Dynamo englisch
These were referred to as "magneto-electric machines" or magnetos. An important development by Wilde and Siemens was the discovery by that a dynamo could also bootstrap itself to be self-excited , using current generated by the dynamo itself.
This allowed the growth of a much more powerful field, thus far greater output power. Self-excited direct current dynamos commonly have a combination of series and parallel shunt field windings which are directly supplied power by the rotor through the commutator in a regenerative manner.
They are started and operated in a manner similar to modern portable alternating current electric generators, which are not used with other generators on an electric grid.
There is a weak residual magnetic field that persists in the metal frame of the device when it is not operating, which has been imprinted onto the metal by the field windings.
The dynamo begins rotating while not connected to an external load. The residual magnetic field induces a very small electrical current into the rotor windings as they begin to rotate.
Without an external load attached, this small current is then fully supplied to the field windings, which in combination with the residual field, cause the rotor to produce more current.
In this manner the self-exciting dynamo builds up its internal magnetic fields until it reaches its normal operating voltage.
When it is able to produce sufficient current to sustain both its internal fields and an external load, it is ready to be used.
A self-excited dynamo with insufficient residual magnetic field in the metal frame will not be able to produce any current in the rotor, regardless of what speed the rotor spins.
This situation can also occur in modern self-excited portable generators, and is resolved for both types of generators in a similar manner, by applying a brief direct current battery charge to the output terminals of the stopped generator.
The battery energizes the windings just enough to imprint the residual field, to enable building up the current. This is referred to as flashing the field.
Both types of self-excited generator, which have been attached to a large external load while it was stationary, will not be able to build up voltage even if the residual field is present.
The load acts as an energy sink and continuously drains away the small rotor current produced by the residual field, preventing magnetic field buildup in the field coil.
The operating principle of electromagnetic generators was discovered in the years — by Michael Faraday.
The principle, later called Faraday's law , is that an electromotive force is generated in an electrical conductor which encircles a varying magnetic flux.
He also built the first electromagnetic generator, called the Faraday disk , a type of homopolar generator , using a copper disc rotating between the poles of a horseshoe magnet.
It produced a small DC voltage. This was not a dynamo in the current sense, because it did not use a commutator. This design was inefficient, due to self-cancelling counterflows of current in regions of the disk that were not under the influence of the magnetic field.
While current was induced directly underneath the magnet, the current would circulate backwards in regions that were outside the influence of the magnetic field.
This counterflow limited the power output to the pickup wires, and induced waste heating of the copper disc. Later homopolar generators would solve this problem by using an array of magnets arranged around the disc perimeter to maintain a steady field effect in one current-flow direction.
Another disadvantage was that the output voltage was very low, due to the single current path through the magnetic flux.
Faraday and others found that higher, more useful voltages could be produced by winding multiple turns of wire into a coil.
Wire windings can conveniently produce any voltage desired by changing the number of turns, so they have been a feature of all subsequent generator designs, requiring the invention of the commutator to produce direct current.
The first dynamo based on Faraday's principles was built in by Hippolyte Pixii , a French instrument maker. It used a permanent magnet which was rotated by a crank.
The spinning magnet was positioned so that its north and south poles passed by a piece of iron wrapped with insulated wire. Pixii found that the spinning magnet produced a pulse of current in the wire each time a pole passed the coil.
However, the north and south poles of the magnet induced currents in opposite directions. To convert the alternating current to DC, Pixii invented a commutator , a split metal cylinder on the shaft, with two springy metal contacts that pressed against it.
This early design had a problem: As with electric motors of the period, the designers did not fully realize the seriously detrimental effects of large air gaps in the magnetic circuit.
Antonio Pacinotti , an Italian physics professor, solved this problem around by replacing the spinning two-pole axial coil with a multi-pole toroidal one, which he created by wrapping an iron ring with a continuous winding, connected to the commutator at many equally spaced points around the ring; the commutator being divided into many segments.
This meant that some part of the coil was continually passing by the magnets, smoothing out the current. The Woolrich Electrical Generator of , now in Thinktank, Birmingham Science Museum , is the earliest electrical generator used in an industrial process.
Independently of Faraday, the Hungarian Anyos Jedlik started experimenting in with the electromagnetic rotating devices which he called electromagnetic self-rotors.
In the prototype of the single-pole electric starter, both the stationary and the revolving parts were electromagnetic. About he formulated the concept of the dynamo about six years before Siemens and Wheatstone but did not patent it as he thought he was not the first to realize this.
His dynamo used, instead of permanent magnets, two electromagnets placed opposite to each other to induce the magnetic field around the rotor.
The dynamo was the first electrical generator capable of delivering power for industry. The modern dynamo, fit for use in industrial applications, was invented independently by Sir Charles Wheatstone , Werner von Siemens and Samuel Alfred Varley.
Varley took out a patent on 24 December , while Siemens and Wheatstone both announced their discoveries on 17 January , the latter delivering a paper on his discovery to the Royal Society.
The "dynamo-electric machine" employed self-powering electromagnetic field coils rather than permanent magnets to create the stator field.
This invention led directly to the first major industrial uses of electricity. For example, in the s Siemens used electromagnetic dynamos to power electric arc furnaces for the production of metals and other materials.
The dynamo machine that was developed consisted of a stationary structure, which provides the magnetic field, and a set of rotating windings which turn within that field.
On larger machines the constant magnetic field is provided by one or more electromagnets, which are usually called field coils. An advantage of Gramme's design was a better path for the magnetic flux , by filling the space occupied by the magnetic field with heavy iron cores and minimizing the air gaps between the stationary and rotating parts.
The Gramme dynamo was one of the first machines to generate commercial quantities of power for industry. Brush assembled his first dynamo in the summer of using a horse-drawn treadmill to power it.
Brush's design modified the Gramme dynamo by shaping the ring armature like a disc rather than a cylinder shape. The field electromagnets were also positioned on the sides of the armature disc rather than around the circumference.
After dynamos and motors were found to allow easy conversion back and forth between mechanical or electrical power, they were combined in devices called rotary converters , rotating machines whose purpose was not to provide mechanical power to loads but to convert one type of electric current into another, for example DC into AC.
They were multi-field single-rotor devices with two or more sets of rotating contacts either commutators or sliprings, as required , one to provide power to one set of armature windings to turn the device, and one or more attached to other windings to produce the output current.
On 14 December , Dynamo appeared in the semi-final of Strictly Come Dancing , as part of a dance routine.
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