Current transformers type JOF are used in high voltage networks within the 24 –550 kV range. They transform high current into standardized values for meters, measuring and protection devices. The active part of the current transformer is located in the head housing.
Based on customer specifications, the optimum design is calculated and the corresponding head housing is determined. The high voltage insulation is based on oil-paper technology. High-grade, PCB-free mineral oil is used. The fine-graded bushing is inside the insulator.
The expansion bellows made from stainless steel is located above the head housing of the current 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 aluminum alloy. These parts can be color-coated on request. All current transformers have either a high-quality porcelain or a high-grade silicone composite insulator. Different creepage distances are available according to the different pollution classes, as specified in the standards. The hermetic sealed housing protects the oil-paper insulation against atmospheric 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 Current Transformers
- Precise electric field control and prevention of local partial discharges through fine graded bushing
- Higher safety through prevention of subsequent arcing
- High operating safety as there are no active parts in the isolator
- Minimum oil volume through optimized design
Easy Primary Changeover
- A clear and easy primary changeover with a ratio of 1:2 pr 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
- The inner side of the instrument transformer is protected against moisture by means of special sealing rings
- All housing 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
- The generously-sized terminal box with a cover that can be opened sidewards, is secured with captive screws. It can accommodate terminal blocks, fuses, spark gaps and sealable covers.
- By default, all terminal boxes have a flange without holes. Cable glands can be pre-installed on request.