Lightning surge protection devices for Power Supply System Terminology of Electrical Characteristics

Surge Protective Device: Device designed to limit transient overvoltages and run-off lightning currents. It consists of at least one non-linear component.

1.2/50 wave: Standardized overvoltage waveform created on networks and which adds to the network’s voltage.

8/20 wave: Current waveform which passes through equipment when subjected to an overvoltage (low energy).

10/350 wave: Current waveform which passes through equipment when subjected to an overvoltage due to a direct lightning strike.

Uc:  Max. Continuous Operating Voltage , which is the root mean square value of the max. voltage which may be applied to the correspondingly marked terminals of the surge protective device during operation.

In: Nominal Discharge Current
Peak value of an impulse current, wave-form 8/20μs,  which the surge protective device is rated for,
according to a certain test programme. It is used to determine the Up value of the surge arrester.

Imax: Max. Discharge Current
Max. peak value of the impulse current 8/20μs, which  can safely discharged by the device. Imax is greater than In.

Iimp:  Lighting Impulse Current
A standardized impulse current curve, with a waveform 10/350μs. Its parameters (peak value, charge, specific power) simulate the loads of natural lighting currents.

Up: Voltage Protection level
Parameter characterizing surge arrester operation by the level of voltage limitation between its terminals and which is selected from the list of preferred values in the standard. This value is greater than the highest value obtained during voltage limitation measurements.

Protection mode:  Common mode (MC): protection between live conductors and earth.
Differential mode (MD): protection between live conductors.

Un:Nominal AC voltage of the network.
Nominal voltage between phase and neutral (AC rms value)