Gramme machine - AbsoluteAstronomy.com

A Gramme machine, Gramme ring, Gramme magneto, or Gramme dynamo is an electrical generator

Electrical generator

In electricity generation, an electric generator is a device that converts mechanical energy to electrical energy. A generator forces electric charge to flow through an external electrical circuit. It is analogous to a water pump, which causes water to flow...

which produces direct current

Direct current

Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...

, named for its Belgian inventor, Zénobe Gramme

Zénobe Gramme

Zénobe Théophile Gramme was a Belgian electrical engineer. He invented the Gramme machine, a type of direct current dynamo capable of generating smoother and much higher voltages than the dynamos known to that point.In 1873 he and Hippolyte Fontaine accidentally discovered that the device was...

, and was built as either a dynamo or a magneto

Magneto

A magneto is a type of electrical generator.Magneto may also refer to:* Magneto , permanent magnetic alternating current rotary generator* ignition magneto, magnetos on internal combustion engines...

. It was the first generator to produce power on a commercial scale for industry. Inspired by a machine invented by Antonio Pacinotti

Antonio Pacinotti

Antonio Pacinotti was an Italian physicist, who was Professor of Physics at the University of Pisa.-Biography:Pacinotti was born in Pisa, where he also died...

in 1860, Gramme was the developer of a new induced rotor in form of a wire-wrapped ring (Gramme ring) and demonstrated this apparatus to the Academy of Sciences

Academy of Sciences

An Academy of Sciences is a national academy or another learned society dedicated to sciences.In non-English speaking countries, the range of academic fields of the members of a national Academy of Science often includes fields which would not normally be classed as "science" in English...

in Paris

Paris

Paris is the capital and largest city in France, situated on the river Seine, in northern France, at the heart of the Île-de-France region...

in 1871.

Description

The Gramme machine used a ring armature, i.e., a series of thirty armature

Armature (electrical engineering)

In electrical engineering, an armature generally refers to one of the two principal electrical components of an electromechanical machine–generally in a motor or generator, but it may also mean the pole piece of a permanent magnet or electromagnet, or the moving iron part of a solenoid or relay....

coil

Coil

A coil is a series of loops. A coiled coil is a structure in which the coil itself is in turn also looping.-Electromagnetic coils:An electromagnetic coil is formed when a conductor is wound around a core or form to create an inductor or electromagnet...

s, wound around a revolving ring of soft iron

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

. The coils are connected in series, and the junction between each pair is connected to a commutator

Commutator (electric)

A commutator is a rotary electrical switch in certain types of electric motors or electrical generators that periodically reverses the current direction between the rotor and the external circuit. In a motor, it applies power to the best location on the rotor, and in a generator, picks off power...

on which two brushes run. The permanent magnet

Magnet

A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets.A permanent magnet is an object...

s magnetize the soft iron ring, producing a magnetic field

Magnetic field

A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...

which rotates around through the coils in order as the armature turns. This induces a voltage

Voltage

Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...

in two of the coils on opposite sides of the armature, which is picked off by the brushes.

Earlier electromagnetic

Electromagnetism

Electromagnetism is one of the four fundamental interactions in nature. The other three are the strong interaction, the weak interaction and gravitation...

machines passed a magnet near the poles of one or two electromagnets, creating brief spikes or pulses of DC resulting in a transient output of low average power, rather than a constant output of high average power.

With enough coils, the resulting voltage waveform is practically constant, thus producing a near direct current

Direct current

supply. This type of machine needs only electromagnet

Electromagnet

An electromagnet is a type of magnet in which the magnetic field is produced by the flow of electric current. The magnetic field disappears when the current is turned off...

s producing the magnetic field to become a modern generator

Electrical generator

Invention of modern electric motor

During a demonstration at an industrial exposition in Vienna

Vienna

Vienna is the capital and largest city of the Republic of Austria and one of the nine states of Austria. Vienna is Austria's primary city, with a population of about 1.723 million , and is by far the largest city in Austria, as well as its cultural, economic, and political centre...

in 1873, Gramme accidentally discovered that this device, if supplied with a constant-voltage

Voltage

power supply, will act as an electric motor

Electric motor

An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...

. Gramme's partner, Hippolyte Fontaine

Hippolyte Fontaine

Hippolyte Fontaine was a French engineer and electrician who worked with Zénobe Gramme on the development of the Gramme machine , and whose contributions were essential to the creation of the dynamo...

, carelessly connected the terminals of a Gramme machine to another dynamo which was producing electricity, and its shaft began to spin."Hippolyte Fontaine." Encyclopædia Britannica. 2010. Encyclopædia Britannica Online. 11 Jan. 2010 . The Gramme machine was the first powerful electric motor useful as more than a toy or laboratory curiosity. Today the design forms the basis of nearly all DC electric motors. Gramme's use of multiple commutator contacts with multiple overlapped coils, and his innovation of using a ring armature, was an improvement on earlier dynamo

Electrical generator

s and helped usher in development of large-scale electrical devices.

Earlier designs of electric motors were notoriously inefficient because they had large, or very large, air gaps throughout much of the rotation of their rotors. Long air gaps create weak forces, resulting in low torque. A device called the St. Louis motor (still available from scientific supply houses), although not intended to, clearly demonstrates this great inefficiency, and seriously misleads students as to how real motors work. These early inefficient designs apparently were based on observing how magnets attracted ferromagnetic materials (such as iron and steel) from some distance away. It took a number of decades in the 19th century for electrical engineers to learn the importance of small air gaps. The Gramme ring, however, has a comparatively small air gap, which enhances its efficiency. (In the illustration, the large hoop-like piece is probably the permanent magnet; the Gramme ring is rather hard to see.)

Principle of Operation

This illustration shows a simplified one-pole, one-coil Gramme ring and a graph of the current produced as the ring spins one revolution. While no actual device uses this exact design, this diagram is a building block to better understand the next illustrations.

A one-pole, two-coil Gramme ring. The second coil on the opposite side of the ring is wired in parallel with the first. Because the bottom coil is oriented opposite of the top coil, but both are immersed in the same magnetic field, the current forms a ring across the brush terminals.

A two-pole, four-coil Gramme ring. The coils of A and A' sum together, as do the coils of B and B', producing two pulses of power 90° out of phase

Phase (waves)

Phase in waves is the fraction of a wave cycle which has elapsed relative to an arbitrary point.-Formula:The phase of an oscillation or wave refers to a sinusoidal function such as the following:...

with each other. When coils A and A' are at maximum output, coils B and B' are at zero output.

A three-pole, six-coil Gramme ring, and a graph of the combined three poles, each 120° out of phase from the other and summing together.

Modern Form of the Gramme Ring

While the Gramme ring permitted a more steady power output, it suffered from a technical design inefficiency due to how magnetic lines of force pass through a ring armature. The field lines tend to concentrate within and follow the surface metal of the ring to the other side, with relatively few lines of force penetrating into the interior of the ring.

Consequently the interior windings of each small coil are minimally effective at producing power because they cut very few lines of force compared with the windings on the exterior of the ring. The interior windings are effectively dead wire and only add resistance to the circuit, lowering efficiency.

Initial attempts to insert a stationary field coil within the center of the ring to help the lines penetrate into the center proved too complex to engineer.

Eventually it was found to be more efficient to wrap a single loop of wire across the exterior of the ring and simply not have any part of the loop pass through the interior. This also reduces construction complexity since one large winding spanning the width of the ring is able to take the place of two smaller windings on opposite sides of the ring. All modern armatures use this externally-wrapped design, although the windings do not extend fully across the diameter; they are more akin to chords of a circle, in geometrical terms. Neighboring windings overlap, as can be seen in almost any modern motor or generator rotor that has a commutator. In addition, windings are placed into slots with a rounded shape (as seen from the end of the rotor). At the surface of the rotor, the slots are only as wide as needed to permit the insulated wire to pass through them while winding the coils.

While the hollow ring could now be replaced with a solid cylindrical core or drum, the ring still proves to be a more efficient design, because in a solid core the field lines concentrate in a thin surface region and minimally penetrate the center. For very a large power-generation armature several feet in diameter, using a hollow ring armature requires far less metal and is lighter than a solid core drum armature. The hollow center of the ring also provides a path for ventilation and cooling in high power applications.

In small armatures a solid drum is often used simply for ease of construction, since the core can be easily formed from a stack of stamped metal disks keyed to lock into a slot on the shaft.

External links

Electricity museum: early motors

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

Description

Invention of modern electric motor

Principle of Operation

Modern Form of the Gramme Ring

See also

External links