Single Panel or Large Bank Switchgear Power Systems

 

The term switchgear is commonly used when referring to the main disconnect point in a building. This is where the power comes into the facility and where the power is distributed to the secondary circuits in the building. Switchgear can mean a single panel with one large main breaker and several smaller breakers or it can be a large bank of panels with dozens of breakers. Whether a single panel or a large bank of breaker panels these are switchgear power systems.

Most small and medium facilities use 480V three-phase power. This is considered low voltage (up to 600V). Some large facilities use medium voltage switchgear power systems up to 2500V and a few high voltage systems go as high as 38kV. There are some applications for DC switchgear up to 1500V and 6000A in the transportation industry. Main switch or breaker amp ratings are typically a few hundred amps for small buildings up to several thousand amps in large facilities. Switchgear is tested for thirty cycles at 15% power factor for short circuits. These high currents require very special switching systems.

switchgear power systems

Common switch types for high current or high voltage systems are bolted contact pressure switches, airframe breakers and vacuum breakers. At one time oil insulated contacts were used but these have been phased-out over the years and replaced with more modern devices. Some facilities use gas insulated switches where the insulating medium is sulfur hexafluoride gas. These special switches are required because opening a high current circuit usually causes dangerous arcing. Gas or vacuum insulated switches suppress arcing when the contacts open. Air frame contacts require some method of quenching arcs. The most common is the magnetic arc chute that uses formed magnets near the opening contacts to breakup and dissipate any arcs. Arcs are dangerous to humans and damaging to switch contacts.

In high current situations, even a small resistance can be a source of heat. This heat can cause damage and even failure of switch contacts. Bolted pressure contact switches combat this heat source by holding the contacts together under mechanical pressure instead of just spring pressure. This eliminates or greatly reduces contact heating as a cause of failure. This is why main switches in switchgear power systems are some form of high pressure contact switches. These are commonly low-voltage power circuit breakers (LVPCB) that are compatible with several standards (ANSI C37.13, NEMA SG-3 and UL-1066).

Commercial and Industrial switchgear power systems

Since switchgear power systems are so important to every commercial or industrial organization, failures can be disastrous. Regular maintenance reduces the chance of catastrophic failure. A regular check for overheating contacts can be done with a laser temperature probe or infrared photography or videography. Any hot spots should be addressed immediately. At least every few years (annually if possible) a hands-on visual inspection of the contacts and switch mechanicals should be performed. All companies want their switchgear to operate flawlessly for many years. Regular maintenance by a qualified and experienced team of technicians helps assure this is so.