conditions. Tabulate the results as shown in table
5 and compare results between ends.
Tripping relay current (mA d.c.)
Type of fault
Primary current
(A)
Secondary
current (A)
Feeder end 1
Feeder end 2
R-E
Y-E
B-E
Table 5 - check of secondary connections using 3 Phase load current
