Quick Links
- Synchronous motors: An introduction
- Chapter I: Synchronous motors General Principles
- Efficiency Synchronous Motors and Experimental Properties
- Stalling of a Synchronous Motor
- Over-excited synchronous motor
- Necessity of synchronism and stability of synchronous operation
- Explanation of Single-Phase Synchronous Motors
- Equations of Synchronous Motors; Analytical Theory
- Symmetrical Polyphase Motors
- Equation of the Synchronous Motor by the Method of Complex Variables
- Excitation of Synchronous Motors
- Shunt-excitation
- Chapter II: Operation of synchronous motor
- Installation of Synchronous Motors
- Current controller
- Starting of Single-Phase Machine
- Starting of Machine with Laminated Field Poles
"We endorse specAmotor. The free electric motor selection platform on the web."
specAmotor has collected data from lots of synchronous, brushless and brushed motors and will objectively calculate the best configuration.
Over-excited synchronous motor
Over-excited synchronous motor
An over-excited synchronous motor, connected to the terminals of an alternator having excessive armature-reaction, can even replace the excitation of the latter. It is observed, indeed, that on suppressing this excitation, the generator continues to run the motor, and furnishes the normal voltage at its terminals; but it can develop only little power. An over-excited motor thus produces an indirect self-excitation which is equivalent to that obtainable from a condenser. There is, in other respects, a complete analogy of effects between the two forms of apparatus.
These experimental results are much too complex to be studied more in detail here. They can be discussed more satisfactorily later, in connection with the theory of these motors and their applications.
Polyphase Synchronous Motors Rotor and Stator shape
If we turn our attention, first, to polyphase synchronous motors, the explanation of the phenomena just described is made easy by the consideration of revolving magnetic fields.
For the sake of brevity we will adopt the terms "rotor" and "stator" to designate the movable and fixed portions, respectively, of the motor, in accordance with the terminology of Professor S. P. Thompson.
Let us take, as an example, a motor having two pairs of pole-pieces, in which the inductive circuit is of movable form (rotor) and the induced is circuit of stationary form (stator).
In the ordinary form of polyphase alternators, the rotor will consist of a crown of iron cores, with protruding poles excited by coils receiving direct current from a separate exciter. The stator, on the other hand, will consist of a circular core of laminated iron having some induced windings disposed in notches or slots in such a manner that the wires in the successive slots shall have alternating currents of different phase passing through them. If we suppose, for example, that we have a winding for four poles and for six phases (three slots per pole) such as is shown in Fig. 7, the wires in the six slots which cover two poles of the stator, as we follow along the periphery of the latter, will have, passing through them, six currents which are out of phase with respect to each other by 1/6 of a period, and which can be represented by the equations
In which T being the common duration of the period of the alternating currents considered, I0 their common amplitude (i.e., maximum value), and i1, i2, i3, i4, i5, i6, being the currents in the slots 1, 2, 3, 4, 5, 6.
It will be seen that, at every one-sixth of a period, the currents in the stator resume the same values, but the latter are displaced one-sixth of the width of a double field (2 poles) in the direction in which the currents succeed each other along the stator. Therefore, the axes radiating from the magnetic fields produced by the windings of the stator displace themselves around this stator with an angular velocity;
