Talk about some issues of surge protective devices (SPDs)
1. Some problems of “OBO style structure”
Chinese surge protective devices (SPDs) mass-production based on Dehn, OBO, and Citel’s structural design. However, with the development of the technology and practice, the accumulation of mature product is constantly changing, such as Dehn, Phoenix, Raycap, OBO, Citel, Hakel, Saltek surge protector, always keep coming up with new styles and models. These changes not only do some fashionable change, differentiation, but there is a lot of the structure and function of the optimization. But look at most of China SPDs factories, they still use an outdated structural design such as OBO style:
1.1 Short-circuit protection contacts style
Comments: To meet the corresponding intensity of lightning current mechanical, reduce the cross-section area of the contacts can improve the ability of short circuit protection, but need to realize that discharge current and short-circuit fusing is a contradiction issue, it need take a lot of experiments, not blindly reduce the cross-section area of the contacts.
1.2 Layout of line
There is a design defect in OBO structure, tripping mechanism, and MOV in the same room, it means the high-voltage contacts and low-voltage contacts in the same room.
(copper braid snap; solder melting)
According to the principle of electromagnetism, Same direction current attract each other, as shown above, when copper braid slightly longer, it will attract between the conductor of same direction current and conductor of opposite direction current, because copper braid is knitting and have the ability of stretch, it makes the result of above
The structure of the OBO style, there is more activity space at this position, it’s easy to pull the line after the current discharge impact, the welding is easy to disconnect.
The salient point on the green plastic bar is an easy drop-down, red indicates on the visible window, it makes misoperation (wrong action). It causes by the same reason as above item 3.
Solder tin slightly more, over-temperature protection will not be able to fully release. The distance of the tripping release is less than 5mm in this OBO style structure, SPD manufacturers should pay attention to it.
MOV and tripping release system in a different room, the distance of the tripping release is approx. 10mm, the plastic bar is not affected by electrodynamic force.
An ignored issue of IP20 surge protective device
Over the years, SPDs testing cares for residual voltage, discharge current, transient overvoltage (TOV), thermal stability, multiple pulses, but ignored the most basic test of low-voltage electrical appliances direct contact.
Within half a year, SPD testing laboratory find many SPD unqualified IP20 class, this problem mostly happens in the old OBO style base, call for Chinese SPD factories don’t produce it anymore, there are many problem and structure defect in old OBO style SPD.
What’re the means of IP20?
Number ‘2’ means prevent 12mm solid (such as Finger size) intrusion, using simulation fingers for validation.
Number ‘0’ means a waterproof level.
Left photography: qualified, the surface of screw subsidence about 1.5 mm
Right photography: unqualified
The status of tighten
After checking, under the condition of SPD housing without any difference, find unqualified IP20 screws isn’t even unqualified when to install into qualified housing.
As photography above, left photography: untouched, screw qualified, right photography: touched, screw unqualified
After the measurement, the specification of the screw is consistent, The problem happens in the structure of metal parts.
The surface of screw is uneven when installed on the structure of metal parts.
and found there is differences in the shape of structure.
or use terminal cover, without examination.