Guidelines for Current Limiting Fuses Application
The application of current limiting fuses for distribution transformer and capacitor protection is not new to the utility industry. However, as DSTAR has recognized, over the years during which current limiting fuses have been applied, transformer and capacitor manufacturer equipment tank specifications have changed, ultimately affecting their energy withstand ratings to an internal fault. As a result, the application of current limiting fuses needs to be re-evaluated in order to determine appropriate guidelines in today’s environment. This issue is even more important as transmission system impedances are decreasing and substation transformer sizes are increasing. As a result, the maximum available fault current that a distribution system can deliver to internal distribution transformer faults is higher than they have ever been. Since energy is a function of current squared, utilities are contemplating the need for current liming fuses where they presently do not exist. The cost comparison of current limiting fuses is much greater than their expulsion fuse counterparts and correct application has a significant economic impact in addition to equipment protection. This DSTAR project is timely and provides useful guidance in this area for the electric distribution community.