Dc motor dc motor theory the dc motor has two basic parts. When dc voltage v is applied across the motor terminals, the field magnets are excited and armature conductors are supplied with current. Because loading will be applied directly on shaft of the motor by means of a belt and pulley arrangement. The principle of the dc motor relies on the concept of commutation.
This paper discusses the speed and torque control of a shunt dc motor through matlab simulink simulations. 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. 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. Download as docx, pdf, txt or read online from scribd. Power supply, dai, direct current machine dc motor 8211, electrodynamometer 8960, timing belt. 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. The field current lf is obtained from an external independent dc source. In this method, we find the mechanical friction and windage and iron losses of the machine. This particular motor is of the permanent magnet type, with wire windings only on the armature. Since they are connected in parallel, the armature and field windings are exposed to the same supply voltage.
A dc motor may be thought of as a series of electromagnets, radially spaced around a common shaft. 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. Brake test is also a method of finding efficiency of dc motors. A belt and brake drum arrangement as shown in the circuit diagram can. Write the necessary magnetic polarities n for north and s for south on the armatures electromagnet pole tips, in order to. Dc starter face plate type suitable for above motor. This method is an indirect method of testing a dc machine. This excessive current would operate the overload device, disconnect the motor from the supply, and thus protect the motor. Shunt dc motor the shunt motor is probably the most common dc motor used in industry today. The connection diagram of shunt motor braking with self and separate excitation is shown in the figure below.
And the armature winding is connected to external supply voltage hence it plays the role of current carrying conductor. It is supplied with one ms powder coated electrical panel fitted with high insulation bakelite sheet. This test can be done in your own workshop using simple hand tools and a. Apparatus range type quantity 1 ammeter 020a mc 1 2 voltmeter 0300v mc 1 3 rheostat 1250. Note that applying brake on any motor amounts to loading it. Though there are separate branches for the flow of armature current and field current. This is very efficient way to find out stray losses in dc shunt motors. It is a direct method and consists of applying a brake to a.
In this article we are going to discuss about brake test on d. Load test on dc shunt motor, dc shunt wound motor, direct. One end of the rope is fixed to the floor via a spring balance s and a known mass is suspended at the other. This commutator and brush connection always keep the direction of the current and the direction of the magnetic field consistent.
This is the best and simplest method to find the efficiency of a constantspeed dc machine e. Speed control of dc shunt motor with field and armature. Analog ammeter and voltmeter are provided on the front panel sheet. What is the break test on a 3phase induction motor. In case of dc shunt motors, armature is disconnected from the supply and a rheostat variable resistor is connected across it. 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 connection diagram for dc shunt machine is shown in the figure below. Direct method of testing of dc machine, also known as brake test. 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. Several paragraphs that explain the motivation of the.
What is dynamic braking or rheostatic braking of dc motor. Now in this article we are going to discuss about retardation test on dc machines. Brake test in one of the most simple way of finding efficiency of any kind of dc machine. In the previous articles we have seen brake test, hopkinsonstest which are essential to find out dc machine efficiency. 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. The connection diagram of dynamic braking of dc shunt motor is shown below. Working principle of dc shunt motor your electrical guide. 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. In the case of a dc motor, the magnetic field is produced by the field winding. Speed controlling of dc shunt motor by field and armature control 8. Before starting the experiment the motor field rheostat must be at minimum position and generator field rheostat must be at maximum position.
A belt around the air cooled pulley has its end attached to the spring balance s1 and s2. This test is performed on only one motor of a batch of similar motors and called a type test. Its operation is based on the principle that when a current carrying conductor is placed in a. When a current carrying conductor is placed in a magnetic field, it experiences a force. The machine is running as a motor at rated voltage and speed. Direct method of testing when conducted on a motor is also known as brake test.
Swinburnes test is the most commonly used and simplest method of testing of shunt and compound wound dc machines which have constant flux. 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. In this method, a brake is applied to a watercooled pulley mounted on the motor shaft as shown in fig. The applied voltage v has to force current through the armature against the back. Scribd is the worlds largest social reading and publishing site. N, given by, this can be graphically explained below. The armature is made of coils of wire wrapped around the core, and the core has an extended shaft that rotates on bearings.
The dc shunt motor is 120vdc with rated speed of 1800 revolutions per minute. We believe that these faqs will be useful for your practical exams and interviews as well. Speed control of dc shunt motor with field and armature rheostat control 79 2. A brushed dc electric motor is an internally commutated electric motor designed to be run from a direct current power source. The motor is loaded directly by means of a mechanical brake load or by means of an eddy current or a calibrated air fan. Electrical machinel dc laboratory manual grietelectrical and. Brake test is basically a load test of induction motor. This is the complete theory of brake test on dc shunt motor including laboratory manual. Dc motor principle a machine that converts dc power into mechanical energy is known as dc motor. The coils in the shunt field are composed of many turns of small wire, resulting in low shunt field current and moderate armature current. What is theory of brake test on dc shunt motor answers.
Brake test on dc shunt motor free download as word doc. Retardation test is also called as running down test. Brake test is used to determine the efficiency of comparatively small motors. Then, knowing the armature and shunt cu losses at a given load current, efficiency can be calculated. Electrodynamometer is an electrical break, in which the breaking force can be varied electrically. For a dc generator the output power is wasted in resistor. 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. Brake test also called as direct loading test of testing the motor. 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. Join date oct 2011 location pak posts 365 helped 22 22 points 1,956 level 10. Retardation test or running down test on dc machines. Two basic methods used for braking a motor dc injection and dynamic photo credit. 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.
The dc shunt motor construction is the same as any type of dc motor. Components of the shunt motor are the armature, labeled a1 and a 2, and the field, labeled f1 and f2. The open circuit characteristics for a dc generator are determined as follows. In this test we get total stray losses nothing but combination of.
If the dc line voltage is constant, then the armature voltage and the field strength will be constant. 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. 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. Dc motors although ac motors are used in most of the cases, dc motors have many applications and used for multipurpose applications. Brake test on dc shunt motor electric motor electrical engineering. Therefore, driving torque acts on the armature which begins to rotate. No load test on dc shunt generator 1 connect the circuit as shown in figure 1 with switches s1 and s2 open. 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. Working principle of dc shunt motor, dc series motor and all other dc motors can be stated as follows. The load test on 3phase induction motor is performed to obtain its various characteristics including efficiency. Retardation or running down test this method is applicable to shunt motors and generators and is used for finding stray losses. Title of the experiment page no 7 retardation test on dc shunt motor. 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.
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. In this test the efficiency of the machine at any load is predetermined. That method is to change the terminal voltage of the motor. As you know that the construction of any type of dc motor is very similar to a dc generator. To conduct load test on dc shunt motor and to find efficiency. Two basic methods used for braking a motor dc injection. Hence dc shunt generator is called constant voltage generator. 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. Swinburnes test and predetermination of efficiencies as generator and motor 7. Dc machines can be tested by three different methods namely direct method, indirect method and regenerative method. The machine under test is speeded up slightly beyond its normal speed and then supply is cut. The speed and the current to the rotor are inversely proportional.
442 931 842 69 530 1030 722 144 660 1502 1286 661 1133 860 1288 636 1295 1296 791 1538 711 307 1169 147 54 1365 1054 795 1388 65 1114 730 388 576 709 502 900