One of the most popular kinds of DC motors is a DC shunt motor, in which the armature winding and field windings are connected in parallel (shunt). The motor has steady speed characteristics under different load conditions because to its arrangement. The DC shunt motor is essential to many industrial and technical applications due to its smooth operation and accurate speed regulation.
Working Principle of DC Shunt Motor
According to Faraday’s Law of Electromagnetic Induction, the DC shunt motor functions. Upon applying a voltage: Both the armature and the field winding are subject to current flow. A magnetic field is created by the field winding. This magnetic field is broken by armature conductors, and the interplay of the magnetic field and current-carrying conductors results in the development of a torque. Fleming’s Left Hand Rule determines the direction in which the motor begins to rotate. Because the DC shunt motor is coupled in parallel with a constant voltage source, one of its fundamental characteristics is that the field current is almost constant. As a result, even when the loads vary, the motor keeps its speed almost constant.
1. Generation of Field Current
The field windings, which are connected in parallel with the armature, receive the entire supply voltage when a DC supply is applied to the motor. Because of its high resistance, a comparatively modest current passes through the field circuit, creating a constant magnetic field.
2. Armature Communication
Current passes through the armature at the same time. A Lorentz force acts on the armature conductors as they move within the magnetic field created by the shunt winding, turning the rotor.
3. Production of Torque
Fleming’s left-hand rule controls the direction of the torque that is generated. Continuous rotation results from the torque created by the interaction of the current-carrying conductors (armature) and the magnetic field (from the shunt winding).
4. Back EMF
Back electromotive force (EMF) is a voltage that opposes the applied voltage and is created when the armature rotates, cutting the magnetic lines of force. By decreasing the net voltage across the armature as speed rises, this back EMF stabilizes the motor’s speed.
The basic idea behind a DC shunt motor is that a current-carrying conductor feels a mechanical force when it is exposed to a magnetic field. The Lorentz force law controls the force’s magnitude, while Fleming’s Left-Hand Rule determines its direction.
1. Configuration of Shunt Field Windings
The armature winding and the field windings are linked in parallel (shunt) in a DC shunt motor. Due to this similar relationship:
Both the armature and field windings get the same supply voltage.
The field winding carries a tiny, nearly constant current and has considerable resistance due to its numerous turns of fine wire. As a result, the air gap between the stator and rotor creates a constant magnetic field.
2. The Movement of Current Through Armature
In addition, current flows through the armature winding as a result of the supply voltage. While the conductors are oriented perpendicular to the magnetic field generated by the field windings, the armature winding is mounted on a spinning core, or rotor.
Construction of DC Shunt Motor
1.Stator
An essential part of a DC shunt motor, the stator is responsible for creating the magnetic field needed for motor operation. The stator, which creates the fixed magnetic field in which the armature moves, stays motionless in contrast to the rotating rotor (or armature). This article explores the different parts, materials, and design factors that go into making a DC shunt motor’s stator.
An overview of the stator
The stator of a DC shunt motor is made up of the following main components:
(Magnetic Frame) Yoke
Cores of Poles
Shoes for Poles
Shunt field coils, or field windings
Interpole (in certain designs, optional)
Every component makes a distinct contribution to the motor’s operation and effectiveness.
Yoke (Magnetic Frame)
Function: The yoke, which makes up the motor’s exterior frame, has two main functions:
For the magnetic flux, it serves as the magnetic return path.
It gives the field windings and poles mechanical support.
Construction: Depending on size and use, cast steel, cast iron, or rolled steel are usually used.
Cast iron is a cost-effective and suitable material for tiny motors.
Laminated steel is frequently used for large machineries in order to reduce eddy current losses.
Function of Pole Cores and Pole Shoes: The motor’s magnetic field is produced and sustained by the poles. Additionally, they offer a surface on which the field windings can be placed.
Parts:
The magnetic flux is concentrated in the pole core.
Pole Shoe: A wider section of the pole core that ensures a uniform flux distribution and lowers magnetic resistance by distributing the magnetic flux over a broader region of the armature core.
Construction: To lessen eddy currents, laminated steel is typically used.
attached to the yoke via welding or bolting.
To keep the shunt field windings firmly in place, the pole shoes frequently feature slots.
Function of Shunt Field Windings: In a DC shunt motor, these windings are in charge of creating the magnetic field. They have a parallel (shunt) connection to the armature circuit.
Features: Copper wire was used because of its superior conductivity.
uniformly wound on the pole cores.
To create the necessary magnetic field with a comparatively small current, have a lot of turns of fine wire.
insulating: To guarantee long life and avoid short circuits, proper insulating is essential.
Windings are insulated using materials such as mica, paper, or varnish.
Compensating poles, or interpoles
Function: By mitigating the armature reaction—the principal field distortion brought on by the armature current—commutation is improved.
positioned between the major poles and linked to the armature in series.
smaller than the main poles in terms of construction.
Additionally, copper conductors are wrapped.
Standard in medium to large industrial DC motors, but optional in tiny motors.
2.Armature
Since the armature is where the electromechanical energy conversion occurs, it is one of the most important parts of a DC shunt motor. The armature of a DC shunt motor has two functions: it transports the armature current and generates torque by interacting with the magnetic field. For the motor to operate effectively and dependably, the armature’s construction and design are crucial.
An Overview of a DC Shunt Motor’s Armature
The armature of a DC shunt motor is made up of a revolving core with windings inserted into slots on its surface. It revolves within a magnetic field produced by the shunt field winding-excited stationary field poles. To drive mechanical loads, torque is produced by the armature’s rotation.
Armature Construction Components
1-Core Armature
Silicon steel sheets are laminated to form the armature core. The cylindrical core is formed by stacking these laminations, which are isolated from one another. The laminated construction’s primary goals are:
to increase the resistance path for eddy currents in order to decrease eddy current losses.
to give magnetic flux a low reluctance path.
to sustain the windings of the armature.
The armature conductors are housed in slots in the outside periphery of the laminations.
2-Windings of Armatures
Insulated copper conductors called armature windings are inserted into the armature core’s slots. Coils are created by connecting these windings in a particular way. In DC machines, armature windings come in two primary varieties:
Lap winding: Every coil is attached to the commutator segment next to it. It is employed in high-current, low-voltage applications.
Wave winding: The coils are attached to variously spaced commutator segments. It is employed in low-current, high-voltage applications.
Depending on the application, both kinds of windings can be utilized in DC shunt motors. To avoid short circuits, the winding needs to be adequately insulated.
3-Commutator
The cylindrical commutator is fixed on the same shaft as the armature. It is made up of copper segments that are separated from one another by mica. The commutator’s primary duties include:
to change the armature conductors’ induced alternating current into direct current at the terminals.
switching the armature conductors’ current direction as they pass beneath alternate poles in order to maintain unidirectional torque.
To provide current to the rotating armature, the commutator cooperates with carbon brushes.
4-Brushes
Carbon or graphite brushes are placed on the commutator’s surface. Brush holders with movable spring pressure hold them in place. Among their responsibilities are:
conducting electricity between the external circuit and the revolving commutator.
maintaining electrical contact in the face of mechanical motion.
Carbon is frequently utilized because of its self-lubricating qualities, which reduce brush wear and sparking for effective operation.
5-Shaft
A steel shaft that supports the mechanical structure and transfers torque to the load holds the armature assembly in place. To guarantee smooth rotation and balance, the shaft needs to be robust, sturdy, and properly machined.
Considerations for Mechanical and Electrical Design
Lamination Thickness: Although they raise manufacturing costs, thinner laminations decrease eddy current losses.
Slot Design: The size and shape of the slot affect the windings’ inductance and magnetic leakage.
Insulation: To withstand electrical and thermal strains and avoid short circuits, high-quality insulation is crucial.
Cooling: To disperse heat produced in the armature as a result of copper and iron losses, proper ventilation or forced cooling is necessary.
Principle of Operation Concerning Armature
Current passes through the armature conductors of a DC shunt motor when a DC voltage is supplied to its armature. The magnetic field produced by the shunt field windings has these conductors. The armature rotates as a result of a torque generated on the conductors by the Lorentz force. The commutator makes sure that each armature conductor’s current flows in a way that continuously generates unidirectional torque.
3-Field Windings
Applications needing a steady speed under variable load circumstances frequently use DC shunt motors. The field winding is a crucial part that gives the motor its ability to function. The term “DC shunt motor” refers to a motor in which the armature winding and the field winding are connected in parallel, or shunt.
1. Field Windings’ Objective
The creation of the magnetic field required for motor operation is the main purpose of field windings. A constant magnetic flux is produced by a current flowing through the shunt field winding when a DC voltage is applied across it. The motor can run thanks to the torque produced by this flux’s interaction with the revolving armature.
2. Place and Assembly
A DC shunt motor’s field windings are coiled around the stator’s poles, which are fastened to the inner rim of the motor’s yoke, or magnetic frame. Every pole is made up of:
a pole core that is laminated to reduce eddy current losses.
a pole shoe, which evenly distributes the magnetic flux throughout the armature.
On the pole cores, the windings are arranged in coils that are tightly coiled. The number of poles is determined by the motor’s design and power rating, and each pole normally has one coil.
3. Configuration of the Winding
In a shunt DC motor:
To achieve high resistance, the field winding is made up of numerous turns of thin wire, often copper.
The high resistance permits the generation of a substantial magnetomotive force (MMF) while restricting the current drawn by the field winding.
In order to ensure a steady magnetic field, the windings are coupled so that neighboring pole windings generate alternating magnetic polarities (i.e., North-South-North-South).
4. Materials Used
Conductor: Because of its excellent conductivity and thermal stability, copper is the most widely utilized material.
Insulation: Usually, enamel or other insulating varnishes are applied to the wire. More mica or fiberglass insulation layers may be applied to motors with higher voltages.
Pole Core: Constructed from silicon steel lamination to minimize eddy current losses and hysteresis.
Yoke: Steel or cast iron that acts as the magnetic flux’s return path.
5. Protection and Insulation
Field winding insulation is essential for preventing electrical failure and short circuits. The following methods are frequently used:
Slot liners are non-conductive substances positioned in between the pole core and windings.
To avoid turn-to-turn failures, interturn insulation is placed in between each winding turn.
Impregnation: To give the coils mechanical strength and moisture resistance, insulating varnish is usually applied after winding and baked in an oven.
Additional protective coatings or housings may be used in areas that are prone to moisture or dust.
6. Thermal Factors
Field windings produce heat because they carry a constant current. The right thermal design is crucial.
Ventilation: To release heat, motors frequently have fans or ventilation ducts installed.
Thermal Class Insulation: Typically rated as Class B, F, or H, materials are selected according to anticipated operating temperatures.
7. Mounting Field Coils
To ensure that the coils fit the pole cores snugly, they are twisted into a particular shape and secured with:
Clamping: Glass tape binding or mechanical clamping.
Impregnation: As previously indicated, varnish impregnation aids in securing the winding.
The coils will stay in place throughout motor operation and vibration if they are mounted correctly.
4-Commutator and Brushes
The commutator and brushes in a DC shunt motor are essential components that guarantee the correct transformation of electrical energy into mechanical energy. These pieces serve as the interface between the machine’s rotating and stationary components, enabling current to enter the spinning armature while ensuring that the windings are flowing in the proper direction. Their design and operation are essential to the motor’s effectiveness, longevity, and functionality. A detailed look at their construction is provided here.
1. Construction of Commutators
A DC shunt motor’s commutator is a cylindrical device that is fixed on the motor shaft and is composed of several copper segments that are isolated from the shaft and from one another. In order to maintain unidirectional torque, it primarily serves as a mechanical rectifier by reversing the direction of the current flowing through the armature windings while the motor rotates.
Important Commutator Elements:
Commutator Sections
Because of its superior electrical conductivity, electrolytic copper was used in its creation.
Each segment represents one or more armature winding coils.
These sections are made up of rectangular bars that are positioned in a circle and parallel to the shaft to create a whole cylinder.
Segment Insulation:
Mica’s excellent dielectric strength and thermal resistance make it a popular choice for insulating between segments.
To minimize short circuiting and to allow for even wear during operation, the mica is put in thin sheets and occasionally undercut.
Support for Commutators:
A mica or micanite cylinder is frequently used as a basis for the entire commutator assembly, which is physically fastened to the shaft and insulated from it.
The risers that join the copper segments to the armature windings are brazed or soldered to them.
2. Construction of Brushes
To keep electrical contact, brushes—stationary conductive elements—press up against the revolving commutator. Brushes are essential for transmitting current between the external circuit and the revolving commutator in a DC shunt motor.
Materials: Graphite or Carbon
Good conductivity, self-lubricating qualities, and low commutator wear make it the most widely used.
For greater current ratings, copper-impregnated carbon is occasionally utilized.
Holders for brushes:
usually composed of non-conductive materials such as fiber-reinforced plastics or bakelite.
They maintain the brush in position and generate axial pressure.
Brush Box (Holder): Brush Assembly
As the brush wears down, a spring-loaded box keeps the brush in position and applies steady pressure to the commutator.
reduces mechanical wear and guarantees proper electrical contact.
The spring mechanism
To keep the brushes in touch with the commutator, springs exert consistent pressure on them.
It is important to optimize spring tension since too much of it leads to wear and too little to ignite.
Pigtail (Adaptable Attachment):
The brush is connected to the external circuit by a braided copper wire, which permits current to flow while allowing for the movement of the brush as a result of wear and vibration.
Brushes and Commutator Interaction:
While in operation:
As the armature rotates, so does the commutator.
Every segment makes contact with the brushes as it rotates.
Through the commutator, the brushes transfer electricity to the armature winding segments.
In order to maintain torque in the same direction while the armature spins, the commutator periodically reverses the direction of the current flowing through the winding segments.
Applications of DC Shunt Motor
1. Use in Industry
a. Machine tools and lathes
Lathes, milling machines, and drilling machines frequently use DC shunt motors. For accurate cutting and shaping tasks, these instruments need to run at a steady speed even when the load changes. The DC shunt motor is perfect for these applications because it can keep its speed almost constant while the load changes.
b. Textile Equipment
For the creation of high-quality fabric, textile mill equipment including spinning frames, looms, and knitting machines need to run at a steady speed. The steady speed control required to preserve uniformity in textile operations is supplied by DC shunt motors.
c. Printing presses
For precise print alignment and ink distribution, printing presses require extremely precise and consistent action. DC shunt motors’ ability to regulate speed makes them appropriate for these delicate applications.
2. Systems of Transportation
a. Electric Traction
DC shunt motors have been utilized in older systems and certain smaller electric locomotives because of their smooth speed control, even though more sophisticated motors are frequently employed in modern electric trains. This is especially useful for trolleybuses and trams.
b. Conveyor Systems
Conveyor belts powered by DC shunt motors can move items at a steady pace in warehouses and industries. These systems frequently need a steady operating condition and a progressive speed adjustment, which DC shunt motors offer.
3. Equipment for Labs and Schools
Labs, research facilities, and educational institutions commonly use DC shunt motors. They are perfect for experiments and demonstrations involving motor speed control, load response, and electrical principles because of their comparatively straightforward design and consistent performance.
4. Fans and Blowers
Industrial blowers and ventilation systems need motors that can operate continuously with little speed variation. DC shunt motors’ smooth operation and capacity for long-duration service make them perfect for this function.
5. Pumps with centrifugation
Centrifugal pumps are powered by DC shunt motors in settings where liquids must be pumped continuously, like cooling systems or chemical facilities. Consistent fluid delivery is ensured by the motor’s capacity to maintain a constant speed under varying loads.
6. Equipment Run on Batteries
DC shunt motors are utilized in battery-operated systems where speed regulation is crucial and load fluctuation is not severe, even though series motors are frequently chosen for high starting torque. These include certain medical devices and conveyors that run on batteries.
7. Light-Duty Hoists and Elevators
DC shunt motors provide the required control and smoothness in tiny elevators or hoisting equipment where speed control is more crucial than beginning torque. However, compound or series motors are utilized for heavy lifting.
Advantages of DC Shunt Motor
1. Features of Constant Speed
A DC shunt motor’s ability to run at a virtually constant speed across a variety of loads is one of its biggest benefits. Assuming a constant supply voltage, the field current stays almost constant due to the field winding and armature being linked in parallel. As a result, a continuous magnetic field is created, which aids in keeping the speed constant even when the load varies.
Because of this characteristic, DC shunt motors are perfect for machines like lathes, conveyors, and machine tools that need a constant speed.
2. Controlling Speed Is Easy
Over a wide range, DC shunt motors provide exceptional speed control. You can regulate speed by:
altering the armature voltage by changing the supply voltage,
altering the field current (via the field circuit’s rheostat), or
utilizing contemporary electronic drives, such as SCRs or choppers.
This two-pronged control strategy enables:
Increasing field current (strengthening the magnetic field) to reduce speed
decreasing field current (weakening the magnetic field) to increase speed.
Applications where variable speed control is crucial, such printing presses or elevators, benefit from these features.
3. Effective Regulation and Capability to Handle Loads
DC shunt motors can withstand abrupt load variations with little effect on speed. The armature current rises with increasing load in order to maintain the necessary torque, but the speed loss is negligible because the field flux hardly changes. Fits well with fans and blowers that need to run steadily under varying loads.
4. Silent and Easy Functioning
DC shunt motors’ design and operation result in quiet operation and steady torque generation. This feature contributes to a longer machine life and a quieter working environment by lowering noise levels and mechanical vibrations.
especially helpful in lab equipment and precision machinery where vibration and noise are undesired.
5. Dependability and Ease of Construction
The design of DC shunt motors is straightforward and sturdy. They are simpler to maintain and repair since they have fewer moving parts than AC motors with intricate control systems.
They are an affordable option for continuous-duty applications because of their dependability.
6. Lower Initial Current Than Series Motors
DC shunt motors draw a reasonably moderate and controllable starting current, in contrast to DC series motors, where the first starting current can be dangerously excessive due to low armature resistance. Because of this, they are safer to start and run, especially in delicate mechanical settings.
