Reluctance
The opposition that a magnetic circuit presents to the passage of magnetic lines through it.
Reactance
The opposition to the flow of an alternating current by an inductive or capacitive element in the circuit.
Resistance
Resistance is defined as the measure of opposition to the motion of electrons due to their continuous collisions, with the atoms of the conductor
Rheostat
A potentiometer or a rheostat is an instrument used to measure and compare potentials without drawing any current from the circuit.
Retentivity
The ability of a magnetic material to retain its magnetism.
Residual Magnetism
The magnetism remaining after the external magnetizing force is removed.
Radian
In a circle, the angle included within an arc equal to the radius of a circle. Numerically, the angle is 57.3o.
RMS Value
The AC current value that develops the same heating effect as the corresponding DC current value. For sine wave currents, the RMS or effective value is 0.707 times the peak value.
Resonance
It is the condition that happens when a circuit’s capacitive and inductive reactances are counterbalanced.
Reactive power
The product of voltage and out-of-phase components of alternating current.
Real power
The average power, or active power, or the real part of the complex power.
Reluctance
It is the ratio of the magnetomotive force (MF) to the magnetic flux in a magnetic circuit.
Reluctance power
The component of the power delivered by a synchronous generator representing the effects of generator saliency.
Reset
The action of a relay as it makes designated responses to decreases in the input.
Reset value
The maximum value of an input quantity reached by progressive decreases that will permit the relay to reach the state of complete reset from the pickup.
Residual voltage
The generated voltage due to the residual flux in the field poles even when the field circuit remains unexcited.
Rotor
The rotating member of a machine, with the shaft.
RPM
RPM is the abbreviation for Revolutions per Minute. This is usually the rotational speed of things like motors.
Relay
A relay is an electromechanical device that can be used to control multiple loads with one control circuit.
Reactive Power
A measure of an inductor’s ability to receive and return energy in a circuit.