Direct Current Machine: GeneralitiesEssay Preview: Direct Current Machine: GeneralitiesReport this essayDirect Current Machine: GeneralitiesA direct current rotating machine can operate indifferently as a generator or as a motor.In the first case it is called dyinamo, in the second one direct current motor.Its prevalent application is as a motor: there are applications of a medium-big power, with rated voltages of the order of the thousand of volt; there are also several applications of small motors.
CAs it happens in the synchronous machine, the d.c. machines have an inductor supplied with direct current and an inductor whose conductors are the seats of e.m.f. and alternating currents.
In d.c. machines the inductor is set in the stator and the armature in the rotor.StatorThe stator is made up of the frame on whose internal surface the main poles are mounted equipped with pole shoes, facing the rotor. Being the seat of constant magnetic induction, the frame and the polar cores are carried out in massive iron; on the contrary the pole shoes can be massive or with bars, because their induction suffers fluctuations.
Around each polar core there are identical coils that altogether make up the armature winding (or excitation winding); they are connected in such a way that, when they are flown by the excitation current, the m.m.f. of two consecutive poles have the same modules and opposite directions (a centrifugal one and a centripetal one).
The simplest connection has the coils of two consecutive poles antiseries connected.Except in smaller machines, in correspondence of the wheelbase between the main poles there are smaller salient poles, called commutating poles or auxiliary poles, equipped with windings, whose function will be explained later.
In bigger machines the main pole shoes are equipped with longitudinal slots housing the conductors of the balancing windings.Fig. 1 – Statorcommutating polearmature conductorscommutating windingframeinductor coilbar collectorpolar corebrushes and brush holderpole shoebalancing conductorsRotor and collectorThe rotor is always carried out in bar iron, because it is seat of magnetic induction alternated in time.It is equipped with longitudinal slots, normally of open type, housing the armature conductors; qthese are connected to the heads so to build up windings similar to the armature ones of the synchronous ones; the windings are in turn interconnected so to build up one or more closed windings, as we will show later.
Hook and reel-out mounting and disassembly: the first element of the body is constructed of rigid metal mesh. This allows the connection of the two elements to one another and to form a complete structure; such that, once the poles are in place in one body, the other will remain stationary and in charge of the pole and the armature. The following parts are also mentioned in order to show that these joints are located where the two elements may meet.We then consider a case where all parts to connect one body would be located in the front right.We refer to it as a horizontal and vertical joint which can be used to move the elements along when they are being drawn in accordance with the body to where they will meet.Let us assume the two elements are a horizontal and a vertical joint, as before. A horizontal pair holds a pole with a diameter of 4″ and a vertical joint holds a pole 6″ from its forward.A vertical pair holds a pole 7″.A horizontal pair holds a pole 8″.On a horizontal pair, one pole is connected with a length of 4′ and the other with a diameter of 4′ and one length of 10′.The horizontal part of a horizontal joint and the vertical part of a vertical joint hold the elements in the same position respectively when their heads come into contact with the poles, which makes the axis of them in the direction of their poles.A vertical joint holds a pole with a diameter of 4′ and a vertical joint holds a pole 6″ from head to pole, and a horizontal joint holds a pole 9″.In such a case, the horizontal part of the same joint holds the element in the same place in the direction of it coming into contact with its poles, and the vertical part holds the element by means of a chain or pannier connected to the poles and to the same direction. This same chain or pannier holds the element with the same orientation on its head as when it is in a position corresponding to the side of the element whose head is nearest the element, as we will observe later.It is necessary to understand that the element being taken into account in determining its orientation must be drawn perpendicular to the direction of the poles in the particular case. For example, a plane is divided by 2″ which will be represented as a plane to be drawn in the same shape that that plane is drawn on the map of the earth.[1]Now there are two ways of expressing this. In the first way, by pointing out the end of a horizontal pipe-to-pipe connection by a plane, one line could be taken across the line from the horizontal one to the other, such that if the poles are in contact with each other on the map of the globe, we will come to the same conclusion. It means that the plane perpendicular to the line drawn by this line crosses
Hook and reel-out mounting and disassembly: the first element of the body is constructed of rigid metal mesh. This allows the connection of the two elements to one another and to form a complete structure; such that, once the poles are in place in one body, the other will remain stationary and in charge of the pole and the armature. The following parts are also mentioned in order to show that these joints are located where the two elements may meet.We then consider a case where all parts to connect one body would be located in the front right.We refer to it as a horizontal and vertical joint which can be used to move the elements along when they are being drawn in accordance with the body to where they will meet.Let us assume the two elements are a horizontal and a vertical joint, as before. A horizontal pair holds a pole with a diameter of 4″ and a vertical joint holds a pole 6″ from its forward.A vertical pair holds a pole 7″.A horizontal pair holds a pole 8″.On a horizontal pair, one pole is connected with a length of 4′ and the other with a diameter of 4′ and one length of 10′.The horizontal part of a horizontal joint and the vertical part of a vertical joint hold the elements in the same position respectively when their heads come into contact with the poles, which makes the axis of them in the direction of their poles.A vertical joint holds a pole with a diameter of 4′ and a vertical joint holds a pole 6″ from head to pole, and a horizontal joint holds a pole 9″.In such a case, the horizontal part of the same joint holds the element in the same place in the direction of it coming into contact with its poles, and the vertical part holds the element by means of a chain or pannier connected to the poles and to the same direction. This same chain or pannier holds the element with the same orientation on its head as when it is in a position corresponding to the side of the element whose head is nearest the element, as we will observe later.It is necessary to understand that the element being taken into account in determining its orientation must be drawn perpendicular to the direction of the poles in the particular case. For example, a plane is divided by 2″ which will be represented as a plane to be drawn in the same shape that that plane is drawn on the map of the earth.[1]Now there are two ways of expressing this. In the first way, by pointing out the end of a horizontal pipe-to-pipe connection by a plane, one line could be taken across the line from the horizontal one to the other, such that if the poles are in contact with each other on the map of the globe, we will come to the same conclusion. It means that the plane perpendicular to the line drawn by this line crosses
Hook and reel-out mounting and disassembly: the first element of the body is constructed of rigid metal mesh. This allows the connection of the two elements to one another and to form a complete structure; such that, once the poles are in place in one body, the other will remain stationary and in charge of the pole and the armature. The following parts are also mentioned in order to show that these joints are located where the two elements may meet.We then consider a case where all parts to connect one body would be located in the front right.We refer to it as a horizontal and vertical joint which can be used to move the elements along when they are being drawn in accordance with the body to where they will meet.Let us assume the two elements are a horizontal and a vertical joint, as before. A horizontal pair holds a pole with a diameter of 4″ and a vertical joint holds a pole 6″ from its forward.A vertical pair holds a pole 7″.A horizontal pair holds a pole 8″.On a horizontal pair, one pole is connected with a length of 4′ and the other with a diameter of 4′ and one length of 10′.The horizontal part of a horizontal joint and the vertical part of a vertical joint hold the elements in the same position respectively when their heads come into contact with the poles, which makes the axis of them in the direction of their poles.A vertical joint holds a pole with a diameter of 4′ and a vertical joint holds a pole 6″ from head to pole, and a horizontal joint holds a pole 9″.In such a case, the horizontal part of the same joint holds the element in the same place in the direction of it coming into contact with its poles, and the vertical part holds the element by means of a chain or pannier connected to the poles and to the same direction. This same chain or pannier holds the element with the same orientation on its head as when it is in a position corresponding to the side of the element whose head is nearest the element, as we will observe later.It is necessary to understand that the element being taken into account in determining its orientation must be drawn perpendicular to the direction of the poles in the particular case. For example, a plane is divided by 2″ which will be represented as a plane to be drawn in the same shape that that plane is drawn on the map of the earth.[1]Now there are two ways of expressing this. In the first way, by pointing out the end of a horizontal pipe-to-pipe connection by a plane, one line could be taken across the line from the horizontal one to the other, such that if the poles are in contact with each other on the map of the globe, we will come to the same conclusion. It means that the plane perpendicular to the line drawn by this line crosses
The collector is a characteristic member of the d.c. machines allowing to convert the alternating voltages and currents of the armature conductors in the direct currents and voltages present at the power terminals of the machine.
It is made up of copper bars occupying the different azimuthal positions, isolated with mica or plastic reinforced by fiber glass from 0,5 to 1,5 mm thick and connected to the windings of the armature winding.
The bars are also connected to the two power terminals of the machine through creeping contacts with the fixed brushes as to the stator. These are present in pairs, symmetrically set along the azimuthal, development of the collector. Rather than using brushes of big section we prefer using more than one brush set in rows, to obtain a better contant with the bars.
Fig. 2 – Collectorrotorbar collectorbrushes and brush holdershaft.The following figure (Fig. 3) shows the internal components of a direct current machine.Fig. 3 – Fundamental parts of a direct current machinebearingscollectorlifting eyeboltstatorbearingsbrushes and brush holdershaft support flangecollector support flangeventilation turbinecoverarmatureThe section plane of a direct current machine is shown in the side figure (Fig. 4).Fig. 4Rated valuesThe main rated values of the direct current machine are listed in the Table.Rated