1. Jimei university Lesson 24 Switchboard ( 配电板 )

2. Jimei university The control and distribution of the electrical energy generated by generators are effected by power distribution equipment, i.e. switchboards.

3. Jimei university Switchboards are either: (a) Main switchboards( 主配电 盘 ), to which the main generators are connected,

4. Jimei university (b) Emergency switchboards( 应 急配电盘 ), to which the emergency generator or emergency battery is connected,

5. Jimei university (c) Section boards (or Sub- boards( 区域配电板 ))or (d) Distribution boards( 分配电 板或箱 ).

6. Jimei university In small equipment, particularly in small cargo ships, most of the motors can be fed directly from the main switchboard,

7. Jimei university but as the size and multiplicity( 多样性 ) of services increase, it becomes necessary to reduce the number of outgoing( 引出的 ) circuits on the main board.

8. Jimei university This is done by grouping some services on one or more section boards (sometimes referred to as sub-boards), supplied by a feeder( 馈线、馈电板 ) from the main board.

9. Jimei university Still further splitting up( 分解 ) particularly in the case of lighting and heating, is usually necessary and

10. Jimei university and this takes the form of distribution boards of small capacity which may be fed either direct from the main board or from a section board.

11. Jimei university G1 G2 Generators E. Generator Bar-bus Main switchboard E. switchboard Lighting Distribution board E. Lighting Motor Motors Section/sub board Transformer

12. Jimei university Switchboard are divided into two classes: i.e. those for a.c. systems and those for d.c. systems.

13. Jimei university Switchboards may be of the open type in which all the essential switch gears( 开关设备、 交换机 ) are exposed on the front of the panel( 仪表盘, 控 制面板 ),

14. Jimei university or of the deadfront type( 正面无接 线式、不带电式、安全式 ) in which all the live( 带电的 ) parts are installed behind the panels and only the operating handles and instruments are on the front.

15. Jimei university The switchboards for a.c. systems differ from the d. c. switch gear in that the open type panels are generally not permissible.

16. Jimei university Deadfront boards can be either of two patterns,

17. Jimei university one having manually-operated switches and circuit- breakers( 断路器 ) with the handles on the front of panels and all the live( 带电的 ) parts at the rear;

18. Jimei university and the other having electrically operated circuit- breakers operated by push- buttons on the front of the panels.

19. Jimei university Usually the panels are interlocked with isolators( 绝缘 子、隔离开关 ) so that the devices can be made dead( 不带 电的 ) before the doors are opened.

20. Jimei university The voltages most commonly adopted for a.c. systems are either 440V or 220V three- phase.

21. Jimei university For d.c. switchboards, there are ammeters, voltmeters, circuitbreakers, tipping devices( 跳闸装置 ) and so on,

22. Jimei university but a.c. requires additional equipment as compared with d.c., such as frequency meters, synchroscope, wattmeters,

23. Jimei university voltage and current transformers( 电压互感器和电 流互感器 ), ammeter switches( 安培表的转换开关 ), voltage regulators( 稳压器、电 压调节器 ), etc..

24. Jimei university Circuit breakers and switches will be three-pole as compared with two-pole for d.c..

25. Jimei university However, in spite of the additional equipment an a.c. switchboard is usually smaller and lighter than the corresponding( 相应的 ) d.c. board

26. Jimei university because of the higher voltage and lower currents and smaller bus-bars( 母排、汇流排 ), etc.

27. Jimei university Electrical supply is always needed, even if only for lighting.

28. Jimei university So after a ship goes into service it is extremely rare for the main bus-bars to be made dead,

29. Jimei university it therefore follows that the bus-bars are continuously alive( 带电的 ) throughout the life of the ship.

30. Jimei university Even when in a shipyard for repair, a shore supply will usually be taken.

31. Jimei university Reading Materials A. Emergency Generator supply

32. Jimei university In the event of a main generating system failure an emergency supply of electricity is required for essential services.

33. Jimei university This can be supplied by batteries, but most merchant ships have an emergency generator.

34. Jimei university The unit is diesel driven and located outside of the machinery space.

35. Jimei university The emergency generator must be rated to provide power for the driving motors of

36. Jimei university of the emergency bilge pump, fire pumps, steering gear, watertight doors and possibly fire fighting equipment.

37. Jimei university Emergency lighting for occupied areas( 居住区 ), navigation lights( 航行灯 ), communications systems and alarm systems must also be supplied.

38. Jimei university Where electrical control devices are used in the operation of main machinery, these too may require a supply from the emergency generator.

39. Jimei university Usually only one emergency switchboard is installed;

40. Jimei university however, for safety reasons large passenger vessels may have two emergency sources of power, thus requiring two emergency switchboards.

41. Jimei university Emergency switchboards normally consist of a generator control panel, a bus tie and distribution panel ( 汇电板和配 电盘 ) and

42. Jimei university and 24-volt, 120-volt, and 450- volt distribution panels in size and number as required.

43. Jimei university Emergency generator switchboards include those devices noted in the foregoing for main switchboard generator control panel plus the following:

44. Jimei university 1. A white light to indicate that the normal supply is available. 2. A green light to indicate that all devices are “set up” for automatic operation.

45. Jimei university 3. A normal supply circuit breaker, unless the automatic bus transfer( 主送电器 ) is of the contactor type.

46. Jimei university 4. A feed back switch when the automatic bus transfer is of the contactor type.

47. Jimei university It is not usual for an emergency generator to require paralleling, so no equipment is provided for this purpose.

48. Jimei university Automatic start up of the emergency generator at a low voltage value is usual on modern installations.

49. Jimei university B. Maintenance of electrical equipments

50. Jimei university With all types of electrical equipment cleanliness is essential for good operation.

51. Jimei university Electrical connections must be sound( 完好的，可靠的 ) and any signs of sparking should be investigated.

52. Jimei university Parts subject to wear must be examined and replaced when necessary.

53. Jimei university The danger from a.c. equipment in terms of electric shocks( 触电 ) is far greater than for similar d.c. voltages.

54. Jimei university Also a.c. equipment often operates at very high voltages.

55. Jimei university Care must therefore be taken to ensure isolation of equipment before any inspections or maintenance is undertaken.

56. Jimei university The accumulation of dirt on electrical equipment will result in insulation breakdown and leakage currents, possibly even an earth fault.

57. Jimei university Moisture or oil deposits will likewise( 同样地 ) affect insulation resistance.

58. Jimei university Regular insulation resistance measurement and the compiling( 汇集 ) of records will indicate( 预示 ) the equipment requiring attention.

59. Jimei university Ventilation passages or ducts may become blocked, with resultant lack of cooling and overheating.

60. Jimei university Oil deposits from a direct coupled diesel engine driving an open generator can damage windings and should therefore be removed if found.

61. Jimei university Totally enclosed machines should be periodically opened for inspection and cleaning since carbon dust will remain inside the machine and deposit on the surfaces.

62. Jimei university Brushgear should be inspected to ensure adequate brush pressure and the springs adjusted if necessary.

63. Jimei university New brushes should be ‘bedded in( 研配 )’ to the commutator( 整 流子，换向器 ) or slipring shape with fine glass paper( 精 细玻璃砂纸 ).

64. Jimei university Sparking at the commutator will indicate poor commutation( 换向、整流 ).

65. Jimei university This may require polishing of a roughened( 粗糙的 ) commutator surface.

66. Jimei university The mica( 云母 ) insulation between commutator segments( 换向片、整流片 ) may require undercutting( 剔槽 ) if it protrudes( 凸出 ), or simply cleaning if deposits have built up.

67. Jimei university Control equipment, such as starters, will require attention to contacts which may be worn or pitted( 有凹痕的 ) as a result of arcing( 电弧放电 ).

68. Jimei university Contactors( 接触器，触头 ) usually have a moving or wiping( 磨擦 ) action as they come together.

69. Jimei university This helps clean the surfaces to provide good electrical contact, and also the arc produced during closing and opening is not at the finally closed position.

70. Jimei university The contactor contact surfaces of frequently used equipment should therefore be subject to regular inspections.