Studies of EHV transmission lines protection based on power balance

The paper proposes a protection theory according to the long line equation and based on power balance. The theory deduces the sampled data of one terminal from the sampled data of another terminal. The in-zone faults or out-zone faults can be judged from the integrated powers, which are integrated with deduced sampled data and real sampled data during a time interval. The results of EMTP simulation show that the theory has the following characteristics: fast operation, with the relay operating in 3/4 of the power frequency period; excellent performance under high resistance; not influenced by the running mode.