Power Transformer

The core supports the winding and provides a low reluctance path for the magnetic flux. It is made by stacking and laminating thin steel sheets. The sheets are insulated from each other by a coating. To reduce eddy current losses and hysteresis losses, the iron or steel sheets are less than one millimeter thick, and their carbon content is maintained below 0.1%. Eddy current is further reduced by alloying the steel with silicon. The vertical sections of the core in which the winding are carried are referred to as the limbs, while the horizontal sections of the core that couples the limbs are referred to as the yokes.

2.Winding in Power Transformers

The winding are made up of copper or aluminum conductor coil with a specific number of turns. Copper is the preferred material since it offers high electrical conductivity and high ductility; these properties reduce the amount of winding and make the material easier to wrap around the core.

A transformer consists of at least two winding the primary and the secondary winding. The primary winding is the winding in which the input voltage is applied, while the secondary winding is the winding that receives the output voltage. The primary and the secondary winding in a phase of a transformer can play as the high voltage (HV) winding or the low voltage (LV) winding:

HV Winding The HV winding has a greater number of turns and consists of a thinner conductor than the LV winding.

LV Winding The LV winding has a fewer number of turns. It consists of a thicker conductor than the HV winding since a higher current is carried in the LV winding.

3.Insulating Materials

Insulating materials are used to isolate the winding from the core, the primary and the secondary winding, and each turn of the winding. These materials protect the transformer from damage. Transformer insulators should have high dielectric strength, good mechanical properties, and can withstand high temperatures.

Paper and press-board can be used as an insulator (i.e., dry-type transformers); however, they have limited service lives and require frequent replacement as these materials can degrade. Hence, transformer oils are more common compared to solid insulating materials. They provide enhanced insulation between conducting parts, act as a coolant for the coil and winding assembly, and have fault detection features. Hydrocarbon mineral oils consisting of aromatics, paraffin, naphthalene, and ole-fins are used as transformer oils. Oil contamination must be prevented to preserve the oil's dielectric properties and insulating features

4.Tap Changer

Tap changers are devices that regulate the transformer’s output voltage as it responds accordingly to the varying input voltage and load by adjusting the number of turns in one winding. This adjustment, therefore, changes the turn ratio. During offloading conditions, the output voltage increases, whereas during loaded conditions, the output voltage decreases. Tap changers are typically connected in the HV winding to make fine voltage regulations and minimize core losses of the transformer. The current is also lower in the HV winding, which minimizes the risk of sparking and igniting the transformer oil.

There are two types of tap changers. On-load tap changers are designed to tap the voltage without disrupting the current flow to the load. Whereas offload tap changers require disconnecting the load of the transformer before operating.

5.Bushings in Transformers

Bushings are insulated barriers that contain the terminal that connects the current-carrying conductor from an electrical network to the ends of the transformer winding. The bushing insulation is typically made from porcelain or epoxy resin. The bushings are mounted over the main tank.

6.Transformer Tank

The transformer tank (or the main tank) houses and protects the core, winding, and other components from the external environment. It serves as the container for the transformer oil. It is constructed from rolled steel plates or aluminum sheets.

7.Conservator Component

The conservator is a tank that serves as the reservoir of the transformer oil and is located above the main tank and bushings. Transformer oil from the conservator is supplied to the main oil tank inside the transformer through a pipeline. The conservator has a flexible bladder that allows the expansion and contraction of the oil. It has an adequate space to allow the expansion of the oil during high ambient temperatures. The conservator is vented to the atmosphere to balance the pressure changes during the expansion and contraction of the oil by in-taking or releasing air.

8.Breather Component

The breather delivers moisture-free air to the conservator by passing air through a small bed of silica gel inside a cylindrical container. The silica gel acts as an air filter that strips and controls the moisture level inside the conservator and the main tank. The breather is connected by a pipeline to the conservator.

Moisture can degrade the insulating properties of the transformer oil or may even lead to internal faults. Therefore, it is necessary to remove the moisture.

9.Cooling System

The cooling system is a critical component of transformers regardless of the insulating material utilized. Power losses occurring in the transformers are in the form of heat increasing the temperature of the winding and the core. Consequently, the temperature of the insulating material will also increase. Without a cooling system, these components may be damaged or decomposed if heated continually. The cooling system of transformers consists of fans, radiators, and cooling tubes. Heat transfer mechanism occurs by natural and/or forced convection and radiation.

For dry-type transformers, cooling may be accomplished by the following methods:

1)Air Natural;2)Air Forced.

For oil-immersed type transformers, cooling may be accomplished by the following methods:

1)Oil Natural Air Natural;2)Oil Natural Air Forced;3)Oil Forced Air Forced;4)Oil Natural Water Forced;5)Oil Forced Water Forced.

10.Explosion Vent

The explosion vent is a metallic pipe with a diaphragm at its free end located slightly above the conservator tank. It releases gases, transformer oil, and energy during internal faults to relieve the excessive pressure inside the transformer, thus preventing the explosion of the transformer. Faults elevate the internal pressure of the transformer to dangerous levels. When such circumstances occur, energy will be released into the atmosphere, destroying the diaphragm at relatively low pressure.

11.Gas Relay

The Gas relay is a device installed along the pipeline connecting the conservator and the main tank. It detects faults in the transformer by sensing the emitted gases to activate the trip and alarm circuits. Once the trip circuit is activated, the circuit breaker will then disrupt the current flow to the primary winding. Emitted gases are generated by the heat released induced by faults.