General introduction of DC motor
Shunt excited DC Motors
Fig 1.3: Shunt Excited DC Motor
Shunt DC motors, also referred to as compound wound DC motors, are a type of direct connection motor where the shunt field winding is connected in parallel to the armature winding, not the series field winding These motors are known for their excellent speed regulation, as the shunt field can be independently excited from the armature windings, allowing for simplified reversing controls.
Shunt DC motors are well-suited for applications that require precise speed control due to their self-regulating speed capabilities However, it is important to note that these motors do not provide high starting torque, which means the load at startup should be minimal Therefore, applications that align with these specifications are ideal for utilizing shunt DC motors.
DC motors include machines tool such as lathes and grinders, and industrial equipment such as fans and compressors.
Compound excited DC motor
Fig 1.4: Compound Excited DC Motor
Compound DC motors feature both series and shunt field windings, providing excellent starting torque However, they may encounter control issues in variable speed drive applications These motors can be configured in two ways: cumulatively or differentially The cumulative arrangement connects the series field to support the shunt field, resulting in increased starting torque but reduced speed regulation Conversely, the differential configuration offers better speed regulation and typically operates at a constant speed.
Compound DC motors are renowned for their ability to deliver high starting torque along with effective speed regulation and control, making them suitable for a variety of applications across different industries Some notable uses of compound DC motors include:
- Compound motors due to their ability to perform better on heavy load changes are used in elevators.
- Due to their high starting torque and better speed control for pressure variations, they are used in shears and punches.
- This kind of motors because of the high starting torque and heavy-duty load is used in steel rolling mills.
- Again due to the capacity of driving heavy loads, they are used in the printing press and cutting machines.
- They are also used in stamping presses to provide high starting torque.
- Their good speed control and high starting torque make them a great choice to be used in mixers.
Small DC machines with fractional kilowatt ratings are primarily utilized as control devices, particularly in techno generators for speed sensing and in servo motors for precise positioning and tracking.
3, The advantage of a DC motor
DC motors offer versatility as they can function both as electric motors and generators under various conditions Their primary advantages include excellent speed regulation and high overload capacity Unlike asynchronous motors that may require costly converters for adjustments, DC motors allow for wide and precise modifications with simpler power and control circuit structures, ensuring high quality and efficiency.
DC motors come in various sizes, each tailored for specific applications; smaller motors are ideal for toys, tools, and home appliances, while larger ones are used in elevators, hoists, and electric vehicle propulsion Despite the rise of AC motors, which offer simpler generation, reduced transmission losses, lower maintenance, and compatibility with explosive environments, DC motors remain essential in applications where AC motors fall short The unique characteristics of DC motors provide significant advantages in various industries, highlighting their continued relevance despite the benefits of AC technology.
DC motors are ideal for applications requiring low-speed torque and adjustable speed, as they allow for precise speed control across a broad range, both below and above the rated speed This capability is particularly evident in shunt-type DC motors, which utilize armature and field control to provide advantages over AC motors Additionally, DC motors exhibit a significantly high starting torque, making them suitable for heavy-duty applications like electric trains and cranes They also feature compact converters and drives, along with a higher power density, and can deliver full torque even at zero speed.
DC motors have been a reliable choice for over 140 years, offering a cost-effective and efficient alternative to AC motors Their simpler design ensures easy maintenance, saving both time and money Upgrading to an AC motor can be significantly more expensive than simply replacing a DC motor, making it a smart choice for repairs This quick replacement process not only restores your system but also minimizes downtime, allowing for seamless operation With these advantages, it's easy to see why DC motors are a preferred option in many applications.
High-intensity uses of electric motors come with disadvantages such as high maintenance requirements and a short lifespan Regular maintenance is essential, including the replacement of brushes and springs that conduct electric current, as well as cleaning or replacing the commutator These components are crucial for effectively transferring electrical power to the rotor's spinning wire windings within the motor.
Sparks generated on the commutator and brushes will be dangerous in an explosive atmosphere.
Expensive price, not high capacity.
Structure and working principle of DC motor
To comprehend how a DC motor operates, it is essential to first examine its construction, which consists of two primary components: the rotor and the stator The rotor serves as the rotating element, while the stator remains stationary Additionally, the armature coil is linked to the DC power supply, facilitating the motor's functionality.
The armature coil features commutators and brushes, which play crucial roles in converting the AC induced in the armature into DC The brushes facilitate the transfer of current from the rotating motor components to the stationary external load Positioned between the north and south poles of either a permanent or electromagnet, the armature is essential for efficient motor operation.
Fig 2.1: Structure of DC Motor
The DC motor can be divided into two main parts: the stationary part (stator) and the dynamic part (Rotor).
The stator of a DC motor is the static component that houses the field windings, supplies power, and constitutes the motor's outer structure It typically consists of two or more permanent magnets and poles, with a coil wound around a magnetic element to create the stator.
The stator is a crucial component of DC motors, serving as a static unit that houses the field windings It plays a vital role by receiving the power supply necessary for the motor's operation.
The magnetic field in electric motors is generated by the magnetic iron core and the surrounding field winding wire The core is typically constructed from 0.5 to 1mm thick electrical engineering steel or carbon steel, which is tightly pressed together In smaller motors, block steel may be utilized The magnetic pole is secured to the motor case using bolts The field winding consists of insulated copper wire, with each coil thoroughly insulated and impregnated with insulating paint before being mounted on the magnetic poles These field windings are connected in series on the magnetic poles, ensuring efficient operation.
The auxiliary magnetic pole is mounted on the main magnetic pole and typically constructed from block steel It features a winding wire similar to that of the main magnetic pole and is securely fastened to the casing using bolts.
The magnetic shaft serves as a crucial component in electric motors, acting as both a magnetic circuit that connects the magnetic poles and as the casing In small to medium-sized electric motors, thick steel is commonly utilized through bending and welding processes, while larger electric machines typically employ cast steel for enhanced durability Additionally, some small electric motors may utilize cast iron for their body construction.
The magnetic frame, also known as the yoke, of a DC motor is constructed from cast iron or steel and is a crucial component of the motor's stator, which is the stationary part of the motor.
The primary role of the motor's outer casing is to create a protective barrier for its intricate internal components while offering support to the armature Additionally, it plays a crucial role in stabilizing the field system by encasing the magnetic poles and field winding of the DC motor.
Field winding: wrapped with insulated copper wire and each coil is carefully insulated into a block, impregnated with insulating paint before being placed on the magnetic pole.
To safeguard electric machines from falling objects that can harm the winding and to prevent electrical contact hazards, the lid serves a dual purpose In small and medium-sized electric machines, it also functions as a bearing holder, typically constructed from durable cast iron.
A rotor is the rotating part of the DC machine that brings about the mechanical rotations.
The inner rotating component, responsible for mechanical rotations, features windings linked to the external supply circuit through commutators Constructed from ferromagnetic materials, both the stator and rotor are separated by an air gap.
The electromotive force is generated within a magnetic circuit composed of ferromagnetic materials, specifically folded technical steel sheets This magnetic circuit features grooves designed to accommodate the armature winding, which is made up of multiple wires interconnected in a specific configuration Each coil contains numerous wire turns, with their ends linked to insulated copper plates known as commutators, which are separated from each other and the shaft The commutator is paired with graphite-made hinges, secured to its wall by springs.
1.2.1, Armature Winding of DC Motor
The armature winding of a DC motor is connected to the rotor, which rotates within an alternating magnetic field, leading to magnetic losses To mitigate these losses, the rotor is constructed from an armature core made of multiple low-hysteresis silicon steel laminations This design effectively reduces hysteresis and eddy current losses, as the laminated steel sheets are stacked to create the cylindrical structure of the armature core.
Slots in the armature core, constructed from the same material as the core itself, are uniformly distributed with copper wire windings around the entire periphery To prevent the conductors from dislodging due to the significant centrifugal force generated during armature rotation in a magnetic field with current supply, fibrous wedges are employed to seal the slot openings.
1.2.2, Armature core of DC motor
The armature core features slots crafted from the same material as the core itself, designed to accommodate an armature winding composed of multiple turns of copper wire evenly distributed around the core's periphery To secure the conductors against the high centrifugal forces generated during the armature's rotation, especially when current and magnetic fields are present, the slot openings are closed with fibrous wedges.
Applications of DC Motors
In the previous chapter, we explored the structure and operating principles of DC motors In this section, we will discuss the various applications of DC motors that are widely utilized in modern technology.
DC motors are widely utilized due to their unique advantages, with small models commonly found in household tools, toys, and appliances In addition to home use, DC motors play a crucial role in industrial applications such as conveyors and turntables, while larger models are essential for braking and reversing functions in various industries.
Hydraulic pumps are crucial in various industries, including construction, mining, manufacturing, and steel production These pumps are often powered by DC motors, which provide variable speed control and high starting torque In many cases, lower-cost brushless DC motors are preferred for their ease of maintenance, making them ideal for large-scale industrial applications.
Small DC motors are favored by manufacturers and hobbyists for children's toys, including remote-controlled cars and trains, due to their user-friendly nature and durability These toys often require varying speeds and movement types, necessitating motors that can operate across a wide range of voltages DC motors meet these diverse specifications, making them an ideal choice for toy production.
DC motors are a popular choice for electric vehicles due to their energy efficiency and durability Additionally, hobbyists favor DC motors, especially series-wound types, for their high starting torque and ability to achieve variable speeds based on voltage input.
Robots, defined as electromechanical devices designed for specific tasks, are popular among hobbyists and engineers alike DC motors are a cost-effective and accessible option for powering components such as tracks, arms, and cameras Their high torque, durability, and efficiency make them particularly well-suited for use in robotics applications.
Hydraulic pumps are vital industrial tools utilized across various sectors, including construction, mining, and steel manufacturing These pumps are powered by DC motors, which offer the advantages of easy variable speed control and superior responsiveness, making them ideal for diverse applications.
The rotor's rotating shaft connects to the impeller, enabling water absorption for daily life and agricultural irrigation High-pressure pump systems, often equipped with air vents to enhance pressure, play a crucial role in industrial pumping and fire protection Additionally, pumps are the primary application of electric motors.
3.1.7, Ventilation system, fan, exhaust fan
Ventilation systems are essential in buildings, factories, schools, and hospitals to ensure a healthy and comfortable environment These systems function like pumps, drawing in outside air through filters and distributing it throughout the space An electric motor powers the exhaust fan, which expels stale air, promoting air circulation This process not only cools the area but also maintains adequate air quality, preventing moisture buildup and the spread of diseases and bacteria.
Electric motors are increasingly utilized in various sectors, including computers, electric vehicles, and industrial freight vehicles, reflecting their growing importance in modern life and production As the world shifts towards reducing fossil fuel consumption, electric motors are not just a passing trend but a vital component of our sustainable future.
As per the characteristics of DC motors, different types of DC motors are applied for different jobs as explained below:
3.2, Applications of Series Excited DC motor
DC series motor is suitable for both high and low power drives, for fixed and variable speed electric drives Because of its high starting torque, this motor uses
Series motors are variable speed motors characterized by lower speeds at higher torques and higher speeds at light or no loads This unique speed-torque relationship makes them ideal for applications requiring high starting torque to quickly accelerate heavy loads.
(ii) Where the load is subjected to heavy fluctuations and speed is required to be adjusted automatically.
As such the series motors are most suitable for electric traction, cranes, elevators, vacuum cleaners, hair driers, sewing machines, fans and air compressors, etc.
Series motors should always be directly coupled with loads or connected through gears, as using belt loads can lead to slippage or breakage If a series motor operates under light loads or no-load conditions, it can reach dangerously high speeds, potentially causing damage to the motor.
3.3, Applications of Shunt Excited DC motor
Shunt motors: From the characteristics of a shunt motor we have seen that it is almost constant speed motor It is, therefore, used:
(i) Where the speed between no-load to full load has to be maintained almost constant.
In applications where loads must be driven at varying speeds, it is essential to implement speed control methods Among these speeds, maintaining one specific speed nearly constant for extended durations is often a critical requirement.
As such the shunt motors are most suitable for industrial drives such as lathes, drills, grinders, shapers, spinning and weaving machines, line shafts in the group drive, etc.
3.4, Applications of Compound Excited DC motor
The cumulative compound motor is known for its high starting torque and excellent speed regulation at elevated speeds, making it ideal for applications such as presses, electric shovels, conveyors, elevators, compressors, rolling mills, and heavy planers.
Compound motors are characterized by a significant reduction in speed under heavy loads, similar to series motors, while maintaining a maximum speed at lighter loads that is safe for operation This unique feature makes them suitable for various applications where both high starting torque and stable speed control are essential.
(i) Where high torque is required at the time of starting and where the load may be thrown off suddenly.
(ii) Where the load is subjected to heavy fluctuations.
As such the cumulative compound, motors are best suited for punching and shearing machines, rolling mills, lifts and mine – hoists, Heavy Planers, etc
3.5, Applications of Separately Excited DC motor
Conclusion
Understanding DC motors is essential for grasping their structure, principles, and diverse applications These motors are utilized in various fields, including televisions, industrial machines, FM radios, DC drives, copiers, and particularly in the transportation sector Their ability to control speed across a wide range makes them invaluable in devices that require continuous rotation.
DC motors are widely utilized in tools, toys, and household appliances, as well as in industrial applications like conveyors and turntables Additionally, large capacity DC motors play a crucial role in functions such as braking and reversing.
DC motors have made significant advancements throughout their development, showcasing a variety of advantages and disadvantages Despite these differences, they serve numerous applications and play a crucial role in various aspects of modern life.