A new pilot distance protection scheme for teed lines
With the rapid development of distributed generators, the teed lines are widely used due to the lower construction cost. The differential protection is a common scheme for teed lines, but it has a high requirement for the synchronization of data sampling. So this paper mainly focuses on the application of distance protection in the teed system. Considering the length difference between three terminal lines and different fault resistances, reliability and sensitivity of conventional distance protection are affected. To solve the problems, a new pilot distance protection scheme for teed lines is proposed. The new scheme based on a comprehensive protection criterion is composed of the main criterion and the auxiliary criterion. In order to ensure sufficient sensitivity and reliability of distance protection, the main criterion adopts an improved permitmode pilot distance protection. When the internal high resistance fault occurs, the main criterion may fail to operate. Therefore a positive sequence voltage amplitude difference criterion is proposed as the auxiliary criterion. Through the effective cooperation of the main criterion and the auxiliary criterion, the new protection scheme can provide sufficient reliability and fast operating response for a variety of internal faults that occurs on the teed lines. Simulation results verify the effectiveness of the new protection scheme.