Circuit Breakers, Melting Fuses and Electronic Fuses - Analysis and Design Rules for Telecom Power Applications

Abstract

Selecting and dimensioning the best circuit protection for an application can be very hard. To make this easier for the employees at Ericsson Power Solutions a guideline has been developed. Questions the employees had regarding circuit protection have been answered. Manufacturers have been consulted and IEC and UL standards have briefly been investigated. A guideline consisting of derating rules for melting fuses and hydraulic magnetic circuit breakers has been developed. Considerations have been made in order for the guideline to be of help when designing circuit protection at Ericsson Power Solutions. One of the main issues has been to determine which current is to be derated since the current often includes ripple. How to investigate if a circuit breaker will endure a pulse was unclear and has now been clarified also both reoccurring and single pulses can now be dealt with. Altitude derating is required above a certain altitude. A general model for temperature influence on trip time for magnetic hydraulic circuit breakers has been determined. Finally, one melting fuse and one circuit breaker were designed according to the guideline. The result was close to the ratings of the protections used today but none the less slightly changed.