DC Machine: Construction, Types & Its Working
Table of Contents
The DC machine can be Classified into two types namely DC motors and DC Generators. Because they contain both AC currents and AC Voltages, the Majority of DC machines are Equivalent to AC machines. Because they convert AC voltage to DC voltage, DC machines only produce DC output. These machines are also known as Commutating machines because the Conversion that this Mechanism performs is known as the Commutator. The type of machine most Frequently used for motors is DC. Torque Regulation and simple speed are this Machine’s main advantages. The DC machine can only be used in trains, mills, and mines. Trolleys and underground tube cars, for instance, both use DC motors. In the past, DC dynamos were Incorporated into the design of Automobiles to charge their Batteries.
What is a DC Machine?
A DC machine is a machine that Modifies energy Electromechanically. A DC machine operates by an electric current flowing through a coil that is Enclosed in a magnetic field. The magnetic field then produces a torque that rotates the DC motor. DC Generators and DC motors are the two Categories into which DC machines fall.
A DC motor converts DC power to mechanical power, whereas the main purpose of a DC generator is to convert mechanical power to DC Electrical power. In industrial settings, the AC motor is frequently used to convert Electrical energy to Mechanical energy. However, a DC motor can be used in situations where there is a need for good speed regulation and a wide range of speeds, such as in electric transaction systems.
Construction of DC Machine
Yoke, pole core and pole shoes, pole coil and field coil, armature core, armature winding otherwise conductor, commutator, brushes and bearings are a few of the essential parts that can be used in the construction of the DC machine. Below is a discussion of a few of the DC machine’s components.
The frame is another term for a yoke. So The yoke’s primary role in the machine is to provide mechanical support for the poles and shield the whole thing from moisture, dust, etc. Cast iron, cast steel, or rolled steel are the materials used to make the yoke.
In the DC machine, the pole shoe is a significant component that also serves to increase the pole’s area. Due to this area, flux can be dispersed throughout the air-gap and extra flux can be transmitted through the air space in the direction of the armature. In addition to using annealed steel lamination to lessen the loss of power caused by eddy currents, cast iron, otherwise known as cast steel, is the material used to construct pole shoes.
Pole and Pole Core
An electromagnet serves as the DC machine’s pole, and the field winding is wound among the poles. The pole emits magnetic flux whenever the field winding is activated. Cast steel and cast iron, as well as pole core, are the materials used for this. So To lessen the power loss caused by eddy currents, it can be constructed using annealed steel laminations.
The edge of the armature core has a huge number of slots. These slots hold the armature conductor. So It offers a low-resistance pathway for the flux produced by field winding. So Low-reluctance, permeability-enhancing materials like cast iron are used in this core. Eddy current loss is reduced through the use of lamination.
This has windings that are damaged near the pole core and is known as a field coil. When current is applied through a field winding, the poles electromagnetically produce the necessary flux. Copper is the primary component of field windings.
The armature conductor can be connected to create the armature winding. When a prime mover turns an armature winding, both a magnetic flux and voltage are induced within the winding. This winding is connected to a circuit outside. Conductive materials like copper are used to make this winding.
The DC machine’s brushes collect the current from the commutator and deliver it to the external load. Brushes deteriorate over time, so check them frequently. Brushes are made of rectangular carbon or graphite, depending on the application.
In a DC machine, the commutator’s primary job is to collect current from the armature conductor and deliver it to the load using brushes. additionally gives a DC motor unidirectional torque. The commutator can be constructed using a sizable number of segments in hard drawn copper’s edge form. The thin mica layer shields the Segments in the commutator.
Types of DC Machines
Separate and self-excitation are the two categories into which the excitation of the DC machine is divided. The field coils are turned on by a separate DC source in a DC machine of the separate excitation type. So In a self-excitation type DC machine, the machine itself supplies the current flow through the field-winding. DC machines can be divided into four main categories, which include the following.
- Separately excited DC machine
- Series wound/series machine.
- Shunt-wound/shunt machine.
- Compound wound / compound machine.
In Separately Excited DC Machine, a separate DC source is utilized for activating the field coils.
The field coils in series-wound D.C. machines are connected through the armature. Because the armature current in a series field winding is so high, only a small number of twists of wire with a large cross-sectional area are used in the series field winding.
The field coils in shunt wound DC machines are connected in parallel through the armature. The shunt field is typically made of a large number of twists of fine wire with a small field current carrying because it receives the entire output voltage of a generator or a motor supply voltage.
A compound machine includes both the series as well as shunt fields. The two windings are carried-out with every machine pole. The series winding of the machine includes few twists of a huge cross-sectional region, as well as the shunt windings, include several fine wire twists.
There are two ways to connect the compound machine. The term “short shunt compound machine” refers to a machine where the shunt-field is allied in parallel by the armature alone. The term “long shunt compound machine” refers to a machine where the shunt-field is allied in parallel by both the armature and series field.
EMF Equation of DC Machine
The DC machine e.m.f can be defined as when the armature in the dc machine rotates, the voltage can be generated within the coils. So In a generator, the e.m.f of rotation can be called the generated emf, and Er=Eg, In the motor, the emf of rotation can be called as counter or back emf, and Er=Eb.
Let Φ is the useful flux for every pole within webers
P is the total number of poles
z is the total number of conductors within the armature
n is the rotation speed for an armature in the revolution for each second
A is the no. of parallel lane throughout the armature among the opposite polarity brushes.
Z/A is the no. of armature conductor within series for each parallel lane
As the flux for each pole is ‘Φ’, every conductor slashes a flux ‘PΦ’ within a single revolution.
The voltage produced for each conductor = flux slash for each revolution in WB / Time taken for a single revolution within seconds
As ‘n’ revolutions are completed within a single second and 1 revolution will be completed within a 1/n second. Thus the time for a single armature revolution is a 1/n sec.
The standard value of produced voltage for each conductor
p Φ/1/n = np Φ volts
The voltage produced (E) can be decided with the no.of armature conductors within series I any single lane among the brushes thus, the whole voltage produced
E = standard voltage for each conductor x no. of conductors within series for each lane
E = n.P.Φ x Z/A
So The above equation is the e.m.f. the equation of the DC machine.
DC Machine Vs AC Machine
The difference between the AC motor and the DC motor includes the following.
|AC Motor||DC Motor|
|AC motor is an electric device which is driven through an AC||DC motor is one kind of rotatory motor used to change the energy from DC to mechanical.|
|These are classified into two types like synchronous & induction motors.||These motors are available in two types like brushes & brushes motors.|
|The input supply of ac motor is alternating current||The input supply of dc motor is direct current|
|In AC Motor, brushes, and commutators are not present.||In DC Motor, carbon brushes and commutators are present.|
|Input supply phases of ac motors are both single and three-phase||Input supply phases of dc motors are single phase|
|The armature characteristics of ac motors are the armature is inactive whereas the magnetic field turns.||The armature characteristics of dc motors are, the armature turns whereas the magnetic field remains inactive.|
|AC Motor has three input terminals like RYB.||DC Motor has two input terminals like positive and negative|
|The AC motor speed control can be done by changing the frequency.||The DC motor speed control can be done by changing the current of the armature winding|
|The efficiency of the AC motor is less because of the loss in induction current & slip of motor.||The DC motor’s efficiency is high because there is no induction current as well as slip|
|AC Motor doesn’t require any maintenance||DC Motor requires maintenance|
|AC motors are used wherever high speed, as well as variable torque, is required.||DC motors are used wherever variable speed, as well as high torque, is required.|
|In practical, these are used in large industries||In practical, these are used in appliances|
Losses in DC Machine
We are aware that the main job of a DC machine is to transform mechanical energy into electrical energy. The power loss occurring in various ways during this conversion process prevents the entire input power from being converted into output power. From one apparatus to another, the kind of loss might differ. In addition to raising the temperature, these losses will reduce the efficiency of the apparatus. So Electrical, copper, core, mechanical, brush, and stray load losses are the different categories for DC machine energy losses.
DC Machine Advantages
The advantages of this machine include the following.
- DC machines, such as dc motors, have a number of benefits, including high starting torque, reversing, quick starting and stopping, and adjustable speeds via voltage input.
- Speed control is good
- These are very easily controlled as well as cheaper when compared with AC
- Operation is Seamless
- Torque is high
- Installation and maintenance is easy
- Free from harmonics
Applications of DC Machine
Currently, AC can be used to generate electrical energy in large quantities (an alternating current). Consequently, using DC devices like motors and generators DC generators are extremely scarce because they are primarily used to excite small and middle-sized alternators. So Industries use DC machines for a variety of processes, including electrolytic, welding, and more.
So In most cases, rectifiers are used to convert AC into DC after it has been generated. As a result, a rectified AC supply is used to suppress a DC generator for use in various applications. So In applications where changes in the severe torque happen, DC motors are frequently used as variable speed drives.
The application of DC machine as a motor is used by dividing into three types like Series, Shunt &Compound whereas the application of dc machine as a generator is classified into separately excited, series, and shunt-wound generators.
Thus, DC machines are the main topic here. Finally, we can infer from the information provided above that DC machines consist of a DC motor and a DC generator. The main purpose of the DC generator is to supply DC sources to the DC machine in power plants. DC motors, on the other hand, are used to power a variety of machines, including lathes, fans, centrifugal pumps, printing presses, electric locomotives, hoists, cranes, conveyors, rolling mills, auto-rickshaws, and ice makers. What is commutation in a DC machine, may I ask you?