Mell Under what conditions does the DC shunt generator fail to self excite?
If resistance is de- creased, it will built up to a some- what higher voltage. OR represents the resistance known as critical resistance. If shunt field resistance is greater than this value, the generator will fail to excite.
What will happen if field resistance of self excited generator is decreased?
What will happen if field resistance is decreased? Explanation: When field resistance is decreased, it will increase field current by Ohm’s law. Thus, field resistance line will lie below the older line of field resistance. Eventually, it’ll intersect OCC afterwards causing increase in no-load voltage.
What prevents a generator from exciting?
Shunt or Self-excited As the generator is rotated, the stator supplies input voltage to the AVR. In addition the AVR has sensors that monitor the output of the stator. If a short circuit occurs in the supply to the AVR, the generator will not have an excitation source. This causes a loss of generator power output.
What causes a low value of residual voltage?
Since a small amount of residual magnetism is present in the field poles, a weak residual voltage is induced in the armature as soon as the armature is rotated. This residual voltage produces a weak current in the field circuit. If the direction of armature rotation is reversed, the brush polarity also is reversed.
What is self-excitation in generator?
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. …
How does a self excited generator generate voltage?
The self-excited generator requires some residual magnetism in the field poles in order to generate the voltage. Looking at Figure 2, when the generator is turned, the residual flux induces a small armature voltage (point 1).
What can cause a generator exciter to fail?
A generator exciter could fail for any number of reasons: -critical failure in the supply lines or windings in the form of a broken or open circuit, caused by a loose connection or physical damage or by a short circuit that compromises insulation and burns a break in a wire
What causes a generator to fail to build up voltage?
Reversal of connections of the field winding destroys the residual magnetism which causes the generator failure to build up voltage. 3. In case of dc series wound generators The resistance in the load circuit may be more than its critical resistance, which may be due to (iv) commutator surface dirty or greasy. 4.
What is a failure of shunt generator to build up?
Due to again in transportation, the machine may lose residual magnetism. This difficulty can be overcome by excitation of the field winding from a separate dc source for some time. After this voltage build-up takes place. If field resistances is more critical resistance then the voltage will not build up.