What are the name of the basic parts of a Power Transformer?
We can not deny the fact that only a handful of electrical engineering students are presently familiar with power transformers especially on what it looks like. Unlike a transformer we found in our homes, a power transformer’s appearance and construction is somewhat more complicated. It is not just a simple winding with a primary and secondary terminal although basically any transformer has one. The function that a power transformer plays in an electrical system is very important that an electric utility can not afford to loss it during its operation. Our discussion here will focus more on the basic parts and functions of a power transformer that are usually tangible whenever you go to a substation. Although not all power transformers are identical, nonetheless they all have the following listed parts in which the way of construction may differ.

parts of power transformer

1. Transformer Tank – this holds the transformer windings and its insulating medium (oil-filled). Transformer tanks must be air-tightly sealed for it to isolate its content from any atmospheric contaminants.

2. High Voltage Bushing – this is the terminals where the primary windings of the transformer terminates and serves as an insulator from the transformer tank. Its creapage distance is dependent on the voltage rating of the transformer.

3. Low Voltage Bushing – like the high voltage bushing, this is the terminals where the secondary windings of the transformer terminates and serves as an insulator from the transformer tank. Low voltage bushing can be easily distinguished from its high voltage counterpart since low voltage bushings are usually smaller in size compared to the high voltage bushing.

4. Cooling Fins/Radiator – in order for the transformer to dissipate the heat it generated in its oil-insulation, cooling fins and radiators are usually attached to the transformer tanks. The capacity of the transformer is dependent to its temperature that is why it is imperative for it to have a cooling mechanism for better performance and higher efficiency.

5. Cooling Fans – can be usually found attached to the cooling fins. Cooling fans can be either be a timer controlled or a winding/oil temperature controlled. Cooling fans helps raises the transformer capacity during times when the temperature of the transformer rises due to its loading. Cooling fans used on the transformer are actuated by the help of a relaying device which when senses a relatively high temperature enables the fan to automatically run.

6. Conservator Tank – An oil preservation system in which the oil in the main tank is isolated from the atmosphere, over the temperature range specified, by means of an auxiliary tank partly filled with oil and connected to the completely filled main tank.

7. System Ground Terminal – system ground terminals in a power transformer are usually present whenever the connection type of the transformer windings has wye in it. This terminal can be found in-line with the main terminals of the transformer.

8. Drain Valve – can be usually found in the bottom part of the transformer tank. Drain valves are used whenever oil replacement is necessary. Through this valve, the replacement of oil in an oil-filled transformer can be easily done simply by opening this valve like that of a faucet.

9. Dehydrating Breather – Dehydrating breathers are used to prevent the normal moisture in the air from coming in contact with the oil in electrical equipment as the load or temperature changes. This reduces the degeneration of the oil and helps maintain its insulation capability. When used with conservator system with a rubber air cell it reduces moisture accumulation in the cell. Some breathers are designed for sealed tank transformers and breathe only at pre-set pressure levels. ABB

10. Oil Temperature/Pressure gauges – these are used for monitoring the internal characteristics of the transformer especially its windings. These gauges help the operator in knowing the level of temperature and pressure inside the transformer (oil & winding). This will also serve as an alarm whenever a certain level is reached that could be harmful to the transformer windings.

11. Bushing Current Transformers – modern transformer construction today now includes current transformers. These are usually found around the transformer terminals which will be later be used for metering and relaying purposes. Its terminals are found in the control panels attached to the transformer.

12. Control Panel – this houses all of the transformer’s monitoring devices terminals and auxiliary devices including the terminals of the bushing current transformers and cooling fans. Control panels are very useful especially when a remote control house is needed to be constructed, this will serve as their connection point.

13. Surge Arresters – this type of arresters are placed right directly before and after the transformer terminals in order to minimize the exposure of the transformer. Like any other surge arresters, its purpose is to clip sudden voltage surge that can be damaging to the winding of the transformer.


  1. please leave a comment or join this site...thanks

    1. me i want to join i want to know the measure the current of transfomer low and high voltage


  3. I think the number 13 item (surge arrester) can't found in the photo is because some power transformer uses surge arresters as a separate device while some power transformer has built-in surge arrester.The type of the power transformer show may be the former.

  4. doesnt show the auxiliary monitoring part, and the buchholz relay

  5. yeah right very use FULL?

  6. beneficial.. include buchholz relay.