This case study was written with the help of Bill Rundle, who was a maintenance engineer at Imerys Minerals and has since retired. The company produces china clay, which is supplied to the ceramics, paper, pharmaceutical and plastics industries.

The company have a number of open cast quarries, refining and drying plants, which are spread between Cornwell and Devon, and altogether consume over 40 MW of power on a continuous 24/7 basis. Power is supplied via their own private 11,000 volt distribution network, which consists of 120 substations and 200 KM of underground cables and overhead lines.

Checking this network for potential problems has become considerably easier for Imerys since they started to use the Ultraprobe 550 to detect critical failures of overhead insulators. After we had carried out some on-site training, Bill very kindly shared the following with us on an e-mail.

"You may recall the overhead line insulator tracking defect, which we detected at the Drinnick site. We had originally made preparations to switch out the overhead line this week, and carry out an inspection and repair."