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FURNACE TRANSFORMERS

Transformers for Induction-Melting furnaces applications

Capacity up to 10 MVA;
AC primary voltage up to 36 kV;
Reactive power of furnace reactors up to 6000 kVAr.

Specialtrasfo has developed a significant experience in the construction of transformers designed to supply induction-melting furnaces. The induction furnace is generally a single-phase load, therefore the plant is provided with reactors and capacitors to balance the load of the three-phase transformer.
The furnace is sometimes provided with two coils and in this case the feeding transformer is a three-to-two-phase Scott connected one.
We manufacture three-phase stepdown transformers, as well as reactors and Scott transformers.
Transformers are oil-immersed, naturally cooled.
Their capacity ranges from 300 kVA to 10 MVA.




ADDITIONAL INFORMATION

Specialtrasfo developed a significant experience in the construction of transformers designed to supply induction-melting furnaces. The induction furnace is generally a single-phase load, therefore the plant is provided with reactors and capacitors to balance the load of the three-phase transformer.

The furnace is sometimes provided with two coils and in this case the feeding transformer is a three-to-two-phase Scott connected one. We manufacture three-phase stepdown transformers, as well as reactors and Scott transformers.




Transformers are oil-immersed, naturally cooled. Their capacity ranges from 300 kVA to 10 MVA. The supply voltage of induction furnaces must be able to vary widely (in the ratio of three to one or even more), depending on the stage of furnace operation.

 

To obtain this voltage variation the feeding transformer is fitted on the low-voltage side with a no-load tapping selector, developed by Special Trasfo. The latter can be operated when the load is isolated from the transformer, which is electrically connected to the high voltage supply, so as to reduce the number of times the h.v. circuit breaker operates. While the maximum number of tapping selector steps is 12, only 8 or 9 are generally required. Its maximum rated current is 2500 A. The l.v. tapping selector is designed for frequent operation and is mechanically operated by a motor drive unit.

For smaller transformers a cover-mounted drive unit is provided, whereas for large transformers the motor drive unit is mounted on the shorter wall of the transformer tank. Both drive units are provided with limit switches to prevent overrunning and a safety circuit to avoid tap-changing, hen the furnace is energized; besides, manual control is made available for emergency use.

Oil conservator, Buchholtz protection relay and dialtype thermometer are standard features and fittings of these transformers. An off-load tap-changer on the h.v. side can be provided if required.

Furnace reactors are single-phase, oil-immersed, naturally cooled. Their reactive power ranges from 150 to 6000 kVAr. Such reactors are iron-core type. The core is built up of cold-rolled oriented-steel laminations and provided with several air gaps within the magnetic field of the windings. We also manufacture voltage-regulating transformers designed to supply glass furnaces. Each couple of the six furnace electrodes is supplied by a single-phase voltage-regulating unit. The three units are delta connected on the primary side. The secondary side is fitted with a no-load tapping selector to obtain coarse voltage regulation, and a series booster transformer, supplied by a voltage-regulating transformer to obtain the on-load fine regulation of the output voltage.