Radial Feed - One primary bushing per phase.
Radio-Influence Voltage (RIV) - A high frequency voltage, generated by all sources of ionization current, that appears at the terminals of electric power apparatus or on power circuits.
Rating - The rating of an arrester - either duty cycle or MCOV rating.
Ratio - A reference to either the turns ratio or the voltage ratio of a transformer.
Reactance - A component of impedance produced by either inductance or capacitance in an ac circuit.
Reactor - A device for introducing inductive reactance into a circuit for motor starting, operating transformers in parallel, and controlling current.
Recloser - An automatic, high-voltage electric switch (see "What is a Recloser?").
Recovery Voltage - The voltage potential established across the open electrodes of an overcurrent protection device after clearing the circuit at a current zero; a term used to designate the voltage impressed by the circuit upon the interrupting device after interruption of the current at or about the time of a natural current zero.
Reduced Capacity Tap - Tap that is not designed to deliver the rated capacity of the transformer.
Reference Current (Iref) - The reference current is the peak value of the resistive component of a power frequency current high enough to make the effects of stray capacitance of the arrester negligible. This current level shall be specified by the manufacturer.
Reference Voltage (Vref) - The lowest peak value independent of polarity of power frequency voltage, divided by the square root of 2, required to produce a resistive component of current equal to the reference current of the arrester or arrester element. The reference voltage of a multi-unit arrester is the sum of the reference voltages of the series units. The voltage level shall be specified by the manufacturer.
Resistor - Any device of material that limits the flow of current when voltage is applied.
Resonance - A state in which the capacitance and the inductance values in a circuit are equal (net reactance is equal to zero) and the only quantity left is resistance.
Resonant Frequency - Frequency at which the voltage and the current at the input terminals are in phase. Reactance is equal to zero.
RMS Line Current - The square root of the average of the squares of all the instantaneous current amplitudes occurring during one cycle.
Routine Tests - Test made by the manufacturer on every device or representative samples, or on parts or materials, as required, to verify that the product meets the design specifications.