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Safety and Reliability: Part 1 of A New Standard

The Standard for Switches and Transformers Has Evolved: “Standard” Switches and Transformers Are Not the Standard Anymore

Once upon a time the Westinghouse Load Interrupter (WLI) was the standard medium voltage switch in the industry. It is used indoors and outdoors and typically found on the primary side of a unit substation transformer. There are many versions of this switch made by a variety of manufacturers. here are some basics:

  • The load interrupter takes up about as much floor space as a full-size refrigerator
  • In the switch, there is exposed bus work, stand-off insulators, and switch parts & fuses
  • It takes some muscle to operate the switch

While these switches are considered reliable, the exposed parts aren’t without challenges:

  • Arc flash hazards; particularly when being operated.
  • They are susceptible to moisture which can lead to catastrophic failure, especially without heaters.
  • They require maintenance to keep them clean and the switches operating properly.

An additional challenge in a “standard” installation, where a fuse load interrupter is the primary disconnect means for a 1000KVA or larger transformer, is that the fuses in the switch are not capable of interrupting a secondary fault quickly enough to prevent significant arc flash hazards (typically greater than Cat 4) and damage on the low voltage side.

Fortunately, technology has advanced and there are better solutions available.

The Vacuum Fault Interrupter (VFI) replaces the exposed switch with a vacuum bottle sealed inside the transformer tank. The VFI can be manually or remotely operated, greatly reducing arc flash hazards. In simpler terms, it is a resettable circuit breaker for medium voltage applications.

A VFI comes with an electronic over-current device to clear faults

  • The protective device can be set to replicate standard fuses types. No spare fuses are needed; simply reset the device.
  • The protective device can be set to standard Time Over-current Curves for better selective coordination.
  • The protection has an input that can be used to remotely trip

The advantages of the VFI mean:

  • It just might cost less than a traditional WLI style switch and transformer. (newer & cheaper!)
  • VFI Solutions typically takes less floor space than a typical air switch.
  • Practically zero maintenance since it is enclosed in the tank of the transformer.
  • Virtually eliminate arc flash hazards when you utilize the option of a dead-front construction.

Flexibility, Compact Design, and Durability

When installing or replacing a transformer, we recommend looking at what is offered instead of going with “the usual” or “what we have always done”. Our industry has been changing rapidly in recent years and there are some truly great products being developed and manufactured. The VisoVac is one of these great products. Eaton’s customized VisoVac is a three-phase medium-voltage

Eaton’s pad-mount VisoVac is a three-phase medium-voltage fault interrupter that utilizes proven vacuum interruption technology and is available with visible isolation and visible grounding capability.

fault interrupter that provides modern capabilities with the classic durability you have come to expect:

  • Compact, low-profile design
  • Flexible switch arrangements
  • Gas, oil and regulation free (environmentally friendly!)
  • No regular maintenance
  • Advanced proven Eaton vacuum breaker technology
  • Manual and remote operation capable
  • 10,000 mechanical operations
  • A higher 25kA or 40kA fault current rating

Basically, that power industry is not what it used to be…it’s BETTER! EMR Associates and the manufacturers we represent stay on the forefront of new technology and reliable power. Contact us for a consultation and competitive pricing!

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