Low-Frequency Drying Equipment for Fully Automatic Transformer Production

Our drying equipment with direct electric low-frequency heating are designed for the fully automatic production of medium and large volumes of different transformers – irrespective of which size or type you are asking for. The high flexibility in batch occupancy is unique not just in the production of distribu-tion transformers.
The parallel introduction of heat through the windings and drying under vacuum allows to achieve shortest process times. The complete process is performed under low vacuum thus ensuring a significantly improved drying quality and reduced depolymerization of the insulation material compared with conventional drying processes.
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Special Conversion

The drying process of the insulation material of distribution transformers under vacuum is significantly accelerated by the use of a low-frequency heating. With specifically developed converters, HEDRICH uses sinusoidal low-frequency heating currents to meet the high requirements for the heating conditions caused by the vacuum.

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Flexible Expandability

The HEDRICH low-frequency equipment concept is expandable from the addition of individual heating units to the upgrade by another production line. So a basic equipment can be subsequently extended without need to replace the essential components like heating units, control system and vacuum pumping unit.

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Checked and Tested

Hermetically closed transformers have to meet increased requirements for the sealing of the transformer housing. The HEDRICH pressure testing and leakage detection equipment checks the seals, their seat, the housing and the welding seams by means of cyclically changing and constant overpressure phases. At the same time the varying overpressures enhance the impregnation quality.

Advantages of low-frequency drying systems

• Special low-frequency converter technology for heating under vacuum
• No air flushing necessary to avoid corrosion
• Minimum depolymerization and aging of the insulation
• Low residual moisture in the insulation
• Very short drying and oil filling times are possible
• Online temperature determination during low-frequency electric heating
• Complete drying and oil impregnation process under vacuum
• Pressure testing and leakage detection equipment for hermetically closed transformers
• Most efficient and fully automated process
• Expandability of equipment to increase production capacities
• Automated database query of process and transformer data
• Stationary and mobile low-frequency systems available


• Distribution transformers
• Medium-voltage transformers
• Small and medium power transformers
• Power transformers after repair in the field

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