Lecture 7
Download as PPTX, PDF0 likes1,411 views
The document discusses different topics related to electrical machines including: 1. Commutation and armature construction in real DC machines, including different winding types like lap, wave, and frog-leg windings. 2. Problems with commutation in real machines such as armature reaction and L di/dt voltages, and solutions like brush shifting and commutating poles. 3. The internal generated voltage and induced torque equations of real DC machines. It also provides more details on the lap winding, describing its features such as the number of parallel current paths equal to the number of poles.
![IE243 ELECTRICAL MACHINES–I
[Cr. Hrs = 3+1] [Marks: 100+50]
By
Asif Ahmed Memon](https://image.slidesharecdn.com/lecture7-150208111322-conversion-gate02/85/Lecture-7-1-320.jpg)
Lecture 7
- 1. IE243 ELECTRICAL MACHINES–I [Cr. Hrs = 3+1] [Marks: 100+50] By Asif Ahmed Memon
- 2. • COMMUTATION AND ARMATURE CONSTRUCTION IN REAL DC MACHINES – The Rotor Coils – Connections to the Commutator Segments • The Lap Winding • The Wave Winding • The Frog-Leg Winding • PROBLEMS WITH COMMUTATION IN REAL MACHINES – Armature Reaction – L di/dt Voltages • Solutions to the Problems with Commutation – BRUSH SHIFTING – COMMUTATING POLES OR INTERPOLES – COMPENSATING WINDINGS • THE INTERNAL GENERATED VOLTAGE AND INDUCED TORQUE EQUATIONS OF REAL DC MACHINES • THE CONSTRUCTION OF DC MACHINES – Pole and Frame Construction – Rotor or Armature Construction – Commutator and Brushes – Winding Insulation • POWER FLOW AND LOSSES IN DC MACHINES
- 3. The Lap Winding lap winding is a rotor winding consisting of coils containing one or more turns of wire with the two ends of each coil coming out at adjacent commutator segments
- 4. The Lap Winding • An interesting feature of simplex lap windings is that there are as many parallel current paths through the machine as there are poles on the machine. • If C is the number of coils and commutator segments present in the rotor and P is the number of poles on the machine, then there will be C/P coils in each of the P parallel current paths through the machine. • The fact that there are P current paths also requires that there be as many brushes on the machine as there are poles in order to tap all the current paths. This idea is illustrated by the simple four-pole motor in Figure 8-15. Notice that, for this motor, there are four current paths through the rotor, each having an equal voltage. • The fact that there are many current paths in a multi pole machine makes the lap winding an ideal choice for fairly low-voltage, high- current machines, since the high currents required can be split among the several different current paths. This current splitting permits the size of individual rotor conductors to remain reasonable even when the total current becomes extremely large.
- 7. The Wave Winding In wave winding, every other rotor coil connects back to a commutator segment adjacent to the beginning of the first coil. Therefore, there are two coils in series between the adjacent commutator segments. Since each pair of coils between adjacent segments has a side under each pole face, all output voltages are the sum of the effects of every pole, and there can be no voltage imbalances.