Transformer Construction

Transformer Construction

The construction of a transformer is simple since there are no moving parts

(i.e. it is a static device). The transformer shown in figure below consists of the

following main parts:

(i) Magnetic core

(ii) Windings

(iii) Conservator tank

(iv) Transformer oil

(v) Radiators

(vi) Bushings

(vii) Breather

(viii)Container

(ix) Buchnolz relay

(i) Magnetic core: It is made of thick silicon steel laminations coated with oxide layer to reduce the iron losses. The thickness of lamination is 0.35mm for 60Hz operation and 5mm for 25Hz operation. It is the common part between the twowindings and helps to link magnetic flux with both the windings.

(ii) Windings: A conventional transformer has two windings. The winding whichr eceives the electrical energy is called the primary winding and the winding which delivers the electrical energy to the load is known as secondary winding. The two windings are electrically separated but magnetically coupled through themagnetic core. The windings are usually made of copper or aluminum with enamel coating. The low voltage winding carries high current so the wire diameter is more than the high voltage winding.

(iii) Conservator tank: It is an air tight cylindrical drum containing transformer oil,placed at the top of the transformer and connected to the transformer tank by a pipe. The main tank is completely filled with oil. The oil in the transformer tank expands due to increase in temperature and contracts when the temperature or load reduces. The function of the conservator tank is to take up contraction andexpansion of oil without allowing it to come in contact with outside air and moisture.

(iv) Transformer oil: It is a mineral oil, obtained by refining crude petroleum used for the following purposes.

• Acts as an insulating medium between windings and tank.

• Protects the tank from dirt and moisture.

• Carries away the heat generated in the core and coils i.e., it is used for cooling purpose.

(v) Radiators: Radiators help in cooling the transformer oil by increasing the surface area. The number of radiators required is independent on the capacity of the transformer and rate of cooling.

(vi) Bushings: The bushings are employed for insulating and bringing out terminals of the winding from the container to the external circuit. Number of bushings is equal to number of phases. These are generally of two types

(a) Porcelain type, which are used for voltage rating up to 33 kV.

(b) Oil filled or Condenser types, which are used for voltage higher than 33 kV.

(vii) Breather: Transformer oil should not be exposed directly to the atmosphere because it may absorb moisture and dust from the environment and may lose its electrical properties in a very short time. To avoid this problem, a breather is provided on the top of the conservator. It mainly consists of a silica-gel. The silica￾gel absorbs the moisture content of air so that the oil contamination can be prevented. The silica-gel which is blue in color turns pink when it absorbs moisture fully. It is replaced periodically as a routine maintenance.

(viii) Container: Cast iron or cast steel air tighted containers are provided with radiators. The container contains the core windings and oil.

(ix) Buchholz relay: It is provided in between conservator tank and transformer tank, to protect the transformers from incipient faults. It is a gas actuated relay. It operates on the generation of gases due to any internal fault in the transformer. In incase of severe internal fault it gives an alarm and disconnect the transformer from supply mains.