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.

Details required on placement of orders: –

Ratio :
This is the Ratio of the primary voltage to the rated secondary voltage. The Primary Voltage can be either 11KV i.e. Connected between the lines or 11KV/ when connected between the lines and earth. The primary voltage also varies depending on the connection i.e 110V or 110V/ root 3 voltage.

Burden :
This is the load connected across the secondary winding expressed in VA depending on the number of meters connected and distance of the meters from the Potential transformer.

Class of Accuracy :
The choice of accuracy class depends on the duty to which the Potential Transformer is put to use. The measuring PT maintains the Ratio and phase angle error over the operating range of 80-120% of Primary Voltage. The protection PTs are used in protection system for operating differential protection relays and maintain accuracy for 5% of the rated voltage given by the voltage factor