Influence Of Open-phasp Condition And Open-phase Fault Condition On Distance Protection Relay

Open-phase condition and open-phase fault condition in power system will affect the performance of distance protection and it becomes an important factor on security and stability of power grid. However, at present, analysis method for this kind of fault is not perfect. The main principle of present approaches is only the numerical calculation to a certain fault. These methods can not obtain the formulation of the post-fault electrical quantities so that it is hard to find out the regularity of this kind of fault.This paper presents fault analysis on open-phase condition and investigates the influence of open-phase condition on distance protection relay. Then it proposes a new calculation method for open-phase fault based on superposition principle. The character of this method is:at first, the open-phase fault network is equivalent to the superposition of a disconnection state before faulting and an additional short-circuited state; secondly, calculating the two states respectively by compound sequence network method and loop current method; finally, superimposing the results acquired. The purpose of the method is obtaining the calculation formula of electric quantity in open-phase fault network. In this paper, two kinds of fault during the open-phase running are calculated:fault occurs on the faulty phase and on the sound phase. The formulation of the post-fault electrical quantities is obtained and the detailed analysis of the influence on distance protection relay is presented in this paper.The analysis of open-phase fault is based on excluding oscillation. Oscillation has been one of the most complex and difficult problems in the application of distance protection. However, at present, oscillation blocking method is generally more complex, but also not perfect. In view of this, the paper proposes a new discrimination method of oscillation based on the calculation of power angle. At first, deducing the calculation formula of power angle under the ideal condition using known and measurable electrical quantities; secondly, judging whether the system is instability and identify oscillation and fault; finally, doing the error analysis to the discrimination method. Results show that the method can identify the fault and oscillation correctly and effectively. It could improve the reliability of the distance protection relay, which can improve grid network security.