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Special projects

Retrofit of transformer ТРДЦН-160000/220

When inspecting the active part of the transformer after the accident deformation of the internal LV windings, insulation breakdown and local rod burning were revealed. Safety transformer tripping was activated in the standard mode.
The reason for the low dynamic resistance of LV windings was semi- spiral design on the soft cylinder.

Produced recalculation, proposed the following measures: to manufacture the spiral winding on a reinforced paper-bakelite cylinder with impregnation and baking.
Regarding the weight and size characteristics of the transformer and high equipment capability TMX of the customer, it was decided to carry out the retrofit ТРДЦН-160000/220 in field.
The design was executed; windings were manufactured and delivered as well as the necessary for the upgrade components. Installation supervision was provided. Further the retrofit was continued: the tap changer and the regulating winding were replaced.


  • Increased reliability of the power supply company.
  • Shipping cost of windings cost to the customer 15 times less than it would cost to transport the transformer to the repair factory (not including associated costs).
  • Increased maintenance intervals 10-fold (from 50 to 500 thousand taps) due to application of a modern tap changing device.
  • The customer received a transformer with a 3-year warranty and statutory service life of 25 years.

Manufacturing of transformer ЭОЦНК-16000/10

On one of the ferroalloy plants to increase power electric furnace unit (EFU) and improving its efficiency, specialists of “Delta Trafo” consistently made a number of upgrades on the feeder transformers   ЭОЦНК-16000/10 to increase rated capacity from 5.5 MVA to 7.0 MVA, further on up to 7,650 MVA. Currently the level of 9.2 MVA (type EOTSNK-16000/10) is achieved.
By optimizing the operating LV range and application of the series capacity device (SCD), EFU is working with cos φ = 0,9-0,96.  Thus the best-in-class specific energy consumption parameters per ton of salable product were achieved.
Since 2006 transformers EOTSNK-16000/10 were put into full production.


  • A significant increase of economic performance of EFU (from 3.5 to 9%) was achieved.
  • Through the application of a modern tap changing device the service intervals were increased from 10 to 600 thousand taps.
  • The overall decline in hot idles of EFU was achieved by improving the reliability of transformers.
  • The layout of the transformer provided interchangeability: connecting to the LV circuit and the cooling system without the reconstruction of the cell.

Manufacturing of transformer ТМН-400/10

At the enterprise of the Rostov region the manufacturing facility was located 12 km from MSDS. Power supply was provided through a 10 kV cable line. In connection with the manufacture development and the increase of power consumption the losses in the line increased by 2 times, the voltage deviation from rated on the current-using equipment inputs - up to 23% at the maximum allowable ± 10%. An attempt of using local voltage stabilizers, as well as uninterruptible power supply sources didn’t solve the problem. The reconstruction of the cable line required substantial investments.

Delta Trafo Ltd. developed a special transformer, combining the advantages of a dividing transformer and auto transformer. When the load increases, due to losses in the cable line, the input voltage changers from 8.0 kV to 10.5 kV, but thanks to the proposed technical solution, consumers are supplied with voltage of 0.4 kV ± 5%, which corresponds to GOST 21128-83 . The regulation is automatic under load not demanding the participation of the personnel.


  • Operation of the existing cable line in the next 5-7 years, with continuing growth of energy consumption.
  • Low cost of a transformer operation. The operating life of the tap changing device is 700,000 operations or 7 years before the first maintenance.
  • Malfunction of office equipment and computers are excluded due to low supply voltage.
  • Operation stabilization with high coefficient of efficiency of electric equipment.

Retrofit of transformer ЭОЦН-8200/10

The transformer worked for more than 40 years. Frequent outages of the on-load tap changer (TC) RNO-17 led to a the furnace shutdown and as a result to the disruption of the production plan. The customer asked about the statements of reasons of buying a new transformer.

During conducting defective it was revealed that insulation due to the natural aging had lost its protective properties. The Contact Group and power drive station (PDS) were no more suitable for further use. The tank and the magnetic core of the transformer were in a satisfactory condition and could be used further on.

A project for the transformer retrofit was devised. New winding (HV, LV, teaser winding, and reactor), HV and LV circuits were made; also a new OLTC was installed.


  • A refurbished transformer with 25-30 years operation period and 12-months warranty.
  • Minimum furnace downtime for transformer maintenance caused by TC device. The first revision of TC device is in 500 thousand tap changings.
  • Interchangeability of transformers is retained.
  • Modernization deadline is 2.5 months (manufacturing of a new one is 6 months), the cost is about 60% of the cost of a new one.

Retrofit of transformer 80 MVA

The company has asked one of the Russian metallurgical companies with the request to determine the current state of transformer TMY-41 (manufactured by ABB) and the possibility of further safe operation. Technical documentation for the transformer was absent.

During the on-site diagnostics it was revealed: the active part of the transformer is in a satisfactory condition, the TC device has ended its lifespan. To extend the time of no-failure operation, the TC device must be replaced and part attachable equipment - the work of this level of complexity is required to execute on a specialized enterprise.


  • Extend the transformer life by 20-25 years.
  • Replacement of worn out components (equipment) minimize the risk of accidents.
  • Lower operating costs due to a TC device with an increased resource.
  • The possibility of commissioning in a short time. Performance time is several times less than for the manufacture of a new transformer of the same capacity.