7PG21 Solkor Rf Applications Guide
1
General
Solkor R & Solkor Rf are well established pilot wire feeder differential protections operating on the current balance
principle. It is suitable for application on privately owned 2 core pilots with loop resistance up to 2000ohms to
protect 2 ended feeder circuits up to 20km in length. Two identical relays are used as a pair with one relay
connected to current transformers at each end of the feeder respectively.
Additional external Pilot Supervision equipment can be supplied to detect pilot cable open circuit which can lead
to protection operation. Solkor relay trip contacts can be connected in series with those of an Overcurrent Guard
relay to avoid operation for damaged pilots during normal load levels. Additional Intertripping equipment can also
be supplied which utilises the pilot connection to initiate a protection operation at the remote end.
The Solkor R/Rf relay has an insulation level of 5kV between pilot connections and the local ground to withstand
voltages induced on the pilot cable due to coupling with the fault current flowing in a parallel path and to withstand
differential ground voltages caused by the flow of fault current. This is generally adequate for distribution feeders
but for higher voltage systems where feeders may be longer and fault levels higher, an additional external
isolation transformer is available for use with the relay in Rf mode to increase the voltage withstand to 15kV. One
transformer should be fitted at each end of the pilot connection.
The R/Rf relay is primarily intended for use in the Rf mode which has the advantage of increased operating speed
but can be simply changed to R mode for compatibility with pre-installed remote end relays which are older 5kv
Solkor R type relays. The Solkor R/Rf relay is not compatible with the older 15kv Solkor R.
©2010 Siemens Protection Devices Limited
Chapter 3 Page 3 of 15
