Introduction to D.C Machines清热解毒的药
世界上第一所大学A D.C machines is made up of two basic components:
－The stator which is the stationary part of the machine. It consists of the following elements: a yoke inside a frame; excitation poles and winding; commutating poles (compos) and winding; end shield with ball or sliding bearings; brushes and brush holders; the terminal box.
－The rotor which is the moving part of the machine. It is made up of a core mounted on the machine shaft. This core has uniformly spaced slots into which the armature winding is fitted. A commutator, and often a fan, is also located on the machine shaft.
The frame is fixed to the floor by means of a bedplate and bolts. On low power machines the frame and yoke are one and the same components, through which the magnetic flux produced by the excitation poles clos. The frame and yoke are built of cast iron or cast steel or sometimes from welded steel plates.
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In low-power and controlled rectifier-supplied machines the yoke is built up of thin (0.5～1mm) laminated iron sheets. The yoke is usually mounted inside a non-ferromagnetic frame (usually made of aluminum alloys, to keep down the weight). To either side of the frame there are bolted two end shields, which contain the ball or sliding bearings.
The (main)excitation poles are built from 0.5～1mm iron sheets held together by riveted bolts. The poles are fixed into the frame by means of bolts. They support the windings carrying the excitation current.
On the rotor side, at the end of the pole core is the so-called pole-shoe that is meant to facilitate a given distribution of the magnetic flux through the air gap. The winding is placed inside an insulated frame mounted on the core, and cured by the pole-shoe.
飞天小魔女The excitation windings are made of insulated round or rectangular conductors, and are connected either in ries or in parallel. The windings are liked in such a way that the magnetic flux of one pole crossing the air gap is directed from the pole-shoe towards the armature (North Pole), which the flux of the next pole is directed from the armature to the
pole-shoe (South Pole).
幼儿园食品安全The commutating poles, like the main poles, consist of a core ending in the pole-shoe and a winding wound round the core. They are located on the symmetry (neutral) axis between two main poles, and bolted on the yoke. Commutating poles are built either of cast-iron or iron sheets.
The windings of the commutating poles are also made from insulated round or rectangular conductors. They are connected either in ries or in parallel and carry the machine's main current.
The rotor core is built of 0.5～1mm silicon-alloy sheets. The sheets are insulated from one another by a thin film of varnish or by an oxide coating. Both some 0.03～0.05mm thick. The purpo is to ensure a reduction of the eddy currents that ari in the core when it rotates inside the magnetic field. The currents cau energy loss that turn into heat. In solid cores, the loss could become very high, reducing machine efficiency and producing inten heating.
The rotor core consists of a few packets of metal sheet. Redial or axial cooling ducts (8～10mm inside) are inrted between the packets to give better cooling. Pressure is exerted to both side of the core by pressing devices foxed on to the shaft. The length of the rotor usually exceeds that of the poles by 2～5mm on either side－the effect being to minimize the variations in magnetic permeability caud by axial armature displacement. The periphery of the rotor is provided with teeth and slots into which the armature winding is inrted.
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The rotor winding consists either of coils wound directly in the rotor slots by means of specially designed machines or coils already formed. The winding is carefully insulated, and it cured within the slots by means of wedges made of wood or other insulating material.
The winding overcharge are bent over and tied to one another with steel wire in order to resist the deformation that could be caud by the centrifugal force.
The coil-junctions of the rotor winding are connected to the commutator mounted on the a
rmature shaft. The commutator is cylinder made of small copper. Segments insulated from one another, and also from the clamping elements by a layer of minacity. The ends of the rotor coil are soldered to each gment.
救援计划On low-power machines, the commutator gments form a single unit, insulated from one another by means of a synthetic resin such as Bakelite.
