An alternative power tracing method for transmission open access

Abstract

The competitive environment of electricity markets necessitates wide access to transmission networks that connect dispersed customers and suppliers. Regardless of market structure, it is important to know whether or not, and to what extent, each power system user contributes to the usage of a particular system component. This information facilitates the restructured power system to operate economically and efficiently. Moreover it brings fair pricing and open access to all system users. Due to non linear nature of power flow, it is difficult to determine transmission usage accurately. Therefore it required to use approximate models, tracing algorithms or sensitivity indices for usage allocation. The tracing methods are based on the actual power flows in the network and the proportional sharing principle. To date several tracing algorithms have been proposed in the literature [1-11]. A novel tracing method is presented in [1-3]. But, even though the approach is conceptually very simple, it requires inverting a sparse matrix of the rank equal to the number of network nodes. In [4] graph theory is applied to trace active power and it is limited to systems without loop flows. Reference [5] is based on the concept of generator ‘domains’, ‘commons’ and ‘links’. Nodal generation distribution factor (NGDF) [7] for active and reactive power allocation is based on time consuming search algorithm. AC power flow tracing algorithms [8], [9] use a complicated line representation to account for the losses and line charging, Detecting and solving the loop flows is a pre requisite to these methods. In order to overcome the difficulties arise in reactive power tracing due to interaction cause by losses, [10] traces active and reactive power using real and imaginary currents respectively. This technique automatically becomes lossless real and imaginary current networks and does not require to model line losses but the method still involves the disadvantages of the concept of ‘domains’ and ‘commons’. Reference [11], proved that real and imaginary current networks are acyclic directed graphs. Then authors attempt to show the share of the generators to the loads, ignoring line charging elements. The above mentioned disadvantages have been the reason for developing a new method to know how much, and to what extent, each generator supplies to each load. The algorithm uses the advantages of real and imaginary current networks along with the basic concept of graph theory. Starting from load flow solutions, it first decomposes line complex currents based on the proportion of generator and network injected currents. The amount of current attributed to each current source in the lines and to each current sink is then used to allocate the contribution from each active and reactive generator to system loads. Shunt elements are handled by introducing additional fictitious nodes.