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Oil Type Distribution Transformer

Yağlı tip dağıtım transformatörleri 36 kV gerilim seviyesine ve 5000 kVa gücüne kadar giriş ve çıkış gerilimlerini istenilen oranlarda değiştiren, işletme sırasında oluşan ısının transformatör yağı ile atılarak izin verilen çalışma sıcaklığını aşmam

Oil-type distribution transformers are transformers which change the input and output voltages up to 36 kV voltage level and 5000 kVa power in desired proportions and provide cooling by means of transformer oil in order not to exceed the permissible operating temperature by eliminating the heat generated during operation with transformer oil. This type of transformer can be examined under 2 (two) main headings with hermetic and expansion tanks:

Hermetic Oil Type Distribution Transformers

They are produced in a power range of 25 - 5000 kVA, up to 36 kV high voltage level, with three or single phase, oiled, naturally cooled (ONAN), idle tap changer or automatic tap changer under load, so that they can be used both inside and outside. Hermetic oil type distribution transformers are manufactured by filling the oil under vacuum by balancing the oil pressure and atmospheric pressure at the desired temperature and not to allow the cooling oil to come into contact with the atmosphere.

As a result of changing oil pressure due to thermal changes in hermetic oil type distribution transformers, internal heat is controlled by natural expansion and contraction of boiler wave walls. Mechanical design and manufacturing is made to withstand these effects.

Hermetic oil type distribution transformers have lower heights compared to transformers with expansion tanks. Therefore it can be used in smaller areas.
Since the oil does not come into contact with the atmosphere in hermetic transformers, it does not require oil change in certain periods as in transformer with expansion tank.

Transformer with Expansion Tank

Transformer with expansion tank is the same as hermetic transformers with core and coil structure. The dimensions of the expansion tanks of such transformers are designed and manufactured as a result of calculations in order to store the expansion of the oil whose volume increases with temperature.
Since the transformers with expansion tanks are open to the atmosphere, the oil pressure is changed due to thermal effects, and the air exchange is provided by taking the moisture of the air through the Silica gel (air dryer) in the transformer tank.
As a result of the air exchange caused by the temperature differences due to the load, the expansion tank transformer which is put into operation loses its Silica gel property  in time and causes humidification of the oil and deterioration of its structure. For this reason, it is necessary to carry out maintenance such as changing the silica gel and measuring the puncture voltage by sampling the oil.

Windings for distribution transformers
Copper or aluminum is used as conductor in low voltage windings. The windings are made of sheet or rectangular paper or nomex insulated wire. If the windings are made of sheets, shellac paper (DDP) coated with resin is used as layer insulation.

Copper or aluminum conductor is used in high voltage windings depending on customer request. The turbines are wrapped with computer-controlled fully automatic machines. Due to the strip insulation paper (craft or thermally improved shellac), the floor insulation is wedge-shaped. The special structure of floor insulation increases the resistance against impact voltage; It helps to create coils without gap, solid and excellent quality.

Nucleus (core)
The cores of the transformers are made of cold-rolled, oriented siliceous sheets. The cores are produced using first class quality sheets. The core sheet selection is made according to the idle loss values requested by the customer. The sheet is stacked without burr on modern cutting machines manufactured by George. The cores are produced with or without step-lap, over-lap, 90º cut holes.

Active Part and Cover
The core, coil and top cover assembly is designed to increase resistance to short-circuit forces. The top cover covering the active parts of standard transformers is mounted to the tank with bolts. Another application is the installation of the active part directly into the tank. The connection parts of the top cover, high voltage insulators and arc horns are made of stainless steel or rust-resistant, special paint-coated materials. Insulators (bushings) accessories, protection box or cable box can be placed on the top of the cover or on the side walls of the transformer according to customer request.

 

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Tank
Tanks and top covers are made of mild steel. The cooling surfaces of the distribution transformers consist of wave walls. Wave walls also form the side surface of the tank. The base plate, sides and frame are welded tightly.
In transformers up to 4000kVA, wave wall can be used as cooling surface. It is also possible to use radiators as cooling surfaces. After welding, each tank must undergo an oil tightness test. Therefore, each tank is put under pressure after it is produced. Finished tanks and top covers are sandblasted in accordance with DIN standards. If the customer has special requests or there are various demands for shot blasting, ELTAŞ A.Ş. Company has the mechanism to meet these requirements. It is possible to take the bushings in the top cover in a box made of sheet metal according to IEC 60144.
According to BS 2562, the cable box can be attached to the sides of the tank.

Painting
The transformers are in RAL 7033 color as standard. Transformer tanks are painted by immersion and spraying method. Dyeing method is chosen according to customer request and working conditions of transformer. ELTAŞ A.Ş.  Company  we can offer transformer with different film thickness or different colors in different applications (zinc plated) according to customer request. In addition, hot-dip galvanized tanks can be manufactured if desired.
Drying and Oil Filling
The active part of the transformers (core, coil, cap) is dried in the ovens under high vacuum. The drying process varies according to the type, power and voltage of the transformer. Oil filling is done under high vacuum.

The main accessories used to protect transformers are as follows:
1. Oil Level Indicator
The magnetic oil level indicator is used to monitor and control the oil level in the expansion tank. Magnetic oil level indicator gives alarm and trip signal in case of sudden changes in oil level.
2. Air Dryer
Air dryers are used in transformers with expansion tanks. The air dryer is connected to the expansion tank. With the help of silica gel, moisture and dust are kept in the expansion tank. The amount of silica gel depends on the amount of oil in the transformer.
3. Oil Temperature Display (Indicator)
The oil temperature gauge placed in the thermometer pockets welded on the lid or on the sides of the tank monitors and controls the top temperature of the oil. It can be with maximum indication, without electrical contact or single or double electrical contact. If the temperature exceeds the estimated values, the contact thermometers give an alarm or trip signal.
4. Buchholz (Gas collection and Alarm) Relay
The Buchholz relay collects gases generated by low and high intensity discharge and arcs within the transformer. It is used in transformers with expansion tanks. The relay can be single or double contact. If a certain amount of gas is collected in the Buchholz relay, it activates both the alarm and the trip signal. In addition, the Buchholz relay emits an alarm signal at a low oil level. The Buchholz relay detects faults such as overheating and signals to prevent the failure from growing.
5. Pressure Relief Valve
Even if a hermetic protection relay is used in transformers, a pressure relief valve is also used. The pressure relief valve serves to relieve the rising pressure in the transformer.
6. Hermetic Protection Relay
For hermetic transformers with a power of 630 kVA and above, a hermetic protection relay is used. This relay includes the functions of the oil gauge, thermometer gauge, Buchholz relay as well as the pressure relay.

In addition, additional accessories such as winding thermometers, digital thermometers, gas collecting units can be installed in oil type power transformers according to customer requirements.

 

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