ommon mode SPD between phase and PE or phase and PEN is installed whatever type of system earthing arrangement (see Fig. 1).
The neutral earthing resistor R1 used for the pylons has a lower resistance than the earthing resistor R2 used for the installation.
The lightning current will flow through circuit ABCD to earth via the easiest path. It will pass through varistors V1 and V2 in series, causing a differential voltage equal to twice the Up voltage of the SPD (Up1 + Up2) to appear at the terminals of A and C at the entrance to the installation in extreme cases.
To protect the loads between Ph and N effectively, the differential mode voltage (between A and C) must be reduced.
Another SPD architecture is therefore used (see Fig.2)
The lightning current flows through circuit ABH which has a lower impedance than circuit ABCD, as the impedance of the component used between B and H is null (gas filled spark gap). In this case, the differential voltage is equal to the residual voltage of the SPD (Up2).
SPDs’ operating characteristics are defined by several technical characteristics. The following are some technical characteristics that should be considered: maximum continuous operating voltage, ac or dc application, nominal discharge current (defined by a magnitude and waveform), voltage-protection level (the terminal voltage that is present when the SPDs are discharging a specific current) and temporary overvoltage […]
Electrical networks are low-frequency and, as a result, propagation of the voltage wave is instantaneous relative to the frequency of the phenomenon: at any point of a conductor, the instantaneous voltage is the same. The lightning wave is a high-frequency phenomenon (several hundred kHz to a MHz): 1. The lightning wave is propagated along a […]
AC Surge Protective Device is an indispensable device for lightning protection of electronic equipment. Its main function is to limit the transient overvoltage that penetrates into power lines and signal transmission lines to the voltage range that the equipment or system can withstand, or to release strong lightning current to the ground, thereby protecting the protected […]
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