DC Inductance

When the current reaches a steady state, the inductor will behave exactly like a resistor. If the power dissipated by the 'inductor' (= current through it X voltage across it) is too high then yes, it will burn, just as any resistor would.

^{_{Note to self - give up while you're ahead.}}

thats it

but then how this concept is over come in dc motor

if u can means plz explain me

TonyS provides a very good link in #3.

I'll try a short answer. I don't think that there is such a thing as a "DC motor". There are motors that you power with a DC voltage but I'll bet every one (except possibly a simple solenoid) uses brushes or circuits to cut, chop or switch the voltage and therefore cycle the magnetic field.

Homopolar (sometimes called unipolar or monopolar) motor is an example of a DC motor that although it does uses brushes, but there is no chopping, cutting, or switching of the voltage involved and the magnetic field does not cycle.

It's true it rotates but it is not actually a motor. A motor is destined to drive something!

'...A motor is destined to drive something!....'

.

As in the way a rail gun or mass driver 'drives' something?

This answer is technically correct, but is not likely to be helpful to someone trying to sort out all the "inductive" effects - and should not be rated as a good answer.

Not all of the effects - I was just clearing up OP's 1).

Knock the GA off if you want - I don't give a bugger.

Click HERE

If the inductor is burning, then reduce the applied voltage until it doesn't.

The Link TonyS provides is good, but takes a while to read.

First thing to understand is that there is more than one thing happening at a time in a DC motor and except for magnetic saturation (can ignore at this level) each sort of does its own thing regardless of the other.

The main "motor/force" part is that a current flowing in a wire in a magnetic field will cause a force at a right angle to the direction of the field and the wire. This is a "x y z" vector thing in the physical world and in mathematics is called a cross- product. The magnitude of the force is in the formula Force= B x I x L (i.e. Magnetic Flux Density x Current x Wire Length).

If that "wire" is put in a structure that makes it move in a circular path, then you have the start of a DC motor (a rotor is just a lot of these "wire lengths" connected together as a coil). Because the force acts at right angles to the magnetic flux lines, if we do nothing else the torque will vary sinusoidally from max positive through zero to max negatives the "wire" rotates around. So to stop the "wire" (i.e. rotor) from fluttering back and forth and to keep it moving the same way and make a motor, we reverse either the magnetic field direction OR current direction at just the right time. This is a simple physical issue and a commutator is typically used change the direction of the rotor current.

You will note that I've not mentioned inductance so far and that we already have a motor.....but there other effects to consider if you want to design something that works as you expect.

To keep things simple, we will just talk about a normal old style motor with a static DC current in a couple of outer field coils that generate the magnetic field across an air gap that a rotor spins in (the rotor is also made of iron to reduce the thickness of this air gap and help make a strong magnetic field with only a small field current). And as mentioned before we assume a commutator is used to switch the current in the rotor.

Every time the rotor current is reversed in direction, there will be inductance effects and iron losses just as if it were outside the motor and supplied independently, HOWEVER, there is one other important difference and that is that the rotor will be spinning and the rotor wires cutting through magnetic flux when the motor is running.

BECAUSE the rotor is spinning in a direction that the current in the rotor causes, the wires in the rotor a forced to cut the field lines of that same magnetic field that BUT(according to the same rules as for inductance) this is always in the direction that works to stop the existing current - this is why it is called a "back emf". The back emf generated by rotor movement is a major voltage and it is he difference between a normal operating motor with modest rotor currents and a stalled or nearly stalled motor with high rotor currents that will quickly heat up and burn out.

You might confuse back emf with inductance because the same rate cutting of flux formulae apply, and because there are minor self inductance and iron losses etc associated with the rotor and its varying current - but the magnitude and origins of the phenomena are different and are calculated/modelled separately.

A concise overview.

An Inductance in a DC circuit is used to produce a Magnetic filed.

In a DC motor and a Generator exciter, the same thing happens. A magnetic field is generated.

DC Motor: An extra circuit provides, via a commutator, a current to the rotor windings. This also is an inductance, but the magnetic field generated is neglected. What is important here is the current flow in the magnetic field generated by the field windings (Inductance?).

Exciter: Here, also, a magnetic field is generated. Now the reverse action (to the DC motor) happens, whereby the movement of the rotor (driven),within the magnetic field, will generate a current etc.

You will find the same effect in almost any electromagnet.

The reson they dont burn out is because of the resistance of the wire in the windings.

The field coils in a Generator or alternator have sufficiently high resistance which limits current flow and therefore dont burn out when DC is applied.

The Stator windings in DC motor on the other hand may actually burn out if the motor is stalled for long enough - in normal operation the current flow into the windings is switched so therefore not strictly DC. Switching could be be produced by poles in the comutator or an external control system.

"The Stator windings in DC motor .. may ... burn out if the motor is stalled for long enough - in normal operation the current flow into the windings is switched..."

You sure about that?

You sure about that?

No

Would you believe armature windings