The value of resistance of shunt field winding beyond which the shunt generator fails to build up its voltage is known as " critical resistance
at a given speed it is the maximum field resistance with which the shunt generator excite.
critical resistance is the maximum resistance beyond which the generator failed to exite. it can b found form the occ of the generator.
Checked Stephen J. Chapman's Electric Machinery Fundamentals page 287. It says: Short Circuit Ratio (SCR) for the synchronous generator is the ratio of the field current required for the rated voltage at OPEN circuit to the field current require for the rated armature current at SHORT circuit.
If you are talking about the field rheostat on a generator, once you have the correct voltage output set, it is very unlikely that it has to be touched again. If it is the generator's first start up, then it is best to set the field on the low side so as not to over excite the generator and drive the output voltage higher that what the generator's specifications are rated at. The field excitation voltage does not have to be set at the minimum position on every start up once it is set for the correct output voltage. A good example of this is a hospital standby generator, it starts up with no human intervention needed.
rectification to the negative voltage
The stationary part of any motor or generator is termed the 'stator', and the rotating part is termed the 'rotor'.The stator comprises the main frame (chassis), the magnetic circuit, and field windings.
critical resistance is the maximum resistance beyond which the generator failed to exite. it can b found form the occ of the generator.
More due to the impedance levels in the generator
the shunt generator wont be started .hehe
Critical field resistance is the limiting resistance, above which a field will not excite
it doesn't develop emf ..........
1. Field Flashing. 2. Resistance of the filed winding should be less than critical field resistance. 3. Speed of the motor should be greater than critical speed. 4. Interchange the field connections. 5. Check the commutator surface and brush.
Possible reasons for failure of voltage buildup... 1) No residual Magnetism, 2) Field connection may be in reverse manner, 3) Field resistance is greater than critical resistance, 4) Speed is less than Critical speed.
self excited generator must be started without any external load attached ,an external load will continuously drain off the build up voltage and prevent the generator from reaching its proper operating voltage. also the presence of residual magnetism plays an important role And the field current resistance should be less than critic field circuit resistance
Checked Stephen J. Chapman's Electric Machinery Fundamentals page 287. It says: Short Circuit Ratio (SCR) for the synchronous generator is the ratio of the field current required for the rated voltage at OPEN circuit to the field current require for the rated armature current at SHORT circuit.
The rotor must have a magnetic field in order to generator voltage in stator winding. The exciter circuit generates this DC filed in the rotor.
The amount of current produced in the armature of a generator is primarily determined by the voltage induced in the armature winding, the resistance of the circuit, and the load connected to the generator. According to Ohm's Law, current (I) is equal to voltage (V) divided by resistance (R) (I = V/R). Additionally, factors such as the speed of rotation of the generator, the strength of the magnetic field, and the number of turns in the coil also influence the induced voltage and, consequently, the current generated.
Code 41 means an open or shorted condition detected in the generator field control circuit