Parallel Operation Of DC Series Generator
The interesting thing about the parallel operation of DC series generator is that DC series generators are not usually employed for supply of power. Instead DC series motors are arranged in parallel to operate as DC series generators during Electric Braking.
- Series generators are rarely used in industry for supplying loads. Some applications like electric braking may employ them and operate two or more series generates in parallel.
- The excitation of the machine I increases, increasing the load current delivered. As the total current is I the current supplied by machine II reduces, so also its excitation and induced emf.
- Thus machine I takes greater and greater fraction of the load current with machine II shedding its load. Ultimately the current of machine II becomes negative and it also loads the first machine.
- Virtually there is a short circuit of the two sources, the whole process is thus highly unstable. One remedy is for a problem as this is to make the two fields immune to the circulating current between the machines.
- With the equalizer present, a momentary disturbance does not put the two machines out of action.
- A tendency to supply a larger current by a machine strengthens the field of the next machine and increases its induced emf . This brings in stable conditions for operation rapidly.
- Here comes the use of equalizer bars in the parallel operation of DC series generators. The possibility of reversal of either machine can be prevented by preventing the flow of circulating current produced due to inequalities of induced emfs of the machines through the series field winding.
- This Aim can be achieved by connecting a heavy copper bar of negligible resistance across the two machines as shown in the figure.
- Now the circulating current does not affect the field winding, but it get confined to the armature and the equalizing bars.
- Now if the armature current increases, the terminal voltage drop occurs and the original condition is restored.