Single phase lockout on a single long line connecting two power systems with particular reference to the Nairobi-Mombasa power transmission line.

Abstract

The possibility of operating a single long H.T. Power transmission line with one phase locked out after a single phase to ground fault occurs on that phase is investigated. Particular reference is made to the Nairobi-Mombasa line. Computer programmes for the solution of asymmetrical faults at more than one location are developed and used to calculate the sequence currents and voltages on the system, plus the power transmission on the lines, with the lockout. Finally the stability of the overall system with the lockout is investigated. The results indicate that for a single phase to ground fault in the middle of the Nairobi-Mombasa line:- (i) Up to 55% of the prefault power can be transmitted on the faulted line. The power transmission on the other lines is not greatly affected. (ii) Sequence currents on the system excep-t.on the faulted line are within reasonable values - that is none of the lines, transformers, o~ generators are overloaded. (ii,i) The system remains stable for a prefault power transfer of 30 MW along the line in either direction. (iv) There is a general rise of Bus voltages~ in some cases of as much as 10%. Therefore it is concluded that~ the Nairobi-Mombasa H.T. transmission line can be operated on a single phase lockout for a limited period when a single phase to ground fault occurs on the line. This conclusion can be extended to cover cases where two major load centres located far apart and connected by a single H.T. line. This has very important implications~ since it means that the two load centres can continue to exchange power with a single phase to ground fault condition present. This gives the systems operators time to take appropriate control actions at the two ends