A G59 application is the formal process and associated technical requirements for connecting certain types of electricity generating equipment to the national grid or a local electricity distribution network in the UK. This application ensures that any embedded generation, such as renewable energy systems or Combined Heat and Power (CHP) units, can operate safely and reliably without negatively impacting the stability and quality of the existing electricity network.
Understanding Engineering Recommendation G59
G59 refers to Engineering Recommendation G59, a technical standard published by the Energy Networks Association (ENA) in the UK. It sets out the requirements for the connection of generating plant to Distribution Network Operator (DNO) networks. While it primarily applies to generators above 16 Amperes per phase (approximately 3.68 kW per phase for single-phase, or 11.04 kW for three-phase systems), specific requirements can vary, and it's essential to consult the latest DNO guidelines.
The core purpose of G59 is to:
- Ensure the safety of grid operators and the public.
- Prevent damage to grid equipment.
- Maintain the quality and stability of the electricity supply for all consumers.
- Facilitate the safe disconnection of embedded generators during grid faults or maintenance.
The Role of the G59 Mains Protection Relay
A critical component in fulfilling G59 requirements, and central to a G59 application, is the G59 compliant Mains Protection Relay. This advanced electronic monitoring device continuously assesses the quality and stability of the mains electricity supply to which the generator is connected.
The relay is programmed with specific, fixed parameters dictated by the Distribution Network Operator (DNO), ensuring strict adherence to grid standards. These parameters typically include:
- Voltage: Monitoring for over-voltage or under-voltage conditions.
- Frequency: Ensuring the grid frequency remains within acceptable limits.
- Rate of Change of Frequency (ROCOF): Detecting rapid changes in frequency that could indicate grid instability.
- Phase Angle: Checking the synchronization between the generator and the grid.
Should any of these parameters fall outside the programmed thresholds, the G59 relay will automatically and swiftly disconnect the embedded generator from the mains supply. This protective action is crucial for preventing:
- Islanded Operation: Where the generator continues to power a portion of the grid even after the main supply has failed, posing a safety risk to engineers working on the lines.
- Grid Instability: Preventing unsynchronized or faulty generation from disrupting the wider network.
- Equipment Damage: Protecting both the generator and grid infrastructure from potentially damaging electrical events.
Why is a G59 Application Necessary?
Submitting a G59 application is a mandatory step for connecting generating equipment above a certain size to the UK electricity network. It provides the DNO with essential information about the proposed generation system, allowing them to assess its potential impact on the grid.
The application process typically involves:
- Submission of Technical Data: Providing detailed specifications of the generating equipment, including the type, capacity, and protection schemes (especially information about the G59 relay).
- Network Impact Assessment: The DNO evaluates how the new generation might affect their network's capacity, voltage, and fault levels.
- Approval and Connection Agreement: Upon satisfactory review, the DNO issues approval, often with specific requirements or modifications needed before connection. A formal connection agreement is then established.
- Commissioning and Testing: Before final operation, the G59 protection relay and the entire generation system undergo rigorous testing, often witnessed by the DNO, to confirm full compliance with G59 standards and safe operation.
This robust application and testing process ensures that all embedded generators contribute positively to the energy mix while upholding the safety and reliability of the national electricity infrastructure.
