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1. AC Machine اعداد الطالب : مروان بن حليم رقم القيد : 219080232 اشراف : أ.سليمان بن رحمة

2. AC Machine Alternating current (ac) is the primary source of electrical energy. It is less expensive to produce and transmit than direct current. For this reason, and because ac voltage is induced into the armature of all generators, ac machines are generally more practical. May function as a generator (mechanical to electrical) or a motor (electrical to mechanical)

3. DC Machine & AC machine DC motor - ends of the coil connect to a split ring to 'rectify' the emf produced AC motor - no need rectification, so don't need split rings.

4. AC Motor As in the DC motor case, a current is passed through the coil, generating a torque on the coil. Since the current is alternating, the motor will run smoothly only at the frequency of the sine wave

5. AC Generator This process can be described in terms of Faraday's law when you see that the rotation of the coil continually changes the magnetic flux through the coil and therefore generates a voltage

6. Generator and Motor

7. How Does an Electric Generator Work?

8. Classification of AC Machines Two major classes of machines: • Synchronous Generators: A primary source of electrical energy. • Synchronous Motors: Used as motors as well as power factor compensators (synchronous condensers). • Induction Motors: Most widely used electrical motors in both domestic and industrial applications . • Induction Generators: Due to lack of a separate field excitation, these machines are rarely used as generators . Synchronous Machines : Asynchronous (Induction) Machines:

9. Synchronous machines are called ‘synchronous’ because their mechanical shaft speed is directly related to the power system’s line frequency. the rotating air gap field and the rotor rotate at the same speed, called the synchronous speed. Synchronous machines are ac machine that have a field circuit supplied by an external dc source.

10. Application of Synchronous Machines : Synchronous machines are used primarily as generators of electrical power, called synchronous generators or alternators. They are usually large machines generating electrical power at hydro, nuclear, or thermal power stations. Synchronous motors are built in large units compare to induction motors and used for constant speed industrial drives Application as a motor: pumps in generating stations, electric clocks, timers, and so forth where constant speed is desired.

11. Speed and frequency The frequency of the induced voltage is related to the rotor speed by: N S = (rpm) where P is the number of magnetic poles f e is the power line frequency. Typical machines have two-poles, four-poles, and six-poles  

12. Construction • Energy is stored in the inductance • As the rotor moves, there is a change in the energy stored • Either energy is extracted from the magnetic field (and becomes mechanical energy – motor) • Or energy is stored in the magnetic field and eventually flows into the electrical circuit that powers the stator – generator

13. Construction • DC field windings are mounted on the rotor (rotating) - which is thus a rotating electromagnet • AC windings are mounted on the stator ( stationary) resulting in three-phase AC stator voltages and currents The main part in the synchronous machines are i) Rotor ii) Stator

14. Rotor There are two types of rotors used in synchronous machines: i) cylindrical rotors or non sailent pole rotors ii) salient pole rotors Machines with cylindrical rotors are typically found in higher speed higher power applications such as turbogenerators . Salient pole machines are typically found low mechanical speed applications, such as hydrogenerators . Salient pole rotors are less expensive than non sailent pole rotors .

15. Salient Pole Type Poles are mounted on the larger circular frame. Field Winding are connected in series. Ends of the field winding are connected to the DC Supply through Slip Rings Poles are Large Diameter and short Axial Length . Laminated to reduced Eddy Current Losses Employed for Low and Medium Speed 120 to 500 RPM (Diesel & Hydraulic Turbines)

16. Parts rotor of salient pole Spider: It is keyed to the shaft and at at the the outer surface, pole core and pole-shoe are keyed to it Pole core and pole shoe: Pole core provides least reluctance path for the magnetic field and pole shoe distributes the field over the whole periphery uniformly to produce sinusoidal wave form of the generated emf . Field winding: placed around the pole core. DC supply is given to it through slip rings. When direct current flows through the field winding, it produces the required magnetic field . Damper winding: At the outermost periphery, holes are provided which copper bars are inserted and short-circuited at both the sides by rings forming damper winding.

17. Non Salient Pole Type Smooth cylindrical rotor or TURBO ALTERNATOR field winding used in high speed alternators driven by steam turbines . Smaller diameter and larger axial length compared to salient pole type machines. Speed 1200 RPM to 3000 RPM. Better Balancing.. Noiseless operation Flux distribution nearly sine wave

18. Parts of rotor of non-salient pole Rotor core: It is keyed to the shaft. At the outer periphery slots are cut in which exciting coils are placed. It provides an easy path to the magnetic flux . Rotor winding or Exciting winding : It is placed in rotor slots and current is passed through the winding in such a way that poles are formed according to the requirement . Stationary contacts called brushes ride on these slip rings to carry current to the rotating field windings from the dc supply.

19. Salient-pole VS Non salient-pole

20. Stator The outer stationary part of the machine; it has the following important parts : Stator frame: It is the outer body of the machine and it protects the inner parts of the machine. Stator Core: Its function is to provide an easy path for the magnetic lines of force and accommodate the stator winding. Stator Winding: Slots are cut on the inner periphery of the stator core .

21. Stator • Coils are placed in slots • Coil end windings are bent to form the armature winding

22. Synchronous Generator Equivalent circuit model – synchronous generator V ∅ = E A – jX s I A - R A I A

23. If the generator operates at a terminal voltage V T while supplying a load corresponding to an armature current I a , then: E a = V T + I a ( R a + jX d ) In an actual synchronous machine, the reactance is much greater than the armature resistance, in which case: Z s jX d Among the steady-state characteristics of a synchronous generator, its voltage regulation and power-angle characteristics are the most important ones. As for transformers, the voltage regulation of a synchronous generator is defined at a given load as: Percent voltage regulation =  

24. Phasor diagaram of a synchronous generator The phasor diagram is to shows the relationship among the voltages within a phase ( E φ ,V φ , jX S I A and R A I A ) and the current I A in the phase.

25. at power factor is lagging: at power factor is leading:

26. L osses In generators, not all the mechanical power going into a synchronous generator becomes electric power out of the machine The power losses in generator are represented by difference between output power and input power shown in power flow diagram below

27. Losses Rotor - resistance: iron parts moving in a magnetic field causing currents to be generated in the rotor body - resistance of connections to the rotor (slip rings) Stator - Resistance: magnetic losses (e.g., hysteresis) Mechanical - friction at bearings, friction at slip rings Stray load losses - due to non-uniform current distribution

28. L osses The input mechanical power is the shaft power in the generator given by equation: P in = app The power converted from mechanical to electrical form internally is given by P conv = ind P conv = 3E A I A cos Where The real electric output power of the synchronous generator can be expressed in line and phase quantities as P out = V T I L cos P out = 3 I A cos and reactive output power Q out = V T I L s in Q out = 3 I A s in  

29. In real synchronous machines of any size, the armature resistance R A is more than 10 times smaller than the synchronous reactance X S ( X s >> R A ). Therefore, R A can be ignored

30. Synchronous Motor V ∅ = E A + jX s I A + R A I A E A = V ∅ – jX s I A - R A I A

31. Power Flow

32. Thank you