Power System Analysis

Ockendon-Medebridge G99 Compliance Project

A solar plant spanning two neighbouring sites, each with different owners, inverters, and control systems, faced a critical challenge in meeting G99 reactive power requirements. When one site could not deliver its share and combining the two still left a shortfall, the project demanded advanced simulations, technical investigations, and close collaboration with stakeholders. The outcome not only ensured compliance but also deepened the team’s expertise in managing the complexities of multi-site renewable projects.
Services:
Power System Analysis
Client:
Enviromena
Consultant:
Rishabh Abhinav, Senior Power Systems Consultant

 

Challenge

The solar plant comprises two adjacent sites: Medebridge, with a 49.9MW connection and Ockendon, with a 40.1MW connection. Each site is separately connected within the substation, ensuring independent operation.  With each site being owned by different developers and equipped with different inverters and Power Park Controllers (PPCs), there were challenges meeting G99 reactive power requirements. The Ockendon site was unable to fulfil its reactive power obligation, and combining the sites did not resolve the shortfall as the inverters could not supply the total required reactive power without exceeding its nominal rating.

Solution

We performed detailed load flow studies on both individual sites and the combined plant using DigSILENT PowerFactory. The simulations confirmed a reactive power deficit in the Ockendon site. To address this, we designed a capacitor bank to supply the deficit reactive power, ensuring compliance. Extensive coordination with developers, consultants, and the Distribution Network Operator (DNO) was required to resolve the issue of having multiple PPCs, as G99 mandates a single PPC governing the whole site.

Our Senior Power Systems Consultant, Rishabh Abhinav led the simulation studies which involved network modelling, configuring dynamic models of inverters and PPCs, and capacitor bank designing.

 

 

Impact

We performed several other RMS studies (Fault Ride Through, Frequency Response tests, and Voltage control tests) as a part of G99 compliance on the combined Ockendon-Medebridge solar plant and it successfully met the compliance. The study report was sent to the DNO for approval, enabling a smooth and compliant operation. The dynamic model of the PPC in this project had some configuration issues in the beginning for which we contacted the manufacturer.

We went through the multiple revisions of the model until it performed efficiently. This project enhanced our consultant’s technical expertise in configuring and debugging dynamic models.

Next Steps

We are currently working on the G55 harmonic compliance for the plant. We also aim to improve preparedness for PPC-related technical challenges in future projects.

 

 

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