VSI/VTD

The VSI and the VTD  range of equipment were introduced in the early 1960’s and instantly became a recognised product all over the world.  There are tens of thousands of units installed on networks of 13.8kV and below, with short circuit levels of up to 43kA. 

Continuous current ratings of up to 3000A were available (3000A being force cooled) and units could be in single busbar or double busbar configuration. The switchgear fixed portion utilised cast resin bushings and after a proven fifty year history, has shown no degradation in these materials at all. 

Employing the R series of ocb’s (<1200A) and the Q series of ocb’s (>1200A) there were considerable variants on each rating – for example, R8/1, R8/2L, R8/2H, R8/3 for the 800A breaker.  It is imperative that the ratings of each variant are understood if network configurations or fault levels change.  There are a variety of ocb internal assemblies and mechanisms utilised – dependent on user specification, vintage, operational duty and fault level requirements.