Transformer: Definition, Types, Construction, Working, and Applications

What is transformer ?

A Transformer is a static electrical device that transfers electrical energy between two or. more circuits through electromagnetic induction. A varying current in one coil of the. transformer produces a varying magnetic field, which in turn induces a varying. electromotive force (e.m.f) or “voltage” in a second coil

What is transformer and its types?

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

Application of transformer ?

Transformers are exclusively used in electrical power systems to transfer power by electromagnetic induction between circuits at the same frequency with very little power loss, voltage drop or waveform distortion.Transformers are important equipment in power distribution system as well as in power electronic system.

Construction of single-phase transformers- 

A single-phase transformer consists of two winding, called primary and secondary windings mounted on a magnetic core. To confine flux to a definite path magnetic flux is used. Transformer cores are made from thin sheets (called lamination) of high-grade silicon steel. The laminations reduce eddy-current loss and the silicon steel reduces hysteresis loss. The laminations are insulated from each other by heat resistant enamel insulation coating. L-type and e-type laminations are used. The laminations are built up into and the joints in the laminations are staggered to minimize air-gaps (which require large exciting currents). The laminations are tightly clamped.

These are two basic types of transformer constructions, the core type and the shell type.

Voltage-regulators-explained-simply

IDEAL TRANSFORMER:

An ideal transformer has the following properties:

• Its primary and secondary winding resistances are negligible.
• The core has infinite permeability(µ) so that negligible mmf is required to establish the flux in the core.
• Its leakage flux and leakage inductances are zero. The entire flux is constricted to the core and links both windings.
• There are no losses due to resistance, hysteresis and eddy currents. Thus, the efficiency is 100 percent.
• It is to be noted that practical (commercial) transformer has none of these properties in spite of the fact that its operation is close to ideal.

An ideal iron-core transformer is shown in figure below. It consists of two coils wound in the same direction on a common magnetic core. The winding connected to the supply V₁, is called the primary. The winding connected to the load, Z₁, is called the secondary.

Ideal Iron-Core Transformer

Since the ideal transformer has zero primary and zero secondary impedance, the voltage induced in the primary E₁ is equal to the applied voltage V₁. Similarly, the secondary voltage V₂, is equal to the secondary induced voltage E₂. The current I₁ drawn from the supply is just sufficient to produce mutual flux ɸ_M and the required magneto-motive force (mmf) I₁,T₁, to overcome the demagnetizing effect of the secondary mmf I₂,T₂, as a result of connected load.

By Lenz’s law E₁, is equal and opposite to V₁, Since E₂, and E₁, are both induced by the same mutual flux, E₂, is in the same direction’s E₁, but opposite to V₁, The magnetizing I_µlags V₁ by 90˚ and produces ɸ_M in phase with I_µ and E₂ lag ɸ_M by 90° and are produced by ɸ_M .V₂, is equal in magnitude to E₂, and is opposite to V₁. below shows the no-load phasor diagram of the ideal transformer.

Load phasor diagram of An Ideal Transformer)

For an ideal transformer, if

a = transformation ratio = turn ratio

then, a = T₁/T₂ = E₁/E₂ V₁/V₂ = I₂/I₁ ……(1)

            I₁ T₁ = I₂ T₂                               …….(2)

            E₁ I₁ = E₂ I₂ = S₂ = S₁               ……..(3)

            V₁ I₁ = V₂ I₂ = S₂ = S₁                   ………(4)

Equation (2) states that the demagnetizing ampere turns of the secondary are equal and also opposite to the magnetizing mmf of the primary of an ideal transformer.

Equation (3) shows that the volt-amperes (apparent power) drawn from the primary supply is equal to the volt-amperes (apparent power) transferred to the secondary without any loss in and ideal transformer. In other words,

input volt-amperes = output volt-amperes

Also,      V₁I₁/1000 = V₂I₂/1000

                (kVA)₁ = (kVA)_{2   ………….}(5)

Or,

input kilovolt amperes output kilovolt amperes

                Thus, the kVA input of an ideal transformer is equal to the kVA output. That is, kVA is the same on both the sides of the transformer.

No Load phasor diagram of An Ideal Transformer

For an ideal transformer, if

a = transformation ratio = turn ratio

then, a = T₁/T₂ = E₁/E₂ V₁/V₂ = I₂/I₁ ……(1)

            I₁ T₁ = I₂ T₂                               …….(2)

            E₁ I₁ = E₂ I₂ = S₂ = S₁               ……..(3)

            V₁ I₁ = V₂ I₂ = S₂ = S₁                   ………(4)

Equation (2) states that the demagnetizing ampere turns of the secondary are equal and also opposite to the magnetizing mmf of the primary of an ideal transformer.

Equation (3) shows that the volt-amperes (apparent power) drawn from the primary supply is equal to the volt-amperes (apparent power) transferred to the secondary without any loss in and ideal transformer. In other words,

input volt-amperes = output volt-amperes

Also,      V₁I₁/1000 = V₂I₂/1000

                (kVA)₁ = (kVA)_{2   ………….}(5)

Or,

input kilovolt amperes output kilovolt amperes

                Thus, the kVA input of an ideal transformer is equal to the kVA output. That is, kVA is the same on both the sides of the transformer.

How Does a Transformer Work?

Answer. A transformer works on the magnetic induction principle. It has no moving parts and is a completely static solid state device, which insures, under normal operating con¬ditions, a long and trouble-free life. It consists, in its simplest form, of two or more coils of insulated wire wound on a lami¬nated steel core. When voltage is introduced to one coil, called the primary, it magnetizes the iron core. A voltage is induced in the other coil, called the secondary or output coil. The change of voltage (or voltage ratio) between the primary and secondary depends on the turns ratio of the two coils.Working

Parallel Operation of  Transformers

The design of Power Control Centre (PCC) and Motor Control Centre (MCC) of any new plant should have the provision of operating two or more transformers in parallel.  Additional switchgears and bus couplers should be provided at design stage. Whenever two transformers are operating in parallel, both should be technically identical in all aspects and more importantly should have the same impedance level.  This will minimise the circulating current between transformers. Where the load is fluctuating in nature, it is preferable to have more than one transformer running in parallel, so that the load can be optimised by sharing the load between transformers.  The transformers can be operated close to the maximum efficiency range by this operation. 

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FAQ Section

  ⚡ A. Basic FAQs (Beginner Level)

Q1: What is a transformer?
A transformer is an electrical device that transfers energy between circuits through electromagnetic induction.

Q2: What is the working principle of a transformer?
It works on Faraday’s law of electromagnetic induction — changing magnetic flux induces voltage in another coil.

Q3: Does a transformer work on AC or DC?
Transformers only work on AC because DC does not create changing magnetic flux.

Q4: What are the main parts of a transformer?
Core, primary winding, secondary winding, insulation, tank, bushings, and cooling system.

Q5: What is the purpose of a transformer?
To step up or step down voltage levels in power systems.

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⚙️ B. Technical FAQs (Intermediate Level)

Q6: Why are transformer cores laminated?
To reduce eddy current losses and improve efficiency.

Q7: What is the turns ratio?
The ratio of primary to secondary turns, which determines voltage transformation.

Q8: What is the difference between step-up and step-down transformers?
Step-up increases voltage; step-down decreases voltage.

Q9: What is the ideal transformer assumption?
Zero losses, infinite permeability, no leakage flux, and perfect coupling.

Q10: What is leakage flux?
Flux that does not link both windings, causing leakage reactance.

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📐 C. Formula-Based FAQs

Q11: What is the transformer turns ratio formula?
[ \frac{V_1}{V_2} = \frac{N_1}{N_2} ]

Q12: What is the current ratio formula?
[ \frac{I_1}{I_2} = \frac{N_2}{N_1} ]

Q13: What is the kVA rating formula?
[ \text{kVA} = \frac{V \cdot I}{1000} ]

Q14: What is the efficiency formula?
[ \eta = \frac{\text{Output Power}}{\text{Input Power}} \times 100 ]

Q15: What is the EMF equation of a transformer?
[ E = 4.44 f N \phi_m ]

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🧲 D. Construction & Design FAQs

Q16: What materials are used for transformer cores?
Cold-rolled grain-oriented (CRGO) silicon steel.

Q17: What is the difference between core-type and shell-type transformers?
Core-type has windings around two limbs; shell-type has windings in the center limb.

Q18: Why is insulation important in transformers?
To prevent short circuits between windings.

Q19: What is the purpose of transformer oil?
Cooling and insulation.

Q20: What is a conservator tank?
A tank that allows expansion of transformer oil.

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🔌 E. Working Principle FAQs

Q21: Why does a transformer hum?
Due to magnetostriction — core expansion and contraction at 50/60 Hz.

Q22: What is no-load current?
Small current drawn to magnetize the core.

Q23: What is load current?
Current drawn when the secondary supplies a load.

Q24: What is voltage regulation?
Change in secondary voltage from no-load to full-load.

Q25: What is a phasor diagram?
A graphical representation of voltage and current relationships.

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🛠️ F. Troubleshooting FAQs (Technician Level)

Q26: Why does a transformer overheat?
Overload, poor ventilation, insulation failure, or oil degradation.

Q27: What causes transformer humming to increase?
Loose laminations or mechanical vibration.

Q28: Why does a transformer trip the breaker?
Short circuit, winding fault, or insulation breakdown.

Q29: What causes low secondary voltage?
Overload, poor connections, or high leakage reactance.

Q30: What causes oil leakage?
Gasket failure or tank corrosion.

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🔧 G. Application FAQs

Q31: Where are transformers used?
Power distribution, electronics, welding machines, UPS, and control circuits.

Q32: What is an autotransformer?
A transformer with a single winding acting as both primary and secondary.

Q33: What is a distribution transformer?
Used to supply low-voltage power to consumers.

Q34: What is an isolation transformer?
Provides electrical isolation between circuits.

Q35: What is an instrument transformer?
Used for measurement (CTs and PTs).

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🔄 H. Parallel Operation FAQs

Q36: Why do transformers need parallel operation?
To share load and improve reliability.

Q37: What conditions must be met for parallel operation?
Same polarity, voltage ratio, impedance, and phase sequence.

Q38: What happens if polarity is wrong?
Short circuit or circulating currents.

Q39: What is load sharing?
Distribution of load between transformers based on impedance.

Q40: Why must percentage impedance be similar?
To avoid unequal load sharing.

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🧪 I. Safety FAQs

Q41: Why must transformers be grounded?
To prevent shock hazards and stabilize voltage.

Q42: What is Buchholz relay?
A gas-actuated protection device for oil-filled transformers.

Q43: What is the danger of overloading a transformer?
Overheating, insulation failure, and fire risk.

Q44: Why is oil testing important?
To check moisture, acidity, and dielectric strength.

Q45: What is the safe temperature rise?
Typically 55°C to 65°C above ambient.

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🧠 J. Exam-Level FAQs

Q46: What is hysteresis loss?
Energy lost due to repeated magnetization cycles.

Q47: What is eddy current loss?
Loss due to circulating currents in the core.

Q48: What is all-day efficiency?
Efficiency over 24 hours considering varying loads.

Q49: What is polarity test?
Test to determine winding polarity.

Q50: What is open-circuit test?
Used to measure core losses.

 principle of T/F
Auto transformer

What is voltage