Introduction to Electrical Power Transformer

Definition of Transformer

A transformer is a static machine used for transforming power from one circuit to another without changing frequency. This is a very basic definition of Power Transformer. Since there is no rotating or moving part so transformer is a static device. Transformer operates on ac supply. Transformer works on the principle of mutual induction.

History of Transformer

If we want to know the history of transformers, we go back to the 1880s. About 50 years before that in 1830 the induction property was discovered, which is the working principle of the transformer. Later, the design of the transformer was improved, which resulted in greater efficiency and smaller size. Little by little the great capacity of the transformers in the range of several KVA, MVA began to exist. In the year 1950, a 400 KV electric power transformer was introduced into a high voltage electrical power system. At the beginning of the 1970s, a unit classification of up to 1100 MVA was produced and 800 KV and even higher KV class transformers were manufactured in the year 1980.

Use of Power Transformer

The generation of electric power at a low voltage level is very profitable. Theoretically, this low voltage level power can be transmitted to the receiving end. This low voltage power if transmitted results in a higher line current which in fact causes more line losses. But if the voltage level of a power is increased, the energy current that causes the reduction in ohmic losses or I2R in the system is reduced, reduction in the cross-sectional area of ​​the conductor, that is, reduction in the cost of capital of the system and also improves the voltage regulation of the system. Because of this, low-level power must be increased for efficient electrical power transmission. This is done by an intensifier transformer on the sending side of the power system network. As this high voltage power can not be distributed to the consumers directly, it must be reduced to the desired level at the receiving end with the help of the reducing transformer. The electric power transformer thus plays a vital role in the transmission of power.

In general, two winding transformers are used where the ratio of high voltage and low voltage is greater than 2. It is cost effective to use a self-transformer where the ratio between high voltage and low voltage is less than 2. Again, a single unit of Three-phase transformer is more cost effective than a bank of three units of single-phase transformers in a three-phase system. But a single three-phase transformer unit is a bit difficult to transport and should be removed from service completely if one of the phase windings breaks down.

Types of Transformer

Transformers can be categorized in different ways, depending upon their purpose, use, construction etc. The types of transformer are as follows,

1.   Step Up Transformer & Step Down Transformer – Generally used for stepping up and down the voltage level of power in transmission and distribution power system network.

2.   Three Phase Transformer & Single Phase Transformer – Former is generally used in three phase power system as it is cost effective than later. But when size matters, it is preferable to use a bank of three single phase transformer as it is easier to transport than one single three phase transformer unit.

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3 PHASE Transformers – different connections

3.  Electrical Power Transformer, Distribution Transformer &Instrument Transformer – Power transformers are generally used in transmission network for stepping up or down the voltage level.  It operates mainly during high or peak loads and has maximum efficiency at or near full load. Distribution transformer steps down the voltage for distribution purpose to domestic or commercial users. It has good voltage regulation and operates 24 hrs a day with maximum efficiency at 50% of full load.  Instrument transformers include C.T & P.T which are used to reduce high voltages and current to lesser values which can be measured by conventional instruments.

4.   Two Winding Transformer & Auto Transformer – Former is generally used where ratio between high voltage and low voltage is greater than 2. It is cost effective to use later where the ratio between high voltage and low voltage is less than 2.

5.   Outdoor Transformer & Indoor Transformer – Transformers that are designed for installing at outdoor are outdoor transformers and transformers designed for installing at indoor are indoor transformers.

6.   Oil Cooled & Dry Type Transformer – In oil cooled transformer the cooling medium is transformer oil whereas the dry type transformer is air cooled.

7.   Core type, Shell type & Berry type transformer – In core type transformer it has two vertical legs or limbs with two horizontal sections named yoke. Core is rectangular in shape with a common magnetic circuit. Cylindrical coils (HV & LV) are placed on both the limbs. Shell type transformer: It has a central limb and two outer limbs. Both HV, LV coils are placed on the central limb. Double magnetic circuit is present. Berry type transformer: The core looks like spokes of wheels. Tightly fitted metal sheet tanks are used for housing this type of transformer with transformer oil filled inside.

Also read

What is Instrument Transformers?

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