From power grids to small chargers, transformer is an essential tool that works like magic! They transfer electrical energy between circuits by changing voltage and current levels without making direct electrical contact. This article describes in depth how transformers function, including their operating principle, construction, types, working mechanism, and practical uses. Whether you're a student, engineer, or simply an enthusiast, this comprehensive book will help you comprehend transformers better than most other basic resources.
What Is a Transformer?
Transformer refers to transferring things from one location to another. A transformer is a piece of equipment that is static or stationary and turns electrical power from one circuit into electrical power with the same frequency in another circuit. Transformers are crucial for electromechanical energy conversion even if they don't have any moving elements. They enable electricity transmission at a voltage level that results in low costs, safe distribution, and utilization by allowing the voltage to be adjusted.
Working Principle of Transformer:
The basis of a transformer’s operation is quite interesting. A potential difference develops across the conductor's terminals whenever a closed conductor is exposed to a fluctuating magnetic field. Here Faraday’s law works.
Faraday’s law: The induced electromagnetic field (emf) in a closed conductor exposed to a fluctuating magnetic field is equal to the flux linkages' rate of change. The induced voltage e = – Ndφ / dt volt
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| Working Principle of Transformer (Source: circuitglobe.com) |
Step-by-Step Working Principle:
1. The primary coil receives an application of alternating current (AC).
2. In the core of the transformer, this current produces a time-varying magnetic field.
3. Through the magnetic core, the secondary coil is connected to the magnetic field.
4. The secondary coil experiences an electromotive force (EMF) as a result of this fluctuating magnetic flux.
5. If the EMF is connected to a load, a current is produced in the secondary winding.
Construction of a Transformer:
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| Construction of a Transformer |
Primary winding: Copper wires are used to wind this straightforward coil. The
necessary magnetic flux is produced by this winding whenever an active AC
source is connected across it. Since it is a closed coil, current flows anytime
an AC voltage is put across it. Additionally, an alternating magnetic field is
created around the coil as a result of this current flow. The transformer's
primary magnetic field is developed via this winding. This winding is known as
the primary winding since it is from this point that the flux generation and
magnetic field creation begin. A transformer's input part is called the primary
winding.
Core: The core provides the windings with robust mechanical support and acts
as the required conduit for the magnetic fluxes. Laminated silicon steel or
soft iron are typically used to make cores. The magnetic fluxes are confined
when they are generated in the primary winding and then move through the core.
A common core connects the primary and secondary windings. The majority of the
generated magnetic fluxes will pass through this magnetic core since it
provides a low reluctance path. Thus, the magnetic core directs them to the
secondary winding.
Secondary winding: The secondary winding has a different number of turns than
the primary, but it is still a copper winding. After going through the magnetic
core, the produced magnetic fluxes will use the mutual induction technique to
connect the secondary winding. The secondary winding terminal, to which the
load is always connected, is where a transformer's output is always taken.
Why Transformer's rating in kVA:
Transformers' rating in kVA instead of kW because their losses depend on voltage and current, not on the power factor. Transformers don't know the type of load, whether it's resistive or inductive. Rating them in kVA ensures they can handle all kinds of loads safely.
Types of Transformers
Transformer Types by Function
1. Step-Up Transformer: Secondary voltage is greater than primary voltage, and
is used in power stations to transmit electricity over long distances.
2. Step-Down Transformer: Secondary voltage is less than primary voltage and
is used in homes and factories to reduce voltage for safe usage.
Types of Transformers (Based on Construction)
1. Core-Type Transformer: Windings surround the core limbs and are commonly
used in high-voltage applications.
2. Shell-Type Transformer: The Core surrounds the windings and offers
better mechanical strength and insulation.
3. Berry-Type Transformer: A core composed of laminated steel sheets arranged in a cylindrical (radial) design is used in a Berry-type transformer, and windings are positioned around the core's perimeter, with the entire system encased in a magnetic shell. These high-efficiency transformers are particularly used in power stations.
According to the phase:
(a) Single-Phase Transformer
(b) Three-Phase Transformer
According to the method of cooling:
(a) Self-Cooled
(b) Air forced cooled
(c) Oil-cooled
(d) Forced oil-cooled
According to the frequency groups:
(a) Power frequency transformers.
(b) Audio frequency transformers.
(c) Radio frequency transformers.
There are many other types of transformers that are present according to the specific applications.
Distribution Transformer: Distribution transformers are used in
distribution network to step down the voltage level for feeding the local
consumers.
Power Transformer: Power transformers are used at each end of
transmission line in generating stations and substations for stepping up or
down the voltage level.
Current transformer: This transformer is used for the measurement of
electric current.
Potential transformer: These are used to step down the voltage to low value
which can be fed to a relay for protection purposes.
Instrument transformers: These called the instrument transformer because their
main function is to transform high currents and voltages to standardized low
and easily measurable values.
Auto transformer: A common winding is used as both primary and secondary
winding.
Losses in Transformers
While transformers are highly efficient (up to 98–99%), some losses do occur:
1. Copper Losses: This loss happens due to resistance in
windings and depends on current: P=I2R
2. Iron Losses: This loss occurs in the magnetic core and includes:
- Eddy current loss (reduced using laminated cores)
- Hysteresis loss (reduced using high-grade silicon steel)
3. Leakage Flux: All magnetic flux don’t link both windings, but rather cause leakage reactance, which can affect voltage regulation
Efficiency of a Transformer
Efficiency is calculated as:
Efficiency=Output Power/Input Power×100%
For large power transformers, efficiency often exceeds 98%. When iron and copper losses are equal, efficiency is maximized.
Cooling Methods
From losses, heat is produced. To manage it, several cooling methods are used:
Air natural cooling: Used for small transformers
Oil-immersed cooling: Used for large distribution
transformers
Forced air/oil cooling: Used for high-capacity industrial
transformers
Applications of Transformers
The utilization of transformers in electrical systems across various sectors:
1. Power Transmission: Step-up transformers boost voltage for long-distance transmission, and step-down transformers reduce voltage near load centers
2. Electronics: Employed in Power adapters, chargers, TVs, radios, etc.
3. Industrial Equipment: Utilized in welding machines, furnace transformers, and isolation transformers. They are customized for specific current and voltage ratings.
4. Measurement & Protection: Current Transformers (CTs) and Potential Transformers (PTs) are used in metering and protection relays
Why Transformers Only Work on AC?
In transformers, voltage is induced by changing magnetic field. Since direct current (DC) provides a constant magnetic field, it cannot induce EMF in the secondary winding. Therefore, transformers do not work on DC. It can also cause overheating and insulation failure due to constant high core flux.
Conclusion
Transformers enable the effective distribution and transfer of electrical power, making them essential components of electrical systems. Voltage transformation is made possible by their electromagnetic induction-based operation, which eliminates the need for physical contact between circuits. Transformers are becoming smarter, smaller, and more efficient due to technological and material breakthroughs. Knowing how a transformer operates is essential to understanding its many uses and serves as a foundation for electrical engineering coursework.
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