NOJA Power

Technical Article

Published 05/2024

Essential Renewable Connection Features with OSM Reclosers

NOJA Power GMK in the Solar Farm in NSW, Australia

The NOJA Power OSM Recloser system is commonly used to integrate grid scale renewable energy to the medium voltage distribution grid.

Connections using underground cables typically use the NOJA Power GMK product, while overhead network connections rely on the pole mounted OSM Recloser system.

Both of these architectures are based on the OSM Recloser with RC Series controls, but the GMK adds capacity for additional assets such as revenue metering and earth switches.

However, this common platform delivers a key list of essential renewable connection features.

In this article, we cover these essential renewable connection features, available on both the pole mount OSM Recloser and ground mount GMK devices as standard.

Multistage Frequency and Voltage Protection

As distribution network integration requirements have evolved, some grid standards call for graded responses to frequency and voltage excursions.

The bigger the deviation from system power quality specifications, the faster the islanding protection should respond.

NOJA Power’s OSM Recloser system with RC series control has 3 stages of over voltage, under voltage and frequency protection.

This allows protection engineers to program varied switchgear interruption response times subject to fault severity.

It also provides flexibility of response, allowing engineers to program the OSM Recloser to issue an alarm at a warning level, before transitioning to a circuit breaker interruption if the voltage or frequency deteriorates further.

This information can be all be reported via SCADA for central network management, improving visibility and reliability of the electricity distribution network.

NOJA Power OSM38 and RC-20 in Victoria, Australia
NOJA Power OSM38 and RC-20 in Victoria, Australia

Power Quality

Power quality is essential for network generators, and as generation assets become more distributed, managing power quality becomes a more expensive challenge.

However, NOJA Power’s OSM Recloser captures power quality metrics, such as Harmonics, Voltage Sags and Swells, and interruption data.

The NOJA Power RC-20 offers even greater power quality capabilities, capturing voltage and current harmonic spectra up to the 63rd harmonic.

This allows a NOJA Power GMK or OSM Recloser with RC-20 control to act as a Power Quality monitor at any point of connection, without additional cost. Problem power quality sites can be identified using the protection asset, in this case the OSM Recloser. Any site which requires further intervention can then be managed with further metering equipment.

This network design topology saves operators large capex, as PQ visibility becomes available throughout the entire network by leveraging the existing Recloser protection fleet.

Protection during Islanded Operations

As microgrid deployment becomes more popular, NOJA Power OSM Reclosers can be used in the open position as a monitor for microgrid issues.

For example, if a NOJA Power OSM Recloser is the connection between a microgrid and the main network, the OSM Recloser continues to monitor voltage on the microgrid side of the breaker.

If an earth fault on the microgrid side causes a Neutral voltage displacement, the OSM Recloser can detect this fault in the open position and report the microgrid fault back via SCADA.

This added layer of protection provides further network protection support without additional telemetry or protection control investment.

NOJA Power OSM Reclosers destined for this application should be installed with the ABC side of the breaker on the microgrid side. This ensures that the Neutral Voltage displacement reading is collected from the microgrid when the device is open.


There are many features included in the standard NOJA Power OSM Recloser system with RC series control, or the NOJA Power GMK, that make this product a popular method for connecting grid scale renewable energy.

“Our RC-20 control with inbuilt highly accurate Power Quality meter adds real value to embedded generation renewable connections where power quality monitoring is mandated,” says NOJA Power Group Managing Director Neil O'Sullivan.

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

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