Before starting the experiment the motor field rheostat must be at minimum position and generator field rheostat must be at maximum position. Analog ammeter and voltmeter are provided on the front panel sheet. This paper discusses the speed and torque control of a shunt dc motor through matlab simulink simulations. In this test the efficiency of the machine at any load is predetermined. In the case of a dc motor, the magnetic field is produced by the field winding.
Hence dc shunt generator is called constant voltage generator. This test can be done in your own workshop using simple hand tools and a. Components of the shunt motor are the armature, labeled a1 and a 2, and the field, labeled f1 and f2. The speed and the current to the rotor are inversely proportional. This is also well known that the dc machines can be used as a generator as well as as a motor, their is the difference of operation in both case i.
If the dc line voltage is constant, then the armature voltage and the field strength will be constant. If you have a dc motor that is malfunctioning or drawing and bleeding power through the wires, there are tests that can be done to test the efficacy of the dc motor. Retardation test is also called as running down test. The machine under test is speeded up slightly beyond its normal speed and then supply is cut. Dc motor principle a machine that converts dc power into mechanical energy is known as dc motor. Now in this article we are going to discuss about retardation test on dc machines. Dc injection braking is a method of braking in which direct current dc is applied to the stationary windings of an ac motor after the ac voltage is removed. The dc shunt motor construction is the same as any type of dc motor.
Scribd is the worlds largest social reading and publishing site. The coils in the shunt field are composed of many turns of small wire, resulting in low shunt field current and moderate armature current. So the load test could be performed in two ways ie, by direct loading by indirectly loading in case of direct loading the motor is provide. Two basic methods used for braking a motor dc injection and dynamic photo credit. Apparatus range type quantity 1 ammeter 020a mc 1 2 voltmeter 0300v mc 1 3 rheostat 1250. This test is performed on only one motor of a batch of similar motors and called a type test.
The machine is running as a motor at rated voltage and speed. Several paragraphs that explain the motivation of the. When dc voltage v is applied across the motor terminals, the field magnets are excited and armature conductors are supplied with current. And the armature winding is connected to external supply voltage hence it plays the role of current carrying conductor. Brushed motors were the first commercially important application of electric power to driving mechanical energy, and dc distribution systems were used for more than 100 years to operate motors in commercial and industrial buildings. Direct method of testing when conducted on a motor is also known as brake test. Brake test is basically a load test of induction motor. Brake test on dc shunt motor free download as word doc. Electrical machines 1 viva questions and answers in this post we had collected some of the most frequently asked electrical machines 1 viva questions with detailed answers. Brake test is also a method of finding efficiency of dc motors. Retardation test or running down test on dc machines.
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. As the armature rotates, back emf eb is induced which opposes the applied voltage v. Electrodynamometer is an electrical break, in which the breaking force can be varied electrically. A dc motor may be thought of as a series of electromagnets, radially spaced around a common shaft. A belt and brake drum arrangement as shown in the circuit diagram can. The connection diagram of dynamic braking of dc shunt motor is shown below. Power supply, dai, direct current machine dc motor 8211, electrodynamometer 8960, timing belt.
No load test on dc shunt generator 1 connect the circuit as shown in figure 1 with switches s1 and s2 open. Join date oct 2011 location pak posts 365 helped 22 22 points 1,956 level 10. Dc starter face plate type suitable for above motor. This is the best and simplest method to find the efficiency of a constantspeed dc machine e.
In case of dc shunt motors, armature is disconnected from the supply and a rheostat variable resistor is connected across it. Since they are connected in parallel, the armature and field windings are exposed to the same supply voltage. When you dont have compensating windings there will considerable effects due to armature reaction, so let us see a non linear analysis of the dc machine. In this article we are going to discuss about brake test on d.
Brake test also called as direct loading test of testing the motor. Working principle of dc shunt motor, dc series motor and all other dc motors can be stated as follows. Brake test on dc shunt motor electric motor electrical engineering. What is dynamic braking or rheostatic braking of dc motor. This commutator and brush connection always keep the direction of the current and the direction of the magnetic field consistent. Two basic methods used for braking a motor dc injection. This is the complete theory of brake test on dc shunt motor including laboratory manual. Dc machines can be tested by three different methods namely direct method, indirect method and regenerative method. The applied voltage v has to force current through the armature against the back. Brake test in one of the most simple way of finding efficiency of any kind of dc machine. In this method, a brake is applied to a watercooled pulley mounted on the motor shaft as shown in fig. Direct method of testing of dc machine, also known as brake test if carried out for a dc motor will be discussed in this post.
Note that applying brake on any motor amounts to loading it. The connection diagram of shunt motor braking with self and separate excitation is shown in the figure below. Electrical machines for mechatronics laboratory 7 4 speed control of series dc motors unlike with the shunt dc motor, there is only one efficient way to change the speed a series dc motor. Thus the speed of dc motor is given by, eb v i a r a. The open circuit characteristics for a dc generator are determined as follows. 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. The connection diagram for dc shunt machine is shown in the figure below. The electric braking of a dc motor is of three types, i rheostatic or dynamic braking, ii plugging or reverse current braking and iii regenerative beaking. A brushed dc electric motor is an internally commutated electric motor designed to be run from a direct current power source. One end of the rope is fixed to the floor via a spring balance s and a known mass is suspended at the other. Retardation or running down test this method is applicable to shunt motors and generators and is used for finding stray losses. For a dc generator the output power is wasted in resistor. This method is an indirect method of testing a dc machine. Load test on dc shunt motor, dc shunt wound motor, direct.
In a shunt motor, the field winding, as we ll as the armature winding, is connected in parallel shunt directly to the dc supply lines. Shunt dc motor the shunt motor is probably the most common dc motor used in industry today. The motor is loaded directly by means of a mechanical brake load or by means of an eddy current or a calibrated air fan. A belt around the air cooled pulley has its end attached to the spring balance s1 and s2. In the previous articles we have seen brake test, hopkinsonstest which are essential to find out dc machine efficiency. We believe that these faqs will be useful for your practical exams and interviews as well. Direct method of testing of dc machine, also known as brake test. What is theory of brake test on dc shunt motor answers. Then, knowing the armature and shunt cu losses at a given load current, efficiency can be calculated. Speed control of dc shunt motor with field and armature rheostat control 79 2. Brake test is used to determine the efficiency of comparatively small motors.
The armature is made of coils of wire wrapped around the core, and the core has an extended shaft that rotates on bearings. This particular motor is of the permanent magnet type, with wire windings only on the armature. Though there are separate branches for the flow of armature current and field current. Title of the experiment page no 7 retardation test on dc shunt motor. What is the break test on a 3phase induction motor. N, given by, this can be graphically explained below. The field current lf is obtained from an external independent dc source. To conduct load test on dc shunt motor and to find efficiency.
Write the necessary magnetic polarities n for north and s for south on the armatures electromagnet pole tips, in order to. Speed controlling of dc shunt motor by field and armature control 8. It is supplied with one ms powder coated electrical panel fitted with high insulation bakelite sheet. Swinburnes test is the most commonly used and simplest method of testing of shunt and compound wound dc machines which have constant flux. When a current carrying conductor is placed in a magnetic field, it experiences a force. Electrical machinel dc laboratory manual grietelectrical and. It is a direct method and consists of applying a brake to a. Because loading will be applied directly on shaft of the motor by means of a belt and pulley arrangement. Theory the back emf for a dc motor is given by, p nz back emf, e b 60 a the number of poles, p the armature conductors, z and the number of parallel paths, a are constant for a particular machine. As you know that the construction of any type of dc motor is very similar to a dc generator. Its operation is based on the principle that when a current carrying conductor is placed in a.
This is very efficient way to find out stray losses in dc shunt motors. At the very onset of load introduction to a shunt wound dc motor, the speed definitely reduces, and along with speed also reduces the back emf, e b. Working principle of dc shunt motor your electrical guide. Therefore, driving torque acts on the armature which begins to rotate. This reduction in the counter emf or the back emf e b results in the increase of the net voltage.
In this method, we find the mechanical friction and windage and iron losses of the machine. The load test on 3phase induction motor is performed to obtain its various characteristics including efficiency. Swinburnes test and predetermination of efficiencies as generator and motor 7. To obtain the performance characteristics of a dc shunt motor by load test.
This excessive current would operate the overload device, disconnect the motor from the supply, and thus protect the motor. Brake test on dc shunt motor electric motor electrical. Speed control of dc shunt motor with field and armature. The dc shunt motor is 120vdc with rated speed of 1800 revolutions per minute. Download as docx, pdf, txt or read online from scribd. That method is to change the terminal voltage of the motor. 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. The principle of the dc motor relies on the concept of commutation. Dc motors although ac motors are used in most of the cases, dc motors have many applications and used for multipurpose applications.
A dc shunt motor also known as a shunt wound dc motor is a type of selfexcited dc motor where the field windings are shunted to or are connected in parallel to the armature winding of the motor. In this test we get total stray losses nothing but combination of. Dc motor dc motor theory the dc motor has two basic parts. 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.
1164 1086 999 1129 1365 9 970 1390 1084 552 578 789 1235 769 304 1140 885 653 1070 903 224 825 592 429 983 343 1540 625 1333 981 256 675 799 1353 784 681 828