Quite frankly, I don't think higher ESD voltages in power sub-stations is justified from the standpoint of the voltage threat. Modern sub-station control rooms are much like office environments and older stations are concrete floors with wooden or metal furnature (and not much of it!).
Perhaps the higher levels are required NOT because ESD is more of a problem, but because a failure could be more catastrophic than in your average office. Improper switching could cause realitively large scale outages and possible damage to the system. Mike Hopkins [email protected] > -----Original Message----- > From: [email protected] [SMTP:[email protected]] > Sent: Thursday, April 01, 1999 11:24 AM > To: [email protected] > Subject: fwd: RE: ESD in Power Station > > If instruments in power stations need more stringent ESD standard, what > about instruments in radio, TV, and cell stations? Did anybody have > similar > extraordinary feelings there? > > Barry Ma > > > > > > > ------------- > Original Text > From: "Mike Hopkins" <[email protected]>, on 4/1/99 7:35 AM: > To: > Cc: > > Didn't mean to mislead -- my comment about "feeling the electricity in the > air" is just that, a subjective feeling.... Maybe ozone played a part; I > was > too young and inexperianced to recognize it if that were the case. More > of > a sensation -- I do remember the 60Hz hum coming from all directions as > soon > as you entered the sub-station...... > > Mike Hopkins > > > -----Original Message----- > > From: [email protected] [SMTP:[email protected]] > > Sent: Wednesday, March 31, 1999 5:36 PM > > To: [email protected] > > Subject: ESD in Power Station > > > > Hi, > > > > Please allow me to pose two questions. > > > > (1) What did Mike Hopkins and Scott Douglas really feel and smell about > > "electricity in the air" when these two boys went to electricity > stations > > with their fathers? My guess -- that's air ions and ozone, which are > > easily > > produced in a strong AC EM field. If this is true, can we say: "The more > > > ions in the air, the easier ESD would happen"? > > (2) The eddy current on moving conductors in a strong H-field would > > produce > > eddy resistance in moving direction. That's a good explanation for slow > > watch on the spot. But my question: "How come an AC (not DC) H-field > left > > the moving iron with residue magnetization which causes the watch > > continuing slow after leaving the station?" > > > > Barry Ma > > ---------------------------- > > From: "Robert Macy" <[email protected]>, on 3/31/99 12:33 PM: > > > > IMHO the magnetic fields go right through the watchcase and either > disrupt > > > > what's going on or can even magnetize the parts. Either way, the parts > > are > > like "stuck" together and the watch won't run well. > > > > Also, my father could never wear a watch, a great gift watch always > would > > stop. The same watch given to my brother, lost ten minutes a day. So > when > > > > I got the watch I was happy when it gained a few seconds a month and > > lasted > > for over ten years. Go figure. > > > > --------------------------- > > From: "Mike Hopkins" <[email protected]>, on 3/30/99 9:48 PM: > > > > Very interesting -- my father also worked for what was then New England > > Power and was a substation operator in Tewksbury, MA -- he also went to > > other smaller sub-stations to switch lines in or out for maintenance or > to > > > > clear trouble problems and I have similar recollections about the > > electricity "in the air" -- you really could feel it! An interesting > side > > note - he could never wear a watch of any kind -- they would either run > in > > > > their own time zones or not work for long at all -- he attributed this > to > > the surrounding electric fields, but I've never figured out how that > would > > > > affect a mechanical watch! > > > > As for ESD (human ESD) as opposed to AC electric or magnetic fields, the > > > levels of 8kV and 15kV (contact/air) are on the high side. Discharges of > > a > > > > few kV happen all the time without us even knowing it; discharges that > we > > feel on a dry day are typically in the 5 to 10kV range, but a 15kV > > discharge from the end of your finger is something you'd remember! Even > > 10kV is pretty uncomfortable...... > > > > Hope this is helpful, but I doubt it would influence the people who > wrote > > the standard... > > > > ------------------------------- > > From: "Scott Douglas" <[email protected]>, on 3/30/99 9:43 AM: > > > > My father worked for the electric utility for many years. There were > > times > > he could take me with him to check on how a substation was working after > > > some maintenance or upgrade was performed. From direct experience I can > > tell you that when you enter the substation building, you can quite > often > > feel and smell the electricity in the air. The electrostatic fields that > > > build up in these environments can be substantial. Yes, everything > inside > > is well grounded, but when you have thousands of volts running around > big > > copper bus bars, switching systems, transformers, etc. you hear the hum > > and > > feel the electricity in the air. Back then, I thought it was really neat > > as > > I did not have the healthy respect that I have since acquired the hard > > way. > > > > One other thought here, would you want your TV going blink just at the > > end > > of the local cricket match or the last quarter of the World Cup > "football" > > > > game? That could happen if some protective device or overcurrent sensor > > got > > zapped and caused a shutdown when there was really no system problem > > requiring a shutdown. > > > > --------------------------- > > From: " Peter Poulos" <[email protected]>, on 3/30/1999 5:54 AM > > > > I've recently been shown a standard published by a European group > called > > UNIPEDE titled "Automation and Control Apparatus for Generating Stations > > > and Substations - Electromagnetic Compatibility Immunity Requirements" - > > > Ref# 23005Ren9523. > > > > This standard generally adheres to the same requirements for immunity as > > > the CE-mark standards, however for ESD it requires 8kV contact and 15kV > > air > > for HV substation environments. As is usually the case, there's no > > rationale provided as to why these level where chosen (something that > > really annoys me about most standards). > > > > Does anyone have suggestions as to why the authors of the standard > would > > expect worse ESD conditions in a substation than they seem to expect in > an > > > > air conditioned, carpeted office? (equipment in environments other than > HV > > > > substations only need meet 6kV contact, 8kV air according to this > > standard) > > > > > > > > Thank you. > > Best Regards, > > Barry Ma > > x4465 > > > > > > > > --------- > > This message is coming from the emc-pstc discussion list. > > To cancel your subscription, send mail to [email protected] > > with the single line: "unsubscribe emc-pstc" (without the > > quotes). For help, send mail to [email protected], > > [email protected], [email protected], or > > [email protected] (the list administrators). > > > --------- > This message is coming from the emc-pstc discussion list. > To cancel your subscription, send mail to [email protected] > with the single line: "unsubscribe emc-pstc" (without the > quotes). For help, send mail to [email protected], > [email protected], [email protected], or > [email protected] (the list administrators). --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
