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Combined Instrument Transformers

Combined instrument transformers type EJOF are used in high voltage networks within the 24-170kV range.  They transform high voltage and high current into standardized values for meters, measuring and protection devices.

The inner construction of  a combined instrument transformer is similar to the construction of the current and voltage transformers.  The current transformer is located in the head and the voltage transformer in the bottom housing of the combined instrument transformer. The fine-graded bushings are inside the insulator.

The high voltage insulation is based on oil-paper technology.  High grade PCB-free mineral oil is used.

The expansion bellows made from stainless steel is located above the head housing of the combined instrument transformer.  This unit acts as volume compensation for the oil in case of temperature variations.  The oil level is indicated by a mechanical system in the window of the  bellows cover.

Advantages of combined instrument transformers

 

  • Reduced transport costs with one unit instead of two
  • Less space needed with just one footprint
  • Lower material costs due to a reduced number of supports and fewer primary connections
  • Lower installation effort as only one unit has to be installed instead of two

Easy primary changeover

  • A clear and easy primary changeover with a ration of 1:2 or 1:2:4 is available
  • The primary changeover is adjusted with one metal plate at one side of the head only
  • No need to dismount or move the primary connections during adjustment

 

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Excellent protection against moisture

  • The inner side of the instrument transformer is protected against moisture by means of special sealing rings
  • All housings are designed with a drainage area to protect the sealing surfaces of the housings against rain, significantly reducing crevice corrosion
  • The housing elements are connected with special stainless steel screws, designed in such a way that no humidity can enter the screw hole

Installation-friendly terminal box

  • The generously-sized terminal box with a cover that can be opened sidewards, is secured with captive screws.  It can accommodate terminal blocks, fuses, surge arrestors, additional auxiliary contacts, spark gaps and sealable covers.
  • By default, all terminal boxes have a flange without holes.  Cable glands can be pre-installed on request
  • An additional terminal box can be supplied upon request