A case study on the alternative solutions for the load flow problem in a 50 kV cable grid

This paper describes a case study on the alternative solutions for a load flow problem in a Nuon 50 kV cable grid in North Holland. This part of the cable grid is typically parallel fed with short distances. The grid is designed to be operated safely under the condition when one of the cable links is out of service, the so-called N-1 condition. Under a certain circumstance, this grid will have an overload problem due to unbalanced load flow, meaning some cables are overloaded while others are under loaded. The transmission capacity of this grid will be insufficient from the year 2015 anyway, under N-1 condition. The ultimate solution is to lay extra cables in this grid, but this is a very costly option. The purpose of this paper is to present the alternative solutions studied to solve the load flow problems so that the investment of laying extra cables can be postponed after year 2010. Three alternative solutions have been studied: inserting a variable impedance, inserting a phase shifting transformer and inserting a UPFC. The effects of the three alternative solutions, both positive and negative, have been compared. The best solution among them has resulted from the technical aspects, operational aspects and economical aspects.