Lesson Nineteen
Marine Electrical Equipment
The complete electrical plant on board ship is made up of power generation equipment,a distribution system and the many power utilising devices,Electricity is used for the motor drive of many auxiliaries and also for deck machinery,lighting,ventilation and air conditioning equipment,A constant supply of electricity is essential for safe ship and machinery operation,and therefore standby or additional capacity is necessary together with emergency supply equipment,Emergency equipment may take the form of an automatically starting emergency alternator or storage batteries may be used.
The complete range of electrical equipment will include generators,switch gear for control and distribution,motors and their associated starting equipment and emergency supply arrangements.
Alternating or direct current
Alternating current has now all but replaced direct current as the standard supply for all marine installations,The use of alternating current has a number of important advantages,for example,reduced first cost,less weight,less space required and a reduction in maintenance requirements,Direct current does how-ever offer advantages in motor control using,for example,the Ward-Leonard system which provides a wide range of speed.
Machine rating
Motors and generators,both d.c,and a.c.,are rated as Continuous Maximum Rated (CMR) machines,This means they can accept a considerable momentary overload and perhaps even a moderate overload for a longer duration.
Temperature affects the performance of all electrical equipment and also the useful life of the insulation and thus the equipment itself,The total temperature of an operating machine is a result of the ambient air temperature and the heating effect of current in the windings,Temperature rise is measured above this total temperature,Adequate ventilation of electrical equipment is therefore essential,Classification Societies have set requirements for the various classes of insulation,The usual classes for marine installations are E,B and F where particular insulation materials are specified and increasing temperature rises allowed in the order stated.
Enclosures
Depending upon the location,a motor or generator will have one of a number of possible types of enclosure,‘Drip-proof’ is most common and provides protection from falling liquids or liquids being drawn in by ventilating air,A ‘watertight enclosure’ provides protection for immersion under a low head of water for up to one hour,‘Weatherproof’,‘hose proof’ and ‘deck watertight’ provide immersion protection for only one minmet,‘Totally enclosed ’ can also be used or an arrangement providing ducted ventilation from outside the manager space,A ‘flameproof ’ enclosure is capable of withstanding an explosion of some particular flammable was that may occur within it,It must also stop the transfer of flame,i.e,contain any fire or explosion,
Direct current generators
A current is produced when a single coil of wire is rotated in a magnetic field,When the current is collected using a ring which is split into two halves,that is,a commutator,a direct or single direction current is produced,The current produced may be increased by the use of many turns of wire and additional magnetic fields.
With many coils connected to the commutator,sparking will occur as the current collecting brushes move across the insulated segments,Commutating poles or interpoles are used to reduce this sparking,They are in fact electromagnets having a polarity the same as the main pole which follows in the direction of rotation,
The magnetic field between the poles is produced by what are known as,field coils”,These coils are excited or energized by the current produced in the machine,The soft iron core of the field coils retains some magnetism which enables a preliminary current generation to build up eventually to the full machine output,The field windings can be connected to the output current in a number of ways—shunt,series or compound,The compound wound arrangement is usual since it provides the best voltage characteristics,
The compound wound generator has two sets of field coils (Fig.1 (a)),The shunt coil has many turns of fine wire and the series coil has a few turns,of heavy wire,The shunt field produces full voltage on no-load which falls off as the load current increases.
Fig.1 Compound d.c,generator
----Field connections
---Characteristic cures
The series field creates an increase in voltage as the load increases,Properly combined or compounded the result is a fairly,constant voltage over a range of load (Fig,1(b)).
Alternating current generators
A coil of wire rotating in a magnetic field produces a current,The current can be brought out to two sliprings which are insulated from the shaft,Carbon bushes rest on these rings as they rotate and collect the current for use in an external circuit,Current collected in this way will be alternating,that is,changing in direction and rising and falling in value,To increase the current produced,additional sets of poles may be introduced.
The magnetic field is provided by electromagnets so arranged that adjacent poles have opposite polarity,These ‘field coils’,as they are called,are connected in series to an external source or the machine output.
If separate coils or conductors are used then several outputs can be obtained,Three outputs are usually arranged with a phase separation of 120o,to produce a three phase supply,The supply phasing is shown in Fig,2,The system is more efficient in that for the same mechanical power a greater total electrical output is obtained,Each of the three outputs for a three phase supply,The separate supplies ate connected in either stander delta formation (Fig,3),The star formation is more commonly used and requires four sliprings on the alternator,The three conductors are joined at a common slipring and have their individual slipring,The central or neutral line is common to each phase,The delta arrangement has two phases joined at each of the three sliprings on the alternator A single phase supply can be taken from any two sliprings.
So far,alternator construction has considered the armature rotating and the field coils stationary,The same electricity generating effect is produced if the reverse occurs,that is,the field coils rotate and the armature is stationary,This is in face the arrangement adopted for large large,heavy duty alternators
Fig,2 Three phase alternator output
The field current supply in older machines comes from a low voltage direct current generator or exciter on the same shaft as the alternator,Modern machines however are either statically excited or of the high speed brushless type,The exciter is required to operate to counter the effects of power factor for a given load,The power factor is a measure of the phase,difference between voltage and current and is expressed as the cosine of he phase angle,With a purely resistance load the voltage and current are in phase,giving a power factor of one,The power consumed is therefore the product of voltage and current,Inductive or capacitive loads,combined with resistance loads,produce lagging or leading power factors which have a value less than one,The power consumed is the product of current,voltage and power factor,The alternations current supplying a load has a voltage drop resulting from the load,When the load has a lagging power factor this voltage drop is considerable,Therefore the exciter,in maintaining the alternator voltage,must vary with the load current and also the power factor,The speed change of the prime mover must also be taken into account.
Delta connection
Fig,3 Star and delta three-phase connections
Hand control of excitation is difficult so use is made of an automatic voltage regulator (AVR),The AVR consists basically of a circuit fed from the alternator output voltage which detects small changes in voltage and feeds a signal o an amplifier which changes the excitation to corrected the voltage,Stabilising features are also incorporated in the circuits to avoid,hunting”(constant voltage fluctuations) or overcorrecting,Various designs of AVR are in use which can be broadly divided into classes such as carbon pile types,magnetic amplifiers,electronic types,etc,
The statically excited alternator has a static excitation system instead of a d,c,exciter,This type of alternator will more readily accept the sudden loading by direct on-line starting of large squirrel cage motors,The static excitation system uses transformers and rectifiers to provide series and shunt components for the alternator field,that is,it is compounded,Brushes and sliprings are used to transfer the current to the field coils which are mounted on the rotor,The terminal voltage from the alternator thus gives the extra excitation to give a steady voltage under any load condition,The careful matching of components provides a system which functions as a self regulator of voltage,Certain practical electrical problems and the compensation necessary for speed variation require that a voltage regulator is also built into the system.
The brushless high speed alternator was also developed to eliminate d.c,exciters with their associated commutators and brushgear,The alternator and exciter rotors are on a common shaft,which also carries the rectifiers,The exciter output is fed to the rectifiers and then through conductors in the hollow shaft to the alternator field coils,An automatic voltage regulator is used with this type of alternator.
(From,Introduction to Marine Engineering,,D,A,Taylor,1983.)
Technical Terms
electrical equipment 电气设备
air conditioning 空调
emergency supply equipment 应急供电装置
alternator 交流发电机
storage battery 蓄电池
switch gear 开关装置，配电装置
alternating/direct current 交/直流（电）
machine rating 机器额定功率
momentary overload 瞬时过载
winding 绕组
insulation 绝缘/绝缘材料
drip proof enclosure 防滴漏（型）外壳
watertight enclosure 水密（型）外壳
weatherproof 风雨密（型）
hoseproof 防溅（型）
single coil of wire 单匝线圈
commutator 整流子
sparking 电火花，点火
current collecting brush 汇流刷
commutating pole 整流（辅助）极
interpole 附加（补偿）磁极
electromagnet 电磁铁
polarity 极性，配极
main pole 主极
field coil 励磁线圈
soft iron core 软铁心
shunt 分流，并联
series 系数，级数，串联
compound复励，混合物
compound wound generator 复励发电机
slipring 集流环
conductor 导体
three phase supply 三相电源
star or delta formation 星型或三角形形式
exciter 励激器
armature 电枢
brushless 无刷型
cosine 余弦
lagging 滞后
stabilizing feature 稳定性
hunting 寄生振荡
fluctuation 脉动，偏差
carbon pile type 碳柱形
magnetic amplifier 磁放大器
squirrel cage motor 鼠笼电动机
brushgear 电刷装置
transformer 变压器
rectifier 整流器
Additional Terms and Expressions
electric power plant 电站
main generator 主发电机
emergency generator 应急发电机
double current generator交直流发电机
protection device 保护装置
load-dispatching board 配电板
distribution network 配电网
connection box 接线箱
watertight box 水密接线箱
A.C,contactor 交流接触器
D.C,contactor 直流接触器
two phase motor 二相电动机
three phase motor 三相电动机
three phase synchronous motor 三相同步电动机
starter 起动器
push button 按钮
knob 旋钮
electric apparatus 电器
condenser 电容器
resistor 电阻器
reactor 电抗器
electromagnetic clutch 电磁离合器
invertor 逆变器
breaker 断路器
relay 继电器
lighting fixture 灯具
pilot lamp 引航灯
side lamp 舷灯
Notes to the Texts
The complete range of electrical equipment will include generators,switch gear for control and distribution,motors and their associated starting equipment and emergency supply arrangements.句中的will表示主语的性能及某种倾向，科技文献中用得较多。
all but在此作“几乎”解释。
Ward-Leonard system解释为“发动机电动机组”，也可以称为“渥特-勒奥那多装置”，俄语中为机组。
Hand control of excitation is difficult so use is made of an automatic voltage regulator(AVR)。
句中so use…至句末世结果状语从句，so=so that，这个从句中的主语部分use of an AVR被谓语（is made）所隔开，参见第二颗注7。
Marine Electrical Equipment
The complete electrical plant on board ship is made up of power generation equipment,a distribution system and the many power utilising devices,Electricity is used for the motor drive of many auxiliaries and also for deck machinery,lighting,ventilation and air conditioning equipment,A constant supply of electricity is essential for safe ship and machinery operation,and therefore standby or additional capacity is necessary together with emergency supply equipment,Emergency equipment may take the form of an automatically starting emergency alternator or storage batteries may be used.
The complete range of electrical equipment will include generators,switch gear for control and distribution,motors and their associated starting equipment and emergency supply arrangements.
Alternating or direct current
Alternating current has now all but replaced direct current as the standard supply for all marine installations,The use of alternating current has a number of important advantages,for example,reduced first cost,less weight,less space required and a reduction in maintenance requirements,Direct current does how-ever offer advantages in motor control using,for example,the Ward-Leonard system which provides a wide range of speed.
Machine rating
Motors and generators,both d.c,and a.c.,are rated as Continuous Maximum Rated (CMR) machines,This means they can accept a considerable momentary overload and perhaps even a moderate overload for a longer duration.
Temperature affects the performance of all electrical equipment and also the useful life of the insulation and thus the equipment itself,The total temperature of an operating machine is a result of the ambient air temperature and the heating effect of current in the windings,Temperature rise is measured above this total temperature,Adequate ventilation of electrical equipment is therefore essential,Classification Societies have set requirements for the various classes of insulation,The usual classes for marine installations are E,B and F where particular insulation materials are specified and increasing temperature rises allowed in the order stated.
Enclosures
Depending upon the location,a motor or generator will have one of a number of possible types of enclosure,‘Drip-proof’ is most common and provides protection from falling liquids or liquids being drawn in by ventilating air,A ‘watertight enclosure’ provides protection for immersion under a low head of water for up to one hour,‘Weatherproof’,‘hose proof’ and ‘deck watertight’ provide immersion protection for only one minmet,‘Totally enclosed ’ can also be used or an arrangement providing ducted ventilation from outside the manager space,A ‘flameproof ’ enclosure is capable of withstanding an explosion of some particular flammable was that may occur within it,It must also stop the transfer of flame,i.e,contain any fire or explosion,
Direct current generators
A current is produced when a single coil of wire is rotated in a magnetic field,When the current is collected using a ring which is split into two halves,that is,a commutator,a direct or single direction current is produced,The current produced may be increased by the use of many turns of wire and additional magnetic fields.
With many coils connected to the commutator,sparking will occur as the current collecting brushes move across the insulated segments,Commutating poles or interpoles are used to reduce this sparking,They are in fact electromagnets having a polarity the same as the main pole which follows in the direction of rotation,
The magnetic field between the poles is produced by what are known as,field coils”,These coils are excited or energized by the current produced in the machine,The soft iron core of the field coils retains some magnetism which enables a preliminary current generation to build up eventually to the full machine output,The field windings can be connected to the output current in a number of ways—shunt,series or compound,The compound wound arrangement is usual since it provides the best voltage characteristics,
The compound wound generator has two sets of field coils (Fig.1 (a)),The shunt coil has many turns of fine wire and the series coil has a few turns,of heavy wire,The shunt field produces full voltage on no-load which falls off as the load current increases.
Fig.1 Compound d.c,generator
----Field connections
---Characteristic cures
The series field creates an increase in voltage as the load increases,Properly combined or compounded the result is a fairly,constant voltage over a range of load (Fig,1(b)).
Alternating current generators
A coil of wire rotating in a magnetic field produces a current,The current can be brought out to two sliprings which are insulated from the shaft,Carbon bushes rest on these rings as they rotate and collect the current for use in an external circuit,Current collected in this way will be alternating,that is,changing in direction and rising and falling in value,To increase the current produced,additional sets of poles may be introduced.
The magnetic field is provided by electromagnets so arranged that adjacent poles have opposite polarity,These ‘field coils’,as they are called,are connected in series to an external source or the machine output.
If separate coils or conductors are used then several outputs can be obtained,Three outputs are usually arranged with a phase separation of 120o,to produce a three phase supply,The supply phasing is shown in Fig,2,The system is more efficient in that for the same mechanical power a greater total electrical output is obtained,Each of the three outputs for a three phase supply,The separate supplies ate connected in either stander delta formation (Fig,3),The star formation is more commonly used and requires four sliprings on the alternator,The three conductors are joined at a common slipring and have their individual slipring,The central or neutral line is common to each phase,The delta arrangement has two phases joined at each of the three sliprings on the alternator A single phase supply can be taken from any two sliprings.
So far,alternator construction has considered the armature rotating and the field coils stationary,The same electricity generating effect is produced if the reverse occurs,that is,the field coils rotate and the armature is stationary,This is in face the arrangement adopted for large large,heavy duty alternators
Fig,2 Three phase alternator output
The field current supply in older machines comes from a low voltage direct current generator or exciter on the same shaft as the alternator,Modern machines however are either statically excited or of the high speed brushless type,The exciter is required to operate to counter the effects of power factor for a given load,The power factor is a measure of the phase,difference between voltage and current and is expressed as the cosine of he phase angle,With a purely resistance load the voltage and current are in phase,giving a power factor of one,The power consumed is therefore the product of voltage and current,Inductive or capacitive loads,combined with resistance loads,produce lagging or leading power factors which have a value less than one,The power consumed is the product of current,voltage and power factor,The alternations current supplying a load has a voltage drop resulting from the load,When the load has a lagging power factor this voltage drop is considerable,Therefore the exciter,in maintaining the alternator voltage,must vary with the load current and also the power factor,The speed change of the prime mover must also be taken into account.
Delta connection
Fig,3 Star and delta three-phase connections
Hand control of excitation is difficult so use is made of an automatic voltage regulator (AVR),The AVR consists basically of a circuit fed from the alternator output voltage which detects small changes in voltage and feeds a signal o an amplifier which changes the excitation to corrected the voltage,Stabilising features are also incorporated in the circuits to avoid,hunting”(constant voltage fluctuations) or overcorrecting,Various designs of AVR are in use which can be broadly divided into classes such as carbon pile types,magnetic amplifiers,electronic types,etc,
The statically excited alternator has a static excitation system instead of a d,c,exciter,This type of alternator will more readily accept the sudden loading by direct on-line starting of large squirrel cage motors,The static excitation system uses transformers and rectifiers to provide series and shunt components for the alternator field,that is,it is compounded,Brushes and sliprings are used to transfer the current to the field coils which are mounted on the rotor,The terminal voltage from the alternator thus gives the extra excitation to give a steady voltage under any load condition,The careful matching of components provides a system which functions as a self regulator of voltage,Certain practical electrical problems and the compensation necessary for speed variation require that a voltage regulator is also built into the system.
The brushless high speed alternator was also developed to eliminate d.c,exciters with their associated commutators and brushgear,The alternator and exciter rotors are on a common shaft,which also carries the rectifiers,The exciter output is fed to the rectifiers and then through conductors in the hollow shaft to the alternator field coils,An automatic voltage regulator is used with this type of alternator.
(From,Introduction to Marine Engineering,,D,A,Taylor,1983.)
Technical Terms
electrical equipment 电气设备
air conditioning 空调
emergency supply equipment 应急供电装置
alternator 交流发电机
storage battery 蓄电池
switch gear 开关装置，配电装置
alternating/direct current 交/直流（电）
machine rating 机器额定功率
momentary overload 瞬时过载
winding 绕组
insulation 绝缘/绝缘材料
drip proof enclosure 防滴漏（型）外壳
watertight enclosure 水密（型）外壳
weatherproof 风雨密（型）
hoseproof 防溅（型）
single coil of wire 单匝线圈
commutator 整流子
sparking 电火花，点火
current collecting brush 汇流刷
commutating pole 整流（辅助）极
interpole 附加（补偿）磁极
electromagnet 电磁铁
polarity 极性，配极
main pole 主极
field coil 励磁线圈
soft iron core 软铁心
shunt 分流，并联
series 系数，级数，串联
compound复励，混合物
compound wound generator 复励发电机
slipring 集流环
conductor 导体
three phase supply 三相电源
star or delta formation 星型或三角形形式
exciter 励激器
armature 电枢
brushless 无刷型
cosine 余弦
lagging 滞后
stabilizing feature 稳定性
hunting 寄生振荡
fluctuation 脉动，偏差
carbon pile type 碳柱形
magnetic amplifier 磁放大器
squirrel cage motor 鼠笼电动机
brushgear 电刷装置
transformer 变压器
rectifier 整流器
Additional Terms and Expressions
electric power plant 电站
main generator 主发电机
emergency generator 应急发电机
double current generator交直流发电机
protection device 保护装置
load-dispatching board 配电板
distribution network 配电网
connection box 接线箱
watertight box 水密接线箱
A.C,contactor 交流接触器
D.C,contactor 直流接触器
two phase motor 二相电动机
three phase motor 三相电动机
three phase synchronous motor 三相同步电动机
starter 起动器
push button 按钮
knob 旋钮
electric apparatus 电器
condenser 电容器
resistor 电阻器
reactor 电抗器
electromagnetic clutch 电磁离合器
invertor 逆变器
breaker 断路器
relay 继电器
lighting fixture 灯具
pilot lamp 引航灯
side lamp 舷灯
Notes to the Texts
The complete range of electrical equipment will include generators,switch gear for control and distribution,motors and their associated starting equipment and emergency supply arrangements.句中的will表示主语的性能及某种倾向，科技文献中用得较多。
all but在此作“几乎”解释。
Ward-Leonard system解释为“发动机电动机组”，也可以称为“渥特-勒奥那多装置”，俄语中为机组。
Hand control of excitation is difficult so use is made of an automatic voltage regulator(AVR)。
句中so use…至句末世结果状语从句，so=so that，这个从句中的主语部分use of an AVR被谓语（is made）所隔开，参见第二颗注7。
