Hence in many places preference is now given to thepolyphase system.
If three or more single-phase currents preserving a fixed difference of phase flow in various parts of a connected circuit, the whole taken together is called a polyphase current.
It is there reduced in voltage by transformers and employed as an alternating current, or is used to drive polyphasemotors coupled to direct current generators to reproduce the power in continuous current form.
Rotating, according as single phase or polyphase current is used.
In polyphase transformers there are two or more magnetic circuits through the core, and the fluxes in the various circuits are displaced in phase.
A polyphasesynchronous motor is self starting, because, before the current has died out in the coils of one phase, it is increasing in those of the other phase or phases, so that there is always some turning effort exerted on the armature.
Wagner squirrel cage armature for polyphase induction motor, as employed on motors of from 5 to 25 horse power.
The simplicity of single phase systems in comparison with polyphase systems, makes them more desirable for small alternating current plants.
Is there any choice between a polyphase transformer and separate single phase transformers for transforming a polyphase current?
Polyphase induction motors may be started by connecting them directly to the circuit with an ordinary switch, and the smaller motors are started in this way in practice.
Singlephase and Polyphase Generators; faults in armature; grounds in generators; connections of different phases; field windings.
For starting, a polyphase resistance completes the circuits of the rotor winding.
The type most commonly used is the polyphase induction motor.
Both carry conductors in their slots, and these conductors in each case form a polyphase winding.
They possess many advantages, especially their ability to run at overload, and consequently a locomotive with polyphasemotor will run up grade without serious loss of speed.
With the polyphase current a motor with a rotating field is used, and they have considerable efficiency as regards weight when compared with the single phase and with the direct current motor.
Where polyphase regulators are required, the connections consist essentially of two sets of single phase connection, and the controller is extended in length so as to contain double sets of drum and contact.
Regulators operating on this principle may be used for theatre dimmers, as controllers for series lighting, and also to adjust the voltage or the branches of unbalanced three wire single phase and polyphase systems.
In what respects do polyphase induction regulators differ in principle from single phase regulators?
Bottom end of stationary element or ~secondary~ of Westinghouse polyphase induction regulator.
Moreover, if a three phase machine be installed, polyphase current will be available in case it may be necessary to operate polyphase motors at some future time.
Its operation depends on the production of a rotating field by the currents of the metered circuits in angularly placed coils, one for each phase in the case of a polyphase indicator.
Furthermore, some polyphase systems give a multiplicity of voltages, and the question arises as to which of these voltages shall be considered the transmission voltage.
How is the line voltage varied by a polyphase regulator?
Polyphase regulators have but little tendency to vibrate because the field across the air gap is the resultant of two or more single phase fields and is of a constant value at all times.
The polyphase induction regulator is similar to the single phase regulator except that both the primary and secondary elements are wound with as many sets of coil as there are phases in the circuit.
Single phase meters indicate the power factor of a single phase circuit, or of one branch of anypolyphase circuit.
Polyphase meters indicate the average angle between the currents and voltages and are superior for polyphase service to meters having only one current coil.
Single phase line, used as basis of comparison in obtaining the relative weights of copper required by polyphase systems, as indicated in figs.
In exceptional cases, as those of polyphase converters, re-entrant circuits are employed, and the armature windings are so constructed that a commutator can be connected to them exactly as in direct current machines.
In polyphase alternators the separate windings of the various phases may be grouped in two ways: 1.
A multiphase or polyphase alternator is one which delivers two or more alternating currents differing in phase by a definite amount.
This type of alternator was designed prior to the introduction of the polyphase systems, to overcome the difficulties encountered in the operation of single phase alternators as motors.
As a general rule, when alternators are employed for lighting circuits, the single phase machines are preferable, as they are simpler in construction and do not generate the unbalancing voltages often occurring in polyphase work.
Machines of this class are not self-exciting, but require an alternating or polyphasecurrent previously supplied to the mains to which the stationary armature is connected.
An interesting device for regulating and reversing has been devised by Mr. Tesla for the purpose of varying the speed of polyphase motors.
The section of this volume devoted to Mr. Tesla's inventions in the utilization of polyphase currents will show how thoroughly from the outset he had mastered the fundamental idea and applied it in the greatest variety of ways.
Mr. Tesla's work ranges far beyond the vast departments of polyphase currents and high potential lighting.
The only advantage of the polyphase machine as thus used is that the whole of the surface of the armature core may be efficiently covered with winding, and the output of the alternator for a given size be thereby increased.
The several phases may be entirely independent, and such was the case with the early polyphase machines of Gramme, who used four independent circuits, and also in the large two-phase alternators designed by J.
The machine starts up as an ordinary polyphase induction motor and the field of the converter is built up as though it were an ordinary dynamo.
Let the polyphase induction motor run idle, that is, with no load.
It is suggested, before undertaking this test, that the instructions for test by the two wattmeter and by the polyphase wattmeter methods be read.
How is a polyphase converter started with alternating current?
The polyphasemeter should give a positive indication, but if each movement be tried separately one will be found to give a negative reading, the other movement will give a positive reading.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "polyphase" in a variety of sentences. We hope that you will now be able to make sentences using this word.
