 Hello, everyone. Myself, Sanjay Udge, Assistant Professor, Department of Electronics Engineering, Valchand Institute of Technology, Sulapur. Today, we are going to discuss generation of three-page AC voltage, learning outcome. At the end of this session, students will be able to analyze concepts of three-phase electrical circuits. Guideline, introduction, advantages of three-phase system over single-phase system, generation of three-phase voltages, mathematical expressions, delta system, star system, introduction. Basic concepts of three-phase system, which is also called as polyphase system. Three-phase system is nothing but three single-phase voltages of equal magnitude, but displaced by 120 degrees. The supply voltages are generated by using a three single-phase and the load, it is also a three-phase type. They are connected either in delta or star. It means that generation of three-phase consists of three single-phase windings and the power to be delivered to the load is also a three-phase type and the most important is they are connected either in delta or star. Advantages of three-phase over single-phase. Generation, transmission, and distribution is far more economical or cheaper as compared to the single-phase system. Moreover, a constant power instead of pulsating power in case of single-phase system is delivered using a three-phase system. More advantages, a three-phase induction motor, it is a self-starting, possesses highest efficiency, having a uniform torque, and provides a minimum vibration. The most important feature of this three-phase system is three-phase induction motor as compared to the single-phase induction motor. A single-phase induction motor requires auxiliary winding for its starting. But in case of three-phase induction motor, it doesn't require auxiliary winding because of the rotating magnetic field. This rotating magnetic field is induced due to this three-phase supply. This rotating magnetic field is established due to the presence of these three-phase voltages with different magnitude, single-phase system. This has been already been discussed in a single-phase system or generation of single-phase voltage. It requires a single-turn coil, which we discussed already. This single-turn coil is rotated in a magnetic field. Generation of electricity requires a conductor, a moment of the conductor, then a magnetic field, and collection of the induced EMF. So this is the single-phase system, three-phase system. In three-phase system, the concept is very similar to the single-phase system. The only difference is, in single-phase, we are using a single coil. Whereas in case of three-phase system, we are using three different coils. These three different coils are overlapped with each other and displaced electrically by 120 degrees. Here you'll find these three-phase windings overlapped with each other with a displacement of 120 degrees electrically. Here you'll find the slip rings. These slip rings are responsible for collection of the induced EMF, three-phase induced EMFs. So in short, the construction is similar as that of the single-phase system. The only difference in this three-phase system is it consists of three different windings. Here you'll find three-phase system. In figure A, you'll find three conductors. A1, A2, one conductor. Conduct number 2, B1, B2. Conductor number 3, C1, C2. Look at this carefully. All these three are displaced by 120 degrees. In figure B, in figure A, these three coils are rotated in anticlockwise direction with an angular velocity omega radians per second. So here the magnetic field is stationary. We're rotating these three coils. In figure B, what you'll find? You'll find this stator having a stationary winding. Again, three windings overlapped with each other displaced by 120 degrees. Here you'll find at the center, the rotating part is the permanent magnet. And the generation of EMAPs, again, based on the Faraday's law of electromagnetic induction due to the cutting of the flux. This is the vector diagram. Here you'll find this EM and EM. This is the length of the vector that represents the maximum value of that particular phase. This is the EM voltage, peak voltage, produced due to A1, A2 conductor. This, again, the maximum peak voltage EM produced due to B1 and B2 conductor. And this is the third one, EM, C1, C2. It's the conductor number three phase waveforms. Now, a important part of the study of this concept of three phase systems. This is the phase one shown by black color, phase two by red color, phase three by blue color. Here, the maximum voltage attained by every phase is one volt, 1.0 volt. But make a note of this is, phase one attains its maximum value at 90 degree, phase two attains its maximum value at 120 degree, and phase three attains its maximum value at 240 degree. So, it means that their maximum value occurring is displaced by 120 degree. In similar manner, phase one will have its zero crossing at omega equals to zero. Phase two red will have its zero crossing after 120 degree. Phase three, it's zero crossing in positive direction will have a phase angle equals to omega t equals to 240 degree. Exercise assignment. What are the instantaneous values of three phase system? Again, coming back to the same diagram, the instantaneous value is that value at which a particular phase attains a particular magnitude. So, look at this. Let us consider at instant omega t equals to 90 degree. At this stage, phase one has attended its maximum value, which is equals to 1.0 volt. At the same instant, phase two, this is the red one, phase two has attended value equals to minus 0.5. Phase three, blue color, also attended value equals to minus 0.5. If you add these three voltages at the same instant, this is 1 volt plus minus of 0.5 plus minus of 0.5 equals to zero. It means that at any instant, the summation of all these three phase voltages is equals to zero. So, this is the very, very important concept. These are the voltage equations. Vry or Van is equal to Vm sine omega t, where Vm is equal to maximum phase voltage, which is shown over here, Van or Vrn. Second is the Vyn is equal to given by Vm sine omega t minus 2 power by 3, that is equals to Vm sine omega t minus 120 degrees. The next one is the, there's the second phase, Vbn. Now the third phase, Vcn or Vbn, is equal to Vm sine omega t plus 2 power by 3 or plus 120 degrees, or it can be written as Vm is equal to Vm sine omega t minus 240 degrees represented by three vectors. So, this Vn, Vbn and Vcn are Vr, Vy, Vb with a phase difference of 120 degrees. Again definitions, line current, phase current, line voltage, phase voltage, line current, line, first of all, phase current. Phase current is the current flowing through a particular phase, whereas line current is the current flowing through a particular line. What is the phase voltage? Phase voltage is the voltage across a particular phase, whereas a line voltage, it is the voltage between two lines. It may be, it may be Ry, between lines Rv, Ry is the line voltage between R and Y phase, where Yb is the voltage between two phase Y and B and Vb, R is the line voltage between the phase R and B. So, this is the difference between star and delta connection. In delta connection, you will find only three wires, this R, Y, B. In case of star connection, you will find it's four-wire system. Economic wind, textbook, electrical technology by B.L. Therager. Thank you.