What is the reason for not building up of voltage in a separately excited dc generator?

What is the reason for DC generator fails to build up voltage?

The failure of the build up process of a dc generator is caused by no residual magnetism, reversed field connection and high resistance of field circuit.

What is the main reason for the voltage drop in a separately excited DC generator as the load is increased?

The self-excited generator exhibits a greater drop in voltage when load is added because the armature voltage is used to produce the current flow in the shunt field. Each time the voltage decreases, the current flow through the field decreases, causing a decrease in the amount of magnetic flux lines in the pole pieces.

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What are three reasons why voltage build up might not occur in a self excited DC generator?

Causes of failure of voltage build-up or armature heating:

  • No residual magnetism. Without any residual magnetism, voltage build-up cannot start. …
  • High field circuit resistances. If field resistances is more critical resistance then the voltage will not build up. …
  • Speed less than the critical speed.

Why does a self excited DC generator fail to build up?

If the field winding is connected in such a way that the flux produced by the field current opposes the residual flux, the generator fails to build up. … A decrease in the field resistance causes the generator to build up faster to a higher voltage.

What should be done if DC generator fails to build up?

The generator fails to build up if the field winding is connected in a way that the field current does not oppose the residual flux. The problem can be fixed by reversing the direction of rotation or changing the field winding connections.

What causes failure of generator to build up?

Common Causes of Generator Failure

  • Battery Malfunction. There are several things that can cause your battery to fail. …
  • Fuel, Coolant, or Oil Leaks. Fuel leaks often happen due to an issue with the pump system. …
  • Low Coolant. Coolant is what keeps your engine from overheating. …
  • Air in Fuel System. …
  • Poor Maintenance.

What are the conditions to build the voltage in a DC generator?

Conditions to build up the voltage in shunt generator:

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The shunt winding should have a residual magnetic field. The direction of the shunt winding and armature winding should be in such a way that flux generated by them should aid together. The shunt winding should have critical winding resistance.

What is the reason behind dropping down of EMF with load in separately excited DC machine?

The internal characteristic of the separately excited DC generator is obtained by subtracting the drops due to armature reaction from no load voltage. This curve of actually generated voltage (Eg) will be slightly dropping.

What is shunt-wound motor?

shunt-wound in Electrical Engineering

A shunt-wound motor or generator has the field and armature circuits connected in parallel. Current in the field windings of a shunt-wound generator is independent of the load current, because currents in parallel branches are independent of each other.

What are the causes for the failure of self excitation?

What are the causes of failure to excite self excited generator?

  • When magnetism is absent.
  • When the field circuit resistance is more than the cv(critical value).

What are reasons that the terminal voltage of a DC shunt generator drops on load?

Direct-Current Machines

For all d.c. shunt generators, the terminal voltage decreases as the machine is loaded for the following reasons: 1. The e.m.f. generated is reduced due to the effect of armature reaction which causes magnetic saturation at one of the pole tips and hence a reduction in the flux per pole.

Which of the following is not a reason behind failing of self exciting machine?

11. Which of the following is not a reason, behind failing of self-exciting machine? Explanation: In case a and b, machine will tend to destroy the residual magnetism present in a core, which will not excite machine.

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