Engineering Recommendation G99 came into force in the United Kingdom on 27th April 2019, replacing the earlier G59 standard. It applies to any new power generation or storage plant seeking connection to the UK electricity Distribution Networks of Distribution Network Operators.
The shift toward distributed generation (also known as embedded generation) has significantly changed the landscape. Unlike the past, where large central power stations supplied electricity, we now have more distributed generators at the local level (e.g., solar panels, wind turbines, etc.)
The G99 application/compliance is a set of engineering recommendations created by the Energy Networks Association (ENA) for the connection of any form of generator, including diesel generators and renewable solutions, to run ‘in parallel’ or ‘synchronised’ with the UKs main distribution electricity networks. It is key that the G99 standard is followed to help ease integration and stabilization to the electrical grid.
Steps to becoming G99 compliant
There is an application process to become G99 compliant and the type of connection needs to be identified. There are 4 different types of applicants:
- Type A: 0.8 kW to < 1 MW and connecting at a voltage <110 kV
- Type B: 1 MW to <10 MW and connecting at a voltage <110 kV
- Type C: 1 MW to <10 MW and connecting at a voltage <110 kV
- Type D: ≥ 50 MW or connecting at a voltage ≥ 110 kV [1]
The process can take up to 12 months and possibly even longer from project planning through to negotiating final connection terms depending on how prepared the applicant is. Even though G99 is classed as an Engineering Recommendation, if an applicant is trying to connect to the UK distribution grid and hasn’t completed this application process, though can demonstrate compliance, they will be refused connection.
What it means to be G99 compliant
G99 compliance ensures that inverters and other generation equipment operate reliably under various grid conditions, reducing the likelihood of system failures or disconnections. Compliance safeguards against potential electrical hazards, such as over-voltages or frequency deviations, and protects both the grid and the end-users.
G99-compliant systems can seamlessly integrate with the grid, promoting efficient energy exchange. In summary, G99 compliance is essential for safety, reliability, and the successful integration of renewable energy sources into the grid, which is why, if you are involved in renewable energy projects, understanding and adhering to G99 requirements is vital.
G99 compliance for Relays
Relays provide crucial protection for both system and plant, capable of initiating disconnection from the grid if there is an identified issue. G99 permits two types of acceptable interface protection; Type Tested Interface Protection and Non-Type Tested Interface Protection.
The use of Non-Type Tested Interface Protection systems will require testing and measurement to verify to the regulator that the protection meets the requirements. If a Non-Type Tested Interface Protection is applied, it is necessary to demonstrate that the relay meets all the requirements of G99.
Type Tested Interface Protection has its protection settings and firmware fixed during manufacture. If the need arises for a change to the original factory settings of the firmware, it must be undertaken by personnel that have been specially trained to perform this task, by the manufacturer, and will be password/pin protected or protected by a physical switch. The design will have been tested and verified to meet the relevant requirements of G99.
Usually, Type-Tested equipment, when installed by qualified personnel, will perform according to manufacturer’s expectations, however in some circumstances, on-site commissioning tests may be required to demonstrate compliance with the requirements of interface protection.
Tests to prove compliance with the standard can include calibration and stability testing of:
- Under/overvoltage protection.
- Under/over frequency protection.
- Rate of change of frequency protection (RoCoF, if used). [2]
RoCoF and vector shift stability testing should be carried out for all Interface Protection relays, whether Type Tested or not. Under/overvoltage protection and under/over frequency protection is only required when the Power Generating Module is operating in parallel.
There is also the generating module’s contribution to fault levels to consider. The risks associated with any overstressing during the short-term paralleling will need to be individually assessed and the process for controlling this risk agreed with the DNO.
How PSC can help
PSC’s global energy experts will help your organization deliver innovative solutions. Our engineers have extensive experience in G99 compliance studies and a proven record of successful applications, working with all types of connection types. PSC can navigate you through the entire process from the application phase to final connection terms.
Learn more about PSC’s Power Protection Services or contact us to find out how we can help.