The operation of paralleling two alternators requires the voltages to be equal and also in phase. The alternating current output of any machine is always changing, so for two machines to operate together their voltages must be changing at the same rate or frequency, and must be reaching their maximum (or any other value) together. They are then said to be \made of a synchroscope when paralleling two a.c. machines. The synchroscope has two windings which are connected one to each side of the paralleling switch. A pointer is free to rotate and is moved by the magnetic effect of the two windings. When the two voltage supplies are in phase the pointer is stationary in the 12 o'clock position. If the pointer is rotating then a frequency difference exists and the dial is marked for clockwise rotation FAST and anti-clockwise rotation SLOW, the reference being to the incoming machine frequency. To parallel an incoming machine to a running machine therefore it is necessary to ensure firstly that both voltages are equal. Voltmeters are provided for this purpose.
Secondly the frequencies must be brought into phase. In practice the synchroscope usually moves slowly in the FAST direction and the paralleling switch is closed as the pointer reached the 11 o'clock position. This results in the incoming machine immediately accepting a small amount of load. A set of three lamps may be provided to enable synchronizing. The sequence method of
lamp connection has a key lamp connected across one phase with two other lamps cross connected over the other phases. If the frequencies of the machines are different the lamps will brighten and darken in rotation, depending upon the incoming frequency being FAST or SLOW. The correct moment for synchronizing is when the key lamp is dark and the other two are equally bright. 87. What device is used to parallel two alternators nowadays?
A. A pointer. B. Two windings
C. A synchroscope D. Two synchronizing lamps 88. When two alternators are said to be \ A. their current outputs are changing
B. their voltages are changing at the same rate
C. they are connected one to each side of the paralleling switch D. they have the same maximum voltage
89. In practice, the paralleling switch is closed as the synchroscope pointer reaches the 11 o'clock position while it is moving ___.
A. in the FAST section B. in the SLOW section C. towards the FAST direction D. towards the SLOW direction 90. The correct moment for synchronizing is when . A. three lamps are equally bright B. three lamps darken in rotation
C. the key lamp is bright and the other two lamps are dark
D. the key lamp is dark and the other two lamps are equally bright
课本第212页
轮机英语管理级教材内容关联题 仅供参考！
The PSCO may determine if responsible ship's personnel are familiar with their duties related to operating essential machinery, such as emergency and stand-by sources of electrical power, auxiliary steering gear, bilge and fire pumps and any other equipment essential in emergency situations. For stand-by generator engine, the responsible ship's personnel should be familiar with the possibilities to start it, automatic or by hand, blackout procedures and load-sharing system. For emergency generator, they must be familiar with the actions which are necessary before the engine can be started, different possibilities to start the engine in combination with the source of starting energy and the procedures when the first attempts to start the engine fail. The responsible
engineering officer should be familiar with which type of auxiliary steering gear system applies to the ship, how it is indicated which steering gear unit is in operation and what action is needed to bring the auxiliary steering gear into operation. The responsible personnel ought to be familiar with the number and location of bilge pumps (including emergency bilge pumps) and fire pumps (including emergency fire pump) installed on board the ship, starting procedures for those pumps, appropriate valves to operate the pumps and most likely causes of failure of bilge pump operation and their possible remedies. The PSCO may also verify whether the responsible personnel are familiar with:
(1) starting and maintenance of lifeboat engine and/or rescue boat engine,
(2) emergency stops, fire detection system and alarm system operation of watertight and fire doors, and (3) change of control from automatic to manual for cooling water and lube oil systems for main and auxiliary engines and maintenance procedures for batteries.
91. According to this passage, for auxiliary steering gear, the responsible ship's personnel should be familiar with . A. the possibilities to start it
B. the procedures when the first attempts to start it fail C. the necessary action to bring it into operation
D. most likely causes of failure of it and their possible remedies
92. 'The possibilities to start it' here means . ①the different emergency situations in which it should be started ②the likely or suitable choices of its starting methods ③the opportunities to get it started
A. ① B. ② C. ③ D. none of ①②③
93. Which of the following is not mentioned in the passage as essential machinery or equipment? A. The incinerator. B. The stand-by generator engine. C. The bilge pumps. D. The watertight doors.
94. According to this passage, as to the emergency generator, the responsible ship's personnel must be familiar with not only the possibilities to start the engine, but also ____. A. the blackout procedures B. the load-sharing system
C. the indication of which unit is in operation D. the source of starting energy
课本第349-350页
Circuit breakers must be capable of making and breaking under normal conditions and also abnormal conditions such as a short circuit. As the circuit breaker must be able to withstand
closing onto a fault conditions without sustaining damage, it is of heavy construction. Fitted with an over current release mid overloads with time lags, a circuit breaker can be used as follows: to control the output of a generator; as a direct on line starter and to control outgoing feeder circuits. On modern switchboards, \the whole circuit breaker can be wound clear of the bus bars, thus full inspection and maintenance can be achieved without the necessity of de-energizing the bus bars.
The \the breaking load and it is essential that the circuit breaker is in the open position before any
attempt is made to withdraw it. A mechanical interlock is fitted arranged to trip the circuit breaker before the winding handle can be inserted.
The breaker also has a mid position. In this position the control circuits are still connected with the bus bar connection isolated. The electrical operation of the breaker can then be tested. Circuit breakers are normally fitted with under voltage protection and tripping is
accomplished by shorting, which releases the latching in mechanism. The no-volt coil may also be open circuited by a reverse power relay and an overload trip fitted with a time delay. 83. A circuit breaker can be used as follows except . A. to control outgoing feeder circuits B. to act as a direct on line starter C. to take the breaking load on line D. to control the output of a generator
84. A \ . A. which can be made clear of the bus bars by using a winding handle B. which can be made clear of the bus bars by plugging in contacts C. whose test can be carried out with the control circuits still connected D. whose test can be carried out with the bus bar connection isolated 85. A mechanical interlock is fitted . A. to take the breaking load when the circuit breaker is being withdrawn
B. to put the circuit breaker, before being withdrawn, in the open position C. to put the circuit breaker, before being withdrawn, in the mid position
D. to take the breaking load when the contacts join the circuit breaker to the bus bars 86. According to this passage, the electrical operation of this kind of circuit breaker can be tested when __ .①the Circuit breaker at mid position ②the bus bar connection is isolated ③the control circuits are linked
A. ① B. ② C. ②③ D. ①②③
课本第218-219页