Improved protection system for phase faults on marine vessels based on ratio between negative sequence and positive sequence of the fault current

This study presents a new method to protect the radial feeders on marine vessels. The proposed protection method is effective against phase–phase (PP) faults and is based on evaluation of the ratio between the negative sequence and positive sequence of the fault currents. It is shown that the magnitude of the introduced ratio increases significantly during the PP fault, hence indicating the fault presence in an electric network. Here, the theoretical background of the new method of protection is firstly discussed, based on which the new protection algorithm is described afterwards. The proposed algorithm is implemented in a programmable digital relay embedded in a hardware-in-the-loop (HIL) test set-up that emulates a typical maritime feeder using a real-time digital simulator. The HIL set-up allows testing of the new protection method under a wide range of faults and network conditions and the experimental results demonstrate its effectiveness in all scenarios conducted. The proposed protection method offers a solution to the protection challenges associated with variability of the short-circuit currents in radial feeders, advancing in this way the traditional mean of protection in maritime feeders, represented by overcurrent relays.