What’s the difference between a NOJA Power VISI-SWITCH® and an OSM Recloser?

From a technical standpoint, an OSM Recloser is a specialist form of Circuit Breaker, and a NOJA Power VISI-SWITCH® is a load break switch.

However, this delineation becomes less clear when considering an OSM Recloser can operate as a remote load break switch.

Some utility network installations may even call for both a NOJA Power VISI-SWITCH® and an OSM Recloser on the same pole. Let’s explore the differences between these devices.

The NOJA Power VISI-SWITCH®

This device is the worlds first solid dielectric enclosed load break switch with visible isolation. It uses a vacuum interrupter and an isolator connected in series, giving it the ability to break electrical load, but also offers visible isolation. The NOJA Power VISI-SWITCH® has an operating mechanism that actuates both the VI and Isolator together and ensures the VI always does the electrical make and break.

The NOJA Power OSM Recloser

The OSM Recloser is officially a type tested Auto-recloser. The OSM Recloser is paired with a Recloser Controller, the RC-10, RC-15 or RC-20. Leveraging the OSM Recloser’s integrated voltage sensing in all 6 bushings, the high precision current transformers, and the NOJA Power RC series controllers, the OSM Recloser can fulfil a multitude of roles. This has earned the device the reputation as a versatile solution to many distribution system protection and control applications, including:

• Overhead Lines Protection
• Underground Cable Protection (with the GMK)
• Capacitor Switching
• Substation Circuit Breaker Applications
• Earth Switching
• Renewable Integration/Connections
• MV Mining Equipment protection
• Remote Load Break Switching
• Sectionalizer

The one thing that an OSM Recloser cannot do alone is be a point of isolation. This feature is the core of the NOJA Power VISI-SWITCH®, to be the world’s only visible point of isolation in an SF6-free, solid dielectric insulated, enclosed load break switch.

“The NOJA Power VISI-SWITCH® was designed following NOJA Power’s key ethos to create environmentally friendly products,” says NOJA Power Group Managing Director Neil O’Sullivan.

“It is a direct replacement for manual SF6 gas insulated enclosed load break switch and eliminates the use of SF6 gas to help our utility customers continue to improve their environmental footprint. It is also an improvement on an SF6 load break switch because they always require the operators to take a leap of faith if the contacts were open when being used as a point of isolation. The NOJA Power VISI-SWITCH® allows operators to visually confirm the contacts are open, providing the advantage of an open air break switch with the increased reliability and security of an enclosed switch.”

OSM Recloser vs NOJA Power VISI-SWITCH®

Let’s review the feature comparison between these products:

The asterisk for the OSM Reclosers’ application in the point of isolation is due to installation practices. A Vacuum Interrupter cannot be used as a point of isolation. However rare that a loss of vacuum event is, if it occurred, the VI would flash over at power frequency voltage. This is acceptable for a circuit breaker device, but not for a load break switch for maintenance. However, to address this practical issue, it is common practice for utilities to install a set of disconnectors in series with the recloser (also known as “links”, or “isolators”).

The recloser can then be used to break the current, and the isolator/disconnector blades can be opened to provide the working point of isolation.

Why use the NOJA Power VISI-SWITCH®?

The NOJA Power VISI-SWITCH® gives some unique advantages over the Recloser and series disconnector assembly.

Firstly, the isolator is shielded from the environment. This ensures that the isolator remains reliable, safe, and free of corrosion or contamination. Legacy air-break load break switches are notorious for this issue. Exposed to the elements for years, the switch corrodes and malfunctions, requiring expensive live-line maintenance before it can be used. The NOJA Power VISI-SWITCH® keeps the isolator contacts out of the weather, making it maintenance free for its 30-year service life.

Secondly, the NOJA Power VISI-SWITCH® provides a means to interrupt the load current alone. Unlike the series disconnectors, It does not require an external circuit breaker to interrupt load current before it can be actuated. This makes the installation cheaper than a Recloser & Disconnector arrangement, and also gives a reliable emergency access if the Recloser needs to be taken out of service for maintenance.

Thirdly, the NOJA Power VISI-SWITCH® is the world’s first opportunity to remove SF6 from network enclosed load break switches. The most popular technique today is to use SF6 LBS, which offer no visible break, but also use the worlds worst greenhouse gas as an insulating medium. SF6 has an atmospheric half life of 3,200 years, and each kilogram of SF6 has the greenhouse equivalent of 23,500 kilograms of CO2. These legacy devices can leak this gas into the environment, and end of life disposal requires gas reclamation. These costs can be extensive for utilities, and the NOJA Power VISI-SWITCH® uses zero SF6 offering a credible alternative to these polluting technologies.

Conclusion

The NOJA Power VISI-SWITCH® offers electrical engineers visible isolation in an enclosed, Solid dielectric insulated switchgear device. This enclosed device offers 30 years of maintenance-free service, all while mitigating the need for SF6 at medium voltage.