Winning when playing hide-and-seek with faults in electrical distribution networks

Keeping the power supply secure and disturbance-free is paramount, so finding faults quickly and reliably in electrical networks is a high priority

For utilities, keeping the power supply secure and disturbance-free is paramount, since power faults rapidly incur losses in business and industrial environments. This makes finding faults quickly and reliably in electrical networks a high priority, they must be found before they cause a bigger problem.

Finding faults in distribution networks has always been a priority, but some of the ongoing changes in distribution networks are adding a new level of complexity to the problem. One of the most prevailing trends is the undergrounding of overhead lines. This not only protects the electrical networks from the environment such as snow storms, strong winds and falling trees, but also has an esthetic aspect, since underground cables do not alter the scenery in the same way overhead lines do.

Another widespread trend is the increasing number of compensated networks, which have improved the reliability of energy distribution, since this type of network remain operational for a limited time, even when a fault condition occurs, since the earth-fault current is compensated by Peterson coils. For overhead lines we can also count on the self-extinguishment of earth-faults, which means fewer auto-reclosing incidents and improved network reliability.

The implementation of a transition from overhead lines to cable networks, has proven challenging. Underground cables introduce higher capacity currents in the electric system, which may lead to unwanted operations in healthy feeders. Modern cables have improved conductivity, which means lower losses, but can cause a longer duration of earth-fault phenomena.

A fault in an electrical network has different characteristics depending on the distance from the measuring point. The most common type of earth-fault is intermittent, which is a very challenging type of fault for conventional earth-fault protection methods. And if these types of faults in the network are not dealt with properly, they tend to develop into permanent faults and cause insulation failures. Intermittent earth-faults cause serious challenges: they cause unselective operation in healthy feeders and unsuccessful or delayed tripping in faulty feeders.

Thanks to extensive study of earth-fault phenomena and numerous field studies, ABB is now able to introduce the multi-frequency admittance-based earth-fault protection. This unique and new protection method works reliably even in these very challenging conditions. The protection function is available in the Relion® product family of protection relays, in the 615, 620 and 630 series, which are most commonly used in medium-voltage switchgear applications.

ABB’s digital switchgear portfolio combines protection, control, measurement and digital communication to enable a safe, flexible and smart electrical network. It is based on the optimized integration of current and voltage sensors into medium-voltage switchgear, combined with the latest Relion protection and control relays and the capability of the IEC 61850 standard for communication.

Visit us at CIRED on June 12-15 in Glasgow, the UK at booth G08, to learn more.

You can learn more about compensated networks and directional earth-fault protetion in this free-of-charge webinar:

Learn more about Relion protection and control relays

Success story: Taking earth-fault protection to the next level in metropolitan Helsinki

Post-fault oscillation phenomenon in compensated MV-networks challenges earth-fault protection – First published at CIRED 2015, Lyon, France

Intermittent earth faults – Need to improve the existing feeder earth fault protection schemes? – First published at CIRED 2003, Stockholm, Sweden