What is needed for a starter to start a dc shunt motor. 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. From the schematic, the field winding is connected between the armature terminals, thus the armature. Dc motor control tips n tricks pdf 36p this note explains many basic circuits and software building blocks commonly used to control motors. 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. You will get all the dc motor mcq important question and answer with explanation for your all electrical engineering competitive exams 1. From the followings, 3 point starters and 4 point starters are used for starting shunt wound motors and compound wound motors. 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. Construction, circuit diagram, and its applications. Three point starter construction, working principle. There are also links to powerpoint slideshows that show the animations seen in the presentations. Important 50 dc motor mcq questions and answers morning.
Manual motor starters, contactors and overload relays. Continuous currents should not exceed 80% of the shunt rating. 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. Once the motor reaches its full speed, it remains constant.
In this position the field winding receives the full supply voltage. First, one is separately excited dc motor and selfexcited dc motor. 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. Lathes, drills, boring mills, shapers, spinning, and weaving machines series motor. Speed control of dc shunt motor with field and armature. At the time of starting back emf in motor is zero which results in high amount of armature current. Clicking on the following links will allow you to down load adobe acrobat files of the class lecture notes. The characteristics of a shunt motor reveal that it is an approximately constant speed motor. The diagram of a 3point starter connected to a shunt motor is shown in fig. 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. When a shunt dc motor reaches its full speed, the armature current is directly related to the motor load. A car may have as many as 20 dc motors to drive fans, seats, and windows. Starting of dc motors dc shunt motor starter shunt.
Consequently, shunt motor will not usually run on a. The shuntconnected dc motor is selected because of its ability to maintain nearly uniform speed while carrying different loads. Motornecessity of a startershum motor starterthreepoint point starterstarting and speed control of series motors. They come in three different types, classified according to the electrical circuit used. 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 output power of any electrical motor is taken from the a armature b field c coupling mounted on the shaft d motor frame ans. Variations of speed can be discussed with the formula n. 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. Electrical machinel dc laboratory manual grietelectrical and. Well, its due to the presence of back emf e b, which plays a critical role in governing the operation of the motor. This motor has a low starting torque and also runs at a constant speed.
Why is the dc series motor rpm higher than the dc shunt. 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. Eb change in eb for various load currents is small, so may be neglected for the time being. 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.
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. Free motor control books download ebooks online textbooks. Dc shunt motor the equivalent circuit of a dc shunt motor model is shown in figure 2. The selfexcited motors are further classified as shunt wound or shunt motor, series wound or series motor and compound wound or compound motor. In this lesson aspects of starting and speed control of d. 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. The series field resistance would be included in the denominator for a series motor. The basic concept behind every dc motor starter is adding external resistance to the armature winding during starting. Since load is very small in a shunt motor, armature current is also very low. 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. Dc motor starters to avoid the above dangers while starting a dc motor, it is necessary to limit the starting current. 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. In electrical terminology, a parallel circuit is often referred to as a shunt.
In general, a dc motor,s stalling torque is equal to its starting torque. The shunt current rating indicates the current that produces a full scale reading on the associated meter. This motor is used when both a high starting torque and good speed regulation is needed. Pdf starting of dc motors using resistors researchgate. Starters for the dc shunt wound and compound wound motors.
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. Seres motorfullwave speed control of a shunt motorthyristor control of a shunt motor thyristor speed control of a series d. 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. Join date dec 2010 location southampton and holiday cottage in wensleydale uk posts 4,863 helped 15 15 points 25,337 level 38. Overload protection should be provided externally, if required. 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. The shunt winding has a large number of turns so that it has appreciable inductance. Speed control of separatelyexcited motorthyristor speed control of d. 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.
Load test on singlephase transformer and three phase transformers. 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. The connection of resistance in this circuit is in series which decreases the initial high current and guards the equipment against any electrical failures. What is a 3 point starter working and drawbacks circuit.
As resistance increased, the value of the field current will reduce. 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. Mo5100, mo495, mo496 manual motor starters magnetic only. Start dc shunt motor with three point starter youtube. Types of dc motor a direct current motor, dc is named according to the connection of the field winding with the armature. Dc shunt motor starter prior to starting, the handle is in the off position. Three point starter switching device are it is an extensively used to start a d. 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. 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.
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. 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. 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. Swinburnes test and speed control of dc shunt 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. Basically main purpose of starter is to limit the starting current which is very high during starting of motor. To obtain the performance characteristics of a dc shunt motor by load test. Classification of dc motor is more common than we may think. The rotor and stator windings are connected in parallel. Speed control of dc shunt motor with field and armature rheostat control 79 2. Noload speed of which of the following motor will be highest. A good material for the poles of a pmdc motor should have the apposite of the above. 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. The main concept behind every dc motor starter is adding external.
Hence, dc motors in which the armature and field windings are connected in parallel are referred to as dc shunt motors. 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. C is applied to a shunt motor, the large inductive reactance of shunt winding will reduce the field current too much. At noload condition, the motor runs at rpm and the armature current takes 6 a.