Electrical Engineering

# Why doesnt a field coil in a DC shunt motor lead to short ciruit when it is a fact that an INDUCTOR is a short circuit to DC?

123 ###### 2009-04-08 03:55:54

Yes, an inductor is a short circuit to dc...that's true....IF the inductor is an ideal one, that is, the inductor has no resistance but has inductance only. Anything in real world, as you know, is not ideal. An inductor is usually made of a copper wire. A copper wire has its own resistance. If an inductor coil is thin and long (i.e. many turns), it will provide an appreciable resistance to DC, and will no longer be a short circuit.

🙏
0
🤨
0
😮
0
😂
0

## Related Questions A circuit is a path for charge particles -- it conducts current. An inductor, a circuit component, generates a magnetic field, when an AC is on. ====================== The purpose of an inductor is to store and release energy in the circuit usually in order to induce a phase shift in the voltage or current passing through it. Inductor stores energy in the magnetic field. Good question! I am a science freak. a tank circuit is basically a circuit of a capacitor and a inductor. A capacitor stores voltage, usually from a battery An inductor is a coil of wires. Whenever a voltage (think of electricity)run across the inductor (think of it as running through it), it creates a magnetic field. basically the capacitor is filled up usually with a battery, and then it comes out the other end of the capacitor through the wire to the inductor which makes a magnetic field and the vice versa. They just keep exchanging. A capacitor appears as a short circuit to AC. An Inductor appears as a short circit to DC. Capacitor stores electrical energy in the form of Voltage, E= 1/2CV2 , Where as an Inductor stores Electrical energy in terms of current, E = 1/2LI2. 1. Capacitor stores an electric field, whereas inductor stores a magnetic field. 2. Capacitor is open circuit for DC, and inductor is short circuit for DC. 3. In an AC circuit, for capacitor, voltage 'lags' current, whereas for inductor, current 'lags' voltage. 4. Energy stored in a capacitor is calculated in terms of voltage (1/2 x CV2), and this is done in terms of current for inductor (1/2 x LI2) Electrikals... An inductor resists a change in current through the creation/destruction of the magnetic field around the inductor. In an IR Circuit, when the electromotive force (the battery voltage) changes, the inductor will create a voltage to oppose the change, causing the current flowing through the circuit to change gradually over time rather than instantaneously. In an ideal IR circuit, the induced voltage is initially equal and opposite to the change in electromotive force, and it decays exponentially, with a time constant proportional to the inductance of the circuit. As current flows in the inductor, a magnetic field is produced. If the current is turned off, as the magnetic field collapses, it induces a voltage in the inductor windings, like a generator. Thus the inductor stores energy in the form of a magnetic field. DC current has no effect on the inductor(can be considered as a short circuit) as the current does not change in a DC supply voltage this one just produces a magnetic field which remains constant , as the magnetic field is not varying no emf is induced in the circuit , so literally it has no effect on the circuit when the supply is of DC voltage.when an alternating current is set up in a circuit , the Alternating current brings a magnetic field in the inductor which is variable (since the current is varying...) this variable magnetic field induces an emf in the circuit (back emf) which opposes the cause that is producing the change (lenz's law)explanation consider a circuit with an inductor connected to an AC voltageduring the positive half cycle when the voltage increases the current also increases in the circuit [take the current direction as clockwise] this causes a variable increasing magnetic field in the inductor , this magnetic field in turn induces current in the circuit which is opposing the increase in the current flow from the original source, the inverse happen during the decreasing half of the half of the positive cycle , here the induced current adds up with the decreasing current opposing the cause that produced this back current (cause :- decrease in current changes the magnetic field so the induced current is produced ..... it is opposing the change because :- the induced current either decreases the increasing current or increases the decreasing current ) Yes, inductors can be said to "absorb" or "store" electrical energy. This energy is stored in the magnetic field that forms around the windings as current flow through the inductor increases. When current through the inductor begins to decrease, the field begins to collapse. The collapsing field generates an electromotive force (EMF) in the windings that opposes the decrease in current. In this way, energy that was stored in the inductor is returned to the circuit, but an a later time. The "delay" here sets the stage for phase shift, but that's another question. A electromagnetic field works by an electrical current flowing through an inductor which induces a magnetic field, as soon as the electrical current is switched off to the inductor, the electromagnetic field collapses. Since DC has zero frequency, hence according to formula X=2*3.14*f(f being frequency), inductance is zero. That is inductor behaves as a short circuit. Now when DC supply is given across inductor, current is first raised from zero to some value, during this period (change of current fromzero to some value), energy in inductor is stored in form of magneticg field. As soon as DC current reaches to its steady value, inductor is equivalent to short circuit to direct current. No self induced emf is produced and Voltage across inductor is zero. When inductor is taken out from the circuit, Vl(voltage across inductor) changes its polarity and goes from zero to negative value but Il (current through inductor) maintains the same direction and magnitude. The energy stored in inductor decays through the resistor and voltage Vl rises gradually to zero and current Il drops gradually to zero. inductor use both ac and dc as per requirment or ratings in dc a inductor generate constant magnetic field.in ac system rotating magnetic field created by inductor The function of an inductor is to store electrical energy in a magnetic field. Inductors resist a change in the flow of the electrons. When you pass a current through an inductor it builds up a magnetic field. When the current source is removed, the magnetic field collapses. The collapsing field induces a voltage in the inductor, returning energy to the circuit. The polarity of the induced voltage is opposite the polarity of the original magnetizing current. ======================= -- When you start pushing current through it, the current rises slower than you push it, because building up the magnetic field takes energy. That energy is stored in the magnetic field. -- When you stop pushing current through it, the current keeps flowing for a while anyway. That's the stored energy pouring out of the magnetic field. AnswerWhen you connect DC voltage to an inductor, it opposes the passage of current, which generates a voltage pulse the is several times the value of the applied voltage. When you disconnect the voltage, the electromagnetic field inside the inductor collapses and all the energy it stored is released to the circuit in the form of another large pulse, but this time with opposite polarity.Remember:Inductors oppose changes in current and they store energy in an electromagnetic field.Capacitor oppose changes in voltage and they store energy in an electrostatic field. When you close an inductive circuit, since an inductor resists a change in current, the initial reaction of the load is to look like a high resistance. As current builds, the resistance falls. With a theoretical source and inductor, current would eventually reach infinity, that is after infinite time, but practical sources and inductors will reach a plateau current. When you open an inductive circuit, again, since an inductor resists a change in current, the inductor attempts to maintain that current, but there is no conductivity for that current so, the inductor presents a high voltage spike in the reverse direction it was initially "charged" with. With a theoretical inductor, and theoretical infinite impedance, the voltage spike would be infinite. Again, practical inductors have a maximum voltage spike, but this spike can still be quite high, even thousands of volts, which can damage the circuit, so it is important to maintain a conduction path for the collapsing field, often a diode, or a resistor/capacitor filter. Yes. That's exactly the situation in the magnetic field of an inductor (coil),or in the dielectric of a capacitor. Both of those circuit elements are energy-storage devices. Well, first of all, nobody ever claimed that the energy is stored 'in the inductor'.The energy is stored in the inductor's magnetic field.Next: When they say that energy is stored, it doesn't necessarily mean that it'sstored like in a box or a jar, and you can fill it up, put it up on the shelf, then comeback and get it in a few days.The energy stored in the magnetic field is steady as long as the current through theinductor is steady. If the current is changing, then the energy in the magnetic fieldis also changing. When the energy in the magnetic field is decreasing, then of coursethe magnetic field is returning some of its stored energy to the circuit, by way of thecurrent. The Nature of InductanceAn inductor is, simply put, an electromagnet, the like of which many of us played with as children. A current through a wire is a flow of charges, and the movement of these charges generates a sort of 'wake' in spacetime, much like the wake of a ship on the ocean. We refer to this wake as a magnetic field, and the equation describing this is called Ampere's Law, which is one of Maxwell's Equations. When an inductor is first activated (when current begins), the flow of charge begins to set up a magnetic field in and around the coil. Since a magnetic field is a real thing, a kind of distortion of spacetime, the act of creating a magnetic field requires energy, and the inductor harvests the energy of the electrons to accomplish this. As a result, the electrons slow, and the inductor can be said to 'resist changes in current' by harvesting and storing energy.Naturally, there is a maximum magnetic field associated with any voltage, just as there is a maximum wake that can be generated by a ship moving at a given speed. When the inductor is 'fully magnetized,' when the magnetic field of the inductor is as large as the given current can possibly support, it stops harvesting energy from the circuit and simply holds on to the steady magnetic field that it has created. If the voltage should decrease, the magnetic field begins to collapse, depositing that energy back into the electrons, speeding them along. Thus, again, an inductor 'resists changes in current' by discharging energy.In conclusion, inductors create magnetic fields for energy storage, and they have a maximum storage of energy for a given voltage. In a 'DC circuit,' the inductor has had sufficient time to build up it's storage of energy and no longer harvests energy from the stream of electrons. It is 'full.'This also explains why the impedance of an inductor is said to be low at low frequencies, where the inductor has time to charge and discharge itself to keep up with the slowly changing voltages, and why that impedance is high at high frequencies, where the inductor is racing to keep up with the changes, constantly harvesting and spitting back energy. An inductor resists a change in current. It does this by converting the current into a magnetic field. If the current then changes, the collapsing or increasing magnetic field will buck the attempted change through electromagnetic energy conversion.

###### ScienceElectronics EngineeringHome ElectricityElectrical EngineeringPhysicsCircuitsElectrical WiringEnergy Copyright © 2020 Multiply Media, LLC. All Rights Reserved. The material on this site can not be reproduced, distributed, transmitted, cached or otherwise used, except with prior written permission of Multiply.