Direct machines working full in Cont.pptx

DC m/c

1. DC Machine Parts Parts of DC Machine (motor and generator) Field magnet The objective of the field system is to create a uniform magnetic field in which the armature rotates. Permanent magnet or electromagnet  Armature Coils of wounded(insulated) wires around an iron. Consists of the core,  the winding, the commutator, & the shaft. Commutator In case of a generator, convert AC voltage into DC voltage. In the case of the motor, the commutator use to produce unidirectional torque. Brush The brushes are used to collect the current from the commutator and supplied to external load circuit of DC Generator. In case of dc motor brushes supply current to the commutator .

2. DC Machine Parts ( Field magnets )

3. DC Armature Windings Armature core

4. DC Armature Windings The slots of the armature core hold insulated conductors that are connected in a suitable manner. This is known as armature winding. In armature winding the working e.m.f is induced.

5. DC Armature Windings Turn : Each loop of wire is called a turn. A turn consists of two conductors connected to one end by an end connector. Coil : A coil is formed by connecting several turns in the series. Winding : A winding is formed by connecting several coils in series.

6. DC Armature Windings The armature conductors are connected to form coils The basic component of all types of armature windings is the armature coil. Each turn insulated from others and from the rotor. Number of conductors in a machine Z=2CNc C = # of coils on rotor Nc = # of turns per coil

7. DC Armature Windings Most of DC armature windings are double layer windings i.e., there are two coil sides per slot. One coil side of a coil lies at the top of a slot and the other coil side lies at the bottom of some other slot.

8. DC Armature Windings Full pitch coil Fractional pitch coil I n terms of armature slots or armature conductors

9. Cont.. Commutator Pitch (Y C ) The number of commutator segments spanned by each coil of the winding. Commutator segments

10. If the end of a coil is connected to a commutator segment ahead of the one its beginning is connected to, the winding is called a progressive winding . If the end of a coil is connected to a commutator segment behind the one its beginning is connected to, the winding is called a retrogressive winding. progressive winding. retrogressive winding. Cont..

11. Armature windings are classified according to the sequence of their connections to the commutator segments Lap Windings Wave Winding Cont..

12. The simplest type of winding construction used in modern DC machines Consists of coils containing one or more turns of wire with the two ends of each coil coming out at adjacent commutator segments The Lap Winding

13. If the end of the coil is connected to the segment after the segment that the beginning of the coil is connected to, the winding is a progressive lap winding and Yc = 1. If the end of the coil is connected to the segment before the segment that the beginning of the coil is connected to, the winding is a retrogressive lap winding and Yc = -1. Progressive lap winding. retrogressive lap winding. The Lap Winding

14. The Lap Winding Simplex Lap Winding –  The distance between the segments of commutator to which the coil ends are connected is 1. Thus commutator pitch is unity. Duplex lap Winding –  In duplex lap winding, the commutator pitch is 2. This means if one coil end is connected to commutator segment 1 then the other is connected to segment 3. Triplex Lap Winding –  The commutator pitch for triplex winding is 3. This means if one coil end is connected to commutator segment 1 then the other is connected to segment 4 M- plex Lap Winding Yc =m Number of current paths, a = mP

15. The Wave Winding The end of one coil is connected to the starting of another coil of the same polarity as that of the first coil. This winding forms a wave with its coil, that’s why called as wave winding Since the coils are connected in series here, also called as series winding.

16. 16 8.2 Commutation in 4 Loop DC Machine Commutation is the process of converting the ac voltages and currents in the rotor of a dc machine to dc voltages and currents at its terminals 4 Loop 2 Pole DC Machine 4 complete loops in slots in rotor Uniform air gap width Uniform Flux Density under pole faces "unprimed" end e.g. (1) of each loop is the outermost wire in each slot, while the "primed" end e.g (1’) of each loop is the innermost wire in the slot directly opposite

17. 8.3 Commutation & Armature Constr - DC Machine several ways in which the loops on the rotor (also called the armature) can be connected to its commutator segments These different connections affect the number of parallel current paths within the rotor The output voltage of the rotor the number and position of the brushes riding on the commutator segments

18. Simplex lap winding Number of parallel paths = Number of poles Number of brushes = number of poles Normally, a coil spans 180 e lec trica l degr ees . Thi s means that when one si de is u nde r the center of a given magnetic pole, the other si de is u n d er the center of a pole of opposite p olarity. T he physical p ole s may not be located 180 me chanica l deg r ees apart

19. 2 pole, 4 slot double layer lap winding Ɵ m = 180

20. 8.3 Commutation & Armature Constr - DC Machine Winding Diagram