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Inductance & Inductive Reactance
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Terms in this set (17)
Factors that affect the inductance of a coil
- number of turns
- permeability
- length of magnetic path
- area
Inductance
The property of a circuit that opposes a change in current. Symbol: L
Unit of measure: Henry
U.O.M. Symbol: H
Induction
The process by which a voltage is produced by the interaction of a conductor and a magnetic field.
Faraday's law
The amount of induced EMF is directly proportional to the rate of change of flux
Three factors that affect the rate of change of flux
- rotational frequency
- flux density
- the angle of cutting
Mutual induction
The generation of an EMF in one conductor or circuit by a change of flux around a separate conductor or circuit.
Transformers
Self induction
The generation of an EMF in a conductor or circuit by a change of flux in the same circuit
Coils (motors, relay coils), transformers
Lenz's law
The polarity of an induced voltage must be such that any current resulting from it will develop a flux that tends to oppose any change in the original flux
And induced voltage will oppose the change that produced it. CEMF
Factors that affect counter EMF
- the inductance of the coil
- the rate of change of current
RL time constant
The inductance of the circuit divided by the resistance. Requires approximately five time constants to reach the maximum or steady-state value. Each time constant will change the current by 63.2%
Formula: t=L/R
Discharge resistor
A resistor connected across the coil to reduce the inductive kick. Reduces arcing at the switch when inductive circuit is opened
Inductive kick
The collapsing magnetic field of a conductor can induce a very high voltage into the circuit. It is dangerous
Inductive reactance
The opposition created by inductance in an AC circuit
Two factors affecting inductive reactance
- Inductance
- frequency
Inductor with DC source
When current is increasing (rate of change of current is maximum)the induced voltage is maximum. When current is zero (starting to increase so rate of change is maximum) the induced voltage is maximum. When the current is maximum the induced voltage is zero
Inductor with AC source
When current is zero the induced voltage is maximum. When current is maximum the induced voltage is zero. Current lags voltage by 90°
Reactive power
The rate at which energy is stored and then returned to the circuit. The product of the reactive voltage and the reactive current
Measured in volt-ampere reactive
Unit of measure: VAR
Symbol: Q
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