Abstract: At the aim of minimizing the power grid company's purchasing electric power cost,an optimal model is set up under the contract for difference,which the grid company can buy power in contract,spot, reserve and interruptible load trade markets. An algorithm of this model is given using heuristic approach. At last,the influence on the electric power purchasing cost of the grid company made by contract for difference and the percentage of contract power quantity is analyzed.

Key words: purchase power cost, contract for difference, interruptible load