Grounding elbow with 25kA fault-closure rating for underground distribution systems

This paper details advancements in the grounding of dead-front underground distribution (UD) systems that yield safer operation and prevent outages. Standard 200 A grounding elbows for UD systems are rated for a maximum fault-closure of 10 kA. A very hazardous fault accompanied by flying bushing fragments will generally result if a fault-closure occurs above 10 kA. Some utilities have been forced to push their 200 A systems above 10 kA; and many others are using 10 kA grounding elbows on their 600 A 25 kA rated systems. This paper documents the design, method, application, and test results of a grounding device rated for a 25 kA fault-closure operation. The device features a current limiting fuse that limits the energy and opens any fault with minimal energy let-thru. The current limiting fuse makes any fault-closure operation much safer for the operator and keeps customers in power by opening the fault.