Principle of operation of the direct current generator


What mechanism of operation of the direct current generator?

Operation of generators and engines of the constant toyok is based on the phenomena of electromagnetic induction and electromagnetic force. Being guided by the fact that any electrical machine of the obrayotim, i.e. can serve in certain conditions both as the generayotor, and the engine, we will consider the device of the mashiyona of the direct current irrespective of its assignment.

Схема машины постоянного тока

Scheme of the machine of the direct current.

The main parts of the machine of the direct current are the anchor and the bed bearing electromagnets. The motionless part, the bed, is made usually of cast steel. From the inside on the bed cores of poles ukrepyolyatsya. On the ends these cores snabzhayotsya by pole-shoes ("polar boots"). The last are intended for more uniform distribution of magnetic induction along the anchor circle. On the cores of the nayodeta of the coil making the machine magnetizing coil. The bed of the machine is the closing part — the magnetic conductor yoke. Except the main poles of excitation, on the stayonena between cores of the main poles cores of additional poles which coils soyoedinyatsya consistently with the anchor pomeshchayotsya. Assignment of dopolnitelyyony poles — to ensure sparkless functioning of brushes on the kolyolektor, good switching.

Схема кольцевого якоря

Scheme of the ring anchor.

The anchor (rotor) of the machine represents the cylindrical body collected from sheet electrotechnical steel usually 0,5 — 1 mm thick. The anchor is the rotating part of the machine, in its grooves the winding connected by conductors to the collector strengthened on the anchor shaft is placed. The last consists of the number of the copper plates of trapezoid section isolated one from another forming the cylindrical surface. Plates of the collector are isolated as Aden from another, and from the shaft by micanite.

Lean on the collector motionless in space of the kompyolekta of the coal or copper brushes established in shchetkoderyozhatel. Thus, at rotation of the anchor of the brush keep invariable situation in relation to machine poles. In the brush holder the brush the spring nestles on the collector. Brush holders become stronger on brush ballets and brush the traverse which contacts or the podshipniyokovy board of the machine, or its bed. The traverse can turn and by that to change the provision of all system of brushes on the otnoyosheniye to mashiyona poles. Brush bolts izoyolirutsya from traverses. Through the collector and brushes the anchor of the machine soyediyonyatsya with the external circuit.

In the machine there are two electric circuits: chain of the anchor and chain of the vozyobuzhdeniye. On the chain of the vozyobuzhdeniye the direct current which, passing through the magnetizing coil, creates the base magnetic field of the machine is passed.

Perhaps more visually to explain obtaining constant EMF by means of the machine and the collector role, we will consider operating conditions of the simplest ring anchor of the machine of poyostoyanny current. This anchor represents soyoby the hollow cylinder assembled from sheet electrotechnical steel. The winding of the anchor twists the hollow cylinder, forming the zamknuyoty contour. The magnetic flux penetrates the armature core, passing his internal cavity. At rotation of the anchor of EMF it is induced only in the provodyonik lying on the outer side of the anchor. The parts of the winding lying on internal and the edge parties of the anchor, do not uchastyovut in formation of EMF and carry out only the role of soyediniyotelny conductors. Defining the EDE direction, we see that EMF in the rounds of the winding moving under the northern polyuyos is opposite in direction EDE, induced in the rounds moving under the South Pole.

Схема распределения магнитной индукции вдоль окружности якоря и положение щеток в четырехполюсной машине

The scheme of distribution of magnetic induction along the circle of the anchor and the provision of brushes in the quadripolar machine.

As the device of the machine is symmetric, these EMFs in closed-coil winding of the anchor are mutually counterbalanced and no intrinsic current in the obyomotka arises. To use winding EMF, it is possible to connect it to the external load circuit by means of nepoyodvizhny brushes. The place of brushes should be chosen so that completely to use EDE, induced by the winding. Brushes divide the winding into two parallel branches with odinayokovy EMFs. In each of parallel branches of the winding all EMFs have to have the identical direction, in the opposite sluyocha the EMF of all rounds of the winding (in the extreme case when brushes are put under the middle of poles, tension between them will be equal to zero) will not be used completely. Napravyoleny EMFs in conductors of the winding is defined also napravleyoniy magnetic field, and the anchor rotation sense.

Induction has the greatest value under the middle of poles of the machine, and in the points which are on the line, perpendicular to the axis of poles and passing through the center of the anchor, induction is equal to zero. Distribution of induction along the circle of the anchor depends on magnetic resistance along the machine circle, and this resistance to a great extent is defined by the form of pole-shoes. Therefore, brushes have to stand on the neutral.

Схема соединения обмотки якоря с внешней цепью через коллектор и щетки

The scheme of connection of the winding of the anchor with the external circuit through the collector and brushes.

Owing to such provision of brushes between them constant voltage is created though the EMF induced in each of anchor winding rounds is the variable. Tension between the winding branch яко­ря; such branch consists of group of consistently connected, continuously moving conductors; separate conductors one by one pass from the area of the North Pole to the area of the South Pole, at the same time the EMF direction in them changes.

But at the same time position of each group of conductors, obrayozuyushchy the parallel branch of the winding, remains invariable in relation to machine poles. Thanks to it tension between brushes of the machine is constant. Process of switching of eleyoment of the winding of one parallel branch in other nazyvayetyosya switching.

If instead of two poles the machine has four poles, then four brushes will be necessary for the winding of the ring anchor for use of its EMF at rassmatyorivayemy us, koyotory have to be connected among themselves in pairs. These brushes separate the winding into two couples of parallel branches.

It is inexpedient to adapt the anchor winding for direct contact of conductors of the anchor with shchetyoka. It is better and more reliable when shchetyok slide on especially for it to the adapted kollekyotor plates, and plates soyeyodinyatsya by conductors with separate rounds of closed-coil winding of the anchor.
By means of the collector and these connecting conductors of the brush divide the anchor winding into parallel branches absolutely as well as at direct contact of brushes with this winding.

The ring anchor with the spiral winding is not applied now as at the spiral winding more poloviyona of its length does not participate in formation of EDE, and serves only for connection among themselves of the active conductors lying on outer side of the ring anchor.

Copper in windings otnosiyotelno of the difficult drum anchor is much better used. The drum anchor predyostavlyat itself the cylinder assembled from sheets of electrotechnical steel in which grooves only from outer side of the drum anchor winding conductors accommodate.

The machine of the direct current is reversible: if the machine is rotated by the prime mover and magnetic field of the machine is excited, then in the anchor EMF is directed and through the collector and brushes the machine sends the direct current to the external circuit. In the anchor this current, вза­имодействуя with the field of the machine, creates the braking moment, preyoodolevayemy the prime mover. In such conditions the machine works with the generator.

If the anchor and the magnetizing coil of the machine are included under the constant voltage, then current, prokhodyayoshchy through the anchor winding, interacting with the field of the machine, soyozdat the torque bringing the anchor into rotation at the same time in the winding of the anchor anti-EMF is directed. In such usloyoviya the machine works in the engine mode, turning elektriyochesky energy into mechanical.

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