Download AVOP-ELEKTRO-SKA-001

Tutorial: Mechanic – electrician
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.
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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
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Three phase has in comparison with one-phase these advantages::
simultaneous presence of two levels of voltage:
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Phase
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Comprehensive 3x400v
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Uncomplicated commencement of the torque is the main advantage allowing function and simple
construction of rotating electric machines
3x230v
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Alternator rotor
Turboalternator 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 rousing3
winding on the rotor.
Three-phase generator of the alternating current
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
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directly proportional to revs and rousing of the rotor.
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.
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Sinus course of voltage or intensity
1) Maximum value
2) Top voltage
3) Effective value
4) Period
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
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Phase and comprehensive voltage
Phase conductor
Phase conductor
Null
conductor
Phase conductor
The voltage induced on individual coils has sine course. The voltage between the
phase and the null conductor is called phase voltage - Effective value of the phase
voltage is 230 V.
The voltage between two phase conductors equals the sum of voltages induced on
two coils and it is called comprehensive voltage.
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• 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
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• Put down the amount of voltage between individual conductors
• Explain the term phase and comprehensive voltage
• Describe which voltages do numbers 1-4 determine.
• Explain the term effective value of alternating voltage
• Amplitude of alternating voltage measured by the oscilloscope is 360V,
what is the effective value?
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Základy elektrotechniky 2, L.VOŽENÍLEK- F. STIBŮREK
www.wikipedia.cz
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