Английский язык для судовых электромехаников - [33]

Resistors are rated in watts, since P = EX 1 — RXRX1 = 1²R, where P — power, is given in watts, R — resistance, is given in amperes.

If a resistor has a resistance of only 2 ohms but its current-carrying capacity equals 2,000 ampere, it is rated as a 8,000,000-W resistor.

Some resistors have a constant value — these arc fixed resistors, the value of other resistors may be varied —these are variable resistors.

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Resistors can be grouped into three basic classes: composition type resistors, film-type resistors, and wirewound resistors. As the name implies, composition resistors are molded rods made from a powdered and electrically conductive mixtures of graphite and an inert plastic binder. Wirewound resistors consist of a wire or metallic ribbon wrapped

around a supporting ceramic form. The film-type resistor is composed of a resistive film of carbon or metal deposited on or inside an insulating cylinder.

Resistors may be either fixed or variable. Continuously variable resistors, as distinguished from adjustable types, may be either composition or wirewound types.

Now speak about some of the details concerning resistors that you know and that are provided by the texts.

42 4

Record your answers on a tape.

1. What is to be done prior to replacing faulty components and adjusting new ones? (See ex. 33).

2. What is a power cam controller?

3. How does one select controllers?

43 12

Use the following suggested topics for discussion:

1. The unit is switched on, the armature oscillates, but the striker fails to strike the cup.

2. Motor fails to start.

3. Old brushes should be replaced. New ones should be ordered.

44 7

Listen to the following text carefully. Make up as many questions as you can. Retell the text.

Electric Drives of Anchor-Handling and Mooring Gear

The electric drives of anchor-handling and mooring gear are used to heave in the anchor and perform mooring operations.

Accordingly, they are used in windlasses, anchor and anchor-mooring capstans, mooring capstans, automatic and non-automatic mooring winches. At present most of these machines are equipped with electric drives having special characteristics which suit the operating conditions of such machines.

According to the USSR Register the power rating of an electric drive used in the anchor-handling gear must be such that the anchor chain is heaved in at a minimum speed of 0.17 m/s with the sprocket pull*, in Newtons.

* тяговое усилие на звездочке.

45 6

Listen to the dialogue and discuss the advantages of being an astronaut.

I Would Be Flying a Space-Craft Now

Mr. Fry: If I were a space pilot I’d be circling the earth now.

Mrs. Fry: I suppose you would.

Mr.: And if you were one too, we’d be going together. I’d be gathering the scientific data, and you be making tea. . .

Mrs. (with determination): No, 1 would not!

Mr: (with a sarcastic smile): And what would you be doing if I may ask? Mrs. (proudly): I would be orbiting!

Mr.: That’s a jolly good idea, and 1 suppose you'd be wearing a space suit, and not that horrible pink dress of yours!'

Mrs.: I’m pretty sure you wouldn't be looking at me anyway.

Mr. (smilingly): I don't know about that, but at any rate I wouldn’t be carrying such a heavy bag of potatoes, and even if 1 were I’d feel nothing in the state of weightlessness. Oh! If only I were an astronaut!... Mrs.: Has it occurred to you what would happen if the launching equipment went wrong? No, darling, 1 definitely don't want you to be a space pilot!

Mr.: Because you don't want to be a widow, I suppose. ..

Mrs. (icily): Because I don’t want to wash the dishes!

46 30

Home exercise, a) Read the text and find the key sentences in all the passages.

Magnetic Controllers

1. Magnetic controllers are self-contained unitized devices which ensure a definite switching sequence in power circuit when the corresponding commands are fed to the control circuits. Besides, whenever necessary, magnetic controllers can be used to effect a definite switching sequence in power circuit as a function of time or control parameters. Controllers provide the means for starting, speed control anti stopping of motors of various types.

2. Magnetic controllers are recommended for use with adjustable-speed and constant-speed motors on application requiring a large number of startings per hour, heavy starting duties and where stringent requirements have to be met as regards stoppage reliability.

3. Controllers for controlling the cage motors of deck machinery are available in splash proof design version.

4. Controllers are available in a large number of design versions to suit a-c electric drives encountered in marine service.

5. Various modifications of controllers differing in circuit arrangement are built up of standard units used in typical arrangements. Magnetic controllers are selected in accordance with the rated current. The maximum load current under the steady-state conditions must not exceed 110% of the rated current and the time during which the rated starting current oil the motor in any winding must not exceed the indicated value.