This board contains all indicating instruments for alternators and feeders.
The guarantee as to efficiency is as follows: On non-inductive load, the alternators will have an efficiency of not less than 90.
From alternators to bus bars the current passes, first, through the alternator switch, and then alternatively through one or the other of two selector switches which are connected, respectively, to the two sets of bus bars.
Diagram showing relative location ofalternators and synchronous motors in plant of Witherbee Sherman & Co.
It is a fact, however, that composite wound alternators do not regulate properly for inductive as well as non-inductive loads.
Alternators are wound for one, two or three phases.
In order to minimize eddy currents, such alternators must accordingly be built with thinner laminations and frequently poorer mechanical construction, resulting in increased cost of the machine.
A current limiting inductance coil (called a reactance) is placed in series with the alternators or transformers.
The deleterious effects of low power factor loads on alternators are even more marked than on transformers.
In order to overcome this defect compensated field alternators have been designed which automatically adjust the voltage for all variations of load and lag.
There are, however, alternators in which the armature revolves, the current being delivered to the external circuit through collector rings and brushes.
The regulation at unity power factor of modern alternators capable of carrying 25 per cent.
The tendency of this construction is to give alternators unusually large dimensions per given capacity.
If such alternators can be purchased at a lower price per unit of capacity than alternators of low voltage plus step-up transformers, there is an apparent advantage for transmission systems in the high-voltage machines.
This advantage may rest in part on a higher efficiency in the alternators that yield the line voltage than in the combination of low-voltage alternators plus step-up transformers.
During the past decade the voltages of alternators have been greatly increased, but have not caught up with the demand for high pressures on long-transmission lines.
The opposite extreme is found in alternators directly coupled to the Parsons steam-turbine, in which, with a speed of 3000 revs.
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.
Although in practice it is impossible to run two alternators in series unless they are rigidly coupled together--which virtually reduces them to one machine--two or more machines can be run in parallel, as was first described by H.
On passing to the separate consideration of alternators and continuous-current dynamos, the chief constructive features of the latter will first be taken in greater detail.
Ring winding was largely employed in early continuous-current dynamos and also in thealternators of Gramme and H.
The running to speed of large turbo-alternators requires considerable care, and should always be done slowly; that is to say the rate of acceleration should be slow.
The governor can be adjusted for speed while the turbine is in operation, thereby facilitating the synchronizing of alternators and dividing the load as may be desired.
In alternating current circuits a precisely similar action takes place between the alternators and synchronous motors, or even between the alternators themselves.
The use of very low frequencies has the disadvantage of departing from standard frequencies, and the probability that the greater cost of transformers and alternatorswould offset the gain.
Since standard alternators are seldom designed to carry their rated kilowatt load at less than 80 per cent.
Such transformers are employed at the generating end of a transmission line to raise the voltage of the alternators to such value as will enable the electric power to be economically transmitted to a distant point.
Radial diagrams of the arrangement and connections of ~Y~ grouping of lap windings and wave windings for three phase alternators are shown by figs.
These alternators may be used as synchronous motors and for this duty are fitted with amortisseur winding in the pole faces which does not interfere with their use as alternators.
Because water wheel alternators are frequently required to operate safely at speeds considerably in excess of normal.
In large machines the brush holder studs are mounted on a stand supported from the base; in small alternators they are usually fastened to the cap of one of the bearing pedestals.
Since alternators may be run at speeds far in excess of desirable engine speeds, it must be evident that both size and cost may be reduced by designing them for high speed operation.
In the design of alternators the drop of voltage on an inductive load is mainly dependent upon the magnetic leakages, primary and secondary.
With bar inductors, as must be evident from the illustration, the maximum cross section of copper can be placed in a slot of given dimension, hence a bar winding is used to advantage for alternators designed to carry a large current.
The double pole equalizer switch 6S should now be closed, connecting the two field windings in parallel and equalizing the compounding, so that any variations of load will affect the two alternators equally.
Diagram of connections of General Electric automatic voltage regulator for several alternators running in parallel with exciters in parallel.
A saturation curve may be taken with full load current in the armature; but this is rarely done, except in alternators of comparatively small output.
What are the conditions when two or more alternators are directly connected together?
How may two or more alternators be started simultaneously?
Step down transformers must be used between the alternators and the lamps to obtain the proper working voltages for the lamps.
The application of large gas engines to the driving of alternators operated in parallel requires an accurate knowledge of the wave form, and a close conformation to a sine wave if parallel operation is to be satisfactory.
The effect of resonance= on the wave forms of alternators has been the subject of much investigation and discussion; it is a matter of vital importance to the engineer in charge of a large alternating current power distribution system.
The connections for operating alternators in parallel are shown in fig.
As the alternators continue to come closer in step, the red glow will gradually fade away until the lamps become dark.
How are the alternators synchronized or brought in phase?
Is a sluggish, or a too sensitive governor preferable on an engine driving alternators in parallel?
Diagram of connections of General Electric voltage regulators for one or more alternatorsusing one exciter.
In some cases, instead of the high-pressure feeders starting from omnibus bars, each alternator works independently and the feeders are grouped together on the various alternators as required.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "alternators" in a variety of sentences. We hope that you will now be able to make sentences using this word.
