Ph Phase

I_imp Defined by three parameters, a current peak value, a charge and a specific energy. Generally relates the IEC definition of a direct lightning strike modelled by a 10/350μs waveshape. This is used for the classification of SPDs for test class I in accordance with IEC61643-1.

Q Charge contained in a test waveform. Expressed in coulombs (As).

W/R Specific Energy relating to a test waveform. Expressed in kJ/μs.

I_max Defined as the peak value of a current through the SPD having an 8/20μs waveshape. This is used for the classification of SPDs for test class II in accordance with IEC61643-1. This is generally recognized for MOV based SPDs as the single shot impulse rating.

I_n Defined as the peak value of a current through the SPD having an 8/20μs waveshape. This is used for the classification of SPDs for test class II in accordance with IEC61643-1. This is known as the nominal discharge current and is generally recognized for MOV based SPDs as the rating of the SPD for 15 such impulses.

I_L The maximum continuous RMS or DC current that can be supplied to a load connected to a two port or series connected SPD.

I_f The current supplied by the electrical power system which flows through an SPD after a discharge current impulse. This is called the follow-on current and is particularly applicable to voltage switching type SPDs such as spark gaps and gas discharge tubes.

I_fi Follow-on current interrupting rating. This is the maximum AC RMS current that a voltage switching SPD such as a spark gap can interrupt.

U₀ The RMS line to neutral voltage of the power system.

U_c The maximum RMS or DC voltage, which may be continuously applied to an SPD.

U_p The let through voltage of an SPD defined for a specified test waveform.

t_A Response time of an SPD to a defined test waveform.

ΔU Voltage drop of a two port SPD at rated current expressed as a percentage of U0.

f_c The maximum usable frequency.