Envelope compensation for high speed digital protection

The time delay compensation method as presented previously by B.S. Ashok Kumar (1986) attempts to reduce the delay introduced by different components of a relaying system. The method uses the transient fault signal, the prefault signal, and a predetermined system time constant to estimate the postfault steady-state signal. While the results were encouraging from the viewpoint of delay reduction, a number of difficulties such as overreaching, singularity at the origin, and oscillations were encountered. Among these, the overreach problem was severe enough to warrant a search for new methods. The authors report the results of a variety of methods that have been tried for reducing the overreach problem. A better convergence function has been identified which gives faster fault detection without increased overreaching. Other problems mentioned above are also reduced by the new method. The method is verified using computed transients of a transmission line