إذا لم تحاول أن تفعل شيء أبعد مما قد أتقنته )رونالد أبدا تتقدم فإنك لن اسبورت(.. يجب أن تثق بنفسك... وإذا لم تثق بنفسك فمن ذا الذي سيثق بك!! )وليام جيمس( First Semester 2018-2019 قد يتقبل الكثيرون النصح لكن الحكماء فقط هم الذين يستفيدون منه ( بابليليوس سيرس(
DC - 18 December 2018 2
Contents Overview of Direct Current Construction Principle of Operation Types of DC Machine Power Flow Diagram Speed Control 18 December 2018 3
Notes آفة العلم النسيان The bane of knowledge is forgetfulness إحذر الرجل الصامت والمياه الراكدة Beware of a silent dog and still water 18 December 2018 4
DC Generator A dc generator is a machine that converts mechanical energy into electrical energy (dc voltage and current) by using the principle of magnetic induction. In this example, the ends of the wire loop have been connected to two slip rings mounted on the shaft, while brushes are used to carry the current from the loop to the outside of the circuit. Principle of magnetic induction in DC machine 18 December 2018 5
Notes آفة العلم النسيان The bane of knowledge is forgetfulness إعترف بأخطائك Admit your mistakes 18 December 2018 6
DC Motor DC motors are everywhere! In a house, almost every mechanical movement that you see around you is caused by an DC (direct current) motor. An dc motor is a machine that converts electrical energy into mechanical energy by supplying a dc power (voltage and current). 18 December 2018 7
Notes آفة العلم النسيان The bane of knowledge is forgetfulness لتكن أهدافك كبيرة... وارض بالملذات الصغيرة Think big thoughts, but relish small pleasures 18 December 2018 8
Advantages & Disadvantages Of D.C. Motors Advantages High starting torque. easy to control Rapid acceleration and deceleration. Speed can be easily controlled over wide speed range. Used in tough gobs (traction motors, electric trains, electric cars,.) Built in wide range of sizes. Disadvantages Needs regular maintenance. Cannot be used in explosive area. High cost. 18 December 2018 9
Notes آفة العلم النسيان The bane of knowledge is forgetfulness كن متواضعا... فكثير من األمور وجدت قبل أن تولد Be modest. A lot was accomplished before you were born 18 December 2018 10
Construction of DC machine Stator with poles visible Cutaway view of a dc motor 18 December 2018 11
Notes آفة العلم النسيان The bane of knowledge is forgetfulness ال تغتب غيرك Don't gossip 18 December 2018 12
Construction of DC machine segments Rotor of a dc motor brushes 18 December 2018 13
Notes آفة العلم النسيان The bane of knowledge is forgetfulness كن حذرا من األشخاص الذين ال يملكون شيئا يخسروه Beware of the person who has nothing to lose 18 December 2018 14
Construction of DC machine Rotor is the rotating part armature Stator is the stationary part - field Armature coil Brushes Stator: non-moving coil Rotor: rotating part 18 December 2018 15
Notes آفة العلم النسيان The bane of knowledge is forgetfulness إدعم منتجات وطنك حتى لو كان ثمنها أكثر من غيرها Patronize local merchants even if it costs a bit more 18 December 2018 16
More loops of wire = higher rectified voltage. ARMATURE In practical, loops are generally placed in slots of an iron core. The iron acts as a magnetic conductor by providing a low-reluctance path for magnetic lines of flux to increase the inductance of the loops and provide a higher induced voltage. The commutator is connected to the slotted iron core. The entire assembly of iron core, commutator, and windings is called the armature. The windings of armatures are connected in different ways depending on the requirements of the machine. Loops of wire are wound around slot in a metal core DC machine armature 18 December 2018 17
Notes آفة العلم النسيان The bane of knowledge is forgetfulness ال تتوقع من المال أن يجلب لك السعادة Don't expect money to bring you happiness 18 December 2018 18
Construction of DC Machine: Armature The rotor or the armature core, which carries the rotor or armature winding, is made of sheet-steel laminations. The laminations are stacked together to form a cylindrical structure. Portion of an armature lamination of a dc machine showing slots and teeth 18 December 2018 19
Notes آفة العلم النسيان The bane of knowledge is forgetfulness حافظ دوما على لياقتك البدنية Get and stay in shape 18 December 2018 20
Construction of DC Machine: Commutator Commutator: a mechanical rectifier, which converts the alternating voltage generated in the armature winding into direct voltage across the brush. It is made of copper segments insulated from each other by mica and mounted on the shaft of the machine. The armature windings are connected to the commutator segments. 18 December 2018 21
Notes آفة العلم النسيان The bane of knowledge is forgetfulness كن لبقا... وال تكن متعجرفا Be tactful... Never alienate anyone on purpose 18 December 2018 22
Construction of DC Machine: Brush The purpose of the brush is to ensure electrical connections between the rotating commutator and stationary external load circuit. It is made of carbon and rest on the commutator. Commutator and Brushes 18 December 2018 23
Notes آفة العلم النسيان The bane of knowledge is forgetfulness ال تقاطع المتحدثين Don't interrupt 18 December 2018 24
Construction of DC Machine: Armature Winding 18 December 2018 25
Notes آفة العلم النسيان The bane of knowledge is forgetfulness كن وفيا Be loyal 18 December 2018 26
Construction of DC Machine: Armature Winding 18 December 2018 27
Notes آفة العلم النسيان The bane of knowledge is forgetfulness عندما تحضر اإلجتماعات... إجلس في أول مكان فارغ يصادفك When attending meetings, sit down front 18 December 2018 28
Lap Wound Armatures ARMATURE WINDINGS are used in machines designed for low voltage and high current. armatures are constructed with large wire because of high current Eg: - are used is in the starter motor of almost all automobiles. The windings of a lap wound armature are connected in parallel. This permits the current capacity of each winding to be added and provides a higher operating current. No of current path, C = 2p ; p = no of poles 18 December 2018 29
Notes آفة العلم النسيان The bane of knowledge is forgetfulness ال تخف من قول "ال أعلم" Don't be afraid to say, "I don't know." 18 December 2018 30
ARMATURE WINDINGS (Cont) Wave Wound Armatures are used in machines designed for high voltage and low current. their windings connected in series. When the windings are connected in series, the voltage of each winding adds, but the current capacity remains the same. are used is in the small generator. No of current path, C = 2 18 December 2018 31
Notes آفة العلم النسيان The bane of knowledge is forgetfulness أينما تذهب لن تجد خيرا من وطنك East or west, home is best 18 December 2018 32
ARMATURE WINDINGS (Cont) Frogleg Wound Armatures the most used in practical nowadays. designed for use with moderate current and moderate armatures voltage. the windings are connected in series parallel. Most large DC machines use frogleg wound armatures. Frogleg wound armatures 18 December 2018 33
Notes آفة العلم النسيان The bane of knowledge is forgetfulness ال تستهن بالوقت والكلمات... فكالهما ال يمكن استعادتها Don't use time or words carelessly... Neither can be retrieved 18 December 2018 34
FIELD WINDINGS Most DC machines use wound electromagnets to provide the magnetic field. Two types of field windings are used : Series field Shunt field Series field windings are so named because they are connected in series with the armature. are made with relatively few windings turns of very large wire and have a very low resistance. usually found in large horsepower machines wound with square or rectangular wire. The use of square wire permits the windings to be laid closer together, which increases the number of turns that can be wound in a particular space. *Square and rectangular wire can also be made physically smaller than round wire and still contain the same surface area. 18 December 2018 35
Notes آفة العلم النسيان The bane of knowledge is forgetfulness إستخدم نجاحاتك الماضية كدرجة سلم لنجاحات قادمة... ال كمقعد تجلس عليه Use your past successes as a trampoline, not an easy chair 18 December 2018 36
FIELD WINDINGS (Cont) Shunt field windings is constructed with relatively many turns of small wire, thus, it has a much higher resistance than the series field. is intended to be connected in parallel with, or shunt, the armature. high resistance is used to limit current flow through the field. When a DC machine uses both series and shunt fields, each pole piece will contain both windings. The windings are wound on the pole pieces in such a manner that when current flows through the winding it will produce alternate magnetic polarities. 18 December 2018 37
Notes آفة العلم النسيان The bane of knowledge is forgetfulness انتهز كل فرصة لتحسين مهاراتك في العمل Seize every opportunity for additional training in your job 18 December 2018 38
MACHINE WINDINGS OVERVIEW Winding armature field Wave C=2 Lap C=2p Frogleg Self excited Separately Excited series shunt compound 18 December 2018 39
Notes آفة العلم النسيان The bane of knowledge is forgetfulness مهما بلغت من العمر... عانق والدتك وقبلها No matter how old you get, hug and kiss your mother whenever you greet her 18 December 2018 40
Principle operation of Generator Whenever a conductor is moved within a magnetic field in such a way that the conductor cuts across magnetic lines of flux, voltage is generated in the conductor. The AMOUNT of voltage generated depends on: the strength of the magnetic field, the angle at which the conductor cuts the magnetic field, the speed at which the conductor is moved, and the length of the conductor within the magnetic field. 18 December 2018 41
Notes آفة العلم النسيان The bane of knowledge is forgetfulness ال تثق بذاكرتك... اكتب كل شيء على الورق Don't trust your memory; write it down 18 December 2018 42
Observes Principle operation of Generator The meter direction. The conductors of the armature loop. Direction of the current flow. 18 December 2018 43
Notes آفة العلم النسيان The bane of knowledge is forgetfulness قل يرحمك هللا كلما عطس أحد أمامك Say "bless you" when you hear someone sneeze 18 December 2018 44
Effects of additional coils When more than one loop is used, the average output voltage is higher and there is less pulsation of the rectified voltage. Since there are four segments in the commutator, a new segment passes each brush every 90 0 instead of every 180 0. Since there are now four commutator segments in the commutator and only two brushes, the voltage cannot fall any lower than at point A. Therefore, the ripple is limited to the rise and fall between points A and B on the graph. By adding more armature coils, the ripple effect can be further reduced. Decreasing ripple in this way increases the effective voltage of the output. Effects of additional coils 18 December 2018 45
Notes آفة العلم النسيان The bane of knowledge is forgetfulness البداية الخاطئة تؤدي إلى نهاية خاطئة A bad beginning makes a bad ending 18 December 2018 46
Effects of additional turns To increase the amount of output voltage, it is common practice to increase the number of turns of wire for each loop. If a loop contains 20 turns of wire, the induced voltage will be 20 times greater than that for a single-loop conductor. The reason for this is that each loop is connected in series with the other loops. Since the loops form a series path, the voltage induced in the loops will add. In this example, if each loop has an induced voltage of 2V, the total voltage for this winding would be 40V (2V x 20 loops = 40 V). Effects of additional turns 18 December 2018 47
Notes آفة العلم النسيان The bane of knowledge is forgetfulness كن حكيما بما يكفي لتعلم أنك ال تعلم كل شيء Be wise enough to know that you do not know everything 18 December 2018 48
DC Motor Operation In a dc motor, the stator poles are supplied by dc excitation current, which produces a dc magnetic field. The rotor is supplied by dc current through the brushes, commutator and coils. The interaction of the magnetic field and rotor current generates a force that drives the motor. 18 December 2018 49
Notes آفة العلم النسيان The bane of knowledge is forgetfulness كن قائدا حينما ترى طريقا ضله اآلخرون Be a leader when you see a path others have missed 18 December 2018 50
Multi-Pole If p is the number of poles, then p/2 cycles of variation of the flux are encountered every complete mechanical rotation. 18 December 2018 51
Notes آفة العلم النسيان The bane of knowledge is forgetfulness العامل السيء يتشاجر مع أدواته A bad workman quarrel s (blames) with his tools 18 December 2018 52
Principle of Operation: Armature Voltage Emf Total = Emf conductor Number of conductor path Emf Total = P N m 60 Z a = P Z N m 60 a Where P -number of poles. Z-total number of armature conductor. a-number of parallel paths, 2 for wave and p for lab. Φ-flux per pole (weber). Nm-speed of motor in the revolution per minute (rpm). 18 December 2018 53
Notes آفة العلم النسيان The bane of knowledge is forgetfulness كن محبا ألولئك الذين ال يحبونك فقد يتغيرون Be loving to those who do not love you, because they may change 18 December 2018 54
Principle of Operation: Armature Voltage ω m = 2πN m 60 N m = ω m 60 2π 18 December 2018 55
Notes آفة العلم النسيان The bane of knowledge is forgetfulness القطة التي ترتدي قفازات ال تصطاد فئران A cat in gloves catches no mice 18 December 2018 56
Developed (or Electromagnetic) Torque Consider the turn shown in the following Figure. 18 December 2018 57
Notes آفة العلم النسيان The bane of knowledge is forgetfulness الغبي ال يسامح وال ينسى والساذج يسامح وينسى والحكيم يسامح وال ينسى The stupid neither forgive nor forget; the naive forgive and forget; the wise forgive but do not forget 18 December 2018 58
Classification of DC Machine 18 December 2018 59
Notes آفة العلم النسيان The bane of knowledge is forgetfulness بعد الشدة ياتي الفرج After black clouds, clear weather 18 December 2018 60
Classification of DC Machine Short- Shunt Long- Shunt 18 December 2018 61
Notes آفة العلم النسيان The bane of knowledge is forgetfulness ال نجاح بدون ألم No gains without pains 18 December 2018 62
DC Machine Representation 18 December 2018 63
Notes آفة العلم النسيان The bane of knowledge is forgetfulness العبرة بالخواتيم It is the end that counts 18 December 2018 64
Magnetization Curve of a DC Machine 18 December 2018 65
Notes آفة العلم النسيان The bane of knowledge is forgetfulness تعرف الشجرة من ثمرها A tree is known by its fruit 18 December 2018 66
DC Motors Equations 18 December 2018 67
Notes آفة العلم النسيان The bane of knowledge is forgetfulness ال جدوى من البكاء على اللبن المسكوب It is no use crying over the spilt milk 18 December 2018 68
DC Motors Equations 18 December 2018 69
Notes آفة العلم النسيان The bane of knowledge is forgetfulness كما تزرع تحصد As you sow, so will you reap 18 December 2018 70
DC Generator Equations 18 December 2018 71
Notes آفة العلم النسيان The bane of knowledge is forgetfulness من ال يخطىء ال يفعل شيئا He who makes no mistakes makes nothing 18 December 2018 72
DC Generator Equations Self-Exited DC Generators 1- Shunt Generator 2- Series Generator 18 December 2018 73
Notes آفة العلم النسيان The bane of knowledge is forgetfulness ماذا ستفعل حينما يكون الشخص الوحيد القادر على مسح دموعك هو من جعلك تبكي What do you do when the only person who can make you stop crying is the person who made you cry 18 December 2018 74
DC Generator Equations 18 December 2018 75
Notes آفة العلم النسيان The bane of knowledge is forgetfulness اذا أردت أن يتم الشىء على أكمل وجه فافعله بنفسك If you want a thing well done, do it yourself 18 December 2018 76
DC Generators Power Flow and Efficiency 18 December 2018 77
Notes آفة العلم النسيان The bane of knowledge is forgetfulness تسكين األلم لمدة ال يعني زواله.. بل على العكس.. إنه يزيد األمر سوءا عندما ستشعر به في النهاية Numbing the pain for a while will only make it worse when you finally feel it 18 December 2018 78
DC Motors Power Flow and Efficiency 18 December 2018 79
Notes آفة العلم النسيان The bane of knowledge is forgetfulness النظافة من اإليمان Cleanliness is next to godliness 18 December 2018 80
Torque-Speed Characteristics Separately & Shunt Exited Motors 18 December 2018 81
Notes آفة العلم النسيان The bane of knowledge is forgetfulness من المتأخر جدا أن تغلق باب اإلسطبل بعد سرقة الحصان It is too late to lock the stable door when the horse is stolen 18 December 2018 82
Torque-Speed Characteristics Series Motors Compound Motors 18 December 2018 83
Notes آفة العلم النسيان The bane of knowledge is forgetfulness الفضول يقتل صاحبه Curiosity killed a cat 18 December 2018 84
Starting of DC Machine 18 December 2018 85
Notes آفة العلم النسيان The bane of knowledge is forgetfulness عند ا إلمتحان يكرم املرء أو هيان After a test men are honoured or disgrace 18 December 2018 86
18 December 2018 87