'Residual magnetism' isn't something that's 'necessary'; rather, it's something you're stuck with, whether you want it or not! Residual magnetism is due to a phenomenon called 'hysteresis', which is derived from a Greek word, meaning 'to lag'.
A bit of background first. If we were to wind an insulated coil around the sample of ferromagnetic material, and pass a current through that wire, we would create and apply magnetic field strength (symbol: H), expressed in amperes per metre, to that sample. This results in a magnetic field being set up within the sample, the intensity of which we call its flux density (symbol: B) expressed in teslas.
If we gradually increase the magnetic field strength, the resulting flux density would also increase until a point, called 'saturation' is reached -at this point any further increase in magnetic field strength will NOT increase the flux density. If we were to graph this behaviour, then the result would look something like an elongated 'S', rather than a straight line. This graph is known as a B-H curve.
Now, if we were to reduce the magnetic field strength to zero, the magnetic flux density would also reduce towards zero (following a slightly-different curve) but would not reach zero when the magnetic field strength reaches zero -in other words, when we remove the magnetic field strength, the sample 'retains' some flux density -and we call this 'residual magnetism' or, more accurately, 'residual flux density' or 'remanance'. This is what we mean by 'hysteresis' -i.e. changes in magnetic flux density lag behind changes in magnetic field strength.
To remove this residual flux density, we would actually need to reverse the direction of the magnetic field strength (by reversing the direction of the current through the coil) until the flux density falls to zero.
Different ferromagnetic materials have different values of residual flux density. For example materials that make good permanent magnets have very high values of residual flux density while others, such as metals used to make transformers, electromagnets, etc., have very low values of residual flux density.
To summarise, residual magnetism is something that occurs naturally and the amount of residual magnetism depends on the type of magnetic material involved. It's not a matter of being 'necessary', it's simply a characteristic of ALL magnetic materials.
1
yes
Two things could have occurred. (1) wrong direction of rotation causing loss of residual magnetism or (2) loss of residual magnetism over long period of no use. can be remedied by "flashing" the shunt field winding howlumf
no residual magnetism in the stator. this can happen with an overload which will occasionally even reverse the output polarity
A motor will turn when only the armature is excited, if there is enough residual magnetism in the field.
This case arises only in series dc generator current should be sent around the poles to magnetize. this current can the source(generator). current is passed through poles if it is loaded. but if it is not loaded current is zero through the field. load voltage should be zero actually.but this dont happen.we use generator frequently.due to this poles are partially magnetized this causes some voltage appear called residual voltageAnswerThere's no such thing as 'residual voltage'; you're confusing it with 'residual magnetism', which exists in the magnetic poles of a self-excited d.c. generator and which enables the build-up of its terminal voltage.
Residual magnetism and remanence are the same thing. The term residual magnetism is often used in engineering applications. Both terms describe the magnetization, and measure of that magnetism, left behind in a ferromagnetic material after the external magnetic field is removed.
Residual magnetism is a property in which certain amount of excitation remains back in the conductor even after the removal of the magnets.
Yes. The field is provided by the shunt windings, which are connected in parallel with the supply. You may be confusing a motor with a generator, as you cannot start a shunt generatorwithout residual magnetism.
residual magnetism
It depends on the context in which you are referring to it, but basically Residual Magnetism is that magnetism remaining in the core of an electromagnet after the coil current is removed. In the widest use of the term, it could be used to refer to that magnetism left in a magnetically susceptible substance when it cools past its Curie point, (paleomagnetism is an example of this).
The residual flux will help the phenomenon of changing flux. So that emf generation takes place.
The magnetic field on Mars is only residual, it collapsed many eons ago.
yes
due to residual magnetism
A36 is paramagnetic. It is fairly good conductor of magnetic field, and it will be atracted to magnets strongly. As far as residual magnetism (can it be magnetized) I don't know for sure. I know you can not make usefully strong magnets out of A36 material, but it may have some residual magnetism.
The retained magnetic flux of the material, even after the removal of the external magnetizing force is known as residual magnetism.
Two things could have occurred. (1) wrong direction of rotation causing loss of residual magnetism or (2) loss of residual magnetism over long period of no use. can be remedied by "flashing" the shunt field winding howlumf