A New Approach to Switchgear
Schneider Electric has introduced an approach to medium voltage switchgear that it says is cheaper, safer and more reliable.
Medium voltage is in the 1,000 volt to 38,000 volt range, according to Joe Richard, the company’s Product Launch Manager. Typically, this is the range of the voltage that comes from a utility. It is reduced, via a transformer, to lower voltages for distribution through the building or campus.
A major piece of equipment associated with electrical distribution is switchgear. These are the vital switches and circuit breakers that break a circuit and keep the juice from flowing. Alternating current (AC), which is used at this point in the flow of electricity in distribution networks, generally is transmitted in phases in order to double or triple the amount of electricity sent. AC varies in amplitude as it travels through a conductor. By slightly offsetting transmissions times, more can be squeezed into (and ultimately out of) the cable or wire.
The metal elements in switchgear that carry the electricity are call bus bars. Obviously, keeping them interfering with each other, either through touching or being close enough to allow arcing, is a major safety and economic consideration.
Until this point, Richard says, the segregation between bus bars was done by air or by SF6 gas, which is hexafluoride. Air was the main approach to in the 1940s and 1950s. SF6 began to be used in the 1980s and 1990s. The reason that these approaches were taken simply was that it was easier. Encasing the bus bars in a substance is difficult because threats of contaminants and imperfections that can lead to problems must be eliminated.
Richard said that Schneider Electric now is encasing the bus bars in epoxy. The company has sold the technology, called 2SIS (shielded solid insulated switchgear) outside the United States since 2013. He said that the first domestic orders recently were written. The approach is UL approved and conforms to the Institute of Electrical and Electronics Engineers’ c37.20.3 standard.
2SIS is not the first use of epoxy in electrical distribution. It is, however, the first time it has been employed within metal enclosed switchgear. On top of the epoxy is a conductive layer that goes to ground. In other words, if electricity does escape the epoxy, the ground layer will usher it to the earth outside the building in a safe and standard manner.
Richard says that the use of epoxy instead of air or gas can positively impact an organization safety and costs in a couple of ways. Safety, as always, is key: “2SIS completely removes exposed live parts from inside the gear,” Richard told Energy Manager Today in an interview. “If someone doing maintenance and didn’t follow the correct procedures, he would still be better protected.”
The cost side also is important. In an air or gas approach, the required distance between bus bars tend to be comparably large. Thus, the overall enclosures are big. The epoxy approach removes space as a variable. This allows either more bus bars to be placed in an existing switch gear enclosure or, if the approach is used for new equipment, smaller devices to be designed. In both cases, less space is used.
Condensing equipment not an incidental benefit. “The world is getting to the point where we have to concentrate more power in the same amount of space,” Richard said. “With things like the IoT and population density increasing we are requiring lot more power. 2SIS makes switchgear smaller and modular. This means that medium voltage can be used where previously only low voltage may have been used.”
Richard added that that second cost-related reason is that the epoxy approach requires far less maintenance that the air and gas technology. Richard said that epoxy must be checked every ten years. Legacy approaches need to be inspected very two or three years, he said.
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