Introduction to Synchronous Generator, Working, Construction, Types & Applications

Hi friends, I hope all of you are fine. In today’s tutorial, we are gonna have a look at Introduction to Synchronous Generator. In electrical engineering particularly in power production, there are 2 main sources of energy conversion, first is the motor and the other is generator. The generator is a device that produces electrical energy and motor produces mechanical power. The motors and generators are further divided into AC and DC motors and generators according to their power generation and use.

The synchronous generator is a type of AC generator. For energy generation in wind turbines, a steam turbine or hydro turbines synchronous generator is used. In today’s post we will have a look at its construction, working, excitation method, etc. so let’s get started with the introduction to a synchronous generator.

Introduction to Synchronous Generator

• The synchronous generator is also known as an alternator, it converts mechanical power into electrical.
• The electric energy we used in our homes or industries is mostly produced by the synchronous generator.
• There are many sources of energy conversion in the world but most of the energy is converted by the synchronous generator.

• They convert mechanical energy into electrical energy up to the 1500 megawatts.
• The synchronous generators used in our industries are constructed by a static or rotating magnetic field.
• The construction of the synchronous generator built by the static field is like the DC generator.
• In the rotating magnetic field generator, the static armature is known as the rotor.

Working Principle of Synchronous Generator

• The working of a synchronous generator is based on Faraday’s Law of electromagnetic induction.

emf= dΦ/dt

• This law says that the rate of change of flux in any device will produce emf in that device. If a device is static and the field is rotating it will also produce field in the device.
• In case of a synchronous generator, the rotor is rotating, and it produces field in the stator.
• For an understanding of emf induced in any device study the article on the voltage induced in the loop

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Synchronous Generator Construction

• In a synchronous generator, there is no residual magnetism to produce self-excitation like the induction motor and induction generator.
• The external direct current supply is given to the rotor and it produces field in the rotor. When we rotate the rotor by a mechanical way, its field link with the stator windings and produce a voltage in the stator.
• There are 2 terms we use to represent windings in the machines first one is armature winding and the other one is field winding.

• The windings that produce the main field in a machine called field winding and the windings that produce voltage is called the armature.
• In case of the synchronous generator, the field windings are the rotor windings and the stator windings are the armature windings.

Stator of Synchronous Generator

• The stator is the static part of the generator it provides the covering for the internal construction of the machine.
• It is constructed by laminated sheets of aluminum, there are slots at its inner periphery which used to hold the windings.

Rotor of the Synchronous Generator

• The rotor of the generator is an electromagnet, it is connected with the external DC source. The external source produces a voltage in the rotor, the field of the rotor induced a voltage in the stator.

• There are 2 main types of synchronous generators.
  • Salient Pole Rotor
  • Non-Salient Pole Rotor

Salient Pole Rotor

• This type of rotor has many no of poles that are manufactured on wheel-like arrangements.
• These poles are constructed from steel and are laminated.
•  The windings of the rotor are wound on these poles and at the corners, windings are controlled by the pole shoe.
• The dia of the salient pole rotor is higher and its axis is short.
• The salient pole rotor has 4 or large no of the pole.
• The given diagram shows the salient pole rotor.

Non-Salient Pole Rotor 

• The word ‘salient’ means to stick out, Non-salient pole is such a pole that is manufactured with the surface of the rotor they are not out of the surface like the salient poles.
• This type of rotor is used where 4 or more poles are required at the stator.

DC Excitation of Synchronous Generator

• As we discussed that the synchronous generator is not a self-start machine. It must connect with the external source.
• To excitation of the generator, the DC supply is connected with the circuitry of the rotor.

• As the rotor rotates so there is some precaution that we should keep in mind, connecting the rotor with the DC source.
  • Try to connect the windings of the rotor with the DC source through the slip ring and graphite-made brushes, if you connect the windings directly with the dc source, it causes serious sparks and the motor will damage.
  • Connect such dc source with the generator that remains permanently connected to the rotor.
• The slip ring is rings made by some metal, they are mounted on the shaft of the generator and have some insulation.
• Every end of the rotor’s windings is joined with the slip rings and the static brushes are mounted on the slip rings.
• The brushes are always mounted on the slip ring because they are made from graphite which has less resistance.
• If one terminal of the DC source is joined with one carbon brush, then the other will be connected with the second brush.
• The important thing you should note is that the dc voltage you provided to the generator should have the same value irrespective of the variation in the speed and angular position of the generator.

Problems of  Slip Ring and Brushes in Synchronous Generator

• As we discussed that we use slip ring and carbon brushes to provide the dc supply to the windings of the rotor. These two components cause some difficulties.
• As the brush is made from carbon that is soft material of nature, so their condition must be monitored after some time and maybe they should be replaced after some time. This process increases the maintenance cost of the machine.
• There is some loss of voltage at the brushes which increases the field current and power loss at the field windings.
• For a smaller synchronous machine, this method of voltage is used because it is a cheap method for these machines.

Brushless Exciters of Synchronous Generator

• The slip ring and brush technique do not work for the larger motor and generator. For dc supply to the rotor, they used brushless exciters.
• The brushless exciter is itself an ac generator, as any machine has 2 circuitries, first is the armature and the other is field.
• When this exciter relates to any synchronous machine, its field circuitry resides on the static part of the synchronous machine and armature circuitry is mounted on the shaft of the machine.

• As the output of the exciter is 3-phase ac which is then converted to dc by the rectification, this rectification circuitry is also connected on the shaft of the synchronous generator.
• Then the output of the rectifier sent to the field circuitry of the rotor. By varying the field current of the exciter, we can easily control the field current of the synchronous generator.
• As there is no physical connection between the stator and rotor of the generator, so the exciter needs a very lesser amount of repairing the slip rings and brushes.
• The arrangement of the brushless exciter with a generator is shown in the given diagram.

Pilot exciter of the Synchronous Generator

• To make the construction of the synchronous generator simplest and the excitation of the generator independent from the exterior circuitry a pilot exciter was introduced on the machine.
• The pilot exciter is also an alternating current generator it has a permanent magnet instead of the armature circuitry which is connected with the shaft and its 3 phase windings are joined with the stator.
• It generates the power for the exciter’s field circuitry, this power then governs the field circuitry of the generator.
• If a pilot exciter relates to the shaft of the rotor then there will be no need of the exterior power supply to operate the generator.
• Most of the synchronous generator also has a slip ring and brushes with the brushless exciter, in case of an emergency backup power supply is exists.
• A given diagram shows the pilot exciter circuit.

Speed of Rotation of a Synchronous Generator

• As we have discussed that the rotor of the synchronous generator is an electromagnet, it joined to the dc source.
• The direction of the field of the rotor will be the direction of the rotation of the rotor.
• The speed rotation of the field in the ac machine has a relation with the frequency at the stator, is given as.

f_e =n_mP/120

• • f_e in this equation is the frequency of the stator.
  • n_m it is the speed of the field.
  • P is the no of poles
• As the speed of the rotation of the rotor is equal to the speed of the field, this equation shows the relation of the rotor speed to the frequency of the stator.
• The electrical energy is generated at the fifty or sixty-hertz frequencies, so the generator should move at a constant speed.
• For example, to produce the sixty-hertz energy in a 2-pole machine the speed of the rotor should be 3600 revolutions per minute.
• And to produce the fifty-hertz energy in a 4-pole machine the speed of the rotor should be 1500 revolution per minute.

 Synchronous Generator vs Induction Generator

• These are some similarities and dissimilarities between synchronous and induction generators that are described here.
• In a synchronous generator, the speed of rotation of the rotor is equal to the speed of the rotation of the field at the stator.

f = (Nx P)/120

• But in the case of a synchronous generator, the frequency of output voltage is controlled by the power system with which it is linked.
• The synchronous generator is not self-excited there is a need of a special direct current source to connect with it.
• While there is no need of a special external source for the induction generator, as it is the self-start machine.
• The presence of carbon brushes and separate dc sources make the complicated construction of a synchronous generator and increase its price.
• But the induction generator is self-start and there is no need of carbon brushes and slip rings so its construction is simplest and its maintenance price is also less.

Feature	Synchronous Generator	Induction Generator
Principle of operation	A rotating magnetic field cuts the stator windings, inducing an electric current	Rotating magnetic field produced by stator windings induces a current in rotor windings
Speed of rotation	Must be synchronized with the grid frequency	Can operate at any speed
Excitation system	Requires a separate DC excitation system	Does not require a DC excitation system
Power factor	Can be controlled	The power factor is lagging
Applications	Large power plants, grid balancing	Stand-alone power generation, distributed generation

Cooling of Synchronous Generator

• When the generator is operated at a heavy load then a huge amount of heat produces in the generator which can be caused of dangerous for the internal structure of the synchronous generator.
• To reduce or minimize heat in the generator there are several methods are used that are described here.

Radial Flow Ventilation System

• In this type of colling method cool air is passed through the stator with the ducts and from another side of the stator it comes out.

Advantages of Radial Ventilation

• In this method of colling power losses for ventilation is less.
• It can be used for both less ratings and high-rating generators.

Hydrogen Cooling of a Synchronous Generator

• In this method, hydrogen is used for the colling of a generator. Before its use for colling its ratio with air must be controlled and keep (9/1) hydrogen to air.
• As if the air exists in environments where hydrogen is performed it can create expulsion.

Difference between Synchronous Motor and Synchronous Generator

• The synchronous generator is such a device that transforms mechanical energy provided by the prime mover to electrical power, but the motor transforms electrical into mechanical energy.
• But these to the motor are similar in physical structure.
• Any synchronous machine either a motor or a generator can provide active power to or get active power from a system connected and provide reactive power to and get reactive power from the system.
• All these 4 possibilities of these machines are shown in a given figure in the shape of the phasor diagram.

• You can note from the given figure that.
• The unique feature of a synchronous generator (providing P) is that internally generated voltage E_A lies ahead Vø, but in case of a motor internal generated voltage, E_A lies behind Vø.
• The different feature a machine (either generator or motor) providing reactive power Q is that E_Acosδ> Vø, irrespective of whether the machine is acting as a generator or as a motor. A machine that is taking Q has E_Acosδ< Vø.

Synchronous Motor vs Synchronous Generator

arameter	Synchronous Motor	Synchronous Generator
Function	Converts electrical energy to mechanical energy	Transform mechanical energy to electrical energy
Operation	Uses electrical power	Generates electrical power
Prime Mover	It need an external power source (electricity)	it needs a mechanical prime mover (e.g., turbine)
Rotational Speed	Rotates at a constant synchronous speed (synchronized with the supply frequency)	Rotates at a constant synchronous speed (synchronized with the mechanical input)
Slip	Runs at zero slip (synchronous speed matches supply frequency)	Operates at zero slip (synchronous speed matches mechanical input)
Excitation	It uses excitation to maintain synchronous speed	needed excitation to produce an electrical output
Mechanical Load	Provides mechanical work to a load	Converts mechanical work into electrical power
Power Factor	operate at lagging or leading power factor	Normally operates at a leading power factor
Applications	Used in industrial drives, pumps, fans, conveyor systems, etc.	Used in power plants, hydroelectric stations, wind turbines, etc.
Connection	Can be connected in star or delta configuration	it connected in star (wye) configuration
Control and Regulation	Can be controlled and regulated easily	It uses external control for synchronization and voltage regulation
Starting	Requires external means (e.g., induction motor) for starting	Self-starting once synchronized with the grid
Electrical Output	Does not generate electrical power output	Generates electrical power output
Excitation Sources	Requires a DC excitation source	Excitation can be provided by external DC source or self-excited

Applications of Synchronous Generator

• These are some applications of synchronous generators that are described here.
• It is mostly used in such a system where constant speed is required.
• They also maintain the power factor of the system.
• Almost all power generation plants use synchronous generators due to the constant frequency providing the capability.

Faqs

Introduction to synchronous generators

A synchronous generator is an electromechanical device that transforms mechanical energy into electrical energy in the shape of alternating current (AC). It is known as a synchronous generator because it should be driven at a constant speed, known as the synchronous speed, to generate AC power of the required frequency.

Details of synchronous generators

A synchronous generator has 2 main parts: the stator and the rotor. The stator is the static part of the generator and comes with a set of windings that are attached to the output terminals. The rotor is the rotating part of the generator and windings that are excited by a DC current. When the rotor is rotated, it produces a rotating magnetic field. The rotating magnetic field produces an AC current in the stator windings.

Types of synchronous generators

There are 2 main types of synchronous generators: salient pole generators and non-salient pole generators. Salient pole generators have a rotor with poles that are separated from each other. Non-salient pole generators rotor with poles that are smoothly distributed about the circumference.

Main parts of a synchronous generator

The main parts of a synchronous generator are:

• Stator: The stator is the static part of the generator and has a set of windings that are attached with the output terminals.
• Rotor: The rotor is the rotating component of the generator and has a set of windings that are excited by a DC current.
• Field poles: The field poles are the permanent magnets or electromagnets that produce the rotating magnetic field in the rotor.
• Air gap: The air gap is the area between the stator and rotor.
• Bearings: The bearings supported the rotor and help it to rotate smoothly.
• Cooling system: The cooling system removes heat from the generator.

Why synchronous generators are commonly used

Synchronous generators are used since they have different advantages than other types of generators, like

• They can operate at a wide range of speeds.
• They can be employed to generate AC power at different frequencies.
• They are very effective
• They are reliable and have a long lifespan.

Why do we use synchronous generators?

Synchronous generators are used in different applications, like

• Power generation: Synchronous generators are used to produce electricity for homes, businesses, and industries.
• Grid stability: Synchronous generators are employed to maintain the stability of the power grid.
• Motor drives: it can be used to drive motors in like as pumps, fans, and compressors.
• Uninterruptible power supplies (UPS): This generator can be used to provide backup power in the case of a power outage.

Advantages and disadvantages of synchronous generators

The advantages of synchronous generators are

• High efficiency
• Wide operating speed range
• Ability to generate AC power at a variety of frequencies
• Good transient response
• Long lifespan

The disadvantages of synchronous generators are

• They are more complicated and expensive than other types of generators.
• They need a DC power source to excite the rotor.
• They can be damaged if they are not synchronized accurately to the grid.

Does a synchronous generator always run with

A synchronous generator always operates with a prime mover, like a steam turbine, water turbine, or diesel engine. The prime mover offers the mechanical energy that is needed to rotate the rotor.

Difference between a normal generator and a synchronous generator

The main difference between a normal generator and a synchronous generator is that a normal generator does not have a rotating magnetic field. The AC current is produced by the relative motion between the stator windings and the rotor. A synchronous generator has a rotating magnetic field, which is produced by the field poles on the rotor. The AC current is produced by the interaction between the rotating magnetic field and the stator windings.

How do you run a synchronous generator as a motor?

To operate a synchronous generator as a motor, the rotor should be connected to a DC power source. The DC power source energizes the field poles on the rotor, which produces a rotating magnetic field. The rotating magnetic field interacts with the stator windings, which induces an AC current in the stator windings. The AC current produces a magnetic field in the stator windings, which opposes the rotating magnetic field. This opposition creates a torque that rotates the rotor.

Is the alternator a synchronous generator?

Yes, an alternator is a synchronous generator. The term “alternator” is used to define to a synchronous generator that is used to produce AC power.

• What is another name for a synchronous generator?

An alternator is another name for a synchronous generator.

• What are the 4 characteristics of a synchronous motor?

The 4 characteristics of a synchronous motor are: * It operates at a constant speed, which is known as synchronous speed.

It can be used as a generator or a motor.

It has a high power factor.

It can be used to control the voltage and frequency of the power grid.

• What is the voltage regulation of a synchronous generator?

Voltage regulation is the variation in the output voltage of a synchronous generator as the load varies

• Are synchronous generators leading or lagging?

Synchronous generators are leading. It shows that the current they geneates leads the voltage they produce.

• What is the frequency of a synchronous generator?

The frequency of a synchronous generator is defined by the speed of the rotor and the different poles.

• Why are synchronous generators operated in parallel?

Synchronous generators are operated in parallel to offer a reliable and stable source of power. When many generators are operated in parallel, they must be synchronized so that they are all generating the same voltage and frequency.

• What is the maximum power developed in a synchronous generator?

The maximum power produced in a synchronous generator is find by the size and design of the generator.

• What are the advantages of synchronous generators over induction generators?

The advantages of synchronous generators than induction generators are

They provdies higher power factor.

It can be used to control the voltage and frequency of the power grid.

It is effective.

• Is synchronous generator self starting?

No, synchronous generator is not self starting. They have to brought up speed through outer power supply, like motor.

• What is a synchronous motor for dummies?

A synchronous motor is a type of motor that operate at a constant speed, which is known as synchronous speed. It is known as synchronous motor since it must be synchronized with the grid frequency in order to operate.

• Do synchronous motors run on AC or DC?

Synchronous motors run on AC.

• What are the 4 methods of starting synchronous motors?

The 4 methods of starting synchronous motors are:

• Direct on-line starting
• Star-delta starting
• Auto-transformer starting
• Ward Leonard starting

• What is synchronous motor?

A synchronous motor is a type of motor that uses a rotating magnetic field to rotate shaft. The rotating magnetic field is produced by a set of electromagnets on the rotor of the motor.

• What is the main advantage of using a synchronous motor?

The main benfit of using a synchronous motor is that it has a high power factor. That define that it uses less reactive power from the grid, which can increases the efficiency of the power system.

• How is a synchronous motor different from a normal motor?

A synchronous motor is different from a normal motor in that it runs at a constant speed. Since the rotating magnetic field of the motor is synchronized with the frequency of the power grid. Normal motors, can run at different speeds based on the load.

You can also read some related topics to a synchronous generator that are listed here.

Synchronous Generator Equivalent Circuit  

Synchronous Generator Phasor Diagram

Synchronous Generator Power and Torque

Synchronous Generator Parameters

Synchronous Generator Operating Alone

Synchronous Generator Parallel Operation

Synchronous Generator parallel with Large Power system

Synchronous Generator Parallel with same Size Generator

Synchronous Generator Ratings

Synchronous Generator Capability Curves

Synchronous Generator Transients

 

 

So, friends, it is a detailed article on the synchronous generator I have mentioned each and everything related to a synchronous generator in this tutorial. See your next tutorial Equivalent Circuit of Synchronous Generator.