Overcurrent protection in power systems: Current methods and improvement potential

Overcurrent protection is very important to ensure power systems are reliable and sustainable. This thesis addresses non-directional and directional overcurrent protection methods. The importance of directional overcurrent protection relays is further emphasized due to the increasing complexity and parallel flow of power in increasingly complex power distribution networks. The first part of the study covers the operating principles of power system components and overcurrent protection relays. In the practical part of the thesis, the SEL411L protection relay was configured and directional and non-directional overcurrent tests were conducted using the Omicron CMC356 test device. Issues such as relay characteristic angle, current transformer polarity, and fault direction determination are completely elaborated. Additionally, parallel line protection system relays' coordination and selectivity are handled with care. Experimental evidence is presented to confirm the key role of directional protection to prevent unnecessary tripping. The outcomes achieved in this thesis provide significant contributions to the way overcurrent protection systems can be optimized in regards to safety and sustainability, providing knowledge in the way more intelligent and sophisticated power systems can be designed.