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13 Cards in this Set
- Front
- Back
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what is torque? what role does torque play in rotational motion of machines?
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-a twisting movement of force along the axis of a rotating body
-helpful in increasing the speed of the rotating object |
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reluctance
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-the property of the core to oppose the flow of magnetic flux through it.
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ferromagnetic material
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material whose permeability is very much larger than 1 and which exhibits hysteresis phenomena
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hysteresis
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-the amount of flux present in the core not only depends on the current supplied to the winding of the core, but also on the previous history of the flux in the core. This dependency on the preceding flux history and the resulting failure to retrace flux path is called hysteresis. a loss
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what are eddy current losses? what can be done to minimize eddy current losses in a core?
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When a piece of iron is placed in a continuously changing magnetic field, then according to faradays law, an EMF is induced in that iron due to mutual induction. Since iron bar acts as a closed circuit, circulating current will be developed in the iron bar and also the iron bar has some resistance to the currents induced in the bar. this resistance causes some power to be lost in the core. these currents are eddy currents and the losses are eddy current losses. to reduce eddy current losses you can laminate the core which reduces the thickness of the core. when you reduce the thickness of the core the resistance of the core will go up which will reduce the losses of the eddy currents.
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Faradays Law
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if a flux passes through a turn of a coil of a wire, a voltage will be induced in the turn of wire.
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what conditions are necessary for a magnetic field to produce a force on a wire?
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F = ilBsin(theta)
-there should be a magnetic field of flux density B -there should be a current flow in the conductor -the angle between the conductor and field axis should be less than 90 |
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What conditions are necessary for a magnetic field to produce a voltage in a wire
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eind= Blvsin(theta)
-there should be a magnetic field of flux density B -the conductor should be moved with some velocity -the angle between conductor axis and field axis < 90 |
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will the current be leading or lagging voltage in an inductive load? will the reactive power of the load be positive or negative?
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-current in an inductive load is lagging the supply voltage by theta degrees.
-since the impedance angle is positive for inductive loads, the reactive power of the load is also positive |
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real power
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P=VIcos()
-component of power supplied by the load, which is actually consumed by the load. -watts(W) |
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reactive power
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Q=VIsin()
-the power that continuously bounces back and forth between the source and the load. represents the energy that is first stored and then released in the magnetic field of an inductor or the electric field of a capacitor -volt-amperes reactive(var) |
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apparent power
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S=VI
-the product of voltage across the load and the current flowing through the load. the apparent power is the actual power that is supplied to the load if the phase angle differences between voltage and current are ignored. |
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power factor
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PF = cos(), where theta is the impedance angle of the load
-in power triangle the quantity 'cos()' is known as the power factor of the load. the fraction of the apparent power S that is actually supplying the real power to a load. |
