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Extended Range



Extended Range Current Transformers

Series 24

The series 24 Extended Range CT's are specified and used by almost all Utilities in Australia.These CT's come with NATA certified Test Reports and have individual Serial Numbers for traceability.

AS 60044.1 specify limits of current error and phase displacement for special application extended range current transformers which have been designed to match the load range capacity of long range kWh meters. The usual EDMI Mk10A/Mk6E/Mk11 current transformer operated meter is rated at 4/20 amps and, for example, if operated by a Type ‘S’ 200/5 current transformer will accurately register a current loading up to 400 amps.

In accordance with AS 60044.1, special application extended range current transformers are designated by class accuracy followed by the letter ‘S’ and rated extended primary current 120% or 150% or 200%. For types ‘S’, ‘T’ and ‘W’ their class accuracy is therefore shown as ‘0.2S’ or ‘0.5S’ and extended range primary current is up to 200%.

In addition to reducing the stock-holding of CTs there is also a major advantage that CT ratio changes are reduced or eliminated. It is recognised that ratio changes, coupled with the associated change in the meter multiplier (or register) and the amended accounting procedure are a major cause of errors in levying charges.

The cost of a CT/CT ratio change can be significant, and even for a small electricity authority can amount to some hundreds of dollars.

These three ratios of CT can cover everything from 2 amps to 3000 Amps!

Extended range CTs have also proven to be of particular benefit in seasonal industries, e.g. milling, where there is a wide variation between minimum and peak activity.

A GRAPHICAL COMPARISON, showing ranges of accuracy of:

  1. Conventional CTs
  2. WF Energy Controls Extended Range CTs
Extended Range Current Transformers - Loading Graph

Materials & Construction

Extended Range Current Transformer - Type S


Epoxy Resin


Fibreglass filled polyester resin


Round clear polycarbonate


Brass, nickel plated


6mm, brass, silver plated with silver plated nuts.
Spring washers - stainless steel.


Type S

Anodised aluminium

Type T

Zinc plated steel

Type W

- Low base - Zinc plated steel
- High base - Anodised aluminium


Bus bar clamps


Tunnel terminals, low base/high base (Type W)

Extended Range CT Types

Extended Range - Current Transformer - 200/5

Type S

Extended Range - Current Transformer - 800/5

Type T

Extended Range - Current Transformer - 1500/5

Type W

Type S: 200/5


Extended Range - Current Transformer - Type S - Dimensions

Type T: 800/5


Extended Range - Current Transformer - Type T - Dimensions

Type W: 1500/5


Extended Range - Current Transformer - Type W - Dimensions