What protection settings must a small wind inverter have under G98?

The protection settings themselves are not chosen by the householder or dialled in by the installer. They are built into the inverter by its manufacturer, confirmed by type testing, and recorded in the ENA Type Test Register, where manufacturers must always lodge their declarations of full compliance³. The householder's obligations are lighter: notify the distribution network operator after installation, and keep the paperwork.

This page sets out what G98 covers, the settings a small wind inverter carries, the trip and reconnection behaviour behind them, and how compliance is proved. It also notes where Northern Ireland differs, because G98/NI is a separate arrangement with its own equipment register⁴.

G98 in a nutshell: what it covers and when it applies

G98 and G99 are technical standards for the protection settings required for generators or storage assets to connect to electricity networks, acting as a safety mechanism to protect both the network and the equipment from faults². The distinction between them is one of size and process rather than of principle. G98 applies to all generation installations up to 16 amps per phase, which is single-phase systems up to 3.68kW and three-phase systems up to 11.04kW¹. G99 covers installations over 3.68kWp, which require prior approval from the DNO⁸.

For a domestic wind turbine, the practical effect is that a machine whose inverter output sits at or below 3.68kW per phase takes the simpler route. The G98 process applies to smaller systems up to 3.68kW single phase, requiring notification after installation⁹. The purpose is stated plainly by the network operator: G98 ensures small-scale generation installations connect to the grid safely and do not compromise network stability, safety or power quality¹.

Two conditions attach to that simplicity. The first is equipment: all small generation installation categories demand that all generating units must be connected via either EREC G99 or G98 type tested inverters¹⁰. The second is that the installation stays within the limit. Where a scheme crosses 3.68kWp, it moves to G99 and needs approval before connection rather than notification after it⁸.

The scope is technology-neutral. G98 is described as covering small-scale electricity generation such as solar panels or wind turbines with a capacity of 3.68kW or less per phase². A wind turbine is treated the same way as a solar array of equivalent inverter rating, which is why the settings discussed below are familiar to anyone who has read a solar inverter datasheet.

The protection settings a small wind inverter must have

The settings a G98 inverter carries are not a single number but a set of functions that together decide when the machine disconnects from the network and when it stays connected. The core functions are voltage protection, frequency protection and loss of mains protection. A mains protection relay product sold for this market describes its offering as adjustable voltage, frequency and loss of mains protections¹¹, which is a fair summary of the categories involved, though on a domestic inverter these are fixed in the type-tested configuration rather than adjustable by the user.

Loss of mains protection is the function that matters most for network safety. If the grid disappears, the inverter must stop exporting, because a generator that keeps energising a dead network is a hazard to anyone working on it. Voltage and frequency protection cover the slower disturbances: a supply that drifts outside the permitted band, or a frequency excursion that signals a mismatch between generation and demand.

The equipment condition is absolute. Generating units connected through the fast track process must use EREC G99 or G98 type tested inverters⁶, and the same requirement applies across the small generation installation categories¹⁰. Type testing is what turns a general claim of protection into a verified one: the manufacturer lodges a declaration of full compliance in the ENA Type Test Register³.

For a household, the independence point is straightforward. The inverter is the component that lets a wind turbine run in parallel with the grid rather than in isolation from it. It also introduces a dependence: the settings are the manufacturer's, the register entry is the manufacturer's, and if the company behind the inverter withdraws from the market the settings do not change but the support around them may. A small wind turbine inverter may need replacing once during the turbine's lifetime⁷, and the replacement must itself be a type tested unit for the connection to remain valid.

Frequency and voltage trip settings: the numbers that matter

The trip settings are the thresholds at which the inverter disconnects. They are defined by the engineering recommendation and verified by type test, which is why a compliant inverter's datasheet carries them as declared values rather than as options. The reason the numbers matter is that they are the boundary between a generator that supports the network and one that trips unnecessarily or, worse, fails to trip when it should.

The capacity figures that sit alongside the trip settings are the ones a householder will actually encounter. G98 applies up to 16 amps per phase, which is 3.68kW single-phase and 11.04kW three-phase¹. The G98 notify-after-install pathway applies for inverter output of up to 3.68kW per phase for most domestic installations⁹. In Northern Ireland the same 16 amps per phase limit governs eligibility, with G98/NI type tested inverters and G99/NI Type A type tested inverters permitted for installations up to that figure⁴.

That last row is worth pausing on. Where an installation includes an inverter, the rating of the installation is assumed to be the inverter's continuous steady state rating¹. The inverter, not the turbine's nameplate, is what the network operator counts. A turbine rated above 3.68kW paired with a smaller inverter can still sit inside G98 on that basis, and a turbine rated below it paired with a larger inverter cannot.

Reconnection settings after a trip

A trip is not the end of the event. The inverter has to decide when it is safe to reconnect, and that decision is governed by reconnection settings that are part of the same type-tested configuration. The general principle is that the inverter waits for the supply to return and stabilise before it resumes export, rather than chasing a flickering supply and repeatedly energising the network.

The practical sequence after a loss of supply is described in inverter support material: restore grid supply if interrupted, tighten or repair AC connections as needed, and restart the inverter after confirming stable AC voltage presence¹². That is a fault-finding sequence rather than a statement of the G98 reconnection delay, but it shows the logic the inverter applies: supply present, voltage stable, then reconnect.

Some protection relays keep a record of recent events. A mains protection relay sold for this market logs the last five trips¹¹, which is the kind of evidence that helps when a recurring trip needs diagnosing. On a domestic wind inverter the equivalent information is usually held in the inverter's own event log, and access to it may depend on the manufacturer's monitoring platform or app. That is a dependence worth naming: the protection settings are autonomous, but reading what they did often is not.

Reconnection behaviour also interacts with the turbine rather than only with the grid. A wind turbine that has been disconnected may be running unloaded, and the inverter's restart has to be coordinated with whatever control the turbine uses. Where a scheme includes a separate protection relay, the relay's settings and the inverter's settings both have to be correct, and the relay is a second device that can itself fail or be misconfigured.

Compliance and witness testing: proving the settings are right

Compliance under G98 rests on documentation rather than on a site measurement of every threshold. The manufacturer's declaration of full compliance sits in the ENA Type Test Register³, and the installer's job is to connect equipment that appears there. For a fast track connection application, the documents required include an approved inverter type test certificate and a G100 declaration⁶.

The forms differ by site. G98 Form A covers installations of generation or storage at multiple premises, and G98 Form B covers a single premises⁸. For a single domestic wind turbine, Form B is the relevant one. The notification itself is not optional even where no prior approval is needed: whether a scheme is G98 or G99 compliant, the network operator needs to be told so it can update its records⁶. For systems able to export up to 3.68kWp, that notification can be made within 28 days of installation⁵. Small systems usually only need the electricity network operator to be notified¹³.

Witness testing is the point at which the declared settings are checked against the installed equipment. The evidence trail is the type test certificate, the register entry and the completed form. Ongoing responsibilities do not end at commissioning: maintenance of the equipment is listed among them¹⁴.

In Northern Ireland the route is separate. G98/NI uses approved equipment, and the eligibility condition is that the installation is within the 16 amps per phase limit and uses approved equipment¹⁵. The compliant equipment list is maintained by NIE Networks⁴. A household in Northern Ireland therefore checks a different register from one in Great Britain, even though the capacity threshold is the same.

Where G98 stops and G99 begins

The boundary is 3.68kWp. Installations over that figure require prior approval from the DNO and fall outside the notify-after-installation arrangement⁸. For a wind turbine, that boundary is reached more easily than for solar, because a turbine's rated output and its inverter's continuous rating are not the same thing, and it is the inverter rating that is assumed for the installation¹.

Above the threshold, the G99 fast track process applies, and any generating units connected through it, including electricity storage, must use EREC G99 or G98 type tested inverters⁶. The equipment requirement does not relax as the scheme grows; it tightens, because approval comes before connection rather than after.

For a household weighing a small wind turbine, the practical reading is this. A machine that stays within 16 amps per phase connects on notification, with the protection settings inherited from a type-tested inverter and evidenced by a certificate. A machine that exceeds it needs approval first. Either way, the settings themselves are not a household decision. They are the manufacturer's declaration, the register's record and the network operator's condition, and the household's part is to keep the connection notified and the equipment maintained.