NOJA Power

Technical Article

Published 06/2024

How a NOJA Power VISI-SWITCH® Provides Isolation


Working points of isolation are a life-or-death consideration. High voltage network operators rely on a working point of isolation to keep their work areas isolated from the high voltage supply.

A failure of insulation can have lethal consequences.

This prompts engineers to design high voltage equipment and switching practices to mitigate this risk, and the NOJA Power VISI-SWITCH® is no exception.

A NOJA Power VISI-SWITCH® installed in NSW Australia © NOJA Power 2024
A NOJA Power VISI-SWITCH® installed in NSW Australia © NOJA Power 2024

How a NOJA Power VISI-SWITCH Operates

A NOJA Power VISI-SWITCH® is the worlds first solid dielectric insulated load break switch with enclosed visible isolation.

It uses two mechanical stages operated by a single movement mechanism to achieve its isolation duty. It’s a Vacuum Interrupter and Enclosed Air Break Isolator in series.

The Vacuum Interrupter provides the current break and make capability, while the isolator provides the “working point of isolation”.

When an operator opens a NOJA Power VISI-SWITCH®, the sequencing mechanism first opens the Vacuum Interrupter to break the line current, then automatically retracts the isolator. The isolator alone provides the Basic Insulation Level, or BIL.

When closing the NOJA Power VISI-SWITCH®, the order of operations reverse. The mechanism closes the isolator while no current is present, and then closes the vacuum interrupter to restore the circuit.

NOJA Power VISI-SWITCH Cross Section Diagram

The NOJA Power VISI-SWITCH® Isolator

The isolator is a sliding rod type contact, with air insulation. This isolator has 65mm of separation in air, providing 121 kV of isolation alone.

This rating does not rely on the Vacuum Interrupter. It is the rating of the isolation gap alone.

The vacuum interrupter only serves to break and make the current, so that the isolator operates “off load” and never has to perform current interruptions.

NOJA Power VISI-SWITCH Cross Section Diagram
NOJA Power VISI-SWITCH Cross Section Diagram

Why not only use the Vacuum Interrupter for Isolation?

A NOJA Power VISI-SWITCH® relies on the Isolator side for isolation, not the Vacuum Interrupter.

This is the component that offers the 121 kV BIL in accordance with the IEC 60071-1 Insulation Coordination Standard.

Vacuum Interrupters can allow non-destructive discharges across their interrupting gap. This is advantageous for circuit breakers, as it increases switchgear resistance to damage. However, in a load break switch, adding the series isolator prevents discharges across the VI from crossing the isolation gap.

It is a unique advantage of the NOJA Power VISI-SWITCH® design – the materials are sustainable, but the series connection of an isolator addresses the isolation shortcomings of vacuum interrupters.

The NOJA Power VISI-SWITCH® is a safe alternative to SF6 based load break switches

The NOJA Power VISI-SWITCH® is a type tested load break switch suitable for use as a working point of isolation. The isolation duty is taken care of by the 65mm enclosed air gap isolator, providing 121 kV BIL alone.

When paired with the VI in series, the NOJA Power VISI-SWITCH® can interrupt load currents up to 800 A, with the isolator only ever being operated off-load, by the sequencing mechanism of the device.

“With net carbon zero mandated by 2050 and most organizations targeting net zero by 2030 the NOJA Power VISI-SWITCH® is the ideal solution to replace SF6 gas switches in your network,” says NOJA Power Group Managing Director Neil O'Sullivan.

For more information, visit or contact your local NOJA Power Distributor.

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