Eet3082 binod kumar sahu lecture_01
- 1. Electrical Machines-II 6th Semester, EE and EEE By Dr. Binod Kumar Sahu Associate Professor, Electrical Engg. Siksha ‘O’ Anusandhan, Deemed to be University, Bhubaneswar, Odisha, India Lecturer-1
- 3. 3 Rotating Electrical Machines ACDC Permanent Magnet Wound Field Separately Excited Self Excited Synchronous Induction Brushless DC Hysteresis Sine wave Reluctance Permanent Magnet Wound Field Salient Pole Non-salient Pole Three Phase Single Phase Wound Rotor Squirrel Cage Split Phase Shaded Pole Universal Resistance Start Capacitor Start Capacitor Start Capacitor Run
- 4. 4 Learning Outcomes: - Students will be able to: Know the basics of a synchronous machine. Know different types of alternators from application point of view. Understand the concept of power generation in hydro and thermal power plant. Know the various sources of power generation in India and Odisha. Analyse the basic concept of emf generation.
- 5. 5 synchronous machines: - Synchronous Machine constitutes of both synchronous motors as well as synchronous generators. An AC system has many advantages over DC system like: i. It is easy to generate. ii. It is cheaper. iii. It can be transmitted over long distances. iv. It is easy to increase or decrease the voltage levels in AC system, etc. Therefore, the AC system is exclusively used for generation, transmission and distribution of electric power. The machine which converts mechanical energy into AC electrical energy is called as Synchronous Generator or Alternator. Synchronous machine can also converts AC electrical energy to mechanical power while running at synchronous speed. In this mode of operation it is called as Synchronous Motor.
- 6. 6 A rotary electric machine whose rotor rotates in synchronization with a rotating field produced by an AC current flowing through its armature winding, is called a synchronous machine. Synchronous machines run at synchronous speed (independent of the loading condition) given by: 120 s f N P Where, ‘f’ is the frequency of the AC current and ‘P’ is the number of poles. Electrical machines which do not run at synchronous speed are called asynchronous machines (e.g. Induction motors).
- 7. 7 In simple terms alternators are the alternating current generators which are widely used in power plants for generating bulk of electricity world wide. Basically there are five different types of alternators: i. Automotive alternators – used in modern automobiles. ii. Diesel-electric alternators – coupled with a diesel engine to generate electricity (Alternators used in Apartments, Multiplexes, etc.). iii. Brushless alternators – used in electrical power generating plants to generate bulk electricity (In Power Plants). Types of Alternator from application point of view: -
- 8. 8 Automotive Alternators Diesel-Electric Alternators
- 9. 9 Brushless alternators: - These alternators are basically used in power plants to generate buck electricity, for example in Hydro-electric power plants, Thermal Power Plants, Nuclear Power Plants etc.
- 10. 10 Schematic Diagram Representing Power Generation in a Thermal Power Station
- 11. 11 Installed Capacity in India as on 29.02.2020. Sources Installed Capacity in MW Coal 2,04,724.50 Gas 24,955.36 Diesel 509.71 Nuclear 6,780.00 Hydro 45,699.22 RES 86,759.19 Total 3,69,427.97
- 12. 12 Installed Capacity in Odisha as on 29.02.2020. Sources Installed Capacity in MW Coal 9,800.00 Gas 0.0 Diesel 0.0 Nuclear 0.0 Hydro 2,124.25 RES 521.69 Total 12,463.94
- 13. 13 Working Principle of alternator: - An alternator works on the principle of Faraday’s Law of Electromagnetic Induction, i.e whenever flux linking with a coil changes an emf is induced in the coil. It can also be described as an emf is induced in a conductor when there is relative velocity between the conductor and a magnetic field (Motional emf). Magnitude of the generated emf in the coil is given by: d e N dt Where ‘N’ is the number of turns in the coil. ‘–ve’ sign indicates that the polarity of induced emf is such that when current flows through the coil it produces a flux to oppose the change of flux causing the generation of emf in the coil (Lenz’s Law).
- 14. 14 Direction of Flux Direction of Current Direction of Flux Direction of Current Direction of Flux Direction of Current Direction of Flux Direction of Current
- 15. 15 Magnitude of the induced emf (Motional emf) can also be determined as: Direction of induced emf/current can also be determined by using Fleming’s Right Rule. sine Blv In this example the direction of magnetic field is towards left, motion of the conductor is upward, so the direction of current is towards the observer. If we mark the polarity of induced emf the end facing the observer (A) is at higher potential (+) with respect to the other terminal (B) (-). ** Current through the source flows from lower potential to higher potential whereas in the external circuit it is from higher potential to lower potential. + - Current A B Where ‘B’ is the magnetic flux density, ‘l’ is the length of the conductor and ‘θ’ is the angle between the magnetic field and velocity.
- 16. 16 N SS N x-axis y-axis (Direction of Magnetic Field) z-axis (Direction of Motion of the Conductor) Direction of induced current/emf I I + - Motion I sine Blv Here ‘θ’ is 2700 (Measured counter clockwise from +z-axis to +y-axis on the yz- plane). So the induced emf is –ve, i.e. if we move through the conductor along the +ve x-axis, there will be a fall in potential (because we will be moving from a higher potential to a lower potential). N SS N x-axis (direction of induced current/emf) y-axis (Direction of Magnetic Field) z-axis I I - Motion + Motion of the conductor Here ‘θ’ is 900 (Measured counter clockwise from -z-axis to +y-axis on the yz-plane). So the induced emf is +ve. v B v B e v B l
- 17. 17 N SS N x-axis y-axis (Direction of Magnetic Field) z-axis (Direction of Motion of the Conductor) Direction of induced current/emf I I + - Motion Lenz’s Law: - By applying the principle of motor operation, (i.e. a current carrying conductor placed inside a magnetic field, experiences a mechanical force) it can be seen that the force experienced by the conductor is opposite to the direction of motion of the conductor causing the generation). Direction of force experienced by the current carrying conductor can also be obtained by using Fleming’s Left Hand Rule. N SS N x-axis (direction of induced current/emf) y-axis (Direction of Magnetic Field) z-axis I I - Motion + Motion of the conductor Force experienced by the current carrying conductor
- 18. 18 Nature of induced emf: - N SS N x-axis y-axis (Direction of Magnetic Field) z-axis (Direction of Motion of the Conductor) Direction of induced current/emf I I + - Motion N SS N x-axis (direction of induced current/emf) y-axis (Direction of Magnetic Field) z-axis I I - Motion + Motion of the conductor Force experienced by the current carrying conductor
- 19. 19 To generate sinusoidally varying emf we need to rotate the conductor so that the angle between the velocity of the conductor and the magnetic filed must change from 0-360 in one cycle of rotation. To achieve this we need to rotate the conductor in a circular path. At position 1, θ=00, at 2, θ=450, at 2, θ=900, at 4, θ=1350, at 5, θ=1800, at 6, θ=2250, at 7, θ=2700, at 8, θ=3150, at 1, θ=3600=00. N SS N Top View N SS N Front View Motion 1 2 37 4 5 6 8
- 20. 20
- 21. 21 One conductor rotating in a magnetic field gives a very small value of induced emf. If we take a single turn coil (two conductors) and rotate it in a magnetic field, we will have an induced emf twice that of with a single conductor. So, in practice a generator has many conductors or coils rotating simultaneously in a magnetic field. + + - - 2 V -2 V
- 22. 22 Thank you