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What is the purpose of field rheostat?
A field rheostat is used to control the current flowing through the field windings of a DC motor or generator. By adjusting the resistance, it alters the strength of the magnetic field, which in turn affects the speed and torque of the motor or the output voltage of the generator. This allows for fine-tuning of performance characteristics in various applications.
Why the armature voltage E changes when the field rheostat is varied in shunt motors?
In shunt motors, the armature voltage ( E ) changes when the field rheostat is varied because altering the resistance in the field circuit affects the field current and, consequently, the magnetic flux produced by the field winding. When the field rheostat is decreased, the field current increases, leading to a stronger magnetic field and a higher back electromotive force (EMF) generated in the armature. This results in a change in the armature voltage, as the increased back EMF reduces the net voltage across the armature. Conversely, increasing the field resistance weakens the magnetic field, reducing back EMF and allowing the armature voltage to rise.
What are the differences of Long shunt vs short shunt generator?
In long shunt the shunt field winding is in parallel to both generator and series field. In short shunt the shunt field is in parallel to generator only.
What are the values of armature and field rheostat to be maintained during starting of a d.c motor?
you want full field while starting 0 Ohms and maximum series on armature then bring the armature resistance to zero as it approaches running speed its a good idea to run with armature at 0 ohms armature will use the same amount of power as the resistor If you want to run at more than base speed you can now weaken the field
Can you use the separately excited shunt generator machine as self excited generator?
You have a seperately excited generator and then you have a shunt generator which has the field winding in parallel with the armature terminals. In DC machines a separately excited generator could be run as a shunt generator provided the field winding is designed to work on the generated voltage. A separately excited alternator needs a DC supply for the field winding. In car alternators that is taken from the main winding via a rectifier and a voltage regulator.
Why motor rheostat kept minimum position generator rheostat maximum position?
the back emf increases so that high currents doesn't pass through the field windings
Why should the generator field rheostat be kept to its maximum at starting?
Keeping the generator field rheostat at its maximum at starting helps to establish a strong magnetic field in the generator, which is essential for generating sufficient voltage to initiate the generation process. This ensures a smooth and stable startup of the generator.
When the rheostat position is changed from minimum position to maximum position in motors what will happens?
the back emf increases so that high currents doesn't pass through the field windings
What is the purpose of field rheostat?
A field rheostat is used to control the current flowing through the field windings of a DC motor or generator. By adjusting the resistance, it alters the strength of the magnetic field, which in turn affects the speed and torque of the motor or the output voltage of the generator. This allows for fine-tuning of performance characteristics in various applications.
Why is the field rheostat of a DC motor kept at minimum position while starting?
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.
What will happen if field rheostat of dc shunt motor is kept at maximum position while starting?
First remember this rheostat is connected in series with the armature to increase the total resistance to limit the starting current, thus achieving max starting torque from the motor
What is critical resistance of the field circuit of a DC generator?
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.
Why the armature voltage E changes when the field rheostat is varied?
This depends on how the motor and wiring. You'll need to provide more information. Series / compound / shunt / differential / self or separately excited / is the rheostat in parallel or series to the field / is the rheostat on the shunt field or series field (if compound)
Define the term critical field resistance?
critical resistance is the maximum resistance beyond which the generator failed to exite. it can b found form the occ of the generator.
How do you select field rheostat range for dc motor?
For a shunt dc motor the rheostat would vary from zero ohms to a value that produces the required minimum field current, but rheostats are not common with shunt motors except as a crude way of controlling the speed. Series dc motors normally use rheostats for starting, especially in trams etc. because the starting torque and current is very high. The rheostat resistance starts at a value equal to the supply voltage divided by the maximum allowable current drawn, and is reduced as the speed builds up.
Why the armature voltage E changes when the field rheostat is varied in shunt motors?
In shunt motors, the armature voltage ( E ) changes when the field rheostat is varied because altering the resistance in the field circuit affects the field current and, consequently, the magnetic flux produced by the field winding. When the field rheostat is decreased, the field current increases, leading to a stronger magnetic field and a higher back electromotive force (EMF) generated in the armature. This results in a change in the armature voltage, as the increased back EMF reduces the net voltage across the armature. Conversely, increasing the field resistance weakens the magnetic field, reducing back EMF and allowing the armature voltage to rise.
Who invented Rheostat?
The rheostat was invented by Sir Charles Wheatstone in the early 19th century. Wheatstone was a prominent English scientist and inventor who made significant contributions to the field of electrical engineering.
