On Tue, 21 May 1996 12:05:42 +0000, Chris Dupres wrote: >Good folk of the PSTC. Some LVD stuff.. > >I have recently been looking at High Voltage connectors, round the >15-20kV operating mark, for use on laboratory equipment, e.g. >electron microscopes etc. > >I've been offered a 15kV connector that has a 30mm distance from the >contact to the nearest point at which a test finger can get, (PTFE >Tube). This seems to meet with the requirements of IEC1010-1 Figure >D.2. clearance distance, but not with the requirements of table D.18, >Creepage distance. (15kV= approx 60mm). > >The implication of this is that just about all the HV connectors on >the market are only good for 10kV or so, even the ones quoting 30kV! > >Questions are: >1. Am I right in expecting HV connectors to meet IEC1010-1? >Particularly the clearance and creepage tables D.18 and Fig D.2.
I also searched in vain for an HV connector which met IEC1010-1 creepage AND didn't cause emc problems. I found one, of European manufacture, which met the creepage requirements but it had so much partial discharge at rated voltage (ac) that it failed emc tests. The manufacturer was contacted but could not resolve the problem. I ended up making my own drywell-type connector, essentially a tube of PTFE or PEEK encapsulated in RTV. The length of the tube was determined by Table D12. The unshielded HV cable was inserted into the drywell tube and the HV connection was made at the far end. It was an expensive, complicated and bulky solution. The creepage requirements for HV connectors in Table D12 seem extreme for many HV applications over 10kVdc, where itÂ’s not unreasonable to insist the user periodically inspect and clean connections to reduce the possibility of failure. In my interpretation, 1010-1 precludes the use of connectors made by companies such as Amp, Caton, Rowe, Dielectric Sciences, and others which do not have the required creepage but instead depend on the seal created by two mated flexible silicone surfaces. As far as I know these HV connectors have been used safely and reliably for years. >2. Do 25kV connectors really have to have 100mm surface distance to >ensure safe use? (table D.18) This would make a 25kV connector 8" long! And this is for a pollution degree of 1! Some connectors like those made by Lemo and Fischer have interlocks which, if used to disable the HV source when the connector is not mated, can reduce creepage requirements to those of basic insulation levels. Grooving or baffling is also used in some connectors to achieve a creepage longer than the overall connector length. >3. Are there any more appropriate standards to use in this respect? I know of none for this type of equipment. In 1010-1 clause D.1 it is stated that for non-mains circuits you can fail to comply with creepage and clearance requirements as long as certain conditions are met. Can anybody explain the intent and implications of this clause? Regards, John Quinlan quinl...@voicenet.com
