MainsPro G59 Mains Protection Relay – ComAp

The world of mains protection is changing, with the introduction of EREC G99-1. G99-1 will replace G59-3.4 on the 27th April 2019. Learn more about this new recommendation from the ENA here.

The ComAp MainsPro is a G59 3.4 and G99-1 non-type tested protection relay for mains-to-parallel applications, including generator sets, cogeneration, micro turbines or renewable energy sources such as photovoltaic plantswind turbines and hydro-electric.


It provides adjustable voltage, frequency and loss of mains protections to safeguard both the distribution network and the generators.

If you are generating power in parallel to the mains, you will need ‘loss of mains’ protection. This is essential to avoid supplying your electricity into an islanded grid, which may lead to possible equipment damage or safety issues.

With MainsPro, no special knowledge is needed for installation and also no additional units are required. This makes it the ideal solution for personnel who are not specifically trained. The unit is designed to fully comply with Utilities’ connection requirements and statutory codes, offering a high level of protection and safety when working in parallel to the mains.

G59 3.4

Changes to G59 saw the implementation of G59 3.4 in July 2018. These updates affect all Non-Type Tested Generating Plants from 50Kw and above commissioned after 31st January 2018.

G59-3.4 has disallowed the future use of Vector Shift protection and provided new RoCoF requirements. Learn more about these changes here. 



G99-1 is an important change to mains protection. When it comes into effect on 27th April 2019, it will replace the current G59-3.4. Equipment that is currently compliant with G99-1 can also be connected under G59-3.4 as it will meet the existing conditions. Learn more here about the changes.


MainsPro G59 relay advantages

There are good reasons why the MainsPro G59 relay has been and remains the market-leading mains protection relay:

  • Unrivalled safety for installers and service engineers. The MainsPro offers years of experience with optimal safety features.
  • Compatibility with DNO testing procedures. A relay failure can lead to expensive commissioning delays while finding a replacement.
  • ‘Out-of-the-box’ compatibility with renewable and traditional power sources. Whatever the generation source, you can install the Mainspro G59 relay and keep total confidence that it will work.
  • Peace of mind. The MainsPro is the market’s premium product. Consultants, contractors and panel-builders know its flexibility and dependability allow them to concentrate on more complex parts of the installation.

MainsPro features

  • True RMS measurement for increased accuracy, reliable evaluation of failures.
  • Rate of change of frequency (ROCOF) protection
  • Symmetrical components for better detection of voltage asymmetry failures.
  • Two stage settings of voltage and frequency protections to cover short term as well as long term disturbances with appropriate priority.
  • Free assignment of 5 relay outputs allows wide range of signaling and trip methods.
  • Free assignment of 4 binary switches to remotely change operation of the unit.
  • Adjustable time delay of Automatic fault reset which avoids necessity of on-site personnel.
  • Universal power supply 8-40 VDC, 85-265 VAC, 110-370 VDC.
  • Selectable voltage range 120/230/400 VAC with over-range to 156/290/520 VAC makes the unit independent on application.
  • Supports 3-phase and 1-phase applications.
  • Last 5 trips record providing evidence of cause of trip.

Advanced communication, display and logging features are also available with the ComAp InteliPro.

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