Jamali - D= University of Science & Technology IRAN
Bahari - D= University of Science & Technology IRAN

In the conventional distance protection the relay setting is fixed and does not change under different system conditions. Settings can only be changed when major changes have occurred in system configurations. Reach accuracy of distance relays is adversely affected by fault resistance combined with remote-end infeed. Therefore, a safety margin is considered to avoid maloperation. A common practice for zone-1 setting is 80% of the line length. In order to have an instantaneous protection for the line, different distance protection schemes using communication channels have been employed. Introduction of digital distance protection has made it possible to use adaptive concepts for the improvement of the relay setting. And several papers have been published in this area. This paper presents a new adaptive setting technique which can improve the relay zone-1 setting up to 95% of the line length. A digital distance relay with this new technique can respond to system conditions that change from time to time. The additional data required by the adaptive relay can be obtained through low speed communication systems such as SCADA , RTU or substation host computers. Computer simulation has been carried out to check the validity of the new technique. The Electromagnetic Transient Program (EMTP) has been used to simulate a 400KV transmission line under fault conditions. Along with the new adaptive technique , one of the latest distance protection algorithms has also been implemented for the simulation studies. The simulation results for different fault conditions show that for fault resistance up to 200 ohms , the new technique can protect the whole line in zone-1. If 5% safety margin for transducers and hardware errors is considered the new technique assures reliable protection for at least 95% zone-1 setting.