From the editors´ desk

This issue has four articles, the first of which is "Density Monitoring of High- Voltage SF₆ Circuit Breakers" by Peter Cheetham and Ali Hellany of the School of Computing, Engineering and Mathematics, University of Western Sydney, Sydney, Australia, and Steven Jones of TransGrid, Australia. The article analyses different aspects of density monitoring which need to be considered to successfully retrofit a HV SF₆ circuit breaker with density-monitoring equipment. A condition-monitoring network needs to be able to provide the user with real-time information of the circuit breaker\´s condition, as well as be able to cope with the installations of new condition-monitoring equipment. A sampling rate of 30 minutes allows for accurate representation of the SF6 density level within the circuit breaker while reducing the number of measurements. Filtering the density measurements between 10 pm and 4 am eliminates fluctuations caused by ambient conditions. The filtering process allows for the early detection of SF₆ leaks that would have been almost impossible to detect from looking at the total density measurement.