At the end of the guide, you will be able to choose the right transformer for your applications.

## What is a Transformer?

A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors – this means that it works by transferring energy using a magnetic field.

It has two or more coils of wire which are usually insulated, wrapped around a laminated iron core. The transformer works on the principle of electromagnetic induction.

When an electric current passes through the primary coil (the coil supplied with power), it creates a circular magnetic flux.

This magnetic flux induces an electromotive force or voltage in the secondary coil (which is not provided with any power). In other words, the transformer changes the voltage level from low to high and vice versa.

## How does a transformer work?

A transformer works on the following principles:

One important transformer working principle is based on Faraday’s law. According to the law, when a magnetic field changes in magnitude or direction in a coil of wire, an emf is induced in that circuit.

This emf will cause the current to flow if the ends are connected by another conductor. The transformer uses this principle. Two coils are wound around a laminated iron core.

One coil is called a primary coil while the other one is a secondary coil. These coils are usually insulated and wired to supply power from an AC source or DC source.

When voltage is applied across the primary it produces circular flux throughout its cross-sectional area. This circular flux cuts the secondary coil and induces an emf (voltage) in the coil.

The direction of transformer current is determined by Lenz’s law of electromagnetic, according to which transformer acts as a closed circuit when there is no change in the magnetic field of the transformer.

The above working principles are explained below with help of diagrams:

– Power transfer or step-up transformer.

The output voltage of this transformer is more than the input voltage because power is transferred from a lower potential level to a higher potential level, which means that it works on the “step-up” principle.

– Power transfer or step down transformer

This type of transformer will have output voltage less than input voltage because power is transferred from a higher potential level to a lower potential level, which means that it works on the “step down” principle.

– Half wave rectifier transformer

This transformer is used as a half-wave rectifier transformer that transfers DC power from one circuit to another through inductively coupled conductors, and the transformer only uses input voltage to supply output voltage.

The transformer will work properly if we connect an AC supply across its secondary coil (output side), and it will function as a step-down transformer i.e., its output voltage will be less than input voltage or there would be no output voltage at all.

In other words, the transformer works as an insulator when there is no current flowing through the primary coil because the transformer acts as a closed circuit under such conditions. In addition, transformers cannot work on DC power.

## Types of transformer

The transformer is made up of three components known as the primary coil, the secondary coil, and the laminated iron core. However, there are various types of transformers depending upon their working principles mentioned in Chapter 2.

The following types of transformers are used in different areas with few exceptions:

### Center tapped transformer

It is two transformers with each transformer having separate primary and secondary coils; however, both these primary coils share one common terminal (center tap), which means that it has three terminals in total (two individual coils and one center tap).

This type of transformer is similar to two transformers connected in series but with only a single output voltage or single output current.

If we connect one transformer by its center tap (the point where both coils are connected) with the transformer having two separate terminals (outputs) then it will act as a transformer having a single output.

### Reactor transformer

This type of transformer works on the principle of reactor i.e., it takes an alternating current at one end and converts it to an oscillating current at another end. That means input power is also an AC which will be converted to DC by the transformer.

### Autotransformer

It looks like a closed coil (wound around the iron core) but we cannot see any connection wire; however, the transformer has three coil windings: primary winding and secondary winding in addition to tertiary winding for neutralizing voltage which results in negligible voltage drop for the transformer.

### Isolation transformer

It is mainly used as a transformer to transfer AC power from one circuit to another, and it has an extremely high impedance so that no current flows through the primary winding and secondary winding (input and output sides).

### Voltage transformer

There is only a single connection between two windings (primary and secondary) i.e., a transformer with only one terminal; however, we can vary its turns ratio by changing its primary coil resistance or interchanging any copper wire connections.

## Transformer Configurations

We know that transformer works on electromagnetic induction principle; however, there are various other types of transformers such as autotransformer which works on self-induction principle due to induced emf in both coils.

– Single-phase transformer :

If we have a transformer to supply power at a single point, then it is known as a single-phase transformer. It will work on the step-down principle if there are two separate terminals (outputs) for example household transformer which provides a 240-volt supply by reducing the 220 volts supply from mains.

-Three-phase power: In a transformer, both primary and secondary windings produce three types of magnetic flux known as the “three phases”.

– Three-phase transformer :

If we have a transformer with six terminals or three separate coils, then it is called a three-phase transformer. We can draw all six types of electrical connections from these three windings for example interconnection between two power stations. Each transformer has its type as well as rating depending upon their usage i.e., voltage ratio as well as current rating, etc.

Transformer core: The transformer core may be of two types, one with laminated iron plate and another with E-shaped magnetic steel. In a transformer with a lamination type iron core, copper wires are wound around it while in a transformer having E shape magnetized sheet an insulated sheet will be inserted between the two coils of the primary and secondary winding.

Voltage regulation: Voltage regulation is a factor that must be considered while buying a transformer for a utilization purpose because if we cannot regulate the voltage properly then either transformer will not work properly or it can lead to a hazardous situation. So, before buying any transformer make sure that it has an electric circuit breaker built inside the case so that you can remotely control the transformer by a switch on/off.

Voltage ratio: It is the ratio of input voltage to output voltage i.e., v1/v2 expressed in percentage form.

Turns ratio: It is also called transformer turns or transformer winding turns, which expresses how many times current will flow through primary winding for example if the transformer has 100 turns on its primary winding and 5 on secondary winding then it is written as 1:5 turns ratio; however, this transformer’s name would be 5 to 1 step down transformer because several revolutions occur in primary coil (turns) are greater than that of secondaries coils (turns).

Transformer action: The transformer changes AC into AC by increasing or decreasing voltage value as well as transformer changes the frequency of the alternating current.

Harmonics: If the transformer does not have a proper magnetic circuit caused by a leakage flux, then it will lead to the generation of harmonics (related to the transformer’s size) which can be minimized by installing an extra transformer with equal or higher capacity than that transformer which is generating harmonics.

Weber capacitance: It is known as ‘saturation’ whereby the transformer gets fully saturated; however, this saturation induces voltage spikes in primary and secondary coils for both single-phase and three-phase transformers. So before purchasing any transformer make sure that it has low watt density because too much wattage causes heating up of transformer winding which eventually leads to its failure.

Resonance coil: The transformer gets excited by the resonance coil which generates the transformer’s magnetization current. However, there are different types of transformer connections available such as star-delta connection, series transformer connection, and transformer banks connection.

Self-excitation: The transformer is self-excited when it has two coils with the same number of turns or equal inductances i.e., the magnetic flux produced by one winding induces the secondary voltage in another winding circuit which further produces transformer output voltage after rectifying process based upon its turns ratio.

Stray capacitance: Stray capacitors exist either on the primary or secondary side to produce an additional voltage across transformer terminals which can be reduced by using a large cross-sectional area of transformer core plate.

Transformer voltage regulation: Voltage transformer regulation ensures that the transformer operates at the desired power factor.

Frequency transformer: A transformer that has a different turns ratio for both primary and secondary circuits is known as a frequency transformer.

Toroidal transformer: It’s a transformer with ring shape magnetic core with winding on it, also this type of transformer does not have a conventional lamination iron core but due to its shape it produces very low watt density so, this transformer can run more load than any other normal transformer. However, there are many types of toroidal transformers available such as the LCLC (Line Coupled Load Coupled) transformer.

Transformer installation: A proper transformer installation includes earth leakage circuit breaker (ELCB), fusing facility, transformer high voltage winding insulation class transformer low voltage winding insulation class transformer earthing arrangement.

Transformer with built-in capacitor: In the case of non-linear load the capacitors are used to provide harmonic compensation for power factor correction that’s why it is called transformer with built-in capacitor.

## Applications and Uses of Transformers

Transformers have a wide range of applications. They are used in industry, residential consumer, and commercial applications. The transformer application can be classified as

Industrial transformer: This transformer is widely used in an industrial environment. The transformer provides voltage step down so that it’s connected to low power machines for their operation.

Residential transformer: This type of transformer is commonly known as an iron core transformer. The transformer is used in household appliances that are less power consuming, so the transformer provides voltage step up or step down for this appliance.

Commercial transformer: This transformer is widely used in commercial electricity usage because it requires a high wattage supply compared to a residential transformer.

The following are some of the applications in various fields where transformers are used.

Primary transformer: transformer is used in generating station where it’s provided rated primary voltage for transformer operation.

Secondary transformer: transformer is used in Distribution transformer substation which provides voltage stepping down for distribution purpose.

Instrument transformer: transformer is used in low-range devices such as ammeter transformer etc.

Electric meter: transformer is used in electric meters where it provides rated voltages for various motors and appliances which are connected to a meter.

Power supply transformer: transformer is used in power supply system which provides DC or AC supply for transformer operation.

Metering transformer: transformer is used to measure voltage and current in metering applications such as transformer load tap changer (LTC) transformer.

Transformer application in transformer oil-filled cables: transformer can be used in transformer oil-filled cable where it provides low power supply source for heating purpose.

## Summary

In conclusion, a transformer is helpful in various applications to provide a proper power supply system for transformer operation.

I hope you will use this guide next time that you want to buy transformers in China.

If you want to contact ICRFQ. We are a reliable wholesale distributor of electric transformers in China.

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