Transient overvoltage protection: The implications of new techniques

The paper presents a comparison of the performance of voltage-switching devices and voltage-limiting devices for late seventies-vintage SPDs as marketed and installed in service panels in the USA and in Europe. Artifacts in the response of a typical oscilloscope to a nearby gap sparkover, and the effect of lead dress inside the panels and outdoor installation are described. Predictably, the performance of a metal-oxide varistor is found preferable to that of a gap-based arrester. Summary Report 664 [ l ] proposes voltage levels of 2500 V for a 120 V circuit and 4000 V for a 220 V circuit (Table 1). Reliability problems can occur from the use of However, these voltages are not consistent with the modern electronic devices without applying appropriate inherent withstand characteristics of electronic appli-protection techniques or using incorrect installation pro-ances. A much lower level (indicated by Category I cedures. Although surge arresters are effective in limit-or I1 of the 664 report) is required, i.e., 800 or 1500 V ing overvoltages, a metal oxide varistor can provide a much lower clamping voltage if installation procedures are taken into consideration. Sparkover voltage measurements , with a specified time rise, measured arrester oerformance. The resDonse of the arresters to a current impulse was investigated and lead effects were identified. Tests indicated that the metal oxide varistor, installed with short leads, provides low clamping voltage.