David Grgic - Faculty of Electrical Engineering, University of Ljubljana Trzzaska ۲۵, SI-۱۰۰۰ Ljubljana Slovenia
Ferdinand Gubina - Faculty of Electrical Engineering, University of Ljubljana Trzzaska ۲۵, SI-۱۰۰۰ Ljubljana Slovenia

Recently, Slovenian power system has gone thought the process of deregulation, which brings new challenges in preventing of transmission lines overloadings. Beside others, there are two well-known approaches to congestion management in deregulated environment. Under the zonal pricing approach, power system is first divided into several zones on such a way, that branches, which are often overloaded, connects these zones. Also, spot market is designed in such a form, that each zone can have its own market clearing price. If there is no congestion between zones, market clearing price is the same for all zones, what is also referred as system price. However, in the case of congestion, market clearing price is set differently in each zone in a such a manner, that trading between zones results on power flows between zones to be smaller or equal to the transfer capability. The problem with zonal pricing is that it does not prevent internal congestion. For this purpose, countertrade approach can be utilized. Here, system operator after results of the trading are known redispatches power generation in such a way, that resulting power flows does not overload any line. Every generation unit can offer an increase or decrease of its production in a similar manner as this is done on a balancing market, while the responsibility of the system operator is to select offers in the most efficient way. For the Slovenian power system is planned that zonal pricing is going to be implemented for cross-border congestion, whereas countertrade approach is going to be utilized to prevent internal congestion. The focus of this paper is the countertrade approach.

congestion management, transmission overloading, transfer capability, generation distribution factors, linear programming