What is a Transformer? Construction, Working, Types, and Uses

What is a Transformer? Construction, Working, Types, and Uses . in a simple way, can be described as a device that steps up or steps down voltage. In a step-up transformer, the output voltage is increased, and in a step-down transformer, the output voltage is decreased. The step-up transformer will decrease the output current, and the step-down transformer will increase the output current to keep the input and output power of the system equal.

Read More : Maintenance of Transformer

It is basically a voltage control device that is used widely in the distribution and transmission of alternating current power. The idea of a transformer was first discussed by Michael Faraday in the year 1831 and was carried forward by many other prominent science scholars. However, the general purpose of using transformers was to maintain a balance between the electricity that was generated at very high voltages and consumption which was done at very low voltages.

What Is a Transformer?

a device used in the power transmission of electric energy. The transmission current is AC. It is commonly used to increase or decrease the supply voltage without a change in the frequency of AC between circuits. it works on the basic principles of electromagnetic induction and mutual induction.

Parts

1	Oil filter valve	17	Oil drain valve
2	Conservator	18	Jacking boss
3	Buchholz relay	19	Stopper
4	Oil filter valve	20	Foundation bolt
5	Pressure-relief vent	21	Grounding terminal
6	High-voltage bushing	22	Skid base
7	Low-voltage bushing	23	Coil
8	Suspension lug	24	Coil pressure plate
9	B C T Terminal	25	Core
10	Tank	26	Terminal box for protective devices
11	De-energized tap changer	27	Rating plate
12	Tap changer handle	28	Dial thermometer
13	Fastener for core and coil	29	Radiator
14	Lifting hook for core and coil	30	Manhole
15	End frame	31	Lifting hook
16	Coil pressure bolt	32	Dial type oil level gauge

Transformer Types

Working voltage range
The medium used in the core
Winding arrangement
Installation location

Based on Voltage Levels

Commonly used types, depending on the voltage, are classified as follows:

Step-up Transformer: They are used between the power generator and the power grid. The secondary output voltage is higher than the input voltage.
Step-down Transformer: used to convert high-voltage primary supply to low-voltage secondary output.

Based on the Medium of Core Used

In a transformer, we will find different types of cores that are used.

Air Core Transformer: The flux linkage between primary and secondary winding is through the air. The coil or windings wound on the non-magnetic strip.
Iron Core Transformer: Windings are wound on multiple iron plates stacked together, which provides a perfect linkage path to generate flux.

Based on the Winding Arrangement

Autotransformer: It will have only one winding wound over a laminated core. The primary and secondary share the same coil. Auto means “self” in the Greek language.

Based on Install Location

Power Transformer: It is used at power generation stations, as they are suitable for high voltage application
Distribution Transformer: It is mostly used at distribution lanes for domestic purposes. They are designed for carrying low voltages. It is very easy to install and characterised by low magnetic losses.
Measurement Transformers: They are mainly used for measuring voltage, current and power.
Protection Transformers: They are used for component protection purposes. In circuits, some components must be protected from voltage fluctuation, etc.

Based on its Phases

Single Phase
Three Phase

Based on its Core Design

Core Type
Shell Type
Berry Type

Based on its usage

Large Power
Distribution
Small Power
Sign Lighting
Control & Signaling
Gaseous Discharge Lamp
Bell Ringing
Instrument
Constant Current
Series Transformer for Street Lighting

Based on Insulation & Cooling

Self Air Cooled or Dry Type
Air Blast-Cooled Dry Type
Oil Immersed, Self Cooled (OISC) or ONAN (Oil natural, Air natural)
Oil Immersed, Combination of Self Cooled and Air blast (ONAN)
Oil Immersed, Water Cooled (OW)
Oil Immersed, Forced Oil Cooled
Oil Immersed, Combination of Self Cooled and Water Cooled (ONAN+OW)
Oil Forced, Air forced Cooled (OFAC)
Forced Oil, Water Cooled (FOWC)
Forced Oil, Self Cooled (OFAN)

Types of Instrument Transformer

Current Transformer
Potential Transformer
Constant Current Transformer
Rotating Core Transformer or Induction regulator
Autotransformer

Working Principle

it works on the principle of Faraday’s law of electromagnetic induction and mutual induction.

There are usually two coils – primary coil and secondary coil – on the transformer core. The core laminations are joined in the form of strips. The two coils have high mutual inductance. When an alternating current passes through the primary coil, it creates a varying magnetic flux. As per Faraday’s law of electromagnetic induction, this change in magnetic flux induces an EMF (electromotive force) in the secondary coil, which is linked to the core having a primary coil. This is mutual induction.

Overall, it carries out the following operations:

Transfer of electrical energy from one circuit to another
Transfer of electrical power through electromagnetic induction
Electric power transfer without any change in frequency
Two circuits are linked with mutual induction

The figure shows the formation of magnetic flux lines around a current-carrying wire. The normal of the plane containing the flux lines is parallel to the normal of a cross-section of a wire.

The figure shows the formation of varying magnetic flux lines around a wire wound. The interesting part is that the reverse is also true; when a magnetic flux line fluctuates around a piece of wire, a current will be induced in it. This was what Michael Faraday found in 1831, which is the fundamental working principle of electric generators, as well as transformers.

Parts of a Single-phase Transformer

The major parts of a single-phase consist of

1. Core

The core acts as a support to the winding in the transformer. It also provides a low reluctance path to the flow of magnetic flux. The winding is wound on the core, as shown in the picture. It is made up of a laminated soft iron core in order to reduce the losses in a transformer. The factors, such as operating voltage, current, power, etc., decide core composition. The core diameter is directly proportional to copper losses and inversely proportional to iron losses.

2. Windings

Windings are the set of copper wires wound over Its core. Copper wires are used due to the following:

The high conductivity of copper minimises the loss in a transformer because when the conductivity increases, resistance to current flow decreases.
The high ductility of copper is the property of metals that allows it to be made into very thin wires

There are mainly two types of windings: primary windings and secondary windings.

Primary winding: The set of turns of windings to which the supply current is fed.
Secondary winding: The set of turns of winding from which output is taken.

The primary and secondary windings are insulated from each other using insulation coating agents.

3. Insulation Agents

Insulation is necessary for transformers to separate windings from each other and to avoid short circuits. This facilitates mutual induction. Insulation agents have an influence on the durability and stability of a transformer.

The following are used as insulation mediums

Insulating oil
Insulating tape
Insulating paper
Wood-based lamination

Read Moe : Can We Replace a 110/220 Turns Transformer with 10/20 Turns?

Ideal Transformer

It has no losses. There is no magnetic leakage flux, ohmic resistance in its windings and no iron loss in the core.

EMF Equation

N₁ – Number of turns in the primary

N₂ – Number of turns in the secondary

Φ_m – Maximum flux in the weber (Wb)

T – Time period. It is the time taken for 1 cycle.

The flux formed is a sinusoidal wave. It rises to a maximum value of Φ_m and decreases to a negative maximum of Φ_m. So, flux reaches a maximum in one-quarter of a cycle. The time taken is equal to T/4.

Average rate of change of flux = Φ_m/(T/4) = 4fΦ_m

Where, f = frequency

T = 1/f

Induced EMF per turn = Rate of change of flux per turn

Form factor = RMS value / average value

RMS value = 1.11 (4fΦ_m) = 4.44 fΦ_m[form factor of a sine wave is 1.11]

RMS value of EMF induced in winding = RMS value of EMF per turn x No. of turns

Primary Winding

RMS value of induced EMF = E₁ = 4.44 fΦm * N₁

Secondary Winding

RMS value of induced EMF = E₂ = 4.44 fΦm * N₂

This is the EMF equation

For an ideal at no load condition,

E₁ = Supply voltage on the primary winding

E₂ = Terminal voltage (theoretical or calculated) on the secondary winding

Voltage Transformation Ratio

K is called the voltage transformation ratio, which is a constant.

Case 1:If N_{2 >} N_1, K>1, it is called a step-up transformer.

Case 2: If N₂< N₁, K<1, it is called a step-down transformer.

Efficiency

Comparing system output with input will confirm efficiency. The system is called better when its efficiency is high.

Fleming’s Right Hand Rule

It states that “if the thumb, the forefinger and the middle finger are held in such a way that they are mutually perpendicular to each other (makes 90° of Angles), then the forefinger points the direction of the field, the thumb points the direction of motion of the conductor and the middle finger points the direction of the induced Current (from EMF).

Why Transformers Can’t step Up Or Step Down A DC Voltage or Current?

It cannot step up or step down a DC voltage. It is not recommendable to connect a DC supply to a transformer because if a DC rated voltage is applied to the coil (primary) of a transformer, the flux produced in the transformer will not change in its magnitude but rather remain the same and as a result EMF will not be induced in the secondary coil except at the moment of switching on, So the transformer may start to smock and burn because;

In case of DC supply, Frequency is zero. When you apply voltage across a pure inductive circuit, then according to

X_L= 2 π f L

Where:

X_L = Inductive Reactance
L = Inductance
f = Frequency

if we put frequency = 0, then the overall X_L (inductive reactance) would be zero as well.

Now come to the current, I = V / R (and in case of inductive circuit, I = V / X_L) …. basic Ohm’s Law

If we put Inductive reactance as 0, then the current would be infinite (Short circuit)…

So, If we apply DC voltage to a pure inductive circuit, The circuit may start to smoke and burn.

Thus transformers are not capable of stepping up or stepping down a DC voltage. Also there will be no self induced EMF in such cases in the primary coil which is only possible with a varying flux linkage to oppose the applied voltage. The resistance of the primary coil is low and as such a heavy current flowing through it will result to the primary coil burning out due to excessive heat produced by the current.

Limitation

To understand the main points, we have to discuss some basic terms related to transformer operation. So lets back to basic for a while.

It is an AC machine that steps up or steps down an alternating voltage or current. A transformer being an AC machine however cannot step up or down a DC voltage or DC current. It sounds a bit weird though. You might be thinking “so are there not DC transformers?”

To answer the two questions whether there are or there are not DC transformers and know “why transformer cannot step up or step down a DC voltage” it’s necessary we know how electric current and magnetic field interact with each other in transformer operation.

Frequently Asked Questions

What is the working principle of the transformer?

It works on the principle of mutual induction.

What are the main parts of a transformer?

Iron core
Primary winding
Secondary winding

When do transformers burn and explode?

It burn and explode when lightning strikes, and during overloading, corrosion, power surges, etc.

What is a transformer?

It a device used for stepping up or stepping down AC voltages.