Oil-immersed transformers

Technical characteristics


«SVEL Power Transformers» Plant evelops and produces different type of transformets such as:

  • Power oil-immersed transformers for an objects of power production,electrified transport and industrial enterprises' substations, power is up to 630 MVA, voltage class is up to 750 kV;
  • Power alterning-current oil-immersed transformers for electricity supply of railroad;
  • Converter transformers for different industries.
Series, type Connection group & phase angle HV MV LV Oil weight Total weight
1 ATDTN-63000/220/110 Yn/∆-0-11 230 121 6,6; 12,0; 36.0 39,4 115,0
2 ATDCTN-63000/220/110 38,0 109,0
3 ATDCTN-125000/220/110 48,4 158,3
4 ATDCTN-200000/220/110 60,0 220,0
5 ATDCTN-250000/220/110 75,0 280,0

Маgnetic circuit

The Маgnetic circuit is made of a cold-rolled grain-oriented electrotechnical steel with low specific losses. Such steel allows to reduce the transformer no-load losses up to 40%. «SVEL Power Transformers» Plant realizes the full steel processing cycle. Cutting of the electrotechnical steel is carried out on automated slitting and cut-to-length lines with the high cut accuracy keeping the steel electromagnetic characteristics.

Cutting and stacking «step-lap» tеchnology and semiautomatic banding effecting the magnetic circuit tightening quality provide low level of no-load losses and noise.

Transformer windings

The power transformer windings are made of copper winding wire. The high-precision automated winding machines for horizontal and vertical winding process with automated forming of wire passage exclude a human-factor aspect. Application of transposed wire increases the winding electrodynamic & mechanical strength at the short-circuit and reduces the added losses.

The winding pressing is carried out in convection vacuum tunnel ovens in three steps: cold pressing, hot and final pressing under vacuum. The constant winding prepressing under drying provides the insulation shrinkage absence and reliability of the transformer operation for the whole service life without capital repair.

Active part assembling

All zones of the power transformer assembling are equipped with movable scaffoldings on air cushion. Up-to-date technical solutions used in designing make the added losses reduced up to 1.5 times. Drying of the асtive part in kerosene vapour ovens and in convection vacuum ovens accelerates drying, satisfying requirements to the moisture content in insulation.

Final assembling

Then the асtive part with tap changer is immersed into the tank which is filled with oil. Tаnks, designed for each transformer, are made by «SVEL» Group at its own production where they undergo pneumatic tests (under vacuum and excessive pressure). Each tank is filled with a necessary oil volume at the automated oil filling station. Control assembling and marking of dismantled units exclude design errors and simplify transformer mounting.


The main insulation is made of high quality transformer cardboard or insulation material completely impregnated with oil to restrict inner partial discharges because of air blisters. To provide the electrodynamic & mechanical strength the winding spacers are made of the compacted transformer cardboard. When designing the insulation is calculated according to the finite-element method.


SVEL transformers are cooled mainly with removable panel-type radiators providing a reliable cooling system with low running costs. To increase the radiator operating efficiency using of fans is possible (oil norm/air force cooling system). Upon request oil-air or oil-water radiators can be used.

Cooling process regulation

The cooling process regulation mainly depends on the cooling system and transformer design. The cooling system elements are selected according to high quality and durability. All necessary signal contacts are in a standard scope of supply.

We design and manufacture transformers with different cooling systems according to the customer requirements:

  • ONAN: Oil Norm / Air Norm;
  • ONAF: Oil Norm / Air Force;
  • OFAF: Oil Force / Air Force;
  • ODAF: Oil Direct / Air Force;
  • OFWF: Oil Force / Water Force.

Transformer monitoring system

Upon customer request the additional functions of control, monitoring and transformer diagnostics can be implemented, increasing safety of power facilities, power transformers of «SVEL»Group:

  • Control of chiller condition and the cooling system efficiency;
  • Calculation of time worked out by each oil pump and fan;
  • The ambient temperature control;
  • Temperature control of the cooling system input and output;
  • Oil moisture control;
  • Аnalysis of gas dissolved in oil;
  • Control of the actual OLTC condition using analogue sensors or according to the drive turning angle;
  • Tape changer commands forming and control in OLTC manual mode;
  • The OLTC drive current control;
  • Detection of the OLTC actual resource depending on the transformer load and inspection time;
  • Detection of faults like «self-act», «switchover failure», «sticking», «synchronization lost»;
  • Winding temperature control and the insulation thermal wear estimation;
  • Oil temperature control in OLTC box;
  • Control of partial discharges and insulation of inputs.

The transformer monitoring system is equipped with sensors measuring the primary parameters, the primary parameters processing units, archiving and visualization blocks, control and exchange with upper level system, integration into the automatic control system.

Our products are equipped with monitoring systems of the following companies: QUALITROL (TG/12), KELMAN (TRANSFIX), MR (TAPGUARD), CE (HYDRAN), МТЕ (HYDROCAL), Vibrocenter (TDM), research and development center «МIRONOMICA» Co ltd, Intera, АВВ, Hyundai.

Оne of the most important monitoring system consists in comparison of the calculated and actual winding working temperature. It guarantees the transformer operation keeping parameters within the limits specified in the technical requirements, exception of emergency shutdown due to long-term control of the transformer state changing, it enables load safe optimization without transformer switching off. Emergency signal is given in emergency situations.

Monitoring system of the OLTC condition enables the transformer reliability increase due to the fault detection system, estimation of the OLTC technical condition under the automatic control system, saving of statistic and analysis data, prognostication, on-line diagnostics.

Upon customer request we can equipped our products with any monitoring systems to meet the customer requirements.

Tests and transportation

The design element quality control is carried out at each manufacturing step. The final routine and type tests are made at the automated test field. The «SVEL-power transformers» test laboratory can do the following tests:

  1. Electromagnetic tests,
  2. Dielectric tests,
  3. Partial discharge measurments,
  4. Insulating strength measurments,
  5. Noise-level measurments,
  6. Temperature-rise tests.

Control of the winding impulse strength is carried out for constant transformer quality improvement.

Transformer undergoes testing at each manufacturing step:

  • magnetic circuit assembling;
  • active part assembling before outputs soldering;
  • active part assembling after outputs soldering and tap-changer connection;
  • final transformer assembling.

When assembling the tests are performed from mobile test posts. All received data are recorded in the central computer, analyzed and displayed in the test report and passport.

Impulse voltage generators up to 2000 kV discharge value are used for high-voltage tests. Test equipment and qualified personnel enable transformer testing in strict compliance with national and international standards ISO, IEC, ANSI and GOST.

Тrаnsportation and mounting

We transport by railway and motor transport, developing optimum delivery schemes all over Russia and CIS countries.

Service department organizes and makes:

  • Installation supervision (technical manual and engineering supervision onsite at the customer objects);
  • Construction-and-assembling operations;
  • Commissioning;
  • Repairing;
  • Servicing (tests, diagnostics, mоnitoring);
  • Training of the customer personnel.

We provide consultative technical support of the customer under execution of works and at the equipment operation.


«SVEL— Power transformers» Plant provides the full quality warranty on the manufactured equipment:

  • 3 years warranty from the commissioning date but nor more than 3,5 years from the date of the transformer shipment from the manufacturing plant;
  • service life — 30 years.

There are 3 main reasons, why oil-immersed transformers by «SVEL— Power transformers» are worth buying:

  1. Reduced no-load losses;
  2. Reduced exploitation cost due to absence of the capital repair necessity in 12 years of operation;
  3. Increased electrodynamic strength of the transformer windings.

Download Oil Immersed Transformers Leaflet