Motors
| What is the difference between a Motor and a Pump? |
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Classification or Types of Motor DC Motor Special Types of Motor AC motor
Induction Motor
3 Phase Induction Motor |
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What is motor? Device that converts electrical or other energy into mechanical energy or imparts motion. What's the difference between a motor and an engine? The real difference, is the fact that "motors" run on electricity, while "engines" run on combustion. Electric motor  Cutaway of a fractional-horsepower single-phase induction motor Cutaway of a fractional-horsepower single-phase induction motor, as used in many light-industrial applications. This motor has a squirrel-cage rotor which is not wired into the electrical circuit. Since a single-phase motor with a squirrel-cage rotor can start from standstill, a secondary circuit is included in which a capacitor is causes the current in a starting winding to lead the applied voltage, thus enabling rotation to begin. When the rotor reaches a certain speed, a centrifugal switch opens and the capacitor circuit is cut out, leaving the motor to run using only its main winding. A device for converting electrical energy directly into mechanical energy. Traditional forms of electric motor are based on the force experienced by a current-carrying wire in a magnetic field. Motors can be, and sometimes are, run in reverse as a generator. Simple direct-current motors consist of a magnet or electromagnet (the stator), and a coil (the rotor) which turns when a current is passed through it because of the force between the current and the stator field. So that the force keeps the same sense as the rotor turns, the current to the rotor is supplied via a commutator – a slip-ring broken into two semicircular parts, to each of which one end of the coil is connected, so that the current direction is reversed twice each revolution. For use with alternating-current supplies, small DC motors are often still suitable, but induction motors are preferred for heavier duty. In the simplest of these, there is no electrical contact with the rotor, which consists of a cylindrical array of copper bars welded to end rings. The stator field, generated by more than one set of coils, is made to rotate at the supply frequency, inducing (see electromagnetic induction) currents in the rotor when (under load) it rotates more slowly, these in turn producing a force accelerating the rotor. Greater control of the motor speed and torque can be obtained in "wound rotor" types in which the currents induced in coils wound on the rotor are controlled by external resistances connected via slip-ring contacts. In applications such as electric clocks, synchronous motors, which rotate exactly in step with the supply frequency, are used. In these the rotor is usually a permanent magnet dragged round by the rotating stator field, the induction-motor principle being used to start the motor. The above designs can all be opened out to form linear motors producing a lateral rather than rotational drive. The induction type is the most suitable, a plate analogous to the rotor being driven with respect to a stator generating a laterally moving field. Such motors have a wide range of possible applications, from operating sliding doors to driving trains, being much more robust than rotational drive systems, and offering no resistance to manual operation in the event of power cuts. A form of DC linear motor can be used to pump conducting liquids such as molten metals, the force being generated between a current passed through the liquid and a static magnetic field around it. |
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Working of Three Phase Induction Motor Objective Questions on Induction Motor 1. Type of single phase motor having highest power factor at full load is 1. shaded pole type. 2. capacitor run. 3. capacitor start. 4. split phase. Capacitor run motor has better running power factor and efficiency and smoother operation. Modern application is ceiling fan. 2. Induction motors have the advantage of 1. all of below. 2. less cost. 3. simple in construction. 4. less maintenance. 3. For a single phase capacitor start induction motor which of the following is valid? 1.Rotation can be changed by reversing main winding terminals. 2.Direction of rotation cannot be changed. 3.Rotation can be changed by interchanging supply terminals. 4.None of these. 4. Which motors are preferred for refrigeration and air conditioning in smaller units? 1. Induction motors. 2. Universal motors. 3. Reluctance motors. 4. Stepper motors. 5. Types of rotating machines 1. both B and C. 2.IM. 3. synchronous machine. 4. transformer. 6. A 230 V, 50 Hz, 4 pole single phase induction motor is rotating in the clockwise ( forward ) direction at a speed of 1425 rpm. If the rotor resistance at standstill is 7.8 O. Then the effective rotor resistance in the backward branch of the equivalent circuit will be 1.2 O. 2.4 O. 3.8 O. 4.10 O. 7. Which of the following motor used in hair dryers? 1. Synchronous motors. 2. Shaded pole IM. 3. Split phase IM. 4. Cage induction motor. 8. Which of the following motor is used in grinders? 1. Capacitor start IM. 2. Capacitor start capacitor run IM. 3. Split phase IM. 4. Synchronous motor. 9. Capacitor start capacitor run provides 1. high staring torque and high power factor. 2. high staring torque only. 3. high power factor only. 4. none. 10. Slip speed is the 1. difference of synchronous speed and actual rotor speed. 2. difference of actual rotor speed and synchronous speed. 3. sum of synchronous and rotor speeds. 4. half of the sum of synchronous and rotor speeds. 11. At slip s = 1 torque developed in machine is 1. starting torque. 2. maximum torque. 3. electromagnetic torque. 4. none. 12. Capacitor fitted with ceiling / table fans is of the value of 1.1 - 2 µF. 2.2 - 3 µF. 3.5 - 10 F. 4.0.1 µF. 13. Which 1 - F motor does operate at high power factor? 1. Capacitor start. 2. Capacitor run. 3. Split phase. 4. Shaded pole. 14. Why are capacitors used with large AC induction motor? 1. Improve voltage level. 2. Improve power factor. 3. Improve power level. 4. Improve current level. 15. Which 1 F motor is used for refrigerator? 1. Capacitor run. 2. Split phase. 3. Universal. 4. Repulsion. 16. What type of dielectric material is used in capacitors used for fans and for power factor correction? 1. Oil impregnated paper. 2. Vacuum. 3. Glass. 4. Mica. 17. A fan blade of length 2R rotates in a time period T in a magnetic field B. The induced voltage in the blade in 1. R2B / T. 2.2RBT. 3. RBT. 4. R2BT. 18. A three phase induction motor has a synchronous speed of 1500 rpm the machine runs at 1460 rpm at a particular load. The slip at this load is ___________. 1.30 %. 2.1.5 %. 3.2.67 %. 4.5 %. 19. A 3 - F, 12 pole, 600 V, 50 Hz star connected IM has rotor resistance and stand still resistance of 0.03 O and 0.5 O respectively. The speed of maximum torque will be 1.240 rpm. 2.450 rpm. 3.470 rpm. 4.540 rpm. 20. A 3 - F, 400 / 200 V, Y - Y connected wound rotor induction motor has 0.06 O rotor resistance and 0.3 O standstill reactance per phase. To make the starting torque equal to maximum torque of the motor the additional resistance required 1.0.24 O. 2.0.45 O. 3.0.78 O. 4.0.66 O.  Examples of electric motors include: fans, washing machines, fridges, pool pumps, vacuum cleaners and fan ovens. What is the difference between a Motor and a Pump? A pump does not convert one form of energy to a different form of energy, but the Motor converts electrical energy to mechanical energy. A pump requires a driving mechanism such as a motor or an engine to operate. The motor only requires an energy source. The motor is a device that is capable of rotating when a voltage is applied. The pump is a device that is used to move fluids. Both of these devices are very important in fields such as electrical engineering, mechanical engineering, civil engineering, constructions, robotics, automobile engineering and numerous other fields. Motor Electric motor, which is more commonly known as the motor, is a device that is capable of converting electrical energy into mechanical energy. Electric motors are divided into two categories based on the form of electricity on which it runs. These two types are DC motors and AC motors. DC motors run on direct current and AC motors run on alternating current. Most electric motors are based on time varying magnetic fields. The axel containing all the moving parts of the motor is known as the armature. The rest of the motor is known as the body. The motor has time varying magnetic fields that are produced by induction coils. In a typical DC motor, the coils are placed at the armature of the motor. In most of the AC motors, the coils are placed on the body of the motor and the armature is composed of permanent magnets. There is also a third type of motors known as universal motors. Universal motors are capable of running on AC voltage and DC voltage alike. Pump A pump is a device that is used to move fluids. Pumps use mechanical energy to transfer these fluids. The most common example for the pump is the air compressor. It takes air from outside and transfer it to the inside overcoming the pressure of the gas inside. The pump is the device which does the work on the fluid in order to get it to a higher energy or entropy state. Most of the mechanical pumps are based on a rotary motion. There are pumps that operate on a linear motion too. Most pumps are driven by either electric motors or fuel engines. A pump does not convert energy to different forms; it rather directs the energy on a desired way. Some energy is always lost as sound, vibrations, and heat; therefore, a pump is not 100% efficient. The three main types of pumps are known as direct lift pumps, displacement pumps and gravity pumps. |