Transmission Cost Analysis Of Power System Considering Congestion Cost

Transimission cost is the basis of the electricity price. The scientific and reasonable electricity price is maden after the characters of transimission cost are be clarified. The congestion cost and transimission loss accounts for only a small portion of the total cost of transmission cost. But it is closely connected with power system power state, it has a significant role to improve the effectiveness of transmission pricing and to help transmission user rationally using transmission resources. This part of the costs closely relates to the physical power flow.It cann't be allocated using financial methods and it should be allocated according to the additional specific economic principles after the physical nature of the power flow distribution is clear.In the premise of the determining power flow of the power system, this paper can get the equivalent circuit network of the power system. According to the classic circuit theories, by mathematical reasoning the current distribution coefficients of the power supply are obtained. The distribution coefficients are decisied only by the power network operation mode (wiring) as well as the network device parameter. The contribution of branches and loads current supplied by every power supply can be obtained through the distribution coefficients. Then based on the current supplied by every power supply this paper puts forward a power flow tracing method.The power flow distribution can be physically defined. In this paper, the method is proved by Kirchhoff's Current Law and power conservation theorem. Without any assuming, the network needn't be equivalent to a lossless network.The method is simple and has small calculations. This is the basis of the transimission cost analysis considering the congestion cost in this paper. In bilateral mode,the bilateral transactions are described as current supplies.Based on the nodes voltage equation, the current distribution coefficients of the transaction current are obtained.According to the coefficients the usage of the branches by the transactions can be obtained and the transimission loss can be allocated to the transactions.In the open electricity market, the electricity business free biding increased congestion opportunity.Congestion management is not only to eliminate the congestion, but also the to allocate the congestion cost.So congestion management can promote the effective use of power system, thereby reduce the congestion opportunities. Before the allocation of congestion costs, this paper first analyzes the congestion resulting from the physical causes, which identifies the congestion responsibility of each market member. Based on the power flow tracing this paper puts forward a congestion cost allocation method. The method includes two steps to achieve congestion cost allocation. First the congestion cost is allocated to congested branches according to marginal mixed incremental cost. Because the power system is nonlinear, it exists the imbalance congestion cost while allocating the congestion cost. The imbalance congestion cost shall be allocated to the congestion branches according to the proportion of marginal mixed incremental cost. Then the power distribution of every branch and load provided by each power supply (transaction) is calculated based on the power flow trancing, considering the active power and reactive power. The power flow change of each power supply in each congested branch can be calculated, and the congestion cost of congested branch is allocated to each power supply (transaction) according to the power flow change. Because of the sum of all the lines power flow change of each power supply is equal to the lines power flow change,the congestion cost allocation method does not produce any trade surplus.And the allocation reflects the principle that is" who use who pay, use much and pay more".The transmission losses are used to correcting quoted price and the variable costs alloction is focus in the other transimission cost allocation methods.But the reachers do not pay attention to how many are the loss costs and the power supply costs.It is the disadvantage of the acquaintance of the system operator to the system running and the understanding of the power supply to the transmission cost.In this paper, the variable costs of the system and the power supply are calculated and allocated. Therefore, after the congetion cost are allocated to the market members according to the influence for the congestion of each market member, each power unit congestion cost is also calculated. Based on branch cost conservation and node cost conservation, this paper calculates unit cost of the power supply at each node considering network loss and congestion cost. The variable cost model of the power system and every power supply considering network losses and congestion cost is established.The model can calculate the entire network variable cost and each power supply to the system output variable cost.