Transformer Cooling Methods

When a transformer is in operation heat is generated due to I2R losses in the windings and core losses. The removal of heat is called cooling.

The following methods are generally used to cool transformers.

Air Natural (AN) Cooling

In a dry-type self-cooled transformer, the natural circulation of the surrounding air is used for its cooling. The windings are protected from mechanical injury by a sheet metal enclosure. This type of cooling is a satisfied tory for low-voltage small transformers to a few kVA.

Air Blast (AB) Cooling

The dry-type forced air-cooled transformer is similar to that of the dry-type self-cooled transformer with the addition that continuous blast of filtered cool air is forced through the core and windings for better cooling. The blast is produced by a fan.

Oil Natural (ON) Cooling

The majority of trans large rating have their windings and core immersed in oil which acts both as a cooling medium and an insulating medium. Oil-immersed transformers are enclosed in a sheet-steel tank. The heat produced in the cores and windings is passed to the oil. Heated oil becomes lighter and rises to the top and its place is taken by cool oil from the bottom of the tank.

The heat of the oil is transferred to the walls of the tank by the natural circulation of the oil. The heat is then transferred to the surrounding atmosphere through natural radiation and convection. The oil gets cooler and falls to the bottom. Thus, the continuous natural circulation of oils takes place.

Plain tanks are economical to a rating of 25 kVA. Above this rating, the large cooling surface is generally provided by using corrugations, fins, tubes (circular or elliptical), and radiator tanks.

Oil Blast (OB) Cooling

In this type of cooling, forced air is directed over the cooling elements of the transformer immersed in oil.

Forced Oil and Forced Air Flow (OFB) Cooling

Oil is circulated from the top of the tank of the transformer tank to a cooling plant. Cool oil is then returned to the bottom of the tank.

Forced Oil and Water (OFW) Cooling

In this type of cooling forced oil flow with water cooling of the oil in the external water heat exchanger takes place. This type of cooling is similar to OFB cooling except that the heat exchanger uses water instead of air for cooling oil. The water is circulated in cooling tubes placed in the heat exchanger.

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Limitations of Terzaghi Theory

Limitations of Terzaghi Theory The value of the coefficient of consolidation has been assumed to be constant. The distance d of the drainage path cannot be measured accurately in the field. The thickness of the deposit is generally variable, and an average value has to be estimated. There is sometimes difficulty 1n locating the drainage face, and sometimes thin previous seams that can act as good drainage faces are missed in the boring operations. The equation is based on the assumption that the consolidation is one-dimensional. In the field, the consolidation is generally 3-dimensional. The lateral drainage may have a significant effect on the time rate of consolidation. The initial consolidation and secondary consolidation have been neglected. Sometimes these form an important part of the total consolidation. In actual practice, the pressure distribution may be far from linear or uniform.

Comparison between VSI and CSI

Comparison between VSI and CSI In power electronic systems, inverters are an essential component that converts direct current (DC) into alternating current (AC). There are two main types of inverters used in power electronic systems: Voltage Source Inverters (VSI) and Current Source Inverters (CSI). Both have their own unique advantages and disadvantages, and the choice of which to use depends on the specific application and the desired outcome. Comparisons between voltage source inverters and current source inverters are as follows. In voltage source inverters, the input voltage is maintained constant and the amplitude of the output voltage does not depend on the load. However, the waveform of load current, as well as its magnitude, depends upon the nature of load impedance. In current source inverters (CSI), the input current is constant but adjustable. The amplitude of output current from CSI is freelance of the load. However, the magnitude of output voltage and its undulation outp

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