Technetters, here is some more information on corona discharge.  By the way, the "correct" term is partial discharge, since the breakdown does not bridge completely the insulation gap;  I believe this term is more commonly used in Europe than the US.  Ceramic materials are quite resistant to degradation.  Next best are naturally occurring organic materials, like paper.  Then come synthetic organics.  In air, the minimum voltage at which partial discharges can occur is about 330 volts.  The voltage depends on the gas pressure and spacing, via Paschen curves, but is always more than 330 volts.  Other gases, like the noble ones, need higher voltages to breakdown.  Sulfur hexafluoride is way up the high scale, which is why utilities have used it in switchgear.  

Louis Hart, Quality Manager
Compunetix Instrumentation Systems Division
412-858-6184

##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
the body:
To subscribe:   SUBSCRIBE TECHNET <your full name>
To unsubscribe:   SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or
847-509-9700 ext.5365
##############################################################