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.