Anglicky v odborných předmětech"Support of teaching technical subjects in English“

Tutorial: Mechanik - elektrotechnik Topic: Basics of electrical engineering the 2nd. year, Three-phase current

Prepared by: Škarka Miloš

Projekt Anglicky v odborných předmětech, CZ.1.07/1.3.09/04.0002

je spolufinancován Evropským sociálním fondem a státním rozpočtem

České republiky.

• Three-phase system is a system of three harmonic voltages of the same frequency and amplitude, which have different, but same phase shift towards each other.

• Three phase has in comparison with one-phase these advantages::• simultaneous presence of two levels of voltage:

• Phase 3x230v

• Comprehensive Line-to-line (or Line) 3x400v

• Uncomplicated commencement of the torque is the main advantage allowing function and simple construction of rotating electric machines

Three-phase alternator construction

Alternator rotorTurboalternator stator in assembly.

Machine set – turbine with alternator

Basic parts of the alternator are immovable stator and a rotor rotating on the shaft. Synchronous alternator has three-phase winding on the stator and so called rousing winding on the rotor.

Commencement of the voltage in alternator

If the turbine or other drive rotates the rotor and there is a direct current passing through its rousing winding, the rotating magnetic field commences. This causes (induces) three-phase alternating voltage in the three-phase stator winding. It is directly proportional to revs and rousing of the rotor.

Three-phase generator of the alternating current

Course of the voltage

All coils are the same and they are located near the same magnet. The course of the voltage will be the same on all coils, but it will differ in the shift in time, the courses on each coil will be delayed. The difference between coils is one third of the rev (120°), the magnet will need one third of the period T to turn from one coil to another, courses will so be delayed for one third of the period.

Maximum and effective value

Effective value of alternating voltage (Uef) is equal to the value of direct voltage, which would give the same average performance, if attached to resistance strain

Sinus course of voltage or intensity1) Maximum value2) Top voltage3) Effective value4) Period

Phase and comprehensive voltagePhase conductor

Phase conductor

Phase conductorNull conductor

230V

Aktivita pro žáky – povinný snímekÚkol, test, otázky … .

• There is a course of voltage on the first coil drawn on the picture. Draw the course of voltage on remaining coils into the picture

• Describe main parts of alternator

• Explain commencement of the voltage on coils

Literature

• Základy elektrotechniky 2, L.VOŽENÍLEK- F. STIBŮREK• www.wikipedia.cz