Lesson Seven Generator Control System
Ensuring the continuity of electric source is very important for safe navigation, and the automatic start of the standby generator, automatic synchronizing and load sharing devices are usually provided on the automated ships.
On computerized and automated vessel, a fully computerized generator control system is used for optimum control of the whole generator system, it is called power management system.
Most of power plants in ships consist of two generators but more often three to four. For reasons of economy it is undesirable to run more sets than necessary for the load. On the other hand call for another set. Under present regulation, preferential; tripping switches off non-essential loads when overloading occurs. This is only a temporary measure and systems are now available for the automatic starting, stopping and synchronizing of sets according to the demand.
Load variations will occur frequently and rapidly with deck machinery or gradually as with refrigerating plant when passing from temperate zone to tropics. In confined waters it is necessary for safety reasons to retain a margin in reserve and to have not less than two sets on the board so an provision must be included in automatic schemes.
The automatic system should include the following features:
(1) Prestart preparations. For diesel sets these will include lubricating oil priming and , in some cases, cooling water pump and fuel oil preparation.
(2) Staring and stopping governed by load demands.
(3) Synchronizing.
(4) kW and kVar sharing.
(5) Maintaining frequency.
(6) Protection against engine mal-operation.
(7) Protection against electrical faults and overload.
(8) Preferential tripping of non-essential loads and restoration when sufficient power becomes available.
Standby sets can be pre-warned by continuous circulation of hot water from the main engine cooling system. Engines using heavy oil may require diesel fuel for starting, changing over automatically to heavy oil when warmed up. It is usual to bring in another set before the loading reached full load on the running set-say 80% to 90% . It is also good practice to incorporate a short time delay, say 20 seconds, to prevent starting on a spurious load demand. To prevent an incoming set being switched repeatedly on to a short circuit it is usual to arrange that it will be locked out after being connected once.
In one system the starters of all large motors are connected to the generator control system by means of relays. If the available margin of power when the start button of a motor is pressed is insufficient, a new generator is brought in and as soon as the extra power is available the motor starts automatically.
A selector switch is used to determine the starting order where there are three or more sets and it will also establish which is to be the base load set. A set under maintenance can also be locked out.
The arrangements for steam are more complex and although the synchronizing and load-sharing techniques, etc. are the same as for diesel sets it is more common to have manual control for starting and stopping. The sequence is basically the same whether on remote manual control or fully automatic, the latter being carried out by a programmed control system.
New Words and Expressions
computerize [kəmˈpjuːtəraiz] vt. 给……装备电子计算机
optimum[ˈɔptiməm] adj. 最适宜的
temperate[ˈtempərit] adj. 温和的
zone[zəun] n. 地带
tropic[ˈtrɔpik] n. 热带地区
retain[riˈtein] vt. 保留，保持
feature[ˈfiːt∫ə] n. 特征，特点
priming[ˈpraimiŋ] n. 启动注油，灌注
govern[ˈgʌvən] vt. 控制，调节
mal-operation[ˌmɑːldəˈmer] n. 不正确运行，误动作
spurious [ˈspjuəriəs] adj. 虚假的
Notes
（1）Ensuring the continuity of electric source is very…
句中“ensuring”是动名词，与后面的“the continuity of electric source”构成动名词短语，在句中作主语，动名词与现在分词同形，阅读使用时请加以区别。动名词或动名词短语在句中可作主语、表语、宾语、介词宾语等。
例如：
Learning a foreign language needs a lot of practice.（作主语）
学习外语需要大量实践。
Electricity stops flowing when the switch is turned off.（作宾语）
开关关掉时，电就停止流通。
The function of the machine is supplying electric energy.（作表语）
这台机器的功能是提供电能。
Before starting the engine you should examine carefully and oil it.（作介词宾语）
机器启动前，你应该仔细检查并加好润滑油。
动名词的否定结构由“not”加动名词组成。
例如：
Trying without success is better than not trying at all.
试验没有成功也比不试验好。
（2）Load variations will occur …or gradually as with…
句中“or”是连词，连接两个并列分句，“or”后面省略了前一分句中的主、谓语。
（3）“confined waters”意思是“狭窄水道”，“water”作“水”解释时是不可数名词；作“海域、水道、洋面”解释时是可数名词，学习时应加以区别。