1. open circuit its shunt field resistance should be less then the critical resistance.
2. If excited on load circuits its shunt field resistance should more then a certain minimum value of resistive which is given by internal
This curve is a OCC curve. Rc is critical resistance. Rsh is shunt field resistance.
2. To oversees the opposing self induced e.m.f in the field coil.
If Rsh grater then Rc the generator will failed to excite.
CONDITIONS FOR BUILD-UP OF A SHUNT GENERATOR:
1. There must be some residual magnetism in the generator poles.
2. For the given direction of rotation the shunt field coils should be correctly connected to the armature.
3. If excited on characteristics.
VOLTAGE REGULATION:
The voltage regulation of a DC generator is the change in voltage. When the load is reduced from rated value to zero expressed as a percentage of voltage regulation.
% VR = [VNL – VFL] / VFL
% VR = [VNL – VRL] / VRL
If , Voltage at no load VNL = 240 V
Q: Why you refer less voltage regulation?
ANS
· We prefer terminal voltage constant
· want VFL high so %VR less.
ARMATURE REACTION:
By armature reaction is meant the effect of magnetic field set up by armature current on the distribution of flux under main pole of a generator.
Armature magnetic field has two effect;
demagnetizes or weakens the main flux. So the induced e.m.f in the armature is decreased.
It cross magnetize or distorts it.
2. If excited on load circuits its shunt field resistance should more then a certain minimum value of resistive which is given by internal
This curve is a OCC curve. Rc is critical resistance. Rsh is shunt field resistance.
- Before loading a shunt generator it is allowed to build up its voltage.
- Usually there is always present Residual magnetism in the poles; hence a small E.M.F. is produced initially. This E.M.F. circulates a small current in the field circuit which increases the pole flux. When flux is increased, generated E.M.F is increased which farther increases the flux.
- OA is the induced E.M.F. due to residual magnetism & Oa flowing current.
- This current aids residual flux and hence provides a large induced E.M.F. Oa. In turn, this increased E.M.F Ob causes an even large current Oc which creates more flux for a still large E.M.F.
- Now the generated e.m.f in the armature has
2. To oversees the opposing self induced e.m.f in the field coil.
If Rsh grater then Rc the generator will failed to excite.
CONDITIONS FOR BUILD-UP OF A SHUNT GENERATOR:
1. There must be some residual magnetism in the generator poles.
2. For the given direction of rotation the shunt field coils should be correctly connected to the armature.
3. If excited on characteristics.
VOLTAGE REGULATION:
The voltage regulation of a DC generator is the change in voltage. When the load is reduced from rated value to zero expressed as a percentage of voltage regulation.
% VR = [VNL – VFL] / VFL
% VR = [VNL – VRL] / VRL
If , Voltage at no load VNL = 240 V
Q: Why you refer less voltage regulation?
ANS
· We prefer terminal voltage constant
· want VFL high so %VR less.
ARMATURE REACTION:
By armature reaction is meant the effect of magnetic field set up by armature current on the distribution of flux under main pole of a generator.
Armature magnetic field has two effect;
demagnetizes or weakens the main flux. So the induced e.m.f in the armature is decreased.
It cross magnetize or distorts it.