The presence of a negative transmission loss rate(TLR)in an inter-provincial electricity trading settlement means that the settled consumed electric quantity is even larger than the supplied one for a specific trading contract

and is contrary to the common understanding that transmission loss is inevitable. However

the current settlement method employed in China Southern Power Grid(CSG)can indeed result in the negative TLR problem that demands appropriate solution. Given this background

the current inter-provincial electricity trading mode and settlement method in CSG are clarified first

and the main factors are analyzed for the negative TLRs in settlement in some months. And the limitations of the current settlement method in dealing with the increasing number of power purchasers are pointed out. To address these issues

a method for the inter-provincial electricity trading settlement considering allocations of unbalanced electric quantity is proposed with respect to the current electricity trading mode. The proposed method is then extended for possible use in the future electricity trading model with multiple power purchasers. The current and proposed settlement methods are next compared by employing actual trading data in CSG

and a complicated trading scenario with multiple power purchasers is designed and analyzed. Simulation results demonstrate the feasibility of the proposed method. This work is supported by National Basic Research Program of China(973 Program)(No. 2013CB228202).