The Problem
IEEE C62.41.1-2002:
IEEE Guide on the Surge Environment in Low-Voltage (1000 V and Less) AC Power Circuits:
“A wide range of phenomena, either resulting from normal system operation or from accidental conditions can produce TOVs … SPDs at the present state of technology as applied for protection against lightning and switching surges do not have the energy handling capability that would be required for limiting these TOVs.” (Page 31)
“TOVs are a type of abnormal event that is difficult to prevent, if not impossible, in the normal course of operation of a power system.” (Page 34)
“Anecdotal reports on varistor (MOV) failure might be explained by assuming the occurrence of a large swell or the cumulative effect of repeated swells.” (Page 51)
What are the lights on your surge protector telling you?; Power Quality Assurance, July/August Edition:
“How would the user be informed on the status of protection after a temporary overvoltage caused failure of the protective element in the TVSS package?’ A temporary overvoltage was selected as the method of failure because there is growing evidence that they cause a large number of the failures – perhaps the majority – rather than ‘large’ surges.” (Page 68)
The Solution
Harris Semiconductor, Transient Voltage Surge Suppression Devices:
“Selenium transient suppressors apply the technology of selenium rectifiers in conjunction with a special process allowing reverse breakdown current at high-energy levels without damage to the polycrystalline structure. These cells are built by developing the rectifier elements on the surface of a metal plate substrate which gives them good thermal mass and energy dissipation performance. Some of these have self-healing characteristics which allows the device to survive energy discharges in excess of the rated values for a limited number of operations, characteristics that are useful, if not ‘legal’ in the unsure world of voltage transients.
“The selenium cells, however, do not have the clamping ability of the more modern metal-oxide varistors or avalanche diodes. Consequently, their field of application has been considerably diminished.” (Page 2-5)
Practical Guide to Quality Power for Sensitive Electronic Equipment:
“Selenium-cell transient suppressors, of specially designed selenium rectifier elements, are occasionally used. They can handle high energy transients and repeated hits very well, but have poor voltage clamping ability. Combination units are available, however, that use selenium devices, custom-made to minimize the undesirable characteristics and take advantage of the desirable ones.” (Page 69)