Induction and Inductive Reactance Flashcards
What is an inductor?
Insulated wire wound around a core.
Air, ceramic, plastic or iron are all considered acceptable core materials.
Yes, however they will all differ in magnetic strength.
What kind of electrical equipment utilize coils?
Motors, transformers, solenoid valves, relays and contactors, electromagnetic lighting ballasts, and line reactors for VFDs.
When a symbol for a core is drawn with two parallel lines next to it, whet is signified by this addition?
The core is a magnetic material like iron.
What factors will affect the inductance of a coil?
The number of wraps of wire,
permeability of the core,
cross-sectional area of the core,
and the length of the magnetic path.
The symbol for inductance is ______, it is measured in ______.
L,
Henrys (H).
What is inductance?
The property of a circuit to oppose a change in current.
What does Faraday’s law state?
The magnitude of induced emf in a conductor is directly proportional to the rate of change of flux cutting the conductor.
What is mutual induction?
When the changing magnetic field around one conductor causes current to flow in a nearby, electrically separate conductor.
What is self induction?
The generation of an emf in a conductor by the change in flux density produced by that same conductor.
This is prevalent in coils and also skin effect.
What does Lenz’s law state?
An induced emf opposes the change that created it.
What factors will affect counter emf?
The inductance of the coil and the rate of change of current.
When an inductor is placed in a DC circuit, how will the current rise to it’s maximum value as the circuit is closed?
The current will rise quickly at first and slow down gradually. It may never reach 100% of it’s steady value.
How can we define the time it takes for current to reach it’s steady value?
We can define it as five time constants, which are defined as the ratio of Inductance to resistance.
How much will the current change in each time constant?
Current will increase by 63.2% of the remaining value to reach it's maximum, after every time constant. Tc1 = 63.2% Tc2 = 86.4% Tc3 = 95% Tc4 = 98.1% Tc5 = 99.4%, Which is essentially 100.
What is an inductive kick? How do we mitigate the damage of this reaction?
When a DC circuit containing an inductor is opened by a near instantaneous switch, the counter emf produced is enormous and may easily arc across the switch.
We can mitigate damage by adding a discharge resistor in parallel with the inductor, which allows a path for the voltage to “discharge”.
What is the effect of an inductor in an AC circuit?
In AC the current continually changes, so we can reason that there will be a continual opposition to current flow. We define this effect as inductive reactance.
How is inductive reactance represented? What is it measured in?
Inductive reactance is X_L, and is measured in Ohms.
What factors will affect inductive reactance?
The frequency of the supply, and the inductance present in the circuit.
How is an inductive circuit classed, regarding time relationships?
We call this type of circuit a LAGGING circuit.
When Reactive power due to induction is positive, how is energy being used?
It is taken by the coil to establish the magnetic field.
When Reactive power due to induction is negative, how is energy being used?
It is delivered back into the circuit by the collapsing magnetic field.
