lesson25 ship main switchboard.ppt

english of marine engineering(operational level);;;;;;;;;3. For small installations, particularly those which do not involve（涉及） paralleling of the generators, simple ironclad switchgear will suffice（足够） and may consist of standard self-contained（自我包含） switches or switch-fuses assembled together to form a combined unit（组合单元）.;It is usual with such units to interlock（互锁） the switch with the lid（盖子） or door, so that the door cannot be opened while the switch is in the closed position and conversely（相反的） the switch cannot be closed when the door is open. ;4. After a ship enters service it is extremely rare for the main busbars（主电网） to be made dead; electrical supply of some sort（种类） is always needed, even if it consists only of lighting　　　;It therefore follows that the busbars are continuously alive practically（几乎） throughout the life of the ship; even in dry-dock（干坞） a shore supply will usually be taken. ;This means that, at any rate（任何情况下） as far as the main switchboard is concerned（就--来说）, routine（常规的） maintenance work must be carried out with live busbars and some thought should be given to this in the design and layout stage（规划）. ; In land practice the necessary provision is made by means of duplicate（二重的） busbars, but space does not permit of this in ships. ; It can be taken care of to a limited extent by sectionalizing（划分） the switchboard by inserting isolators（绝缘体）, and splitting（分离） of the lighting feeders（支线） can also help, but in large installations draw-out type（抽出型） switchgear is undoubtedly（无疑的） the best solution.;It has been already emphasized（强调） that a.c. is much more lethal（致命的） than d.c. at voltages much lower than those which are standard for d.c., ; and on no account（决不） should work even of the simplest nature be undertaken（执行） on live a.c. apparatus（设备） without fully protecting the operator. ; If rubber gloves（橡皮手套） are used they should be of the type specially made for the purpose and they should be periodically tested to ensure that they are in