Manufacturing Process
Proven Systems is the backbone for delivering customer satisfactory and quality product .Flow chart of activities, as listed below, helps us in fulfilling the objective.

Flow Chart of Manufacturing Activities:

  1. Client’s purchase order is reviewed for Technical & commercial requirement.
  2. After Order acceptance CT design is finalized.
  3. Requisite Raw materials / items   ordered.
  4. Manufacturing Information. in our standard format,  issued to production shop.
  5. Test & Inspection Instructions, in our standard formats,  issued .
  6. Inspection of Incoming materials.
  7. Stage checks/ Tests during   manufacturing.
  8. Final test
  9. Dispatch clearance.
  10. Packing - as per requirement.

Core Material: Normally a toroid (Round or Rectangular)  made  of CRGO material is used as Core material but selection of grade and  characteristic  much depends upon the design parameters. For precision grade metering CT Ni-Fe alloy(Mu metal)  or Nano crystalline material may have to be used.
Winding Conductor: For secondary winding- copper wire is the best choice. In case of window type CTs primary winding  is not part of CT. For Bar primary and wound primary CTs primary conductor size is decided by the primary current & short time thermal and dynamic currents where applicable.
Insulation Material:  For CTs to be installed in oil filled transformers and Reactors  thermal Class “A” Insulation materials (105oC) viz Electrical grade Paper, Press board cotton based tapes etc are used. For CTs to be mounted in air enclosed chambers -varnish over winding  with  overall PVC  Fiber glass tape insulation or epoxy can be used .

Practice at AU Electro Machines for manufacture of Bushing CTs:
Core Insulation:
Since secondary winding of a CT is always of 1.1 KV Class hence needs electrical insulation for 1.1 KV  class only, Weight and size of core varies very widely ,say from few grams to few hundred Kgs hence while designing core insulation this aspect also is of great importance     
While smaller cores are insulated with few layers of paper & cotton tape, heavier cores are protected with petelled rings and washers wound with cotton tape, as per our standard practice.

Winding:    
Winding normally  is done using Electrical grade Copper wire with Enamel or paper covering.

Overall Finishing:

Over the winding, insulation is provided with the same considerations as over the core and overall finished with a layer of superfine cotton tape. Finally wrapped with a protective film 

Secondary Leads & their marking.

Relevant standards have specified methodology  for CT Terminal marking . This  however is also provided by the client to match with it’s wiring diagram. For proper identification each lead is provide with indelibly marking. For CTs used in Transformer oil suitable non metallic material is used.
CTs for use in oil filled power transformers , to provide flexibility, the leads are made of paper insulated and sleeved stranded copper wire, approx 750 mm long, crimped to winding wire and  provided with suitable size of lug crimped at the end.
(We at AU Electro machines use stranded lead with 1mm paper insulation).

Rating Plate Markings:
A rating plate carrying information as per relevant specification and/or any additional information is provided on each CT.  For CTs for use in transformer oil these are made of Non metallic material.