transformer types

Types of Transformer

There are various types of transformer use in the electrical power system for different purposes, like generation, distribution and transmission and utilization of electrical power.

The different types of transformer are Step up and Step down Transformer, Power Transformer, Distribution Transformer, Instrument transformer comprising current and Potential Transformer, Single phase and Three phase transformer, Auto transformer, etc.

Transformers Based on Voltage Levels

These are the most commonly use transformer types for all the applications. Depends upon the voltage ratios from primary to secondary windings, the transformers are classified as step-up and step-down transformers.

Step up and Step down Transformer

This type of transformer is categorize on the basis of a number of turns in the primary and secondary windings and the induced emf.

Step-up transformer transforms a low voltage, high current AC into a high voltage, low current AC system In this type of transformer the number of turns in the secondary winding is greater than the number of turns in the primary winding. If (V2 > V1) the voltage is raise on the output side call Step-up transformer

Step-up Transformer
Step Up transformer

Step down transformer converts a high primary voltage associated with the low current into a low voltage, high current. With this type of transformer, the number of turns in the primary winding is greater than the number of turns in the secondary winding. If (V2 < V1) the voltage level is lower on the output side call Step down transformer

Step-Down Transformer
step down transformer

Transformer Based on the Core Medium Used

Based on the medium placed between the primary and secondary winding the transformers are classified as Air core and Iron core

Air Core Transformer

Both the primary and secondary windings are wound on a non-magnetic strip where the flux linkage between primary and secondary windings is through the air.

Compared to iron core the mutual inductance is less in air core, i.e. the reluctance offer to the generated flux is high in the air medium. But the hysteresis and eddy current losses are completely eliminate in air-core type transformer.

Air Core Transformer
Air-Core Transformer

Iron Core Transformer

Both the primary and secondary windings are wound on multiple iron plate bunch which provide a perfect linkage path to the generate flux. It offers less reluctance to the linkage flux due to the conductive and magnetic property of the iron. These are widely use transformers in which the efficiency is high compare to the air core type transformer.

Iron Core Transformer
Iron Core Transformer

Current Transformer

The current transformer is use for measuring and also for the protection. When the current in the circuit is high to apply directly to the measuring instrument, the current transformer is use to transform the high current into the desired value of the current required in the circuit.

The primary winding of the current transformer is connect in series to the main supply and the various measuring instruments like ammeter, voltmeter, watt meter or protective relay coil. They have accurate, current ratio and phase relation to enable the meter accurately on the secondary side. The term ratio has a great significance in CT.

For example, if its ratio is 2000:5, it means a CT has an output of 5 Ampere when the input current is 2000 amp on the primary side. The accuracy of the Current Transformer depends upon many factors like Burden, load, temperature, phase change, rating, saturation, etc.

In the current transformer, the total primary current is the vector sum of the excitation current and the current equal to the reversal of secondary current multiply by turn ratio.

types-of-transformer-eq


Where,
primary current Ip 
Is – secondary or reversal current
I– excitation current
KT – turn ratio

Types of Transformer

There are various types of transformer use in the electrical power system for different purposes. like generation, distribution and transmission and utilization of electrical power.

The different types of transformer are Step up and Step down Transformer, Power Transformer, Distribution Transformer, Instrument transformer comprising current and Potential Transformer, Single phase and Three phase transformer, Auto transformer, etc

Various Types of Transformer

The various types of transformer are explain in detail below.

Step up and Step down Transformer

This type of transformer is categorize on the basis of a number of turns in the primary and secondary windings and the induced emf.

Step-up transformer transforms a low voltage, high current AC into a high voltage, low current AC system In this type of transformer the number of turns in the secondary winding is greater than the number of turns in the primary winding. If (V2 > V1) the voltage is raise on the output side and is call Step-up transformer

Moreover, Step down transformer converts a high primary voltage associated with the low current into a low voltage, high current.

With this type of transformer, the number of turns in the primary winding is greater than the number of turns in the secondary winding. If (V2 < V1) the voltage level is lower on the output side and is call Step down transformer

Power Transformer

The power transformers are use in the transmission networks of higher voltages. The ratings of the power transformer are as follows 400 KV, 200 KV, 110 KV, 66 KV, 33 KV. They are mainly rate above 200 MVA. Mainly installed at the generating stations and transmission substations. They are design for maximum efficiency of 100%. They are larger in size as compared to the distribution transformer.

At a very high voltage, the power cannot be distribute to the consumer directly, so the power is step down to the desire level with the help of step-down power transformer. The transformer is not load fully hence the core loss takes place for the whole day, but the copper loss is base on the load cycle of the distribution network.

If the power transformer is connect in the transmission network, the load fluctuation will be very less as they are not connect at the consumer end directly, but if connect to the distribution network there will be fluctuations in the load.

The transformer is load for 24 hours at the transmission station, thus, the core and copper loss will occur for the whole day. The power transformer is cost-effective when the power is generate at low voltage levels. If the level of voltage is raise, then the current of the power transformer is reduce, resulting in I2R losses and the voltage regulation is also increase.

Distribution Transformer

This type of transformer has lower ratings like 11 KV, 6.6 KV, 3.3 KV, 440 V and 230 V. They are rate less than 200 MVA and use in the distribution network to provide voltage transformation in the power system by stepping down the voltage level where the electrical energy is distribute and utilize at the consumer end.

The primary coil of the distribution transformer is wound by enamel coat copper or aluminum wire. Therefore, A thick ribbon of aluminum and copper is use to make secondary of the transformer which is a high current, low voltage winding. Resin impregnate paper and oil is use for the insulation purpose.

The oil in the transformer is use for

  • Cooling
  • Insulating the windings
  • Protecting from the moisture

The various types of the distribution transformer are categorize on the following basis.

  • Mounting location
  • Type of insulation
  • Nature of supply

The distribution transformer less than 33 KV is use in industries and 440, 220 V is use for the domestic purpose. It is smaller in size, easy to install and has low magnetic losses and is not always load fully.

As it does not work for constant load throughout 24 hours as in the daytime its load is at its peak, and during the night hours it is very lightly load thus the efficiency depends on load cycle and is calculate as All Day Efficiency. The distribution transformers are design for maximum efficiency of 60 to 70%

Uses of Distribution Transformer

  • Used in pumping stations where the voltage level is below 33 KV
  • Power supply for the overhead wires railways electrified with AC
  • In urban areas, many houses are fed with single-phase distribution transformer and in rural areas, it may be possible that one house requires one single transformer depending upon the loads.
  • Meanwhile,Multiple distribution transformers are use for industrial and commercial areas.
  • Used in wind farms where the electrical energy is generate by the windmills. There it is use as a power collector to connect the substations which are away from the wind energy generation system.

Instrument Transformer

  • They are generally known as an isolation transformer. Instrument transformer is an electrical device use to transform current as well as a voltage level. The most common use of instrument transformer is to safely isolate the secondary winding when the primary has high voltage and high current supply so that the measuring instrument, energy meters or relays which are connect to the secondary side of the transformer will not get damaged. The instrument transformer is further divide into two types
    • Current Transformer (CT)
    • Potential Transformer (PT)The current and potential transformer is explain below in detail

Current Transformer

current transformer (CT) is a type of transformer that is used to reduce or multiply an alternating current (AC). It produces a current in its secondary which is proportional to the current in its primary.

transformer Equation


Where,
primary current Ip 
Is – secondary or reversal current
I– excitation current
KT – turn ratio

Potential Transformer

The potential transformer is also called as the voltage transformer. The primary winding is connected across the High voltage line whose voltage is to be measured, and all the measuring instruments and meters are connected to the secondary side of the transformer.

Moreover, The main function of the Potential transformer is to step down the voltage level to a safe limit or value. The primary winding of the potential transformer is earthed or grounded as a safety point.

For example, the voltage ratio primary to secondary is given as 500:120, it means the output voltage is of 120 V when the 500 V is applied to the primary.

Single Phase Transformer

A single-phase transformer is a static device, works on the principle of Faraday’s law of mutual Induction. At a constant level of frequency and variation of voltage level, the transformer transfers AC power from one circuit to the other circuit. There are two types of windings in the transformer. The winding to which AC supply is given is termed as Primary winding and in the secondary winding, the load is connected.

Three Phase Transformer

If the three single-phase transformer is taken and connected together with their all the three primary winding connected to each other as one and all the three secondary windings to each other, forming as one secondary winding, the transformer is said to behave as a three-phase transformer, that means a bank of three single-phase transformer connected together which acts as a three-phase transformer.

Three-phase supply is mainly used for electric power generation, transmission and distribution for industrial purpose. It is less costly to assemble three single-phase transformer to form a three-phase transformer than to purchase one single three-phase transformer. The three-phase transformer connection can be done by Star (Wye) and Delta (Mesh) type.

One Comment to “Types of Transformer”

  1. Amazing topic

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