TMG series (hermetically sealed oil) power transformers rated for 16-2500 kVA, voltage class 6-10-20/0.4 kV, are encapsulated in corrugated transformer tanks filled with degassed oil contained in a vacuum chamber. The corrugated tanks provide the necessary cooling surface and do not need removable coolers.
The design of TMG transformers involves sealed tanks without expanders. The expander-free design ensures that the oil does not come in contact with the environment, thereby preventing humidification, oxidation, and sludge formation. Thanks to the above, the dielectric properties of the oil are preserved during the entire service life.
The voltage is controlled by changing the HV winding taps with a no-load tap changer (NLTC) in manual mode with the load and voltage removed.

“Transformer” hermetically sealed oil power transformers are designed specifically for energy-intensive customer of large cities. They are compact in size and highly reliable. TMG “Transformer” is an excellent solution for refurbished substations and newly constructed power facilities.11

Advantages
— compact
size; — cost-effective;
— improved specifications; 
— overload resistance; —
minimum operating costs; 
— safety.

Design features
 The magnetic core of the transformer is assembled according to the step-lap stacking principle from plates made of cold-rolled electrical steel. To date, this is the most advanced technology for manufacturing magnetic core transformers. High-grade steel (grade E3409, E3410, E3411) used for the manufacture of the magnetic circuit reduces no load losses and noise coming from the transformer. 

  
HV windings — multilayer cylindrical windings made of copper/aluminum wire with paper or enamel insulation. The interlayer insulation cone-laying technology increases the insulation strength, thus increasing the service life of the transformer. 

  
The LV windings are made of copper/aluminum wire (rated for up to 250 kVA) and aluminum/copper strip (rated for over 250 kVA). The strip allows reducing axial stresses that occur during short circuit by about 10%. The advantages of windings made of tape also include high dynamic resistance to short-circuit currents, significant simplification of the cooling channel design, more uniform distribution of heat along the winding, uniform distribution of current density along the winding, and small difference of electric potentials between adjacent turns. LV winding taps — busbars or rectangular wires. 

The transformer corrugated tank is made of high-grade steel (1.2 mm thick steel sheets) by automatic welding of corrugated boards using a robotic plant manufactured by Motoman. The design of the tank has a plug for draining the oil. All tanks undergo pressure testing – they are kept under pressure for 12 hours. 

  
The active part is attached to the transformer cover, which allows you to quickly install it or remove it from the tank without removing the HV and LV bushings.
The sealing gaskets are made of composite material called rubber cork, which has a longer service life compared to rubber especially at subzero temperatures. 
The design of the tap changer ensures rigid fixation of the tapping steps, which prevents the changer from going into intermediate positions. 
The design of the swivel wheels and feet allows you to move the transformer in both longitudinal and transverse directions.
The transformer is grounded on both sides. 

  
The transformers are filled with purified degassed (under vacuum) transformer oil with a breakdown voltage in a standard surge arrester of not less than 45 kV.