A new approach towards surge suppression and insulation monitoring for medium voltage motors and generators

Some 30 years ago, extensive investigations were launched into the root cause of premature winding failures of a large number of MV motors. This resulted in the discovery that pre-strike and re-strike switching transients were responsible. Field measurements proved the presence of these transients and provided the necessary information for developing models to understand the mechanisms involved. This understanding permitted the RC device, attached to the motor parameters in such a way that pre- are eliminated. The incorporation arrester deals with other spurious impulses. The combined ZnO and and sold in 55 countries over the name ZORC. design and development of an terminals, which alters circuit strike and re-strike transients of a Zinc Oxide (ZnO) surge high magnitude steep fronted RC device has been marketed past 26 years under the trade However, some international markets required type tests which presented a problem with the original ZORC design configuration. This prompted a re-design which resulted not only in the capability for meeting the new test requirements, but also provided a platform for more efficient international manufacture and, in addition, a unique "window" for seeing into the winding and supply system of the protected equipment. This window is provided by the capacitance in the RC circuit and is particularly good because of its relatively high value. By adding a purpose designed sensing circuit, combined with advanced analog and digital signal processing techniques, the ZORC+ becomes an extremely effective sensor for on-line monitoring of the condition of the winding insulation of the protected motor, generator or dry type transformer. It is more effective than coupling capacitors used for this purpose because of the wider frequency response afforded by the ZORC+. This permits seeing deeper into the windings and gives significantly improved coverage, which has always been a weakness of conventional coupling capacitor sensors.