Visual inspection and electrical testing of the armature and fields give the maintenance personnel an understanding of the condition of the motor. When the supply current reverses, both the magnetic field and the armature current are reversed. Terreblanche were given a plant tour at commutator engineering pty ltd, randfontein. Present the scope hardcopy of the starting transient and determine the experimental peak value of current. The conductors of the armature of a dc generator are connected to commutator segments.
Later when the armature was mounted, the motor working at least 350 rpm use an special stone to help to set the brushes, the stone is applyed directly on the commutator and in the same rotation direction. Commutation process in dc machine can be explained by assuming commutator bar width is equal to brush width and insulation between the commutator bar is of negligible thickness. Dc motor generator module to demonstrate and explain the operation of. Commutator appearance guide in addition to the physical appearance of the surface of the commutator, the skin or patina film is of equal importance for the good running of the carbon brushes. Notes disconnection from the power supply confirmed see chapter 6. This is a nonmoving part of the magnetic circuit on which a winding is wound in order to produce a. The addition of a compensating winding yields the compensated series motor, overcoming excessive commutator sparking. A specially designed series commutator motor may be operated from a singlephase alternating voltage supply. In the dc motor, as the current to the rotor windings is connected to and disconnected from the dc source through the commutator segments, arcing at the brushes occurs due to the periodic interruption of the current in the rotor windings inductors. In a dc generator, the induced current reverses its direction after every 180 degree electricalrotation of a coil. The rotor in a typical brushless motor incorporates a fourpole permanent magnet and a smaller sensor magnet. The brushes must ride on the commutator smoothly with little or no sparking and no brush noise chatter. A wellknown type of commutator motor, which has been used as a fan drive where speed regulation with minimum loss is required, is the schrage motor. Now when the armature starts to rotate by an external force in dc generator, the coils situated in the armature also rotate.
Having a dirty commutator can cause a poor connection between the brushes resulting in the motor not functioning correctly. What is the function of a commutator in a dc motor. However, in brushless dc motor there are no brushes and commutator. Construction of dc motor in detail, there is a yoke magnetic frame, pole core and pole shoes, the armature core, armature winding conductor, commutator, and brushes and bearings. The resulting motor is only practical in the smallest sizes.
Construction of dc motor all parts of dc motor in details. Engelbrecht, explained and showed the process of making and assembling a commutator for a dc motor. Aug 21, 2014 build a simple dc motor with brushes and commutator tim callinan. Its main fincation as far as the dc motor is concerned is to commute or relay the supply electric currnet from. Commutation in dc motor in order to produce unidirectional force or torque on the armature conductors of a motor, the conductors under any pole must carry the current in the same direction at all times. However, we can make some attempt to show a bit of what the brushcommutator system does. This conversion of ac into dc is accomplished through the use of a commutator. Current flows through two of the coils whenever a voltage. Alternatingcurrent commutator motor electrical engineering.
On the other hand, in case of dc motor when the supply was given is dc it is converted from dc to ac and provided to the armature windings so that in order to produce the rotational torque. The brush and commutator system of this class of motor involves quite a lot of black art, and there are still aspects of how they work which are poorly understood. Armature winding pole pitch coil span commutator pitch. Instead, the commutation of the windings of a bdc motor is done mechanically. To test, set your ohm meter to the rx1 scale, touch probes to bars 180 degrees apart all around the commutator.
Maintaining the condition of the commutator is the most important aspect of dc motor unit upkeep. The singlephase series motor is an attempt to build a motor like a dc commutator motor. A dc motor must have 100% field strength to produce its maximum torque and to keep the armature. Brushed dc motor fundamentals microchip technology. The coils are shorted via brush segment with alternate change in influence of poles. Its operation is based on the principle that when a current carrying conductor is placed in a.
Commutator segment an overview sciencedirect topics. Basics of dc motors for electrical engineers beginners. That frame comprises the motor casing, along with two or more permanent magnet pole pieces. Note that the rotor of a dc motor is also referred to as the armature. How to maintain carbon brushes, brushholders, commutators and slip rings a major player in the industry worldwide, mersen o. In dc generator the commutator converts from ac induced current produced in the armature windings is converted to dc and gives to the external load connected. On the other hand, in case of dc motor when the supply was given is dc it is converted from dc. Nov 26, 2017 construction of dc motor in detail, there is a yoke magnetic frame, pole core and pole shoes, the armature core, armature winding conductor, commutator, and brushes and bearings. Dc motor fault zone analysis is a vital part of any dc motor maintenance program.
The following are the main parts of a dc generator. Let us also consider that the width of the commutator bar is equal to the width of the brush and current flowing through the conductor is i c. Ac commutator motors may be either singlephase or polyphase. If you are also replacing the brushes of a motor, it is also important to clean the commutator before usage again. A brushless dc bldc motor construction is similar to the synchronous motor with permanent magnets on rotor. But there is a good similarity with a dc motor also as far as construction is concerned. Explain the effect of motor reaction in a dc generator.
The business was subcontracted by delba to construct a new commutator for a dc motor used by columbus at zm1, coiler motor. The creation and maintenance of an acceptable brush film, as well as the avoidance of metal transfer, burning and other destructive conditions, are key to ensuring the commutators condition. A commutator in a dc machine has alternate bands of copper and mica. Jan 08, 2019 a commutator in a dc machine has alternate bands of copper and mica. What are the uses of a commutator and slip ring in a motor.
For the explanation of commutation process, let us consider a dc machine having an armature wound with ring winding. Mathematical modeling of brushless dc motor and its speed. During seating, the carbon brush must be tightly held in place against the. Jan 07, 2016 the operating principle of a dc motor is based on the interaction between the magnetic field of a rotating armature and the magnetic field of a fixed stator. Figure 21 illustrates a typical dc motor rotor with its main parts. Sawa characteristics of flat commutator on dc motor for automotive fuel pump ieice of japan technical report, emd200374, 2003. Sep 22, ac commutator motors, like comparable dc motors, have higher starting torque and higher speed than ac induction motors. An905 ds00905bpage 2 2010 microchip technology inc. By reversing the current direction in the rotating windings each half turn, a steady rotating force torque is produced. As the north pole of the armature is attracted to the south pole of the stator and viceversa, a force is produced on the armature, causing it to turn. This video is integrated as part of our generators page.
Later when the armature was mounted, the motor working at least 350 rpm use an special stone to help to set the brushes, the stone is applyed directly on the commutator. Commutation in dc machine or commutation in dc generator. You have seen various connection methods there such as shunt, series, and separate field. The common dc motor has a permanent magnet, 3 coil windings and rotating mechanical switches called commutator for each coil figure 1a. Commutators are used in direct current dc machines. Build a simple dc motor with brushes and commutator youtube. Explain how you measured the dc resistance and why you did it this way. The commutator in a dc motor directs the applied dc voltagecurrent to the specific coilcoils such that the resultant space flux in the armature is displaced ideally 90deg with respect to the.
Implementing a predictive maintenance program takes a pm program to the next level. These motors have high torque at low speed and low torque at high speed as shown in fig 15 due to its characteristics it is used in places where high torque is required at low speed. Commutators acts as rectifier for a dc generator and inverter for a dc motor. It comprises a rotor with a primary winding, connected to the supply by slip rings, and a low voltage commutator. Pdf characteristics of carbon and copper flat commutator on. Pdf characteristics of carbon and copper flat commutator.
The brushes may also be lifted to prolong bush life. Describe the cause of sparking between brushes and commutator. As the shaft rotates, the commutator reverses the flow of current in a winding. The business employs 15 permanent employees and does all the relevant work required on site. Textbooks on brushed dc motor talk about inductive kickback when we disconnect the power supply from the motor and the stuff to protect against it e. Function of commutator in dc generator full details.
May 07, 2020 sep 22, ac commutator motors, like comparable dc motors, have higher starting torque and higher speed than ac induction motors. It is cylindrical structure mounted on the shaft through commutator hub. Dc motor troubleshooting based on the easa technote troubleshooting dc motors. A wide variety of dc motor commutator options are available to you, there are 1,149 suppliers who sells dc motor commutator on, mainly located in asia. Commutator motors pdf in chapter 1, you have read about electromagnetbased dc motors. Commutator in a dc machine converts ac to dc or dc to ac. In this situation, two opposite sides of the coil lie under two opposite poles. Commutator is simply a mechanical rectifier the voltage generated in the armature, placed in a rotating magnetic, of a dc generator is alternating in nature.
Motor may make a humming noise and the circuit breaker or fuse will trip. Dc motors although ac motors are used in most of the cases, dc motors have many applications and used for multipurpose applications. Discuss and explain your observations on direction of rotation. In a motor the commutator applies electric current to the windings. Video tutorial on how to clean the commutator of an armature for a motor. What is the function of a commutator in a dc motor and a. Each part of those has its identity and great importance, advantage and sometimes problems, now we will separately explain each part. If this condition exists, the motor needs to be replaced. Maintenance measurement of commutator temperature immediately after opening the inspection access check status of commutator. If the coil span is equal to the pole pitch, then the armature winding is said to be full pitched. A dc motor is composed of the following main parts.
These windings are electrically connected with commutator. This mechanical rectifier commutate the alternating current produced in the armature winding of the dc generator into a direct current and keep the torque from reversing its direction and that happens by the commutator and the help of the stationary brushes, we simply can say that the commutator works like a bridge rectifier. Pdf dc motor dc motor theory cahtayu cahtayu academia. This guide is designed for the use of all professionals in indus. To keep the torque on a dc motor from reversing every time the coil moves through the plane perpendicular to the magnetic field, a splitring device called a commutator is used to reverse the current at that point. Custom designs as a standard feature tecowestinghouse motor company dc motors are designed and built for long life and minimum maintenance. The commutator of dc motor is a cylindrical structure made up of copper segments stacked together but insulated from each other by mica. The commutation in dc machine or more specifically commutation in dc. This figure shows that the electrical contact between the segments of the commutator and the external dc source is made through brushes. Brushless dc motor control with hall sensors using. The creation and maintenance of an acceptable brush film, as well as the avoidance of metal transfer, burning and other destructive conditions, are key to ensuring the commutator.
Since a commutator motor can operate at a much higher speed than an induction motor, it can output more power than a similar size induction motor. Now when the armature starts to rotate by an external force in dc generator, the coils situated in the armature also. Yoke pole core or pole shoes field coils armature core armature winding commutator brushes and bearings 2. In the dc motor, the current polarity is altered by commutator and brushes. It comprises a rotor with a primary winding, connected to the supply by slip rings, and a low voltage commutator winding in the same slots.
Other articles where alternatingcurrent commutator motor is discussed. The commutation in dc machine or more specifically commutation in dc generator is the process in which generated alternating current in the armature winding of a dc machine is converted the voltage generated in the armature, placed in a rotating magnetic field, of a dc generator. Dc motor principle a machine that converts dc power into mechanical energy is known as dc motor. Jul 11, 2019 physical concept of commutation in dc machine. In the dc motor, as the current to the rotor windings is connected to and disconnected from the dc source through the commutator segments, arcing at the brushes occurs due to the periodic. Ac commutator motors ac motors electronics textbook. The arcing has a very highfrequency spectral content. While when a motor is operating, only back emf caused by the rotation matters. Build a simple dc motor with brushes and commutator tim callinan. Disassemble motor and inspect the armature for a burnt coil. Subfractional horsepower permanent magnet brushed dc motors the category of dc motor that is the least expensive, easiest to use, and thus the most popular, is the subfractional horsepower permanent magnet brushed dc motor. The singlephase ac version suffers a double line frequency torque pulsation, not present in the polyphase motor.
792 1187 1125 1103 409 505 805 463 467 106 246 705 1416 1505 815 466 818 973 1473 567 617 690 852 1046 865 758 1030 86 17 1235 749 403 1372 1365 564 269 1449 1047 63 1395 1418