I. Answer the following questions:

1. What is power electronics designed for?

2. Name main forms of electrical power conversion

3. Explain the principle diffidence between rectifier and inverter.

4. Does input voltage of a cycloconverter have fixed amplitude and frequency?

5. What is the typical application of a cycloconverter?

6. Try to explain the difference between litz wire and single-stranded wire. Are they conductors?

7. What is the task done by a diode in the electrical circuits?

1. Translate into English words in brackets and then the sentences

Into Russian:

1. Advent of silicon-controlled rectifiers, led to the development of a new area of application called the (силовая электроника)

2. For low voltage, high current applications, a pair of (трёхфазный), three-pulse rectifiers interconnected by an (межфазовый трансформатор)

3. There are several types of diodes available, selection of а (нужный, соответствующий диод) is very important for reliable operation of a circuit.

4. Traditionally (устойчивые, постоянные характеристики) refers to the state of a circuit characterized by either a dc response or a sinusoidal response.

5. Many of the inverter and switch-mode power supply circuits operate at a much (высокая частота) and these circuits need diodes that (включать и выключать) fast.

6. Before the application the (номинал по току) of the capacitor at the (рабочая частота) should be checked before its use.

7. A typical application of а (повышающий преобразователь частоты) is to use it for controlling the speed of an ас (тяговый двигатель).

2. Translate the following text: Conductors

Conductors are materials having a low resistance, so that current easily passes through them. The lower the resistance of the material, the more current can pass through it. Most solid materials are classified as insulators because they offer very large resistance to the flow of electric current. Metals are classified as conductors because their outer electrons are not tightly bound, but in most materials even the outermost electrons are so tightly bound that there is essentially zero electron flow through them with ordinary voltages. And silver and copper are the best conductors. The advantage of copper is that it is much cheaper than silver. Thus, copper is widely used to produce conductors. One of the common functions of wire conductors is power supply to a load, for example a traction motor. Since copper wire conductors have a very low resistance they produce a min voltage drop while electrical current passes.

The conductor implies that the outer electrons of the atoms are loosely bound and free to move through the material. Most atoms hold on to their electrons tightly and are insulators. In copper, the valence electrons are essentially free and strongly repel each other. Any external influence which moves one of them will cause a repulsion of other electrons which propagates, “domino fashion” through the conductor.

Most materials change the value of resistance when their temperature varies.