Consider a single phase induction motor with standstill rotor as shown in the fig. You should also make a dc measurement of stator winding linetoline resistance using a dmm. Rotating three phase magnetic field figure 1 shows a cross section of an elementary induction motor, with six poles on the stator. Therefore a single phase induction motor is not selfstarting and requires some particular starting means.
The motor is mounted in a test rig that allows one to control the torque applied to the motor shaft and to measure both rpm and torque. Target motor theory motorola 3phase ac induction motor vector control 5 figure 32. The stator winding of this machine is conventional, very much like that of an induction motor. The induction coil actually functions as a transformer primary, with the workpiece to be heated becoming the transformer secondary. The rotor of an induction motor can be a squirrel cage rotor or wound. This theory for single phase states that a stationary pulsating magnetic field can be resolved into two rmf, each of equal magnitude but rotating in the opposite direction. How cross field theory expains about single phase induction motor.
Consider a single phase induction motor with standstill rotor as shown in following figure. The fieldoriented theory is the base of a special control method for induction motor drives. Ac induction motor vector control, driven by etpu on mpc5500, rev. Firstly the equivalent circuit is developed on the basis of double revolving field theory when only its main winding is energized. Overall view and cross section of an asynchronous motor the motor. Record all nameplate information for the induction motor. The induction motor is made up of the stator, or stationary windings, and the rotor. As soon as the rotor begins to turn, a speed emf e is induced in the rotor conductors, as they cut the stator flux f s. The rotor will constantly be turning to align its magnetic field with that of the stator field. Double revolving field theory of single phase induction motor.
Ac induction motor vector control, driven by etpu on mpc5500. It has been more than a century since the principle of the operation of induction motors was discovered. Single phase induction motors,and their starting methods. Consider a single phase induction motor with standstill rotor as shown in the below figure. Because the magnetic field rotates in this way, an ac motor does not need power or mechanical aid to be applied to the rotor. When the induction coil is placed next to or around a workpiece, the lines of force concentrate in the air gap between the coil and the workpiece. The crossfield theory of alternatingcurrent machines ieee xplore. Its the stationary part which has a laminated stamping used to reduce eddy current losses on its external surface. The operating principle of the singlephase induction motor is more complex than that of the. In the pulsating field, the rotor does not rotate due to inertia. Single phase induction motor, theory of operation double revolving field theory. Single phase induction motor double revolving field theory the threephase induction motor starting torque inversely depends on the slip this implies that a small positive slip 0.
Induction motors achieve both these objectives, which is why they now are used in well over 90% of all motor applications. Each of these components rotates in the opposite direction i. This voltage increases as the rotor speed increases. One is known as the double revolving field theory, and the other is cross field theory. The first industrial motors of this type were constructed at the end of the nineteenth century and soon gained the favor of users who appreciated their raggedness, simplicity and relatively low manufacturing cost compared to dc commutator motors. Cross field theory another theory which can also be used to explain why single phase induction motor is not self starting is crossfield theory. With this control method, induction motors can successfully replace expensive dc motors. Due to this flux, emf gets induced in the rotor conductors due to transformer action.
Of course, single phase induction motors have the same construction of single phase motors, but dont apprehensive ill repeat it to add small vital additions. When a 1 phase supply is connected to the stator winding, a pulsating magnetic field is produced. Double revolving theory is perhaps the easier of the two explanations to understand 4. What is the cross field theory in a singlephase induction. Working principle of a single phase induction motor.
Working principle of a single phase induction motor circuit globe. The cross field theory of single phase induction motor the cross field theory of single phase induction motors looks at the induction motor from a totally different point of view. They are available in a wide range of power ratings. The singlephase induction motor operation can be described by two methods. According to the double field revolving theory, this. The cross field theory of single phase induction motor. Theory of heating by induction 7 tromagnetic, or flux around it. Sensored field oriented control of 3phase perm magnet. E vbl where v, b, and l are all perpendicular to each other if the left vertical side of the spinning coil moves at velocity v, the component of v perpendicular to b is v sin. The performance of the single phase induction motor is analysed by the two theories. Two theories have been suggested to find the performance of a single phase induction motor. The equivalent circuit of a single phase induction motor can be obtained by two methods named as the double revolving field theory and cross field theory.
The basic idea behind the double field revolving theory is that any alternating quantity can be resolved into 2 equal components rotating in opposite direction. This peculiar behaviour of the motor has been explained in two ways. A tutorial in ac induction and permanent magnet synchronous motors, vector control with digital signal processors, fred flett, analog devices, 1994. This is the normal situation encountered with power electronic input signals.
Distributed and concentrated windings distribution, pitch and winding factors e. Cross field theory electrical engineering interview. An induction motor can therefore be made without electrical connections to the rotor. Ac induction motor speedtorque characteristic squirrelcage ac induction motors are popular for their simple construction, low cost per horsepower and low maintenance they contain no brushes, as do dc motors. Before going into the details of revolving field theory, first we should know why do we need to study this theory. Constructional features of round rotor and salient pole machines armature winding integral slot and fractional slot windings. Double revolving theory is perhaps the easier of the two explanations to understand.
The motor then produces a constant torque and not a pulsating torque as in other singlephase motors. What is the cross field theory in a singlephase induction motor. The singlephase induction motor in his theory and calculation of electricalapparatus. Operating principle the singlephase induction motor operation can be described by two methods. Ideally, the rotation changes direction at a constant angular rate.
Double revolving theory is perhaps the easier of the two explanations to understand so we will discuss the double revolving theory only. The stator winding is excited by the single phase a. The stator consists of a series of wire windings of very low resistance permanently attached to the motor frame. In an induction motor, the electric current in the rotor needed to produce torque is obtained via electromagnetic induction from the rotating magnetic field of the stator winding. Induction motor working principle types of induction motor. A single phase induction motor consists of a single phase winding on the stator and a cage winding on the rotor. Both the theories are similar and explain the reason for the production of torque when the rotor is rotating. Introduction in specific applications such as propulsion purpose, the induction motor has to operate at speeds higher than the rated one, the field flux weakening is required which denotes the strategy by which the motors speed can be increased above the rated speed. Consider a single phase induction motor with standstill rotor. When the rotor is at a stand still 0 rpm the rotating magnetic field of the stator cuts the conductors of the rotor at a. Cross field theory in single phase induction motors. The motor then runs as a singlephase induction motor. The cross field theory of single phase induction motors looks at the induction motor from a totally different point of view.
The objection to the rotating field theory, that it is applicable to induction motors only, would be a reference to text books will show that the mathematical treatment is usually based on the so called cross field theory. This control is based on projections which transform a threephase time and speed dependent system into a two coordinate d and q coordinates time invariant system. Sensored field oriented control of 3phase permanent magnet. Revolving field theory is used for the analysis of behavior of single phase induction motor. As a voltage and a current is applied to the stator winding terminals, a magnetic field is developed in the windings.
The rotating magnetic field the basic idea of an electric motor is to generate two magnetic fields. Both the theories are similar and explain the reason for. Torque is defined as the cross product of armature current and stator flux. This book is an early treatment of ac induction and permanent magnet synchronous motors with emphasis on vector control using digital signal processors. Revolvingfield polygon technique for performance prediction. Electrical study of the dc motor shows that the armature current and the stator flux can be independently. Payment options order history view purchased documents. Nowadays this method has become general in induction motor drives of high precision. Equivalent circuit of a single phase induction motor the equivalent circuit of a single phase induction motor can be obtained by two methods named as the double revolving field theory and cross field theory. What is common to all the members of this family is that the basic physical process involved in their operation is the conversion of electromagnetic energy to mechanical energy, and vice versa. An equivalent circuit, similar to the equivalent circuit of a three phase motor, can represent each field the parameters of the two circuits are the same. The outer winding consists of bars of smaller crosssection shortcircuited by end rings. Cross field theory consider a single phase induction motor with standstill rotor as shown in the fig. Equivalent circuit of a single phase induction motor.
Well, a single phase induction motor with its main winding alone can be represented as shown in figure below. According to the crossfield theory, the components but differs. An ac motor works by applying alternating current to stator windings, which produce a rotating magnetic field. When a voltage is applied to the stator of an induction motor, a magnetic field begins to rotate in the stator.
Revolving field theory of single phase induction motors. A rotating magnetic field is a magnetic field that has moving polarities in which its opposite poles rotate about a central point or axis. Single phase induction motor double revolving field theory each of the rotating fields induces a voltage in the rotor, which drives current and produces torque. An induction motor also known as an asynchronous motor is a commonly used ac electric motor. An induction motors rotor can be either wound type or squirrelcage. An induction motor or asynchronous motor is an ac electric motor in which the electric current in the rotor needed to produce torque is obtained by electromagnetic induction from the magnetic field of the stator winding. Field orientated control the field orientated control foc consists of controlling the stator currents represented by a vector. The rotor will rotate via the magnetic field and create torque on the drive shaft of the motor. Sensorless field oriented control sfoc of induction motor im drives estimate the mechanical position of the rotor and the field orientation by means of. This is a key principle in the operation of the alternatingcurrent motor rotating magnetic fields are often utilized for electromechanical applications such as induction motors and. Double revolving field theory and cross field theory are two ways of explaining the same phenomenon in single phase induction machines.