Resin Cast Potential Transformer

In AC circuits, for measuring large voltages a specially constructed accurate ratio Potential Transformers are used. Their function is to reduce the supply Voltage to a value small enough to be easily measured with standard low range AC instruments of moderate size and capacity. The advantages of using Potential Transformers for range extension of AC meters are many fold.? The instrument is isolated from line voltages hence it can be grounded.? It is possible to achieve standardisation of instruments and meters at secondary ratings of 110V. ? Several instruments can be connected from a single transformer. ? The power connected in measuring circuits is low. Potential Transformers of dual purpose Metering & Protection are also commonly used. An additional secondary winding is provided which is connected in open delta so that in the event of an earthfault on any of the phases, appropriate voltage is developed across the open delta terminals which is then used to actuate a tripping mechanism. Resin Cast Potential Transformers are dry type transformers the active part of which is completely embedded in quartz loaded Epoxy Resin by using vacuum moulding technique. After moulding the resin is hardened by polymerisation. The main insulation between Primary and Secondary & Earth is obtained by this epoxy resin. These transformers are of compact design with high mechanical and electrical properties. These are non-hygroscopic and hence give very good insulation properties even in given humid conditions.