What do you mean by build up voltage?
Because of presence of small residual flux in the field poles, DC Shunt Generator will have a small voltage at its terminal even though the switch S is open when driven at rated speed. …
How the voltage is built up in a dc shunt generator?
Voltage building in shunt generator: When the armature is rotated, the residual flux in the field winding will induce a small voltage in the armature. The induced voltage in armature generates a flux and it will aid with field flux and the net flux will increase further.
What are the causes of failure to build up voltage?
No residual magnetism, reversed field connection and high resistance of field circuit are responsible for the failure of build up process of a dc generator.
How the voltage is buildup when field current is zero?
If field circuit is open then there is no field flux i.e. no voltage build up. Now, if we reduce the field current to zero then due to residual magnetism property of the field core it would hold some flux which leads to slightly increase the voltage above 6 Volt.
What is self excitation system?
a kind of excitation of generators where the magnetic field of the main poles is excited by a current supplied to the windings of the main poles from the armature (rotor) winding. Self-excitation is made use of most often in DC generators.
What are the causes for the failure of self excitation?
Reasons for failure of self exication of DC generator
- Absence of Resuidal Magnetism.
- Wrong field winding connection.
- Wrong direction of Rotation.
- Resistance of Field-winding (Rf) > Critical Resistance (Rc)
- Speed of Rotation (N)< Critical speed (Nc)
What is necessary condition for voltage build up in self excited?
What is/are the necessary conditions for voltage build up in self excited generator? Poles should contain residual flux. Field winding should be properly connected to armature winding. Field winding resistance should be less than critical resistance.
What causes voltage buildup in a self excited generator?
In Brief, the following condition must be satisfied for voltage buildup in a self-excited generator. There must be sufficient residual flux in the field poles. the field terminal should be connected such a way that the field current increases flux in the direction of residual flux.
How does voltage build up in a shunt generator?
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.
What are the essential conditions of the voltage build up of a self?
You need sufficient residual magnetization in the field coil’s iron to get generation started. Otherwise, “flashing” the field coil with an external source may be necessary to start, e.g. at initial start-up with a previously unmagnetizwd coil core.
What happens when the voltage build up is reversed?
Under this condition, the voltage buildup is in the reversed direction. Obviously, the generator will operate at rated voltage but with reversed polarity. If desired, the reversed polarity can be corrected by using an external d.c. source to remagnetise the field poles in the correct direction. This procedure is known as field flashing.