I2t - A composite electrical quantity used as a measure of comparative potential energy; the specific joule integral, measured as ampere to seconds; a comparative electrical quantity used to help associate energies of fuses under conditions where actual energy calculations are impossible to use.
IEC - International Electrotechnical Commission.
IEEE - Institute of Electrical and Electronics Engineers.
Impedance - The obstruction to the flow of current in an ac circuit. The transformer impedance is made up of the internal resistance and reactance which creates a voltage drop caused by current flowing in the windings. Impedance losses are a combination of heat (I2R) losses in the conductor, eddy current loss, and losses in other parts of the transformer caused by stray currents.
Impulse - A current surge.
Impulse Tests - Tests which ensure a satisfactory level of insulation and the ability of a device to withstand, within certain limits, overvoltage surges (such as lightning strikes) that may occur in service.
Inrush Current - The initial momentary surge current demand before a load resistance of impedance increases to its normal operating value.
Inrush Restraint - A restraint feature that can make the fault indicator inoperable to inrush currents.
Insulation - A material having a high resistance to the flow of electric current; insulation over underground conductor is made of either EPR or XLPE material.
Insulation Coordination - The review of the protective level of the arrester and the insulation level of the equipment to be protected to ensure that the arrester is adequately protecting the equipment.
Insulation System - A balanced combination of materials (kraft paper, oil, porcelain, etc.) which provides dielectric strength to a device.
Insulator - Any material which does not allow electrons to flow through it.
Intermediate Class Arrester - A classification of 3-120 kV rated arresters with higher energy handling capability and durability compared to a Distribution Class Arrester. In addition, pressure relief capability is required.
Interrupter - An element designed to interrupt specific currents under specified conditions.
Interrupter Switch - An air switch, equipped with an interrupter, for making and/or breaking specified currents. NOTE: The nature of the current made or broken, and/or both, may be indicated by suitable prefix; that is, load interrupter switch, fault interrupter switch, capacitor current interrupter switch, etc.
Isolation Link - A small metal link used in series with a Bay-O-Net link or MagneX interrupter. During transformer failure, the isolation link will melt so the opened primary circuit of a faulted transformer cannot be re-energized by the line crew. An isolation link has melt characteristics, but no fault clearing capabilities.
Isolator - CPS's trademark for the arrester disconnector.