Toronto Hydro Electric System Limited is a municipal electric distribution utility in Canada. The Stations Department is comprised of engineers and engineering technicians, and oversees the maintenance and development of substations in the Toronto area. At present, the Stations Department is completing the Protective Relays Replacement Project, which will replace the current electromechanical relays, shown in Figure 1, in one of the power substations with newer relays. Protective relays are used to detect abnormal conditions within electrical systems; circuit breakers are automatically triggered protective electrical switches that activate when system malfunctions are detected. The current protective system is complicated and occupies large amounts of space. Many of the components are obsolete, and the cost of maintenance is extremely high, as some components are no longer in production. Additionally, the old relays have been used for over 20 years. As distribution systems span large areas and affect large groups of people, it is essential for methods of protection and security to exist within the system.
In addition to her regular duties at Toronto Hydro, Lili Zheng, a 3rd year electrical engineering co-op student from the University of Waterloo, was asked to research different protective relay types for the Protective Relays Replacement Project.
Figure 1 - Use of an electromechanical relay in a distribution system
This case study provides students with an opportunity to perform the responsibilities of distribution engineers. Using course concepts and the provided reading material, students will apply the engineering design process to evaluate possible courses of action for the replacement of old relays at a power substation. The case study tests and builds on a student’s knowledge of the power distribution system.