О v
line at the rated speed with a medium towline diameter: P= —— where P — power rating, kW; Q>r — rated towline pull, kN; r>r — rated value of towline heaving speed, m/s; n — efficiency of the driven gear.
4. The design power must be equal to or below the 30-min motor power rating for non-automatic winches and 60-min power rating for automatic winches operating in the impulse mode. The above’ power must be developed by the motor at the rated speed.
Hometask: Ex. 10, 15, 18.
The third class period
19 3
Listen to the sentences and define in each of them the meaning of the word “unit”.
1. The alternator voltage is fed to the AVR unit via fuses and exciter switch. 2. The standard units are those of current, voltage and resistance.
3. So the unit positive charge has been given energy in the amount of volts, by chemical action during its passage through the battery. 4. Apart from general acquaintance with the principle of operation and the design of separate components and the unit as a whole, it is required to analyze thoroughly the arrangement of separate parts in the unit.
20 4
Listen to the recorded text and give it a suitable title.
Each ship is to be provided with at least two main sources of electric power. If these sources are generators, at least one of them is to have its own independent prime mover.
The number and output of the main generators are to be determined with regard to the following operating conditions of the ship: running conditions, manoeuvring, emergency conditions in operation of main sources of electric power, other operating conditions in accordance with the purpose of the ship.
The output of main sources of electric power and of power converters is to be such; that in case of a failure of any one source or converter, the remaining sources would ensure power supply to the systems essential for navigation and safety of the ship under running or emergency operating conditions.
Total output and momentary overload capacity of all a-c generator sets feeding the ship’s mains is to be sufficient for starting the most powerful electric motor with maximum starting current under most severe starting conditions in case of a failure of any of the generators available.
In this case there should be no drop in voltage or frequency that could cause a fall out of synchronism or stop of the generator prime mover as well as spontaneous switching-off the running machines and apparatus.
21 7
Fulfil or explain the following:
1. Diagram the construction and principle of operation of AVR.
2. With your diagram explain in detail the operation of AVR.
3. Explain the formula: P = ■.
22 5
Record your answers on a tape.
1. What is meant by a “frequency measuring circuit”?
2. What circuits are mounted on a printed board of AVR?
3. How can you tell when alternator voltage changes?
4. How do towing winches operate?
Listen to the recorded story and say what was wrong in the woman’s
note.
When Toronto’s hydroelectric company converted from 25 cycles to 60, considerable advance planning was necessary. Residents, depending on their location in the city, were assigned specific dates when they might expect a call from the power company and were! advised to have someone at home on that day. One woman, unable to postpone her social activities but anxious to co-operate, left this note: “Please, leave the cycles on the porch!”
The fourth class period
26 % 2
In the following sentences insert Infinitives. Compare your results with the text.
1. The regulators permit . .. constant voltage of generators under various amount of load and power factor. 2. This signal is used . .. the alternator voltage if the frequency drops below 95% of nominal frequency.
3. The alternator voltage will . . . automatically in proportion to the frequency. 4. .. . correct load sharing between parallel running alternators, the alternator voltage is made current dependent.
27
Choose a suitable end to complete the
a)
1. The reaction was feared...
2. Lack of oxygen is credited...
