Like most professions, engineering has developed a language of its own. This is needed to convey very specific and precise information. Fuse design engineers, for instance, make a very clear distinction between an overload condition and a short-circuit condition. (Overloads are in the range of ~200% of the fuse's rating while short-circuits are 10X or more.)
Recently, a few of us Mouser Bloggers had a discussion on the term "High Voltage". Lynnette Reese was asking about present-day design activity at high voltages and what techniques were used to modulate High Voltage AC signals from analog control circuits.
The discussion pretty quickly turned to defining "High Voltage". Let the Geek Speak commence!
I noted that to a power distribution engineer, the threshold for HV would be something like 40kV. They often refer to 25kV switchgear as "medium voltage". Littelfuse defines it this way:
“The terms ‘Medium Voltage’ and ‘High Voltage’ have been used interchangeably by many people to describe fuses operating above 600 volts. Technically speaking, medium voltage fuses are those intended for the voltage range from 2,400 to 38,000 Vac. High voltage fuses are for circuits carrying voltages greater than 38,000 Vac." (source)
To a consumer electronics / communications system engineer, the threshold is probably more like 800V. Insulation and arcing take on a much more aggressive characteristic at those levels. These are typical limits of high voltage Silicon-Controlled Rectifiers (SCRs, a.k.a. thyristors) and is about the peak voltage of a 480V AC line.
Mike Parks, another Mouser blogger, mentions that. "In my shop, anything that can deliver more than 30V gets slapped with a warning sticker. I think that is simply a very conservative estimate, though I do believe given certain skin conditions (salinity, moisture, etc.) 50V can deliver dangerous current to a human body."
Rudy Ramos is a Technical Project Manager at Mouser Electronics. He has experience in the support of a lot of front end wafer fab equipment for the likes of TI, National, and Hitachi, and notes that the semiconductor manufacturing process requires lots of specialized equipment that incorporate a horde of technologies including high voltage. Says Rudy:
"A good majority of the equipment requires both high voltage and high current for either the actual manufacturing process or as a source of power to do the job, as is the case with a scanning electron microscope (SEM). The SEM requires very high voltage power supplies in order to produce the electron beam that traces the object being scanned/inspected (silicon). Ion Implanters on the other hand, are capable of ion beam energies in the range of 200KeV or higher." Another piece of equipment, plasma dry etch equipment, uses both RF and Microwave to produce the plasma used to process the silicon wafers. Both energy sources are high current and high voltage."
In Bill Schweber's article “Designing at Very High Voltages: Everything Changes, Especially Your Way of Thinking,“ he basically states that products used at high voltages of 600V - 1500V+ are typically made for specific purposes. That is, most electrical/electronics devices that operate at high voltages are not commodity-type items. Protection against high voltages associated with electrostatic discharge are much more common, but the expectation is that the extreme voltage will be very brief. However, for more commonly known applications like x-rays, MRIs, solar, electric trains/light rail, and power distribution, there are very specific custom catalog and made-to-order products.
I would be very interested in hearing from you on the challenges you've faced in dealing with high voltage applications. How did you control the high voltages? Did you have issues with arcing or insulation? How did you maintain isolation between the HV signals and your control signals? How did you assure the safety of the people working around the equipment? And please....feel free to use Geek Speak!!
Kelly Casey is VP of Engineering for FM Technical Consulting, and holds a Bachelor of Science Degree in Electrical Engineering from the University of Nebraska, as well as a Master of Science Degree in Electrical Engineering from the Georgia Institute of Technology. Previously, Mr. Casey has held various roles at Bourns, Littelfuse, and Teccor Electronics.
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