Definite Time Overcurrent Research Articles

Definite time over-current protection on transmission line using MATLAB/Simulink

This paper has investigated the application of the definite time over-current (DTOC) which reacts to protect the breaker from damage during the occurrence of over-current in the transmission lines. After a distance relay, this kind of over-current relay is utilized as backup protection. The overcurrent relay will provide a signal after a predetermined amount of time delay, and the breaker will trip if the distance relay does not detect a line failure. As a result, this over-current relay functions with a time delay that is just slightly longer than the combined working times of the distance relay and the breaker. This DTOC is tested for various types of faults which are 3- phase fault occurring at load 1, 3-phase fault occurring at load 2, a 3-phase fault occurring before primary protection, and the behaviour of voltage and current with a failed primary protection. All the results will be obtained using the MATLAB/Simulink software package.

Overcurrent protection against multi-phase faults in MV networks based on negative and zero sequence criteria

Adequate power system protection plays crucial role in ensuring reliability of electricity supply, thus it is a key challenge for distribution system operators to increase the effectiveness of protection schemes operation and protection equipment itself. The main goal of the paper is presenting a multi-criteria protection algorithm that may boost effectiveness of power lines’ short-circuit overcurrent relays in medium voltage networks in case of various two phase faults. The idea of enhancing protection performance is based on fault current symmetrical components’ analysis and specifically on using negative and zero sequence currents as criterial values for overcurrent line protection used against such faults. The paper describes in detail the proposed solution and analyses its performance based on medium voltage network simulations carried out using DIgSILENT PowerFactory software. Promising simulation results can be observed for definite time overcurrent protection relays used in reactance-earthed networks, as introduction of the proposed method proved to increase the zone of effective operation twice comparing to the traditional phase current based solutions. Moreover, in the proposed solution, coordination of protection settings for small earth-fault current values, which are identified by other protection relays, is not necessary. The proposed solution may complement the traditional algorithms for short-circuit protection (I≫) used in modern protection relays monitoring the level of negative and zero sequence current, and therefore may significantly improve the effectiveness of detecting various phase-to-phase faults in the considered MV line protection zone.