How do synchronous machines work?
Magnetic field in the synchronous machine is created by the direct current proceeding on the magnetizing coil. The need for the isyotochnik of the direct current for the power supply of the magnetizing coil - very essential lack of synchronous machines.
Usually magnetizing coils receive energy from the direct current generator of the parallel excitation (возбудителя) which is on one shaft with the main machine.
Its power is 1-5% of power of the synchronous machine. At the small power feed circuits of magnetizing coils of synchronous machines from the alternating current main via rectifiers are widely used.
The principle of action of the synchronous generatoyor is based on use of the law of elekyotromagnitny induction. In fig. of 1 pokayozan the simplest three-phase winding, soyostoyashchy of three coils shifted on 120 ° and placed on the rotor (anchor).
Kayotushki is connected among themselves in the star or the triangle and connected to three kontaktyony rings on which place motionless brushes. In coils at rotation of the anchor the variable EMFs in time equal on amplitude and dephased on 2/3 are induced.
Modern synchronous generators make on lineyyony tension up to 16000 V (sometimes above), isolation of contact rings and which brushes represents big complexity. The main lack of such design - availability of the sliding contact in the chain of the main power of the machine. For its exception the anchor winding, i.e. the induced part, place on the stator, and polar system with the magnetizing coil - on the machine rotor.
The magnetizing coil receives the power supply through contact kolyyoets. In this case the sliding contact is in the chain of low power and tension in the chain of the magnetizing coil is rather small (no more than 500 V).
The stator of the synchronous machine has the same device, as well as the stator of the asynchronous machine.
Depending on the rotor device, distinguish two designs of synchronous machines:
- with yavnovyrazhenny poles;
- with neyavnovyrazhenny poles.
In machines with rather small rotating speed rotors carry out with yavnovyrazhenny poles. On the rotor (fig. 2 and) the yavnovyrazhenny poles consisting of the poyolyusny core 1 on which the coil of the magnetizing coil 3 withheld by the pole-shoe 2 is located evenly place. Such device of the rotor facilitates performance of the magnetizing coil, but at big rotating speed cannot be used as does not provide the necessary mechanical durability.
Therefore at big rotating speed rotors carry out with neyavnovyrazhenny poles (fig. 2). Such rotor is izgoyotavlivat in the form of the cylinder on which part of the surface there are grooves. In grooves stack magnetizing coil conductors, zayoty grooves get jammed and front connections of the magnetizing coil pull together with steel bandages.
Depending on the sort of the prime mover which privoyoditsya in rotation the synchronous generator the last is called the hydrogenerator (the prime mover - the hydraulic turbiyona), the turbine generator (the prime mover - the steam turbine) and the diesel generator (the prime mover - the diesel).
Gidrogeneyoratora - usually low-speed salient pole machines with the large number of poles which are carried out with the vertical arrangement of the shaft. Turbine generators - the high-speed not salient pole machines which are carried out now with two poles. The rotor of the modern turbine generator is done of the integral steel forging. On the part of the surface of the rotor of the vyfrezovana grooves for placement of the magnetizing coil. Diesel generators - the salient pole machines with the horizontal arrangement of the shaft.
Synchronous machines of small power (up to 15 kVA) and neyovysoky tension (to 380/220 B) make with motionless polar system and the rotating anchor (like machines of the direct current). The synchronous motor has no printsipialyyony constructive differences from the synchronous generator. On the statoyora of the engine place the three-phase winding, at inclusion kotoyory in network of three-phase alternating current the rotating magnetic field is created. On the rotor of the engine place the vozbuzhyodeniye winding included in network of the source of the direct current.
Current of the vozbuzhyodeniye creates the magnetic flux of poles. The rotating magnetic field of currents of the winding of the stator entrains rotor poles. At the same time the rotor can rotate only with the synchronous frequency, i.e. with the frequency equal to rotating speed of the field of the stator. Thus, the frequency of the synchronous motor is strictly constant if the frequency of current of the power line is invariable.
The main advantage of synchronous motors - the possibility of their work with consumption of the leading current, i.e. the engine moyozht to represent the capacitive load for network. Such dviyogatel raises cos of all enterprise, compensating the reaktivyony power of other receivers of energy.
Synchronous motors have smaller, than at asynchronous, sensitivity to voltage variation of the power line, the vrayoshchayushchy moment at synchronous motors is proportional to the napryayozheniye of network in the first degree whereas at asynchronous — to tension square.Top