Salient-pole Synchronous Motor Research Articles

Oscillatory Torques During Synchronous Motor Starting

A fundamental characteristic of the salient-pole synchronous motor is a twice-slip frequency torque pulsation during acceleration. Although frequently neglected, sound application engineering requires an understanding of this subject. The way twice-slip frequency torques are produced in synchronous machines is discussed, as are the effects of these torques on mechanical system considerations such as critical speeds and stress buildup in shafts. Finally, specific areas of design coordination between designers of electrical power systems, synchronous motors, and the mechanical components of the system are suggested.

On the Condition for Pull into Step of Salient-pole Synchronous Motor

On the Condition for Pull into Step of Salient-pole Synchronous Motor

Pulling-Into-Step of Reluctance Synchronous Motors

The analysis of the pulling-into-step phenomena of salient-pole synchronous motors with dc field excitation gives unsatisfactory results when applied to reluctance motors (without dc field excitation). This difficulty can be overcome by taking the dynamics of the system into full consideration. By considering the rotor, the coupling, and the load as one dynamic system, satisfactory results can be obtained. It is found that the rigidity of the coupling plays a major role in the synchronization process. The analysis can be readily programmed on an analog computer and the effects of the various system parameters studied. Boundaries for the parameters within which synchronization takes place can be obtained; outside these boundaries the reluctance motor fails to pull-into-step.

Two-speed salient-pole synchronous machines

A constant-speed drive is not, in its nature, what industry usually requires. On the contrary, the ability either to change speed uniformly over a declared range, or to obtain two or more alternative fixed speeds, is commonly very advantageous. Like the squirrel-cage induction motor, the salient-pole synchronous motor has secured wide use because of its many well-known virtues. This is in spite of its inherent fixed speed, which is only sometimes required and is often actually disadvantageous.

Two-speed single-winding salient-pole synchronous machines

Previous work on 2-speed single-winding squirrel-cage induction motors, using the principle of pole-amplitude modulation, has now been extended to synchronous machines, and really simple and satisfactory 2-speed salient-pole synchronous motors have been designed, constructed and tested. This paper records the basic principles involved and illustrates these by reference to an industrial 10/8-pole motor of this type, for which test results are given. Such motors can equally well be used as generators, either to give a choice of output frequency for a given speed of prime mover or to maintain the output frequency constant in spite of a change of driving speed.

The permanent-magnet synchronous motor

A synchronous motor, constructed by modifying an induction motor by fitting a permanent magnet inside the squirrel-cage rotor, is very useful for drives where synchronous operation is required or where the drop in speed of an induction motor is too great. The paper presents a theory of operation of this type of motor and suggests an empirical design method. The analysis is based on the 2-axis theory of the salient-pole synchronous motor and shows how the properties of the permanent magnet can be taken into account.The principal difficulty in designing the motor arises from the demagnetizing effect on the magnet of the heavy currents which flow when the motor is started up and synchronized. The analysis consists of two parts. First, the performance characteristics are related to the direct-axis and quadrature-axis characteristics, which show separately the variation of flux and magnetomotive force on each axis. A method is then developed for calculating the axis characteristics from the B/H curve of the permanent magnet and the dimensions of the machine. In this way the performance can be predetermined.The method is verified by tests on an existing machine. Finally, two other designs, which could be expected to give improved performance, have been worked out.

A Torsional Vibration Problem as Associated With Synchronous Motor Driven Machines

Certain component failures in synchronous-driven high-inertia rotating equipment may be traced to a phenomenon peculiar to the starting characteristic of a salient-pole synchronous motor: A synchronous motor contributes a pulsating torque during the starting cycle. Though this fact is well known in itself, it has not been associated with the effect it may have on a high inertia load. The pulsating torque may excite a torsional resonance, which will in turn induce very high stresses in the driven train members.

Current Loci of Salient-Pole Synchronous Motors: An Extension of Blondel Theory [includes discussion

Current Loci of Salient-Pole Synchronous Motors: An Extension of Blondel Theory [includes discussion

Starting performance of salient-pole synchronous motors

IN recent years, two papers on the subject of salient-pole synchronous motors have been published in which practical methods for calculating the starting performance are derived on the basis of considerations that take into account all the unsymmetrics of this type of machine; the authors of these two papers are respectively H. V. Putman and T. M. Linville. Application of the Putman method gives at small values of the slip torque values that are somewhat too high; on the other hand, application of the Linville method is rather laborious, especially when the damper cage has a relatively large number of bars per pole. In view hereof, the author presents in this paper another method of calculating the starting performance of a salient-pole synchronous motor, a method which also takes into consideration all the unsymmetrics of this machine. This new method is, on the one hand, much simpler to apply than the Linville method, while on the other hand, it leads to more accurate results than the Putman method. It has been used for many years in the calculation and design of machines of various ratings and speeds, and has always given satisfactory results.

Starting Performance of Salient-Pole Synchronous Motors

IN recent years, two papers on the subject of salient-pole synchronous motors have been published in which practical methods for calculating the starting performance are derived on the basis of considerations that take into account all the unsymmetrics of this type of machine; the authors of these two papers are respectively H. V. Putman and T. M. Linville. Application of the Putman method gives at small values of the slip torque values that are somewhat too high; on the other hand, application of the Linville method is rather laborious, especially when the damper cage has a relatively large number of bars per pole. In view hereof, the author presents in this paper another method of calculating the starting performance of a salient-pole synchronous motor, a method which also takes into consideration all the unsymmetrics of this machine. This new method is, on the one hand, much simpler to apply than the Linville method, while on the other hand, it leads to more accurate results than the Putman method. It has been used for many years in the calculation and design of machines of various ratings and speeds, and has always given satisfactory results.

Salient pole motors out of synchronism

An extension of the development and application of methods of tensor analysis is given here, applied to the predetermination of the subsynchronous performance characteristics of salient pole synchronous motors.

Salient Pole Motors Out of Synchronism

An extension of the development and application of methods of tensor analysis is given here, applied to the predetermination of the subsynchronous performance characteristics of salient pole synchronous motors.

Pull-In Characteristics of Synchronous Motors

The differential analyzer has proved its worth in solving various types of difficult problems, of which the determination of the pull-in characteristics of salient pole synchronous motors is typical; but even with the aid of this device it has been necessary in solving this problem to make several simplifying assumptions. The differential analyzer recently completed at the University of Pennsylvania, however, is sufficiently comprehensive in design so that few assumptions are necessary, and the major electrical transients and mechanical forces may be taken into account. Typical solutions obtained by means of this analyzer are presented herewith, together with practical pulling-into-step criteria.

The simplex synchronous motor

Salient-pole synchronous motors with phase-connected damper windings are capable of developing high starting and pull-in torques with low starting current, as revealed by information given here.

The Pulling into Step of a Salient-Pole Synchronous Motor

A synchronous motor started as an induction motor must pass through an electro-mechanical transient after the field circuit is supplied with electrical excitation in order to change its action from that of an induction motor to that of a synchronous motor. The calculation of this problem has been difficult because the differential equation of motion is of a non-linear type of which no analytical solution has been made. The integraph at the Massachusetts Institute of Technology has given a new and direct method of solving equations of the type encountered in these pulling-into-step transients. In this paper are compiled the results of many integraph solutions which were made after combining the factors that influence the performance of such machines into ratios and relative factors so that the results will apply to all practical cases. From the solutions several generalizations are made which can be directly applied to determine whether or not any type of salient-pole synchronous motor will synchronize properly. These solutions take into account inertia, saliency, incompleteness of amortisseur windings, load, switching angle, and field current, and assume negligible armature resistance, negligible rotor leakage reactance, no saturation, constant load torque near synchronous speed, and negligible electrical transients. Oscillograph tests of a 160-hp. motor and a sample calculation are given.

Starting Performance of Salient-Pole Synchronous Motors

This paper presents an analysis of the sub-synchro-nous speed phenomena of a salient pole synchronous motor in which formulas and equivalent circuits are developed, making it possible to calculate the torque and current for a broad range of Conditions. Equations in terms of the impedances of the direct and quadrature axes are first derived from the revolving field point of view. The equivalent circuits for the two axes are then set up and expressions for the separate impedances of the circuit elements established. Adequate means of taking into account the combined effects of salient poles, incomplete amortisseur windings, and open or closed field windings are presented. The results obtained are illustrated by a comparison of the predicted performance and test data for a large 60-pole motor. The calculated distribution of current between the amortisseur bars of the same motor is shown by curves. Other curves show the calculated performance of the motor with and without continuous end rings between the poles and with the field winding open and closed. A final example shows the theoretical effects of changing the positions of the bars in the poles of a large waterwheel generator.

Abridgment of starting performance of salient-pole synchronous motors

This paper presents an analysis of the sub-synchronous speed phenomena of a salient-pole synchronous motor in which formulas and equivalent circuits are developed making it possible to calculate the torque and current for a broad range of conditions. Equations in terms of the impedances of the direct and quadrature axes are first derived from the revolving field point of view. The equivalent circuits for the two axes are then set up and expressions for the separate impedances of the circuit elements established. Adequate means of taking into account the combined effects of salient poles, incomplete amortisseur windings, and open or closed field windings are presented. The results obtained are illustrated by a comparison of the predicted performance and test data for a large 60-pole motor. The calculated distribution of current between the amortisseur bars of the same motor is shown by curves. Other curves show the calculated performance of the motor with and without continuous end rings between the poles and with the field winding open and closed. A final example shows the theoretical effects of changing the positions of the bars in the poles of a large waterwheel generator.

Starting performance of synchronous motors

This paper deals with the theory underlying the starting performance of the salient pole synchronous motor equipped with damper windings. The theory, while involving some approximations, is accurate enough for practical engineering calculations. Formulas are developed for the starting torque, pull-in torque and inrush. A method is also given for calculating the speed torque curve from standstill to synchronous speed. Due to the fact that the damper winding is not continuous around the periphery and due to the presence of the single-phase field winding, the rotor circuit is not a perfect polyphase secondary but is unbalanced to some extent. In order to take care of this unbalance, it is necessary, in addition to the usual system of positively rotating vectors, to employ a second system of negatively rotating vectors as is done in unbalanced three-phase problems. The stator resistance has been disregarded in working out the general case of the unbalanced or partial polyphase secondary in order to obtain a torque formula which will be simple and at the same time accurate enough for practical calculations. Mr. Q. Graham is working on this problem and expects to present in an Institute paper, in the near future, the general solution including the stator resistance. The use of the double squirrel-cage type of damper winding in salient pole machines has been examined both theoretically and experimentally. Other methods of obtaining unusual starting performance are suggested and the results of some actual calculations presented.

Starting Performance of Synchronous Motors

This paper deals with the theory underlying the starting performance of the salient-pole synchronous motor equipped with damper windings. The theory, while involving some approximations, is accurate enough for practical engineering calculations. Formulas are developed for the starting torque, pull-in torque and inrush. A method is also given for calculating the speed torque curve from stand still to synchronous speed. Due to the fact that the damper winding is not continuous around the periphery and due to the presence of the single-phase field winding, the rotor circuit is not a perfect polyphase secondary but is unbalanced to some extent. In order to take care of this unbalance, it is necessary, in addition to the usual system of positively rotating vectors, to employ a second system of negatively rotating vectors as is done in unbalanced three-phase problems. The stator resistance has been disregarded in working out the general case of the unbalanced or partial polyphase secondary in order to obtain a torque formula which will be simple and at the same time accurate enough for practical calculations. Mr. Q. Graham is working on this problem and expects to present in an Institute paper, in the near future, the general solution including the stator resistance. The use of the double squirrel-cage type of damper winding in salient-pole machines has been examined both theoretically and experimentally. Other methods of obtaining unusual starting performance are suggested and the results of some actual calculations presented.

A two-speed salient-polesynchronous motor

S. H. Mortensen: Mr. Wieseman's paper brings out, clearly, the fact that two-speed synchronous motors can be built economically, and that a machine of this kind properly proportioned will practically maintain all the virtues of the standard salient-pole synchronous motor. The field of application for a motor of this kind is at the present time rather limited. The only application the speaker can think of in addition to the ones Mr. Wieseman has mentioned is that for driving two-speed pumps such as are sometimes used with condenser installations.