Basic Construction And Working Of A DC Generator.

DC Generator- 

A dc generator is an electrical machine which converts mechanical energy into direct current electricity. This energy conversion is based on the principle of production of dynamically induced emf. This article outlines basic construction and working of a DC generator.

Construction Of A DC Machine:

Note: A DC generator can be used as a DC motor without any constructional changes and vice versa is also possible. Thus, a DC generator or a DC motor can be broadly termed as a DC machine. These basic constructional details are also valid for the construction of a DC motor. Hence, let's call this point as construction of a DC machine instead of just 'construction of a dc generator'.

The above figure shows constructional details of a simple 4-pole DC machine. A DC machine consists of two basic parts; stator and rotor. Basic constructional parts of a DC machine are described below.

1. Yoke: The outer frame of a dc machine is called as yoke. It is made up of cast iron or steel. It not only provides mechanical strength to the whole assembly but also carries the magnetic flux produced by the field winding.
2. Poles and pole shoes: Poles are joined to the yoke with the help of bolts or welding. They carry field winding and pole shoes are fastened to them. Pole shoes serve two purposes; (i) they support field coils and (ii) spread out the flux in air gap uniformly.
3. Field winding: They are usually made of copper. Field coils are former wound and placed on each pole and are connected in series. They are wound in such a way that, when energized, they form alternate North and South poles.



Armature core (rotor)

4. Armature core: Armature core is the rotor of a dc machine. It is cylindrical in shape with slots to carry armature winding. The armature is built up of thin laminated circular steel disks for reducing eddy current losses. It may be provided with air ducts for the axial air flow for cooling purposes. Armature is keyed to the shaft.
5. Armature winding: It is usually a former wound copper coil which rests in armature slots. The armature conductors are insulated from each other and also from the armature core. Armature winding can be wound by one of the two methods; lap winding or wave winding. Double layer lap or wave windings are generally used. A double layer winding means that each armature slot will carry two different coils.
6. Commutator and brushes: Physical connection to the armature winding is made through a commutator-brush arrangement. The function of a commutator, in a dc generator, is to collect the current generated in armature conductors. Whereas, in case of a dc motor, commutator helps in providing current to the armature conductors. A commutator consists of a set of copper segments which are insulated from each other. The number of segments is equal to the number of armature coils. Each segment is connected to an armature coil and the commutator is keyed to the shaft. Brushes are usually made from carbon or graphite. They rest on commutator segments and slide on the segments when the commutator rotates keeping the physical contact to collect or supply the current.

Commutator

Working Principle Of A DC Generator:

According to Faraday’s laws of electromagnetic induction, whenever a conductor is placed in a varying magnetic field (OR a conductor is moved in a magnetic field), an emf (electromotive force) gets induced in the conductor. The magnitude of induced emf can be calculated from the emf equation of dc generator. If the conductor is provided with a closed path, the induced current will circulate within the path. In a DC generator, field coils produce an electromagnetic field and the armature conductors are rotated into the field. Thus, an electromagnetically induced emf is generated in the armature conductors. The direction of induced current is given by Fleming’s right hand rule.

Need of a Split ring commutator: 

According to Fleming’s right hand rule, the direction of induced current changes whenever the direction of motion of the conductor changes. Let’s consider an armature rotating clockwise and a conductor at the left is moving upward. When the armature completes a half rotation, the direction of motion of that particular conductor will be reversed to downward. Hence, the direction of current in every armature conductor will be alternating. If you look at the above figure, you will know how the direction of the induced current is alternating in an armature conductor. But with a split ring commutator, connections of the armature conductors also gets reversed when the current reversal occurs. And therefore, we get unidirectional current at the terminals.

Types Of A DC Generator:

DC generators can be classified in two main categories, viz; (i) Separately excited and (ii) Self-excited.
(i) Separately excited: In this type, field coils are energized from an independent external DC source.
(ii) Selfexcited: In this type, field coils are energized from the current produced by the generator itself. Initial emf generation is due to residual magnetism in field poles. The generated emf causes a part of current to flow in the field coils, thus strengthening the field flux and thereby increasing emf generation. Self excited dc generators can further be divided into three types -
    (a) Series wound - field winding in series with armature winding
    (b) Shunt wound - field winding in parallel with armature winding
    (c) Compound wound - combination of series and shunt winding

You can learn more about types of a DC generator/machine here.

"Types of lllumination system,

1-Direct Lighting - this method is Lighting system direct is low down 

Indirect lighting refers to fixtures that direct the light upward to bounce off of the walls or ceiling to light the room.  Direct lighting, on the other hand, directs the light downward, directly onto the surface below.

Typically, direct light fixtures provide a better light source for detailed tasks such as cooking or reading.  However, they can also become a source for glare, since the lightbulbs are often exposed and directly in your eyes when you look upward toward the fixture.  Pendant lights and chandeliers that direct light directly onto the surface of a table or countertop are great examples of direct lighting.  They are more often used in kitchens than in dining spaces; kitchens require great task lighting, while dining rooms work best with softer lighting.

Squirrel-cage rotor-

A squirrel-cage rotor is the rotating part of the common squirrel-cage induction motor. It consists of a cylinder of steel laminations, with aluminum or copper conductors embedded in its surface. In operation, the non-rotating stator winding is connected to an alternating current power source; the alternating current in the stator produces a rotating magnetic field. The rotor winding has current induced in it by the stator field, and produces its own magnetic field. The interaction of the two magnetic fields from these two sources produces torque on the rotor.

By adjusting the shape of the bars in the rotor, the speed-torque characteristics of the motor can be changed, to minimize starting current or to maximize low-speed torque, for example.

Squirrel-cage induction motors are very prevalent in industry, in sizes from below one kilowatt (fractional horsepower; less than 1 hp) up to tens of megawatts (10,000s of horsepower). They are simple, rugged, and self-starting, and maintain a reasonably constant speed from light load to full load, set by the frequency of the power supply and the number of poles of the stator winding. Commonly used motors in industry are usually IEC or NEMA standard frame sizes, which are interchangeable between manufacturers. This simplifies application and replacement of these motors.

Structure-

The motor rotor shape is a cylinder mounted on a shaft. Internally it contains longitudinal conductive bars (usually made of aluminium or copper) set into grooves and connected at both ends by shorting rings forming a cage-like shape. The name is derived from the similarity between this rings-and-bars winding and a squirrel cage.

The solid core of the rotor is built with stacks of electrical steel laminations. Figure 3 shows one of many laminations used. The rotor has a larger number of slots than the stator and must be a non-integer multiple of stator slots so as to prevent magnetic interlocking of rotor and stator teeth at the starting instant.2

The rotor bars may be made of either copper or aluminium. A very common structure uses die cast aluminium poured into the rotor after the laminations are stacked. Some larger motors have aluminium or copper bars which are welded or brazed to end-rings. Since the voltage developed in the squirrel cage winding is very low, no intentional insulation layer is present between the bars and the rotor steel.

Theory-

The field windings in the stator of an induction motor set up a rotating magnetic field through the rotor. The relative motion between this field and the rotor induces electric current in the conductive bars. In turn these currents lengthwise in the conductors react with the magnetic field of the motor to produce force acting at a tangent orthogonal to the rotor, resulting in torque to turn the shaft. In effect the rotor is carried around with the magnetic field but at a slightly slower rate of rotation. The difference in speed is called slip and increases with load.

The conductors are often skewed slightly along the length of the rotor to reduce noise and smooth out torque fluctuations that might result at some speeds due to interactions with the pole pieces of the stator. The number of bars on the squirrel cage determines to what extent the induced currents are fed back to the stator coils and hence the current through them. The constructions that offer the least feedback employ prime numbers of bars.

The iron core serves to carry the magnetic field through the rotor conductors. Because the magnetic field in the rotor is alternating with time, the core uses construction similar to a transformer core to reduce core energy losses. It is made of thin laminations, separated by varnish insulation, to reduce eddy currents circulating in the core. The material is a low carbon but high-silicon iron with several times the resistivity of pure iron, further reducing eddy-current loss, and low coercivity to reduce hysteresis loss.

The same basic design is used for both single-phase and three-phase motors over a wide range of sizes. Rotors for three-phase will have variations in the depth and shape of bars to suit the design classification. Generally, thick bars have good torque and are efficient at low slip, since they present lower resistance to the EMF. As the slip increases, skin effect starts to reduce the effective depth and increases the resistance, resulting in reduced efficiency but still maintaining torque.

The shape and depth of the rotor bars can be used to vary the speed-torque characteristics of the induction motor. At standstill, the revolving magnetic field passes the rotor bars at a high rate, inducing line-frequency current into the rotor bars. Due to the skin effect, the induced current tends to flow at the outer edge of the winding. As the motor accelerates, the slip frequency decreases and induced current flows at greater depths in the winding. By tapering the profile of the rotor bars to vary their resistance at different depths, or by constructing a double squirrel cage, the motor can be arranged to produce more or less torque at standstill and near its synchronous speed.^[3]

Number of Poles Required Calculation

AC Induction Motor Number of Poles Formula & Calculator--

AC induction motor number of poles calculator - step by step calculation, formula & solved example problem to find the number of poles required to attain a certain synchronous speed. Line frequency & synchronous speed are the key elements in this calculation

Formula-

The below mathematical formula is used in this calculator to determine the number of poles required to attain a certain synchronous speed of an induction motor

Solved Example--

The below step by step solved example problem may helpful for users to understand how the input values are being used in number of poles calculations.

Example Problem--
Find the number of poles to design an induction motor to attain the synchronous speed Ns = 1500 rpm, whose line frequency f = 100 Hz?

Solution--

The given data
f = 100 Hz
Ns = 1500 rpm

Step by step calculation
Formula to find p = 120f/Ns
substitute the values in the above formula
= (120 x 100)/1500
p = 8

In the field of electrical engineering while designing an induction motor for certain synchronous speed, finding the number of poles is important. The above formula, step by step calculation & solved example problem may be useful for users to understand how the values are being used in the formula to find the number of poles, however, when it comes to online for quick calculations, this calculator helps the user to perform & verify such calculations as quick as possible.

AC और DC मोटर में अंतर

Difference Between DC and AC Motors

AC motor और DC motor में क्या अंतर है ?

1. करंट --

● AC motor केवल alternating current ( प्रत्यावर्ती धारा ) पर कार्य करती है

● DC motor केवल Direct current ( दिष्टधारा ) पर कार्य करती है

2. सप्लाई -

● AC motor में स्टेटर को प्रत्यावर्ती इनपुट सप्लाई से जोड़ा जाता है
● DC motor में स्टेटर और आर्मेचर दोनों को DC इनपुट सप्लाई से जोड़ा जाता है

3. Starting torque -

● सामान्यतः AC motor का starting torque काम होता है
● सामन्यतः DC मोटर का Starting torque अधिक होता है

4. Size -

● AC मोटर का आकार कम होता है
● डीसी मोटर का आकार अधिक होता है

5. बैटरी द्वारा चालान -

● AC मोटर को बैटरी द्वारा सीधे उपयोग नही किया जा सकता क्योंकि बैटरी में दिष्टधारा होती है जबकि AC मोटर केवल प्रत्यावर्ती धारा पर कार्य करती है

● DC मोटर को बैटरी द्वारा सीधे ही उपयोग किया जा सकता है

इसके अलावा AC मोटर और DC मोटर दोनों एक ही सिद्धांत पर कार्य करती हैं ।

एक फेजी प्रेरण मोटर & तीन फेजी प्रेरण मोटर

इंडक्शन मोटर प्रकार

एक फेजी प्रेरण मोटर

• स्प्लिट-फेज प्रेरण मोटर
• कैपेसिटर-स्टार्ट प्रेरण मोटर,
• कैपेसिटर-स्टार्ट कैपेसिटर रन प्रेरण मोटर,
• रेसिस्टैंस स्प्लिट-फेज प्रेरण मोटर,
• शेडेड पोल प्रेरण मोटर

तीन फेजी प्रेरण मोटर

• स्क्वैरेल केज
• स्लिप-रिंग
• 
  

AC मोटर का आविष्कार किसने किया

आधुनिक युग में लगभग सभी काम पावर के कारण ही किया जाता है वह चाहे किसी भी तरह से यूज की जाए पावर के बिना आज के कुछ भी कम नहीं होता है और आज के समय में बहुत तेजी से विकास हो रहा है वह चाहे किसी भी चीज का हो चाहे कपड़ा इंडस्ट्रियल है या किसी भी तरह की कोई गाड़ियां मोटर सभी बहुत तेजी से बढ़ते जा रहे हैं आज लगभग हर क्षेत्र में किसी न किसी चीज का उद्योग या कंपनी चल रही होती है पहले के मुकाबले आज के समय में बहुत तेजी से सामान को ले जाया और बनाया जा रहा है बड़े बड़े उद्योग धंदे चल रहे हैं और उन उद्योग धंधों के अंदर एक चीज ऐसी होती है

जो कि सबसे ज्यादा यूज़ की जाती है जी हां हम बात कर रहे हैं मोटर की मोटर एक ऐसी युक्ति है जो कि विद्युत से चलती है यह युक्ति विद्युत के बिना तो नहीं चलती लेकिन जब चलती है तो यह बहुत से लोगों के  बराबर अकेली काम करती है पहले लोग हाथों से काम करते थे जब मोटर नहीं थी लेकिन धीरे-धीरे जैसे जैसे विकास हुआ तो मोटर का आविष्कार किया गया जब मोटर आई तब इतनी खास नहीं थी लेकिन समय के साथ साथ में भी बदलाव होते गए और बहुत सी अच्छी अच्छी मोटर बनाई गई जो की बहुत तेजी से काम कर सकती थी मोटर यदि आप किसी भी चीज़ में लगाते हैं और उसको विद्युत प्रदान करते हैं तो यह अपने आप काम करना शुरु कर देती 

आजकल लगभग सभी बड़े बड़े उद्योगों में मोटर इस्तेमाल करके काम किया जाता है जैसे बड़े-बड़े कपड़े मिलो में मोटर से मशीन को चलाया जाता है मोटर नहीं तो किसी इंजन या दूसरी मशीन कि तरह इतना शोर करती है और ना ही उसका इतना ज्यादा खर्च होता है और मोटर बहुत ही थोड़ी सी जगह में लगाया जा सकता है इसलिए आजकल बहुत सी जगह मोटर का इस्तेमाल किया जाता है वैसे तो हम हर जगह मोटर को देखते हैं लेकिन मोटर कोई एक प्रकार की नहीं होती यह भी अलग-अलग तरह की होती है मोटर कितने तरह की होती है यह हम आपको नीचे बताएंगे

तो आज हम आपको इस पोस्ट में मोटर के सभी प्रकार के बारे में बताएंगे और मोटर से संबंधित कुछ रोचक जानकारी आपको देंगे लेकिन आप याद रखें हम आपको इस पोस्ट में सिर्फ AC बिजली मोटर के बारे में ही जानकारी देंगे तो आप नीचे दी गई जानकारी को अच्छी तरह से पढ़ें यह आपके लिए बहुत ही जरूरी है

Ac मोटर का आविष्कार किसने किया

एक इंडक्शन मोटर एक AC बिजली की मोटर होती है ये मोटर विद्युत शक्ति को मकनिकल शक्ति में बदलती है और ये यह मोटर सबसे अधिक उद्योगों उपयोग में आता है जिसके कारण इसे उद्योगों का वर्कहॉर्स कहते हैं। इसमें घिसने वाला कोई अवयव नहीं है जिससे यह बिना मरम्मत के बहुत दिनो तक चल सकता है क्योकि इस मोटर  में बहुत ज्यादा पॉवर देती है|

सबसे पहले 1824 में, फ्रेंच भौतिक विज्ञानी फ़्राँस्वा Arago चुंबकीय क्षेत्र घूर्णन के अस्तित्व तैयार की गया , Arago के घुमाव, जो मैन्युअल पर और बंद स्विच बदल कर, वाल्टर Baily प्रभाव में पहली आदिम इंडक्शन मोटर के रूप में 1879 में प्रदर्शन किया उसके  बाद में 1887 में टेस्ला अक्टूबर और नवंबर 1887 में अमेरिकी पेटेंट के लिए आवेदन किया है और उन्होंने 1887 में एक मॉडल तेयार किया और उसी समय उन्होंने उस पर कम करना शुरु कर दिया और उन्होंने एक इंडक्शन मोटर तेयार की जो AC बिजली पर चलती है |

यह मोटर दो प्रकार की तेयार की गई थी एक तो ऐसी जिसमे एक फेज और एक जिसमे तीन फेज और यह पॉवर के हिसाब से बनाई गई थी जिसमे एक फेज है वो तो घरो में उपयोग ज्यादा की जाती है इन्हें फ्रैक्शनल हॉर्शपॉवर मोटर भी कहते हैं। जैसे पंखों, धुलाई की मशीनों के मोटर आदि और जो तीन फेज की मोटर है वो उद्योगों उपयोग में ज्यादा आती है |