Choose your region and language



Current transformer COF (25 - 170 kV)

Reliable oil-insulated top-core design current transformer for outdoor use

COF  oil-insulated current transformersfor outdoor installations are based on a top core design. All our current transformers are built-to-order to customer specifications. COF current transformers can meet many applications for metering and protection with a number of dome sizes for up to three independent cores from 25 kV up to 170 kV. This current transformer is available with either porcelain or silicone rubber insulators, with ANSI 70 gray porcelain insulator considered as the standard product. Hermetic sealing of the design is accomplished using a gas cushion above the oil to prevent free-breathing outside moisture-laden air.

The COF demonstrates reliable performance in service with a low field failure rate that is lower than the industry average. This design has been installed all over the western hemisphere from desert to arctic climates.


  • Revenue metering 
  • Protective relaying
  • System control and indication of power flow

Why Hitachi Energy?

  • For revenue metering and protection in high voltage networks, the oil-paper insulated current transformer COF has a long, reliable service reputation in the industry and is versatile for meeting the most demanding applications.
  • Excellent application engineering support to ensure optimum solutions 
  • Designed for diverse environmental conditions
  • Designs specific to critical applications such as wide range metering, capacitor bank monitoring and other demanding uses
  • Head type design allows for higher current application without special coolers and expense 
  • Short primary transition in the dome lends itself to high short-circuit capability
  • Dielectrically stringent production includes hermetically sealed design with 100% partial discharge testing

Brief performance data

Installation Outdoor
Design Top coretype
Insulation Oil-paper
Highest voltage for
25 - 170 kV
Max. primary current Up to 3,400 A
Short-circuit current Up to 120 kA/1 sec
Insulators Porcelain (silicon rubber optional)
Creepage distance ≥ 25 mm/kV (longer on request)
Service condition  
  • Ambient temperature
-40 ºC to +40 ºC (standard)
  • Design altitude
Maximum 1000 m (standard)
  *Other temperatures and altitudes are possible
Accuracy Meets all IEEE metering and protection classes
(0.3%, 0.15%, C100, C200, C400 and C800)

IEC also available on request

Something caught your eye?

Our sales team will get in touch with you