Inductive Transformer SF6

Voltage transformers type EGF are used in high voltage substations within the 245 –550 kV range. They transform high voltage into standardized, equivalent values for meters, measuring and protection devices. The active section of the voltage transformer is located in the pressure-resistant foot housing. The iron core is on earth potential. The secondary windings are directly positioned on the iron core. The secondary windings are passed through an SF6 /air bushing into the terminal box. The high voltage connection is implemented via a short-circuit proof aluminum pipe. The electrical field distribution along the insulator is optimized by a special layout of the control electrode inside the silicone composite insulator. The housing components consist of helium- tight, corrosion-resistant cast aluminum. All housing components under pressure are individually type-tested according to applicable pressure vessel standards. The SF6 gas density is monitored by a temperature- compensated gas density monitor with alarm contacts. The special design means the function of the gas density monitor can be checked without dismounting it. A corrosion-resistant metal rupture disc, protected by a metal cover, is located at the top of the housing and ensures safe pressure relief in case of error. The generously designed terminal box is equipped with a cover that opens sidewards. Pure SF6 gas is used for ambient temperatures up to -40°C. The transformer is filled with a mixed gas for lower ambient temperatures up to -60°C.
Advantages
■■ High operating safety through optimized current distribution in the field-controlled bushing
■■ Low weight and high creepage resistance through the use of composite insulators
■■ Special iron core provides protection against any Ferro resonances
Excellent protection against moisture
■■ Precise function is ensured through temperature compensation down to -60°C.
■■ The density monitor is equipped with two alarm contacts to signal a pressure loss.
■■ The density monitor can be checked without dismounting it via a special test connection.
■■ A solid metal cover protects the density monitor against mechanical damage and direct sunlight.
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, additional auxiliary contacts and sealable covers.
■■ The terminal box is equipped as standard with a blind flange. Cable glands can be installed on request.
■■ The terminal box has a protected ventilation aperture to prevent condensation.

Inductive Transformer Oil-Paper

Voltage transformers type EOF are used in high voltage networks within the 24 –245 kV range. They transform high voltage into standardized values for meters, measuring and protection devices.
The active part of the voltage transformer is located in the foot housing. The high voltage insulation is implemented in oil-paper technology. To achieve this, a high quality PCB free mineral oil is used. The fine graded bushing is inside the insulator.
The expansion system is located in the head of the voltage transformer. This unit acts as volume compensation for the oil in case of temperature variations. For voltage transformers of 24 –72 kV, a highly flexible, temperature- resistant membrane made from fluoroelastomers (VITONR) is used. Voltage transformers > 72 kV have an expansion cell made of stainless steel. The oil expansion is indicated by a mechanical system in the window of the bellows cover. All metal housings and flanges are made from a corrosion resistant aluminum alloy. These parts can be color coated on request.
All voltage 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 oilpaper insulation against atmospheric influences. The generously sized terminal box has a cover which can be opened sideward. 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
■■ Protection of the secondary winding from transient overvoltage in the high-voltage network through capacitive coupled shielding
■■ Protection against occurring Ferro resonance through low operating inductance in the iron core
■■ High operating safety as there are no active parts in the insulator
■■ Minimum oil volume through optimized design
Fine grade bushings
■ The fine graded bushing is designed to ensure an optimum distribution of the electric field.
■ The bushing is fixed in a way, that it is short-circuit-safe and secondary arcs are prevented.
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.