How Generators and Transformers Work: Key Principles for Students
These two devices work based on Faraday’s law of electromagnetic induction principle. The “Generators” generate current, and transformers convert between current and voltage. Here, we discuss in detail the important concepts of generators and transformers.
Table of Content
Generator and Transformer: An Introduction
What is an Electric Generator?
Working Principle of an Electric Generator
Types of Generator
AC generator- types, applications
DC generator- types, applications
What is a Transformer?
Working principle of a Transformer
Types of transformer
Application of transformer
What is a Generator?
A generator is defined as a machine that, with the help of magnetic induction, changes the mechanical energy into electrical energy.This is possible due to the revolution of coils in a magnetic field, i.e., a generator consisting of exterior fields also maybe because of the revolution of two electromagnets around a fixed coil, i.e. a generator consisting of internal fields.
An Electric Generator: Working Principle
The generator is made of a rectangle-shaped coil having several copper wires which wound over an iron core. This coil is called the armature. The function of this armature is used to increase the magnetic flux. A strong permanent magnet is being placed, and the armature rotates in between these magnets. Here the magnetic lines produced are perpendicular to the armature's axis. There are two slip rings also connected to the armature’s arms. These rings are used for providing movable contact, and two metallic brushes are also connected to the slip rings, which help in passing current from the armature to the slip rings. Finally, the current is passed through a load resistance that is connected across the two slip-rings.
The position of the armature keeps changing at different time gaps. At the stage when the magnetic field lines are positioned perpendicular to the coil, the coil is then rotated in the magnetic field to increase the induced e.m.f produced. It occurs in this position as the number of intercepting-magnetic field lines are maximum here.
Types of Generators:
The generators are classified further into two types as AC generators and DC generators:
AC Generators:
AC-generators are also known as alternators. The principle of its working is based on electromagnetic induction.
AC generators are classified into two types:
Induction Generator: It does not require any DC excitation, frequency control or regular control. The induction concepts happen when inductor coils turn in the magnetic field, producing a current and a voltage.
Synchronous Generators: These are large size generators that are generally used in power plants. These are considered as rotating field or armature types. In the rotating armature type, the armature is positioned at the rotor and the field is at the stator end. The current in the rotor armature is taken through brushes and slip rings. These generators are used for low power requirement applications.
However, the Rotating field type of alternator is widely used due to its high power generation capability, and it does not require slip rings and brushes.
Two-phase or Three Phase-Generators:
The two-phase generator generates two different voltages, and each voltage is considered a single-phase voltage. However, both the generated voltages are not entirely dependent on each other.
The three-phase alternator has 3 single-phase windings present apart in such a way that 120º displaces the voltage generated in any of the phases from the other two.
These generators are used in applications like naval, oil and gas extraction, wind power plants and mining machinery etc.
Application Advantages of AC Generator:
As they do not require brushes, these Generators are generally maintenance-free.
These generators are small in size in comparison to DC generators.
Losses are relatively less than DC machines.
AC Generator breakers are relatively small in size than DC breakers.
DC Generators:
The DC generator is used for converting mechanical energy into direct current electricity.
It is typically found in off-grid type applications. These generators give a continuous power supply directly into electric storage machines and DC power grids without the use of novel equipment. In the case of the DC generator also, the working principle is based on Faraday’s law of electromagnetic induction.
When the conductor is placed in the varying field, an electromagnetic force is induced in the conductor. The magnitude of this emf, i.e. induced, can be determined with the help of the emf - equation used for DC generators. Induced current circulation takes place within its closed path. According to Fleming’s right-hand rule, the direction of induced current can be determined.
Emf- equation of the DC generator is given as:
Eg = P Ф NZ / 60 A
Where
P is the number of field poles.
Φ is the flux produced / pole in Weber.
Z is the total no.’s of armature conductors.
A is the no.’s of parallel paths in the armature.
N is the rotational speed of armature in round per minute (rpm)
Types of DC Generators:
There are three main types of DC Generators:
Permanent Magnet DC Generator:
There is no need for external field excitation in Permanent magnet type DC generators as it has permanent magnets for producing the flux.
Application: These may be used for low power applications like dynamos etc.
Separately Excited DC Generator:
This separately-excited DC generator requires external field excitation for producing the magnetic flux. Here we can also vary the excitation for getting variable output-power.
Application: These are used in the electroplating process and electrorefining applications etc.
Self-Excited DC Generator:
Self-excited DC generators can produce their magnetic field when it is as they have residual magnetism in the poles of the stator. These are very simple in design, and there is no requirement of the external circuit to vary the field excitation.
These self-excited DC generators are further classified into three, i.e. shunt, series, and compound-generators.
Application: These generators are used in applications like charging of batteries, welding, ordinary lightening-applications etc.
Advantages of DC Generators:
Following are the main advantages of the DC generator:
In this case, the cost of cables comes to be less as there is no shielding from radiation required.
Here, the fluctuations in the generator can be reduced by a constant arrangement of the coils.
In the case of the DC generator, the operating features depend on the field winding etc.
Transformer: An Introduction
The device converts the voltage as the higher or lower voltages. There are different voltage levels, used when electrical power is generated, during the transfer.
A transformer is usually made of two coils, i.e. primary/field and secondary/inductance, between which are kept apart so that there is no electrical contact in between. When we allow passing a current through the primary coil, there is a generation of the magnetic field which changes. However, it maintains the same frequency. It results in generating an alternating voltage in the secondary coil at the same time. An alternating current passes through a secondary coil during the closed electrical circuit.
The greater the difference in between the number of windings in the primary and secondary coils, the greater will be the difference in between their voltages also, so they are directly proportional.
Working Principle of Transformer:
The transformer’s working principle is based on mutual inductance between the two circuits, which are linked by a common magnetic flux.
Types of Transformers:
Two types of transformers are there, as given below:
Step-Up Transformer:
These transformers convert a low voltage into a high voltage. In this case, the number of turns in the primary coil is less than in the secondary coil, i.e. Np <Ns.
Step-Down Transformer:
These transformers convert a high voltage when the current decreases into a low-voltage when the current increases, the no. of turns in the primary coil is greater than the number to the secondary coil, i.e. Np ˃ Ns.
As per Faraday’s law of electromagnetic induction, the induced e.m.f is given by:
e = - d Ф / dt
ep = - d Фp / dt
es = - d Фs / dt
By using the above equations, we get,
es = Ns x Np x ep
The ratio Ns / Np = K
Apart from this, there may be different types of transformers based on various parameters as follows :
Based on Design
Core-type transformer
Shell-type transformer
Based on the Cooling Method
Oil filled self-cooled type.
Oil-filled water-cooled type.
Airblast type etc.
Applications of Transformer:
Following are three basic applications of Transformer:
To step up the current and voltage.
To step down the current and voltage.
Prevention of DC to the next circuit in the DC transformers etc.
FAQs on Generator and Transformers: Concepts, Types, and Applications
1. What is the main difference between an electric generator and a transformer?
The primary difference lies in their function regarding energy conversion. An electric generator is a device that converts mechanical energy into electrical energy. In contrast, a transformer does not generate energy; it transfers electrical energy from one circuit to another, changing the voltage and current levels of an alternating current (AC) supply.
2. How does an electric generator work based on its principle?
An electric generator operates on the principle of electromagnetic induction. This principle states that when a conductor (like a coil of wire) moves through a magnetic field, or when the magnetic field around it changes, an electromotive force (or voltage) is induced across the conductor. This induced voltage drives the electric current, thus generating electricity.
3. What are the main types of electric generators?
Electric generators are broadly classified into two main types based on the kind of current they produce:
- AC (Alternating Current) Generators: These produce an electric current that periodically reverses direction. They are the most common type used for large-scale power generation.
- DC (Direct Current) Generators: These produce an electric current that flows in only one direction. They are often used in specific applications like battery charging and DC motors.
4. What is the fundamental purpose of a transformer in an electrical system?
The main purpose of a transformer is to change the voltage of an alternating current to a different level. It is used to step-up (increase) voltage for efficient long-distance power transmission and to step-down (decrease) voltage to safe levels for use in homes and businesses. This ability to change voltage is crucial for the modern power grid.
5. How can you tell the difference between a step-up and a step-down transformer?
You can identify them by the number of turns in their coils. A step-up transformer has more turns in its secondary coil than in its primary coil, which increases the voltage. A step-down transformer has fewer turns in its secondary coil compared to the primary coil, which decreases the voltage.
6. Why do transformers only work with alternating current (AC) and not direct current (DC)?
Transformers function based on the principle of mutual induction, which requires a constantly changing magnetic field to induce a voltage in the secondary coil. Alternating current (AC) naturally creates this changing magnetic field as it flows back and forth. Direct current (DC) flows in one direction and creates a steady, unchanging magnetic field, which cannot induce a voltage in the secondary coil. Therefore, transformers are incompatible with DC.
7. If a generator already produces electricity, why is a transformer still necessary in a power grid?
While a generator produces electricity, it's often at a voltage that is not efficient for long-distance travel. Transmitting power at low voltage over long distances results in significant power loss due to heat. A transformer is used to step up the voltage to a very high level for transmission, which reduces current and minimises this loss. Another transformer then steps the voltage down to a safe, usable level before it enters our homes.
8. What are the main causes of energy loss in a real-world transformer?
Even highly efficient transformers lose some energy, primarily in four ways:
- Copper Loss: Heat produced due to the electrical resistance of the copper windings.
- Hysteresis Loss: Energy lost as the magnetic domains in the iron core repeatedly reverse direction.
- Eddy Current Loss: Small circulating currents induced in the iron core by the changing magnetic field, which generate heat. Using a laminated core helps reduce this.
- Flux Leakage: When not all of the magnetic field from the primary coil links with the secondary coil.
9. What is the magnetostriction effect and why does it cause transformers to hum?
Magnetostriction is a property of ferromagnetic materials, like the iron core of a transformer, that causes them to slightly change their shape or dimensions when subjected to a magnetic field. As the alternating current flows, the core expands and contracts minutely with the changing magnetic field. This rapid vibration, happening 50 or 60 times per second, creates the characteristic humming sound associated with transformers.
10. Can a transformer be used in reverse? For instance, can a step-down transformer function as a step-up one?
Yes, theoretically, a conventional transformer is a reciprocal device. If you connect a power source to the secondary coil of a step-down transformer, it will act as a step-up transformer. However, transformers are often specifically designed and optimised for a particular direction of power flow, considering factors like insulation levels and winding thickness, so using them in reverse may not be as efficient or safe as using a purpose-built one.
