11kV Resin Cast CTs & PTs

Resin Cast current 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 and earth is obtained by this epoxy resin and hence CTs have a lot of technical advantages.

Use of epoxy resin for insulation

» Compact design for high mechanical and dielectric properties. The considerable reduction in dimensions reduces space and switchgear panel width.
» No fire spread and hence no permanent damage to the equipment; Even after a surface flashover reconditioning is easy by a thorough cleaning of surface.
» Epoxy is non hygroscopic and hence gives very good insulation properties even in severe humid conditions.
» Non ageing. The moulding has a non wearable glossy surface and has a very high degree of toughness. Therefore the CT requires no maintanence except for the clearing of dust contamination on the surface.
» As there is no oil for insulation the CT can be mounted in any direction to suit the switchgear design.
» The current terminals are provided with sufficient area thereby avoiding any overheating of joints.
» Based on the dynamic current rating additional clamping facility is provided for the terminals.
» For higher current ratings window tupe CTs type WR can be used which will give additional saving in space required for terminal connections.
» For window type CTs equipotentialising facilities are provided with cast nuts and thereby permanent and sure connections can be made.
» For window type CTs large window openings are provided so that the busbars can be run through without any special bending and with one thickness gap between individual bars as done in the switchgear.
» Sufficiently long creepage surfaces are provided to ensure better surface tracking properties.


The basic designs are available in three major types to cover the entire range of 11KV Resin Cast CTs for primary currents upto 2500A.

» The wound primary cast resin PR type for low ratios.
» The bar primary cast resin BR type for higher ratios.
» The window types cast resin WR type without primary for still higher ratios.

The PR type is a wound primary type CT designed to cover primary currents from 25 amps to 300 amps. The bar type BR CTs are designed with a bar as primary. These CTs can cover a range of primary currents from 300 amps to 1000 amps. All higher ratings of primary Currents are covered in WR type of Window CTs.


» While ordering please specify the Short Time Rating, Insulation Level, VA burden, type of CT and Model.
» When specifying the burden please consider the total connected items and see that the actual burden is as close to the rating as possible. However one of the standard rating as per IS2705 may be adopted.
» When specifying the accuracy class please ensure that the requirements of certain relays or any other specific requirements are taken care of.
» While selecting the primary current of the CT ensure that the calculated maximum load current in the system falls within the range from 50% to 100% of the selected ratings in general cases.
» Avoid combining too many ratios in the same CT.
» Clearly indicate any dimensional limitations in switchgear panel, if any.

These transformers have been successfully type tested for a Short Time Current rating upto 44KA for 1sec at CENTRAL POWER RESEARCH INSTITUTE , Banglore.