UK G99 Type C and D Fault Ride Through and Reactive Power Guide

Key Takeaways

• EREC G99 is a legal requirement for certain generators connecting to the distribution network in Great Britain on or after 27 April 2019.
• All generators in Great Britain must have Loss of Mains (LoM) protection compliant with EREC G59, with an updated compliance date of 1 September 2022.
• The Rate of Change of Frequency (RoCoF) setting for LoM protection is now 1Hz/s with a definite time delay of 500 milliseconds, replacing vector shift.
• Specific public details regarding Fault Ride Through (FRT) and reactive power requirements for Type C and D generators are not explicitly detailed in general public sources from Distribution Network Operators.

What is EREC G99 and why does it matter for Type C and D generators?

Engineering Recommendation G99 (EREC G99) outlines the technical requirements for connecting generation equipment to the distribution networks in Great Britain. It is a legal requirement for certain generators connecting on or after 27 April 2019. This recommendation ensures that larger generating plants, including those classified as Type C and Type D, operate safely and reliably when connected to the national grid.

The electricity distributor has a duty to make a connection between its distribution system and any premises or another distribution system for the purpose of conveying electricity. However, this duty has exceptions, such as circumstances beyond their control, potential breaches of regulations, or if it is not reasonable in all circumstances to require them to do so.

Understanding Loss of Mains (LoM) Protection

Loss of Mains (LoM) protection is a critical safety feature designed to check if a generator is still connected to the supply network. This protection prevents a generator from continuing to energise a section of the grid that has become isolated from the main network, which could pose a safety risk to engineers working on the lines.

All generators connected to distribution networks in Great Britain must have LoM protection compliant with Engineering Recommendation G59. The compliance date for these updated EREC requirements was 1 September 2022. Previously, some LoM protection relied on a method called vector shift. However, where LoM is provided by vector shift, it must be removed and/or replaced with Rate of Change of Frequency (RoCoF).

RoCoF is the rate at which frequency changes and is used to detect the absence of the connection to the system. It disconnects the site if that RoCoF exceeds a specific value. The updated RoCoF setting requirement has been changed to 1Hz/s with a definite time delay of 500 milliseconds.

Fault Ride Through (FRT) and Reactive Power for Larger Generators

Fault Ride Through (FRT) capability refers to a generator's ability to remain connected to the grid and continue operating during short periods of voltage dips or disturbances. Reactive power is essential for maintaining grid voltage stability. Larger generators, such as those classified as Type C and Type D, are expected to provide specific FRT and reactive power capabilities to support grid stability.

However, specific details on Type C and Type D fault ride-through requirements and reactive power capabilities are not explicitly detailed in the publicly available sources from Electricity North West. These requirements are typically complex and depend on the specific characteristics of the generating plant and its connection point. They are usually found in more detailed Engineering Recommendations, grid codes, or specific connection agreements.

Compliance Requirements and Enforcement

Compliance with grid connection requirements, including EREC G99 and updated LoM protection, is mandatory for generators in Great Britain. Any generators who are not compliant and therefore require updates to their protection will be subject to an enforcement programme. This programme could ultimately result in the de-energisation of generation assets. Becoming compliant makes generation more reliable and less likely to trip off, ensuring more consistent generation.

What you can check yourself, and what you cannot

As a generator owner or operator, you can check that your system's Loss of Mains protection settings align with the current EREC G59 requirements, specifically the RoCoF setting of 1Hz/s with a 500 millisecond time delay. You should also verify that any older vector shift protection has been removed or replaced.

However, you cannot perform the detailed testing or verification of Fault Ride Through capabilities or reactive power performance for Type C and D generators yourself. These are complex technical assessments that require specialised equipment and expertise, typically carried out by accredited engineers or the Distribution Network Operator (DNO). Changing grid-protection settings without proper authorisation and expertise can breach your connection agreement and compromise grid safety.

What the published sources do not tell you

The publicly available sources from Electricity North West do not explicitly detail the specific requirements for Type C and Type D Fault Ride Through (FRT) and reactive power. These gaps include:

• Specific details on Type C and Type D fault ride-through requirements.
• Reactive power requirements for different generator types (Type C and D).
• Exact definitions and distinctions between Type C and Type D generating plants.
• Specific tests and procedures for fault ride-through for Type C and D generators.
• Specific reactive power capabilities or control requirements for Type C and D generators during grid disturbances.
• Specific voltage and frequency ranges for fault ride-through for Type C and D generators.
• Specific reactive power response times or accuracy requirements for Type C and D generators.
• Specific reactive power control modes (e.g., voltage control, power factor control) for Type C and D generators.

These details are typically found in more in-depth ENA guidance documents, the ENA Type Test Register, or are communicated directly by the Distribution Network Operator during the connection application process.