Hi all, so im working on a project titled controlling the speed of a single phase induction motor. Squirrel cage induction motors have poor starting torque and high starting currents. In particular, the squirrelcage induction motors are widely used electric motor in home and industrial. Single phase motors characteristics electrical a2z. What are the torqueslip characteristics of a 3phase. However, with variable frequency drives, these disadvantages can be overcome. In this paper an improved steady state model of single phase induction motors is derived to investigate major motor characteristics like torque speed, input power, output power, etc. In the single phase induction motor we have forward and backward fields.
In a single phase motor we have only a single field winding excited with alternating current. A single phase induction motor with main winding arranged for direct connection to power source and auxiliary winding connected in series with a capacitor. The rotor will constantly be turning to align its magnetic field with that of the stator field. In unity slip, the forward and the backward field produce equal torque but in opposite direction so the produced net torque equals zero so the motor fails to start the single phase induction motor isnt self. Characteristics of induction motors nidec corporation. Torque characteristics of single phase induction motor for. Torque slip characteristics in three phase induction motor as the induction motor is located from no load to full load, its speed decreases hence slip increases. The 3 phase set of currents, each of equal magnitude and with a phase. Speed torque characteristics in three phase induction motor uptill now, we have seen torque slip characteristics of an induction motor. All ac motors have the same basic components, a stator and rotor. Split phase and capacitor start induction run csir motors both of these motors share similar electrical characteristics and exhibit moderate running efficiencies 45% to 50%.
The equation of the torque is given as shown below. Determination of the torquespeed characteristic of induction motor in electric machinery education rade buinac, veselko tomljenovic electrical engineering department, polytechnic of zagreb konavoska 2, zagreb, croatia rade. Split phase motors have moderate starting torque and do not employ the use of start capacitors to. Performance characteristics of three phase induction motor the equivalent circuits derived in the preceding section can be used to predict the performance characteristics of the induction machine. The main disadvantage of squirrel cage induction motor is poor speed control and low starting torque. Typical torque speed characteristics of induction motor when supplied from variable voltage at rated frequency are given in fig. In twopole single phase motors, the torque goes to zero at 100% slip zero speed, so these require alterations to the stator such as shadedpoles to provide starting torque. The basic idea of an electric motor is to generate two magnetic fields. Due to their low cost, splitphase induction motors are the most popular singlephase motors in the market.
The speed of the induction motor is characterized by the term known as the slip. The speedtorque characteristic of an induction motor can be modified by effect of voltage variation in induction motor. Torquespeed characteristics of three phase squirrel cage. Torque speed characteristics of 3phase induction motor. Single phase induction motor three phase induction motor single phase induction motor there are probably more single phase ac induction motors in use today than the total of all the other types put together. The magnetization current i m flowing in the motor s equivalent circuit fig. The stator is almost similar to the stator of single phase. The stator is the stationary coils in the motor where the current is produced to create the.
In unity slip, the forward and the backward field produce equal torque but in opposite direction so the produced net torque equals zero so the motor fails to start the singlephase induction motor isnt selfstarting, its another reason to know why it isnt selfstarting. Torque speed characteristic of an induction motor torque speed characteristic is the curve plotted between the torque and the speed of the induction motor. This may be achieved by converting a single phase supply into two phase supply through the use of an additional winding. Types of single phase induction motors electronics hub. They are based on the fact that the induction motor torque at a given slip varies as the square of the voltage. The name capacitor starts itself shows that the motor uses a capacitor. Firstly, the single phase induction motors are mostly provided with concentric coils. It is logical that the least expensive, lowest maintenance type motor. Some single phase induction motors are also called squirrel cage motors because of the rotors similarity. Universal motor construction, working and characteristics. Variable voltage variable frequency vf control theory an induction motor compared to a dc motor has some major advantages such as.
Before going to the operation and characteristics of split phase induction motor we should first understand why single phase induction motor is not selfstarting to make a single phase induction motor selfstarting, we should somehow produce a rotating magnetic field. As induction motors are widely being used, their speed control may be required in many applications. Different speed control methods of induction motor are explained below. The slip is defined as the ratio of difference of synchronous speed and actual rotor speed to the synchronous speed of the machine. The important characteristics of the splitphase induction motor are given below, the starting torque is 150 to 200 percent of the full load torque with a starting current of 6 to 8 times the full load current.
Speed torque characteristics of 3 phase induction motor. As we have already discussed the torque of the induction motor in the topic torque equation of an induction motor. Unlike threephase ac, however, singlephase ac cannot create a rotating magnetic. The torque slip curve for an induction motor gives us the information about the variation of torque with the slip. A 3 phase induction motor can be used for different applications with various speed and load requirements. The motor then operates as a single phase induction motor and continues to accelerate until it reaches the normal speed. At the step before the design phase, it is helpful to run an analysis and evaluation using the finite element method fem to understand a single phase induction motor s characteristics by accounting for induced current and magnetic saturation characteristics. Another theory which can also be used to explain why single phase induction motor. Singlephase induction motors are widely used as small output motors for the drives in household electrical appliances and office machinery, like fans and washing machines, because they can use singlephase ac, the typical power source for home electronics. Torque slip characteristics of three phase induction motor. Torque slip characteristics of three phase induction motor the torque slip curve for an induction motor gives us the information about the variation of torque with the slip. The number of torque changes based on a given speed of the load. Threephase induction motor torquespeed characteristics.
Speed and torque behavior of three phase induction motor based on torque equation. But in practice, it is not possible to give initial torque to rotor externally hence some modifications are done in the construction of single phase induction motors to make them self starting. Speed torque characteristics in three phase induction motor. Ac induction motors are one of the most common types of motors used in a variety of applications due to the fact that they run off of ac voltage which is readily available at every outlet. The motor then runs as a singlephase induction motor. The single phase motor stator has a laminated iron core with two windings arranged perpendicularly.
While researching on the internet i came across this one circuit that proposes a model that uses a microcontroller and a triac circuit and a. Although single phase induction motor is more simple in construction and is cheaper than a 3 phase induction motor of the same frame size, it is less efficient and it operates at lower power factor. Capacitor start single phase induction motor working and. The construction of the stator of the single phase induction motor is similar to that of three phase induction motor except there are two dissimilarities in the winding part of the single phase induction motor. Single phase induction motors multiple choice questions. The starting winding is opened by the centrifugal switch when the motor attains about 75% of synchronous speed. A capacitor start motors are a single phase induction motor that employs a capacitor in the auxiliary winding circuit to produce a greater phase difference between the current in the main and the auxiliary windings.
Torquespeed characteristics of three phase squirrel cage induction motor aim to obtain the torque speed characteristics tn r of a three phase squirrel cage induction motor using 1. This curve is called the torque speed characteristic curve. Determination of the torquespeed characteristic of. Torque slip characteristics of induction motor full guide. Torqueslip characteristics in three phase induction motor. Torque slip characteristics of single phase induction motor. A single phase induction motor requires separate starting circuitry to provide a rotating field to the motor. A universal motor is a special type of motor which is designed to run on either dc or single phase ac supply. The slip is defined as the ratio of the difference of synchronous speed and actual rotor speed to the synchronous speed of the machine. Performance characteristics of three phase induction motor. Pdf on may 3, 2019, ahmed m t ibraheem alnaib and others published single phase induction motors find, read and cite all the research you need on researchgate.
Notice and disclaimer the information in this publication was considered technically sound by a consensus among persons engaged in its development at the time it was approved. As mentioned above that, due to the rotating magnetic field of the stator, the induction motor becomes self starting. Information guide for general purpose industrial ac small. The single phase induction motor resembles, three phase, squirrelcage motor except that, at full speed, only a single winding in the stator is excited. Capacitor start induction motor its phasor diagram. The important performance characteristics in the steady state are the efficiency, power factor, current, starting torque, maximum or pullout torque.
Single phase motors may be classified into the following basic types. When a motor is designed in such a way that impedance of the aluminum conductor of the rotor is reduced, its efficiency is increased in a high speed range. The motor then produces a constant torque and not a pulsating torque as in other singlephase motors. Single phase induction motor the single phase induction machine is the most frequently used motor for refrigerators, washing machines, clocks, drills, compressors, pumps, and so forth.
Split phase induction motor operation and characteristics. That is why, universal motors generally comes built into the device they are meant to drive. The single phase induction motor is much the same in construction as the three phase motor. To compare the performance of induction motor with d. Single phase ac motors are as ubiquitous as they are useful serving as prime power sources for a seemingly limitless array of small. If the rotor speed is less than the synchronous speed n s, the machine acts as a motor. We can derive an equation from the equivalent circuit that allows the calculation of the torque for a given value of slip. However, the slip at which the maximum torque occurs changes with rotor resistance. A single phase induction motor is inherently not selfstaring can be shown easily. In this chapter, we shall focus our attention on the construction, working and characteristics of commonly used single. However different motor designs will affect the shape of the curve and the locked rotor current. Torque speed characteristics of induction motor slip. Single phase induction motors are used primarily for domestic and lightindustrial applications where three phase supply is generally not available. There is one extra winding placed in the single phase induction motor in order to make the single phase induction motor self starting therefore the single phase induction motor consists of two winding.
Generally, this, where 100% is equal to synchronous speed, as determined by the mains frequency and number of pole pairs. The normal operating region for the induction motor is the nearly linear portion between rated speed and synchronous speed. Speed torque characteristics of the single phase repulsion motor. Refer back to this diagram as the operational requirements of the single phase motor are discussed. These motors are generally series wound armature and field winding are in series, and hence produce high starting torque see characteristics of dc motors here. Bse induction motors principle operation and torque speed. Construction, working, torque speed characteristic and application. Torque slip characteristics of induction motor electrical4u. The above value becomes somewhat larger with small single phase motors. Figure 1 showed a plot of induction motor torque vs speed from zero to synchronous speed. A set of torque speed characteristics is shown in figure 6. In a split phase motor, the running winding should have a high resistance and low inductance single phase induction motors multiple choice questions and answers pdf free download,interview questions,objective type questions,lab viva manual.
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