EJOF (24-170) kV


  • Oil-paper insulated
  • Guaranteed accuracy over entire service life
  • Explosion-tested casing
  • Fine-graded bushing
  • Low space requirements for installation

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

General description

Combined instrument transformers type EJOF are used in high voltage networks within the 24-170 kV range. They transform high voltage and high current into standardised 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 transformer. 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.

All metal housings and flanges are made from a special aluminium alloy. These parts can be colour coated on request.

All combined instrument transformers have either a high-quality porcelain or a high-grade silicone composite insulator. Different creepage distances are availab- le according to the different pollution classes, as specified in the standards.

The hermetic sealed housing protects the oil-paper insulation against atmos- pheric influences.

The generously sized terminal box has a cover which can be opened sidewards. This allows easy connection of the secondary cables. The terminal box has a flange without holes by default. Cable glands, circuit diagram and individual safety instructions can be preinstalled on request.

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
primary changeover
  • A clear and easy primary changeover with a ratio 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.
Excellent protection against moisture
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 drain-age area to protect the sealing surfaces of the housings against rain. This significantly reduces crevice corrosion.

  • The housing elements are connected with special stainless steel screws. They are designed in such a way that no humidity can enter the screw hole.
Installation-friendly terminal box
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 preinstalled on request.

  • An additional terminal box can be supplied on request.
combined transformer type EJOF
Technical data
combined transformer type EJOF
Type EJOF24
StandardIEC / IEEE
Highest voltage for equipmentkV243672.5123145170
Rated power-frequency withstand voltagekV5070140230275325
Rated lightning impulse withstand voltagekV125170325550650750
FrequencyHz16.7 / 50 / 60
Primary rated currentA≤ 5000
Secondary rated currentA1 / 5
Rated short-time thermal current [Ith]kA / 1s≤ 63
Rated dynamic current [Idyn]kA≤ 160
Accuracy class CT part0.1-3; 0.2S; 0.5S; P; PR; PX; PXR; TPX; TPY; TPZ
Accuracy class VT part0.1-3; 3P; 6P
Rated thermal limiting output VT partVA≤ 1500≤ 3000
Max. simultaneous burden (cl. 0.2)VA200300
Max. number of CT cores7
Max. number of VT windings 5
Height of unit*Amm159115911791248426592959
Height to primary terminal*Bmm114511451345203822032503
Depth of unit including terminal boxCmm526526526710710730
Depth of unit baseDmm360360360500500500
Width of unit baseEmm360360360520520520
Distance between screw holes at baseFmm310310310450450450
Min. creepage distance*mm104010401900308037704394
Approximate weight*kg295295470500515550

*with standard composite silicone insulator, creepage distance 25 mm/kV