A G10 or EGIP (embedded generation interface protection) relay is a supplementary grid protection device that acts as a critical safety shield for commercial scale solar PV systems connected to the electricity network in Ireland. Its primary job is to instantly and automatically disconnect your solar installation from the grid in the event of a fault or power outage, ensuring the upstream safety of the distribution network.
Why is a G10 Relay Necessary?
The core principle behind the G10 relay is the safety of utility workers. If the main electricity grid goes down for maintenance or repair, workers must be certain that the lines are de-energised. A solar PV system, however, will continue to generate power as long as the sun is shining. The G10 relay prevents your system from exporting its power onto a dead grid, a scenario that would be extremely dangerous for line workers who believe the network is off.
How Does a G10 Relay Work?
The G10 relay is an intelligent device that constantly monitors the quality of the electricity from the grid. It specifically watches key parameters like:
- Voltage: Is it too high (over-voltage) or too low (under-voltage)?
- Frequency: Is it stable at the standard 50Hz, or is it deviating?
If any of these parameters go outside the strict limits defined by the EN 50549-1 standard (the European standard for generators connected in parallel with distribution networks part 1), the relay will instantly "trip" a contactor or breaker, physically disconnecting your solar inverters from the ESB network.
When is a G10 Relay Required in Ireland?
A G10-compliant grid protection relay is a mandatory requirement for any grid-tied generation system that falls within small and large scale solar generation projects. This means it is required for all systems that need an NC5, NC5a or NC8 application with ESB Networks. Essentially, all commercial solar installations above 50kVA three phase rating require one.
The Role of the G10 in ESB Witness Testing
The correct installation and configuration of a type tested G10 relay is the most important part of the ESB witness test. During this test, an ESB Networks engineer will require a demonstration of the relay's functionality. This involves safely simulating grid fault conditions to prove that the G10 relay detects the fault and disconnects the system within the specified timing parameters. A successful G10 test is the final gate to getting your system fully commissioned.
About the Author
This guide was written by the engineering team at SMC Energy. As Chartered Engineers with deep expertise in electrical systems and grid compliance, we are committed to providing clear, accurate information to help businesses navigate their renewable energy journey in Ireland. Contact us for expert advice on your project.