Why Utilities Use NOJA Power OSM Reclosers as Sectionalisers

Globally, NOJA Power’s OSM Recloser is commonly used as a replacement for aged Sectionalisers. Decades ago, Recloser prices were far higher than sectionalisers. As global demand for reclosers has increased, economies of scale has brought the prices in line. In some jurisdictions, buying a remote control sectionaliser is now more expensive than a recloser, despite the technical superiority of the recloser product.

Today, the use of a sectionaliser is largely a legacy standard and operational works practices inertia. There isn’t a compelling reason defining why a sectionaliser should be chosen over a ”Recloser-with-isolator-links” combination.

Many utilities worldwide have realized this market movement, and leading network operators have made the switch, and here’s why.

Sectionalisers are automatic switch devices used in power distribution. They don’t have the ability to interrupt faults, instead they look for the interruption action of “upstream” breakers, and then open while the line is dead to reduce the outage area of a fault.

The engineering principle is to minimize the amount of overhead line that is taken out, when a fault occurs.

Sectionalisers “count” the number of upstream protection operations – that is, a recloser tripping and reclosing the line to interrupt the fault. After the sectionaliser has seen sufficient faults and corresponding zero currents (the interruptions), it opens while there is no current. When the upstream recloser closes after this action, power is restored up until the sectionaliser, and only lines downstream of the sectionaliser experience the outage.

There are two advantages to sectionalising. Let’s consider the traditional sectionaliser application case.

Firstly, they add more “sections” to a line, than what could be achieved with protection grading alone. If a substation circuit breaker is set to trip at 1000ms, and there are 4 reclosers on the line, then an example of time grading would have 800ms, 600ms, 400ms and 200ms for the tripping time of devices downstream. If a “grading margin” of 200ms is required between each device, then engineers have reached the maximum number of sections.

However, Sectionalisers can be fit in-between these devices, further reducing the network size.

Sectionalisers don’t race each other to trip, they wait until the upstream device trips. This allows the aforementioned 5 network sections to become 10 or more, as more sectionalisers are added.

If we assume there are spur-feeders off the mainline, sectionalisers become even more compelling, allowing the mainline to remain in service and graded.

But let’s consider the modern case.

Most modern recloser systems with microprocessor control, such as NOJA Power’s OSM Recloser, can use a grading margin of 100ms, rather than 200ms.

This allows utilities to deploy 8 reclosers on a feeder, before adding sectionalising. This also greatly reduces momentary outages. Unlike the traditional case where customer connections made between a sectionaliser and its upstream recloser have momentary outages, converting them all to modern reclosers means only faulted sections see momentary outages.

If further sectionalization is needed, then Reclosers can be configured to operate as a sectionaliser, just as NOJA Power’s OSM Recloser can do today.

Decades ago, sectionalisers used to be cheaper than a protective device, because they didn’t need to interrupt fault current themselves. However, advances in manufacturing technology and volume makes a recloser a cheaper alternative than a sectionaliser, despite being technologically superior.

The only other advantage of SF6 sectionalisers are their inherent isolation capability. However, this can easily be met by including a set of isolation links on the Recloser installations.

When an overhead device is used as a working point of isolation, the works crews are going to attend the site anyway to install the line earths. Pulling a set of links manually, locally, is a superior alternative when considering the protection and control versatility of a Recloser installation.

“Our OSM reclosers are the complete solution for overhead medium voltage switchgear today for both reclosing, sectionalizing, open points, automation and isolation with the addition of a set of disconnect links as part of the install,” says NOJA Power Group Managing Director Neil O'Sullivan.

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