Elimination of partial overloading of generators under unbalanced operating conditions of power systems

Unbalanced operating condition in a power system can cause partial overloading of the generators in the network, a condition where one or two of the three phases of the generator become overloaded even if the total 3-phase power output of the generator is within its specified limit. Partial overloading of generators beyond certain limits is undesirable and must be avoided. Distribution systems are often subjected to highly unbalanced operating conditions. Introduction of distributed generations (DGs), therefore, has rendered today's distribution systems quite susceptible to this problem. Mitigation of this problem requires the issue to be addressed properly during analysis, operation and planning of such systems. Analysis, operation and planning of power networks under unbalanced operating condition require 3-phase load flow study. The existing methods of 3-phase load flow are not equipped to take into account any limit on the loadings of the individual phases of the generators. In the present work, a methodology based on Newton-Raphson (N-R) 3-phase load flow with necessary modifications is proposed. The proposed methodology is able to determine the safe loading limits of the generators, and, can be adopted for operation and planning of power networks under unbalanced operating conditions to overcome the above difficulties. Test results on IEEE-37 bus feeder network are presented to demonstrate the effectiveness of the proposed method.