69 kV Line Relay Upgrade
A central Indiana Municipal owns and operates a 69 kV subtransmission loop that feeds their eight 69 kV to 13.8 kV distribution substations. The 69 kV line protection provided by various electromechanical relays was beginning to fail resulting in several unexpected and unacceptable outages. They enlisted ENTRUST Solutions Group to design and replace all the electromechanical 69 kV line protection with microprocessor based SEL relays.
The municipal needed to complete all the 69 kV line protection relay upgrades without interrupting any of the 13.8 kV power to their customers.
ENTRUST Solutions Group designed and implemented a switching plan where the 69 kV loop was opened and de-energized one line segment at a time. This allowed the distribution to be fed from the other direction on the loop. The relays were upgraded on one end of the de-energized line segment and tested and then the relays at the other end of the de-energized line segment were upgraded and tested. Once relays at both end of the de-energized line segment were upgraded, final testing for line differential functions was completed. The line segment was then returned to service. This process was then repeated until all the protective relays around the 69 kV loop had been upgraded. There were total of six (6) 69kV line segments and respectively 24 new microprocessor relays were put in service.
New 69 kV line protection consisted of an SEL-311L and test switches for primary protection, and an SEL-351S and test switches for backup protection and reclosing functions. A Shark meter and test switches were also installed at each panel to replace existing analog meters. Protection included overcurrent, zone distance, line differential and breaker fail functions. The newly installed SEL relays were integrated into the clients existing SCADA system with the synchronized satellite clock to help with any future fault analysis.