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Medium Voltage Load Break Switches

 

 

 

 

Medium voltage load break switches control power to circuits with voltage ratings from 1kV to 52kV. They are used in a variety of applications and are differentiated from non-load break switches because as the name suggests they can safely be opened while power is flowing through the cricuit that they are installed in.

Applications include:

  • Selector Switches - Sometimes called A-B switches which select which power source will be used to energize the primary of a transformer.
  • Power Distribution - A group of switches, can be with or without a main, which direct power to various locations in a factory or other large facility.
  • Primary - For a single transformer powering a secondary switchgear.
  • Isolation - To de-energize equipment not being used or so that the switchgear can safely be serviced.

Typical ratings for the most common switches used on a 2.4kV through 15kV will have a continuous rating of 600 amp but are most often fused well below that.

They can be designed for use both indoor and outdoor and are used to interrupt the flow of power under both normal and emergency situations. They are most often operated manually but some are also equipped with a motor driven mechanism with a shunt trip which allows them to be opened and closed remotely.

The components of a medium voltage load break switch include the switch body and housing, contacts and mechanism and arc extinguishing medium. The arc extinguishing medium can be air, vacuum of SF6 (sulfur hexafluoride) gas. Vacuum and SF6 gas are used when a medium is needed to provide effective current interruption with minimal contact wear. Air is a cost effective option, especially if the switches will see minimum cycling.

 

 

 

As with any mechanical or electromechanical device, regular scheduled maintenance is required. This includes visual inspection, lubrication of mechanism and contact joints, testing of insulators and conductivity testing of the closed switch to ensure minimum internal resistance. Frequency of this maintenance will vary depending on factors including frequency of operation and environmental considerations. Failure to properly maintain these switches can and will result in non-scheduled power outages with damage to surrounding property and can injure or kill personnel in the area.

Many switchgear installations are in service well past the time that the OEM stopped supporting them or items may have long lead times which will extend the time of the unintended outages causing loss of production that run into tens or hundreds of thousands of dollars. This makes your local used equipment dealers like National Power Equipment invaluable. NPE not only has switches and parts in stock and available for quick shipment but also the experience and knowledge to guide you through pitfalls in things like parts interchangeability that wouldn't otherwise be apparent in the field. As always, knowledge and information is critical. Gather not only nameplate information but photos of both the overall switch and details of the parts in question. This will make it much easier for NPE to live up to its motto of "The right part, at the right price, right now!"