A Log-Tabel Based Algorithm For Implementing Microprocessor Time-Overcurrent Relays

The difficulties that arise in implementing the time-overcurrent relay characteristic on microprocessor systems are due mainly to two factors. Firstly, data acquisition is usually linear whereas curve scales are logarithmic. Secondly, we have to calculate the main variable, namely the normalized fault current given as the ratio of the measured line current to the preset pickup value in a system in which the latter quantity should preferably be adjustable.