Inductance
Series-opposing
A connectin of coils in which the coil current produces opposing magnetic fields for each coil.
Series-aiding
A connection of coils in which the coil current produces the same direction of magnetic field for both coils.
Transformer
A device that uses the concept of mutual inductance to step up or step down an alternating voltage.
Variac
A piece of test equipment that provides a variable output voltage.
Counter emf
A term used to discribe the effect of an induced voltage in opposing a change in current.
Autotransformer
A transformer made of one continuous coil with a tapped connection between the end terminals. Has only three leads and provides no isolation between the primary and secondary
Ferrite core
A type of core that has high flux density, like iron, but is an insulator. A ferrite core used in a coil has minimum eddy current losses do to its high resistance.
Stray capacitance
A very small capacitance that exists between any two conductors separated by an insulator. For example, the capacitance can be between two wires in a wiring harness or between a single wire and a metal chassis.
Impedance matching
An application of a transformer in which the secondary load resistance is stepped up or down to provide maximum transfer of power from the generator to the load.
Leakage flux
Any magnitic field lines that do not link two coils that are close to each other
Phasing dots
Dots on the primary and secondary leads of a transformer schematic symbol that identify those leads having the same instantaneous polarity.
Lenz's law
States that the polarity of an induced voltage must be such that it opposes the current that produces the induced voltage.
Inductance
The ability of a conductor to produce an induced voltage in itself when the current changes. L can also be difined as the characterisitics that opposes any change in current.
Mutual inductance
The ability of one coil to induce a voltage in another coil nearby. Two coils have a mutual inductance, Lm of 1 H when a current change of 1 A/s in one coil induced 1 V in the other coil.
Henry
The basic unit of inductance. 1 H is the amount of inductance that produces 1 volt of induced voltage when the current varies at the rate of 1 A/s
Eddy current
The current that flows in a circular path through the cross section of the iron core in a transformer.
Coefficient of coupling k
The fraction of total flux from one coil linking another coil nearby.
Efficiency
The ratio of power output to power input. In a transformer, power out is secondary power and power in is primary power.
Turns ratio
The ratio of the number of turns in the primary to the number of turns in the secondary of a transformer.
Stray inductance
The small inductance of any length of conductor or component lead. The effects of both stray inductance and stray capacitance are most noticeable at very high frequencies.
Reflected impedance
The term used to describe the transformation of a secondary load resistance to a new value as seen by the primary.
Volt-ampere
The unit of the apparent power that specifies the power rating of a transformer. The product VA is called the apparent power because it is the power that is apparently used by the transformer.
