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.

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.


Single phase resin cast PT with fuse : VT2
Two phase resin cast PT : VT4
Single phase resin cast PT with fuse : VT5
Single phase resin cast PT without fuse : VT6
3phase resin cast PT without fuse fixed type : 3VT1
3phase resin cast withdrawable type PT with fuse : 3VT2
3phase resin cast Fixed type PT with fuse : 3VT3