Behavior of Low-Voltage Surge Protective Devices Under High-Current Derivative Impulses

It has been observed by scientists that maximum rate of change of current with respect to time of subsequent return strokes could be as high as 150 kA/mus. This fact is not reflected in the present day testing of surge protecting devices (SPDs). Usually, they are tested with 8/20 mus current impulses the time derivative of which are considerably less than the time derivatives of subsequent return stroke current pulses. When SPDs are subjected to current impulses with a high-current derivative, the voltage yields on their terminals will be highly influenced by the inductance of the lead connections. Therefore, a high di/dt impulse current can produce a voltage across the SPDs terminals that can exceed the threshold level of the protected equipment, causing partial or permanent damage in their insulation. In this study, the behavior of few selected surge protective components for fast current transients is analyzed and compared with standard 8/20 muS current impulses. The experiment was performed on disk type varistors and ceramic type gas discharge tubes (GDT). The result show that, the clamping voltages due to fast transients for tested component is considerably greater than the ones observed with standard 8/20 muS current impulses.