Market power implication on congested power system: A case study of financial withheld strategy

Market power refers to the ability of generators in influencing the energy prices above competitive level to obtain more profits. It may be the cause of transmission congestion that limits transfer capability in an interconnected area. Hence an independent system operator (ISO) must be able to detect the conditions in which market power has been practiced to guarantee a secure competition and economical operation of the electricity market. To cope up with transmission congestion to assess market power, an optimal power flow (OPF) based on shift-factor methodology to find out a new indicator, called congestion-based dynamic dispatch index has been proposed. One of the beneficial feature of the proposed method is the ability to recognise accurately the most potential generator to exercise the market power. A generator bidding scheme represented by financial withheld strategy is then utilised to investigate the dynamic condition of power market. An analysis on the power market performance to identify potential generators in exercising market power is also presented. The results show that transmission congestion condition may be created unnaturally by this particular bidding strategy. It prevents some cheap generators to supply their outputs and allows all more expensive generators within the congested zone to gain more profits at the cost of other market participants.

► A composite method to assess market power with a congestion-based index is proposed.
► The method recognises the most potential generator to exercise market power.
► Bidding scheme is employed to investigate the dynamic condition of power market.
► Congestion condition may be created unnaturally by financial withheld strategy.
► Expensive generators within congested zone are scheduled but gain more profits.