NOJA Power

Technical Article

Published 03/2022

Top 5 Build Options for a NOJA Power GMK

The NOJA Power GMK is trusted worldwide as a reliable way to protect and control underground electrical equipment. Whether it’s a renewable generation connection, industrial three phase load, or even rolling stock, the NOJA Power GMK has delivered reliability and cost savings.

Key to its success are the varied GMK build options. With these options integrated into the GMK and factory tested in Brisbane, Australia, commissioning and on-site engineering becomes much more simple.

To see more of our successful use cases, visit NOJA Power GMK.

“The beauty of our GMK product is its flexibility to provide the complete medium voltage grid interface solution in one, easily customised to meet customers' exact requirements,” says NOJA Power Group Managing Director Neil O’Sullivan.

In this article, we explore 5 of the most commonly requested build options for a NOJA Power GMK.

1. Earth Switch

Any consideration of asset ownership should consider works practices. When using a GMK, engineers often integrate many components of a single line diagram into the single assembly.

Adding an Earth Switch is a welcome addition on most GMK projects, as it allows operators to use the circuit breaker for current interruption, then the earth switch for equipment earthing, followed by unplugging the DIN Terminals for isolation.

The NOJA Power GMK Earth Switch Option incorporates a pad-lockable, mechanically interlocked earth switch within the GMK assembly. This ensures the earth switch cannot be closed while the breaker is closed, meeting works practices requirements and enhancing operator safety.

Inside of NOJA Power GMK with Interlocked Earth Switch and Three Phase metering PT
The High Voltage Compartment of a NOJA Power GMK, fitted with optional Interlocked Earth Switch (top) and Three Phase metering PT (bottom) © NOJA Power 2022

2. Metering Equipment

With the GMK’s most common application being private infrastructure and renewable generation, metering equipment is high on the list of build options.

Metering CTs can be specified by the procuring engineer, and NOJA Power build these CTs into the connection bay. Connections are wired back to a terminal block in the Low Voltage compartment, and the inclusion of an optional Revenue Meter completes the meter installation.

A NOJA Power GMK Complete with Revenue Meter and additional Power Quality Instrumentation © NOJA Power 2022
A NOJA Power GMK Complete with Revenue Meter and additional Power Quality Instrumentation © NOJA Power 2022

3. Integrated Auxiliary Voltage Transformer

Some GMK sites require a self powered design.

In these cases, NOJA Power can fit an additional step down transformer in the GMK, providing auxiliary supply for the control and instrumentation. This addition makes the GMK more versatile and mobile through removing reliance on an external low voltage supply.

Of course, if onsite DC or LV AC is available, the control instrumentation can be powered from this source too.

4. Differential Protection CTs

Among the most simple, elegant, and rapid protection techniques, differential protection provides sensitivity and reliability beyond point protection solutions.

These CTs can be Low Voltage insulated, as the insulated underground cables are brought through the CTs before being terminated onto the DIN Terminals. This offers a significant cost advantage over MV insulated CTs.

The GMK has provision for optional differential protection CTs, with outputs being wired back to the Low voltage compartment terminal block.

The GMK High Voltage Cable Bay with Differential Protection CTs (bottom) and Earth Bar © NOJA Power 2022
The GMK High Voltage Cable Bay with Differential Protection CTs (bottom) and Earth Bar © NOJA Power 2022

5. Power Quality Instrumentation

These days, most new GMKs that require Power Quality monitoring use NOJA Power’s flagship RC-20 Recloser Control. This unit offers power quality monitoring the 63rd harmonic, meeting application requirements for most renewable generation and industrial connections.

If additional power quality metering is required, it’s a case of including the additional sensors in the build and wiring their connections to the low voltage cabinet. The GMK has plenty of mounting real-estate for third party relays and equipment.

A NOJA Power GMK connecting renewable energy to the Medium Voltage Distribution Grid © NOJA Power 2022
A NOJA Power GMK connecting renewable energy to the Medium Voltage Distribution Grid © NOJA Power 2022

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