Parallel operation of DC Shunt generator
Parallel operation of DC shunt generator is similar to the operation of two storage batteries in parallel.
- In the case of generators we can alter the external characteristics easily while it is not possible with batteries.
- Before connecting the two machines the voltages of the two machines are made equal and opposing inside the loop formed by the two machines.
- This avoids a circulating current between the machines. The circulating current produces power loss even when the load is not connected.
- In the case of the loaded machine the difference in the induced emf makes the load sharing unequal.
Load Sharing of Parallel Connected DC Generators
- The load sharing between shunt generators in parallel can be easily regulated because of their drooping characteristics.
- The load may be shifted from one generator to another merely by adjusting the field excitation. Let us discuss the load sharing of two generators which have unequal no-load voltages.
- Let E1, E2 = no-load voltages of the two generators
- R1, R2 = their armature resistances
- V = common terminal voltage (Bus-bars voltage)
Then V = E1 − I1R1
= E2 − I2R2
- Thus current output of the generators depends upon the values of E1 and E2. These values may be changed by field rheostats.
- The common terminal bus-bar voltage will depend upon
- the emfs of individual generators and
- the total load current supplied.
- It is generally desired to keep the bus-bars voltage constant. T