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

1. 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.

2. Electromotors An inductive (asynchronous) machine is a rotary electric machine where its magnetic circuit is divided by the small gap into two parts: the stator and the rotor. Both parts have a winding. One winding (usually on the stator) is connected to the source of the alternating current and the other (usually on the rotor) is connected on short distance short circuited and current in it comes from the electromagnetic induction, which is similar to the transformer. That's why we call it an inductive machine.

3. The three-phase inductive motor is simple, reliable in operation and it doesn‘t require any special service or maintenance. It is being manufactured in wide range ofperformance: from a few watts up to 20MW with a very wide rotation range from tens of rotations per minute up to 100 000 rot/min. According to the design of a motor we distinguish: • a) motors with the „squirrel cage“ armature on the short b) motors with the binderwound armature

4. Function principle The rotary field created by the stator has a higher speed than rotor revs. The basis of asynchronous motor function is a creation of the rotary magnetic field, which comes from the alternating current passing through the winding of the stator. This magnetic field induces the voltage in the rotor and a formed current causes the power for rotating the rotor. Rotary field revs are determined by the frequency of the powering voltage taken from the network and by the number of poles in the three-phase motor. Where f is the frequency of the current and p is the number of pole pairs in the stator

5. terminal casing metal bundle of the stator ventilator terminal stator winding bearing shaft metal bundle of the rotor short circuit circle

6. Main parts The motor with the „squirrelcage“ armature on the short has the rotor winding made of bars, which are short-circuitedat the end connected on the short by conductive circles. The magnetic circuit is composed of laminatedmetals to minimize losses caused by turbulent currents.

7. The woundbinder armature – Except of the bundle of rotor metals there are even collecting circlets on the shaft. In rebates of metals there is a three-phase rotor winding made of insulated conductors connected to the star, rarely to the triangle. The winding of the rotor is connected to three collecting circlets, which can be also connected to active resistors used for the engine start. Armature with circlets Brushes on the collector

8. Stator winding Consist of three coils rotated by 120° powered by the three-phase current. This creates rotary magnetic field.

9. There are two ways how to connect the asynchronous motor Terminal of the asynchronnous motor connected to the star and to the triangle. In case of the connection to the star the voltage on coils is 230V In case of the connection to the triangle the voltage on coils is 400V

10. Describe and explain • Main parts of the asynchronous motor • The difference between the squirrel cage armature on the short and the woundbinder armature • Describe the picture • What is the voltage on coils?

11. Describe and explain Picture 1 Picture 2

12. Sources • Wikipedia.cz • http://www.myinfo.sk • http://referaty-seminarky.cz • http://fei1.vsb.cz