The motor serves the purpose of converting electrical energy into mechanical form. Motors are categorized into AC motors and DC motors based on the type of power supply. In this post, we will talk about the different types of three-phase induction motors with working and applications.
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The induction motors especially three-phase induction motors are by and large used AC motors to convey mechanical power in modern applications. 80% of the motor is a three-phase induction motor among all motors used in undertakings. Consequently, the induction motor is the fundamental motor among any excess types of motor.
A three-phase induction motor is a type of AC induction motor that deals with a phase supply when diverged from the single-phase induction motor where the single-phase supply is supposed to work. The three-phase supply current makes an electromagnetic field in the stator winding which prompts the production of the torque in the rotor bending of the three-phase induction motor having a magnetic field. Next, we will be Going Through Faraday's Law of Induction Motor.
Faraday's law of electromagnetic induction is a significant decision that figures out the fundamental movement of a three-phase induction motor. It was sorted out by Michael Faraday and portrays the association between a changing magnetic field and the prompted electromotive force (EMF).
The basic idea of Faraday's regulation is summarized as follows
Exactly when the attractive field around a conductor changes, it induces an electromotive power (EMF) in the conductor. The size of the induced EMF corresponds comparatively with the speed of progress of magnetic flux through the conductor.
Three-phase power is a type of electrical power transmission or distribution wherein three sinusoidal voltages of a similar recurrence are produced or utilized. It is a typical strategy utilized in electrical systems, industrial systems, and huge electrical motor. The three-phase system is more proficient and gives a more steady power supply contrasted with a single-phase system.
Here are the key components and attributes of three-phase power:
The construction of an induction motor is exceptionally basic and robust. It has predominantly two sections :
As the name recommends, the stator is a fixed piece of the motor. The stator of the induction motor comprises of three primary parts;
The stator outline is the external piece of the motor. The capability of the stator outline is to offer help to the stator core and stator winding. It gives mechanical strength to the inward pieces of the motor. The casing has balances on the external surface for heat dissemination and cooling of the motor.
The enclosure is cast for small machines and is produced for a large machine. Depending on the applications, the enclosure is constructed from die-cast or fabricated steel, aluminum/aluminum alloys, or stainless steel.
The stator core's function is to carry the alternating magnetic flux, leading to hysteresis and eddy current losses. To limit these losses, the core is coated with high-quality steel stampings with a thickness ranging from 0.3 to 0.6 mm.
These stampings are protected from one another by stain. All stampings stamp together looking like the stator center and fixed it with the stator outline.
An inward layer of the stator core has various number of slots.
The stator winding is positioned within the available spaces inside the stator core. The stator winding consists of three phases, and a three-phase power supply is provided to it.
The motor's pole count is determined by the internal arrangement of the stator winding, and it Controls the motor's speed. When the number of poles is higher, the speed is lower, whereas if the number of poles is fewer, the speed is higher. The poles are generally two by two. Subsequently, the absolute number of poles generally a much number. The connection between simultaneous speed and number poles is as displayed in the below equation,
Ns = 120f / P
Where;
f = Supply Frequency
P = Total Number of Poles
Ns = Synchronous Speed
As the end of winding connected with the terminal box. Consequently, there are six terminals (two of each phase) in the terminal box.
As per the application and sort of turning over techniques for motors, the stator winding is associated in star or delta and it is finished by the association of terminals in the terminal box.
As the name proposes, the rotor is an rotating part of the motor. As indicated by the type of rotor, the induction motor is delegated;
The development of the stator is same in the two kinds of induction motor. We will examine the kinds of rotors utilized in 3-phase induction motor in the accompanying part of types of three phase induction motor.
Three phase motors are arranged mainly in two classes in light of the rotor winding (Armature coil winding) for example squirrel cage and slip ring (wound rotor motor).
The condition of this rotor is seeming to be the condition of the enclosure of a squirrel. As a result, this motor is referred to as an induction squirrel cage motor. This kind of rotor is easy to make and durable to make. In this way, basically 80% of the induction motor is a squirrel confine induction motor.
The covered center of the rotor is shaped like a tube, and the outside edges have spaces. The spaces are not equivalent anyway it is skewed eventually. It helps with magnetic locking between the stator and rotor teeth. It achieves smooth action and diminishes the mumbling commotion. Because it increases the length of the rotor guide, the rotor resistance gets bigger.
Instead of a rotor winding, the squirrel cage rotor is made up of rotor bars. Aluminum, metal, or copper make up the rotor bars. End rings permanently shorten rotor bars. It creates a complete closure in the rotor circuit in this manner. Mechanical support is provided by welding or propping the rotor bars to the end rings. The rotor bars are short-circuited. Along these lines, it is ridiculous to hope to add external assurance from the rotor circuit. In this sort of rotor, the slip rings and brushes are not used. As a result, the construction of this kind of motor is simpler and more durable.
Slip-ring Induction Motor are generally called wound rotor motor. The rotor is made up of a tube-shaped center with slots on the outside edges. The rotor winding is placed inside the slots. In this type of rotor, the winding is arranged in such a way that the number of rotor winding slots matches the number of stator winding poles. The rotor winding can be related as a star or delta. The slip-rings are connected to the end terminals of the rotor windings. As a result, it is referred to as a slip-ring induction motor engine. The external block can without a doubt interact with the rotor circuit through the slip-ring and brushes. Likewise, it is uncommonly useful for controlling the speed of the motor and dealing with the starting force of the three-phase Induction Motor.
The outside opposition is used solely for the starting reason. The rotor copper loss will be increased if it remains connected while the system is operating. For the initial condition, a high rotor resistance is extremely advantageous. During the initial state, the rotor circuit is linked to the outside resistance in this manner. The metal collar short-circuits the slip-rings when the motor is running close to the actual speed. By this arrangement, the brushes and outside obstruction is taken out from the rotor circuit.
Copper loss from the rotor and brush friction are both reduced as a result of this. The rotor advancement is fairly perplexed stood out from the squirrel keep engine in light of the presence of brushes and slip-rings. This motor requires more maintenance. As a result, this motor might be used in applications requiring high starting force and variable speed control. In any case, the slip-ring induction motor is superior to the squirrel confine induction motor.
Variable Speed Control: One of the main advantages of slip-ring motors is the ability to control the speed and power by moving the external block related with the rotor windings. Because of this, they are suitable for applications that require variable speed.
High Starting Torque Control: Slip-ring motors can give high starting torque, and the external devices can be changed as per control the starting torque.
Smooth Acceleration: The ability to control the rotor resistance results in less mechanical pressure during starting and a smoother speed increase.
Complex Construction: Slip-ring motors have a more marvelous improvement as a result of the external securities and slip rings, inciting higher gathering and backing costs.
Higher Maintenance: The slip rings and brushes in the rotor require high maintenance, and the external devices are require.
Lower Efficiency: Due to the complexity of the rotor development and the additional losses in the external protections, slip-ring motors typically have lower performance than squirrel confine motors.
The stator winding is covered at 120˚ (electrically) to one another. When the stator winding is supplied with a three-phase power source, it results in the induction of a rotating magnetic field (RMF) within the stator circuit.
The speed of the rotating magnetic field is known as synchronous speed (NS).
As per Faraday's law, EMF induced in the guide because of the pace of progress of transition (dφ/dt). The rotor circuit cut the stator magnetic field and an EMF actuated in the rotor bar or rotor winding.
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The rotor circuit is a nearby way. Thus, because of this EMF current will move through the rotor circuit.
Presently, we realize that the current-conveying guide actuates the attractive field. In this way, the rotor current prompts a second magnetic field. The general movement between the stator flux and rotor flux, the rotor begins to rotate to diminish the reason for relative movement. The rotor attempts to get the stator transition and starts rotating. The heading of revolution is given by the Lenz's law. Furthermore, is toward the rotating magnetic field induced by the stator.
Here, the rotor current is created because of inductance. Hence, this motor is known as the induction motor.
The speed of the rotor is not exactly the speed of synchronous speed. The rotor attempts to get the alternating attractive field of the stator. Yet, it never gets it. Consequently, the rotor speed is slightly less than the synchronous speed. The synchronous speed is determined by the number of poles and the supply frequency. The difference between the rotor's actual speed and the synchronous speed is referred to as slip.
When the rotor's actual speed matches the synchronous speed, the slip is zero. However, in the case of an induction motor, this scenario is never encountered. This is because, at zero slip, both speeds are equivalent, resulting in no relative movement. Consequently, no electromotive force (EMF) is induced in the rotor circuit, and the rotor current becomes zero. As a result, the motor cannot operate. Despite this limitation, the induction motor is extensively used in industries due to its numerous advantages outweighing its disadvantages.
In conclusion, the three-phase induction motor stands as fundamental equipment and broadly used in electrical machine in different industrial applications. Its robust design, simplicity, and efficiency make it a favored decision for controlling a huge number of devices, from pumps and fans to conveyer systems. The motor's operation depends on the principles of electromagnetic induction, where the cooperation between the stator and rotor magnetic fields induces a rotating motion.
The main advantages of the three-phase induction motor is its self-starting capability, so for this advantage there is no need to external devices. Its ability to work with a constant speed under varying loads adds to its dependability in practical applications. Additionally, the absence of brushes in the design of the motor reduces the maintenance requirements, which contributes to its durability and longevity.
Despite these merits, it's fundamental to consider the motor's limitations, such as the difficulties in speed control and its inherent tendency to operate at synchronous speed. Engineers and analysts constantly investigate advancements, including the coordination of modern day control techniques and materials, to improve the motor's performance, efficiency, and flexibility in advancing modern scenes. In conclusion, the three-phase induction motor stays a foundation in electrical engineering, balancing conclusion with viability and consistently developing to meet the needs of different applications.
Let us assume that, A Three-phase induction motor with a synchronous speed of revolutions per minute (RPM) and a slip of 5%. The motor is connected to a 50Hz three-phase supply. Find the synchronous speed, actual rotational speed and Frequency of the Induced EMF.
Synchronous Speed
The synchronous speed (Ns) can be calculated using the formula
Ns = 120 x frequency / Number of Poles ,
For a 50 Hz supply and a motor with 4 poles:
Ns = 120 x 50 / 4 = RPM
Actual Rotational Speed
N = Ns x ( 1 - slip)
Given slip is 5% ( 0.05):
N = x ( 1 - 0.05) = RPM
Frequency of the Induced EMF
The slip frequency (fslip) is given by :
fslip = Frequency x Slip
For a 50 Hz supply and a slip of 5% :
fslip = 50 x 0.05 = 2.5 Hz
Hence, The induced EMF frequency in the rotor is 2.5 Hz.
What is a 3 Phase Induction Motor?
An electric motor converts electrical energy into mechanical energy, which is then supplied to different types of loads. Among the various types of motors, A.C. motors operate on an alternating current (A.C.) supply and can be categorised into synchronous motors, single-phase induction motors, three-phase induction motors, and special purpose motors. Of these, three-phase induction motors are the most commonly used for industrial applications because they do not require a starting device, making them efficient and cost-effective.
A 3 phase induction motor gets its name because the rotor current is induced by the magnetic field rather than direct electrical connections.
Operating Principle of a 3 Phase Induction Motor
The operating principle of a 3 phase induction motor is based on the production of a rotating magnetic field (r.m.f.). This principle is crucial for understanding how these motors work effectively in various applications.
Production of a Rotating Magnetic Field
The stator of a three-phase induction motor contains overlapping windings, offset by an electrical angle of 120°. When connected to a three-phase A.C. supply, the stator creates a rotating magnetic field that rotates at synchronous speed.
Synchronous Speed (N_s) = (120 x Supply Frequency) / Number of Poles
Typical motors are configured with 2, 4, 6, or 8 poles, impacting their speed and performance.
Production of Magnetic Flux and Torque Generation
For a three-phase induction motor to produce torque and generate mechanical movement, the rotor must carry current. Here’s how this process works:
Slip in Induction Motors
The difference between the synchronous speed of the stator and the actual speed of the rotor is called the slip. Slip is essential for the induction process, as it ensures that a relative motion exists between the rotating magnetic field and the rotor conductors. Without this difference, no e.m.f. would be induced, and therefore no torque would be generated.
Advantages of 3 Phase Induction Motors
A three-phase induction motor has several distinct advantages that make it suitable for industrial use:
Applications of 3 Phase Induction Motors
Due to these advantages, 3 phase induction motors are widely used in various industrial applications, including pumps, conveyors, compressors, and more. Their ability to convert electrical energy into mechanical energy efficiently makes them ideal for environments where reliability and minimal maintenance are crucial.
Three-phase induction motors are a cornerstone of industrial machinery, valued for their simplicity, efficiency, and cost-effectiveness. Understanding their principles, including the creation of a rotating magnetic field, slip, and the methods of torque production, is key to appreciating their widespread use in industrial settings. If you’re considering solutions that require robust and reliable mechanical power, a 3 phase induction motor is often the best choice.
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