Thus starting methods of dc motor is facilitated by means of a starter, or rather a device containing a variable resistance connected in series to the armature. The high number of turns allows a strong magnetic field to be generated, but the smaller gauge wires provide a high resistance and limit the current flowing through the shunt coil. They come in three different types, classified according to the electrical circuit used. Basically main purpose of starter is to limit the starting current which is very high during starting of motor. Once the motor reaches its full speed, it remains constant. Pdf starting of dc motors using resistors researchgate. In this position the field winding receives the full supply voltage. There are also links to powerpoint slideshows that show the animations seen in the presentations. This motor has a low starting torque and also runs at a constant speed. Three point starter switching device are it is an extensively used to start a d. The shunt winding has a large number of turns so that it has appreciable inductance.
At noload condition, the motor runs at rpm and the armature current takes 6 a. Manual motor starters and switches general purpose. Speed control of dc shunt motor with field and armature rheostat control 79 2. Dc shunt motor starter prior to starting, the handle is in the off position. Lathes, drills, boring mills, shapers, spinning, and weaving machines series motor. What is a 3 point starter working and drawbacks circuit. Manual motor starters, contactors and overload relays. A car may have as many as 20 dc motors to drive fans, seats, and windows. The 3 point starter connects the resistance in series with the circuit which reduces the high starting current and hence protects the machines from damage. In a manual shunt motor starter a over load relay is connected in series and no volt relay in parallel with the load 6 over load relay is connected in parallel and no volt relay in series with the load. The dc shunt motor construction is the same as any type of dc motor. Load test on singlephase transformer and three phase transformers. Continuous currents should not exceed 80% of the shunt rating. Noload speed of which of the following motor will be highest.
The rotor and stator windings are connected in parallel. Mo5100, mo495, mo496 manual motor starters magnetic only. Type of starter fordc motor two point starter for dc series motor three point starter for shunt motor four point starter for compound motor forac motor dol starter stardelta autotransformer variable frequency drive 6. The rotor and stator are each connected from a different power supply, this gives another degree of freedom for controlling the motor over the shunt. A 4 point starter protects the armature of a dc shunt motor or compound wound dc motor against the initially high starting current of the dc. Starters for the dc shunt wound and compound wound motors. It not only overcomes the difficulty of a plain resistance starter, but also provides additional protective features such as over load protection and no volt protection. Dc motor starters to avoid the above dangers while starting a dc motor, it is necessary to limit the starting current. The characteristics of a shunt motor reveal that it is an approximately constant speed motor.
Pdf direct current motors have been used since the early 20 th century and was a dominant among all the other motors available at that time. The connection of resistance in this circuit is in series which decreases the initial high current and guards the equipment against any electrical failures. Speed control of dc shunt motor with field and armature. When a shunt dc motor reaches its full speed, the armature current is directly related to the motor load. As resistance increased, the value of the field current will reduce. In electrical terminology, a parallel circuit is often referred to as a shunt. Construction, circuit diagram, and its applications. A good material for the poles of a pmdc motor should have the apposite of the above. Working principle from the above circuit diagram, we can conclude that if we want to increase the speed of the shunt motor, we will vary the field resistance. You will get all the dc motor mcq important question and answer with explanation for your all electrical engineering competitive exams 1. The output power of any electrical motor is taken from the a armature b field c coupling mounted on the shaft d motor frame ans. In general, a dc motor,s stalling torque is equal to its starting torque.
Well, its due to the presence of back emf e b, which plays a critical role in governing the operation of the motor. A 3 point starter is a device that helps in the starting and running of a dc shunt motor or compound wound dc motor similar to a 4 point starter now the question is why these types of dc motors require the assistance of the starter in the first place. In dc shunt motor the armature and field winding are connected in parallel across the supply voltage the resistance of the shunt winding. Brushed dc motor drive circuits, brushless dc motor drive circuits, stepper motor drive circuits, drive software, writing a pwm value to the ccp registers with a midrange picmicro. The shunt field windings of a dc shunt motor are made of smaller gauge wire, but they have many more turns than a serieswound dc motor.
The principle of starting a shunt motor will be seen from figure 4 which shows the faceplatetype starter, the starting resistance being in between the segments marked 1, 2, 3, etc. This motor is used when both a high starting torque and good speed regulation is needed. Join date dec 2010 location southampton and holiday cottage in wensleydale uk posts 4,863 helped 15 15 points 25,337 level 38. A 3 point starter is a device that helps in the starting and running of a dc shunt motor or compound wound dc motor similar to a 4 point starter. Dc motor control tips n tricks pdf 36p this note explains many basic circuits and software building blocks commonly used to control motors. Learners examine the operation of a dc shunt motor and its characteristics. A threepoint starter is an electrical device, used for starting as well as maintaining the dc shunt motor speed. Hence the armature current differs and the speed of a dc shunt motor will continue constant which is shown in the fig dotted line ab. The diagram of a 3point starter connected to a shunt motor is shown in fig. Seres motorfullwave speed control of a shunt motorthyristor control of a shunt motor thyristor speed control of a series d.
Three point starter construction, working principle. Dc shunt motor the equivalent circuit of a dc shunt motor model is shown in figure 2. In this lesson aspects of starting and speed control of d. Starting of dc motors at the time of starting n 0, the induced emf of a motor is zero such that the current drawn from rated voltage supply would be. Classification of dc motor is more common than we may think. Types of dc motor a direct current motor, dc is named according to the connection of the field winding with the armature. A 4 point starter protects the armature of a dc shunt motor or compound wound dc motor against the initially high starting current of the dc motor the 4 point starter has a lot of constructional and functional similarity to a 3 point starter, but this special device has an additional point and coil in its construction as the name suggests. A compound dc motor connects the armature and fields windings in a shunt and a series combination to give it characteristics of both a shunt and a series dc motor. The basic concept behind every dc motor starter is adding external resistance to the armature winding during starting. First, one is separately excited dc motor and selfexcited dc motor. The shuntconnected dc motor is selected because of its ability to maintain nearly uniform speed while carrying different loads. The series field resistance would be included in the denominator for a series motor. However, short term currents that occur in motorstarting or enginecranking can exceed the shunt rating by a factor of 2 or more without damage to the shunt or meter.
At the time of starting back emf in motor is zero which results in high amount of armature current. Eb change in eb for various load currents is small, so may be neglected for the time being. Overload protection should be provided externally, if required. Starting of dc motors dc shunt motor starter shunt. The selfexcited motors are further classified as shunt wound or shunt motor, series wound or series motor and compound wound or compound motor. This contrasts with the series connection of a dc motor that provides a significant speed drop when there is an addition or reduction of load. Consequently, shunt motor will not usually run on a. To start the motor, the handle is moved manually and when it makes contact with the resistance stud 1 it is in the start position. Speed control of separatelyexcited motorthyristor speed control of d. The starting handle is held in position by the novolt coil, marked nv, which automatically allows the starter to return to the off position if the supply fails. Whenever the shunt motor load is increased e b vi a r a and flux reduces as a result drop in the armature resistance and armature reaction. Since load is very small in a shunt motor, armature current is also very low.
Clicking on the following links will allow you to down load adobe acrobat files of the class lecture notes. Class mms and mrs manual motor switches and manual reversing switches are designed to operate single or threephase ac or dc motors up to 10 hp ac and 2 hp dc. Swinburnes test and speed control of dc shunt motor. Important 50 dc motor mcq questions and answers morning. Why is the dc series motor rpm higher than the dc shunt. There are various types of dc motor starters, such as 3 point starter, 4 point starter, noload release coil starter, thyristor controller starter etc. What is needed for a starter to start a dc shunt motor. To obtain the performance characteristics of a dc shunt motor by load test. This motor can be constructed with the basic parts like field windings stator, a commutator and an armature rotor the working principle of a dc shunt motor is, whenever a dc motor is turned on, then dc flows throughout stator as well as the rotor. Hence, dc motors in which the armature and field windings are connected in parallel are referred to as dc shunt motors. As shown in figure 3, when a pulley with radius r is attached to the motor and force of f is applied to the pulley,s circumference, the torque generated, tl. Start dc shunt motor with three point starter youtube.
Free motor control books download ebooks online textbooks. A three point starter is considered suitable for a shunt motors b shunt as well as compound motors c shunt, compound and series motors d all d. The main concept behind every dc motor starter is adding external. The shunt current rating indicates the current that produces a full scale reading on the associated meter. Electrical machinel dc laboratory manual grietelectrical and. C is applied to a shunt motor, the large inductive reactance of shunt winding will reduce the field current too much.