NESO Compliance Process – Simulation Studies

At Aurora Power Consulting we routinely carry out compliance studies for large Grid Scale projects. The process can be challenging, and also time consuming. NESO currently are allowed 15 working days to review each UDFS submission, but are currently seeking to increase this to 20 days, and up to 6 weeks for EMT models and SSO studies.

We have put together a simple flowchart that shows the typical process that is followed. The stages are how we as a company group studies, and find that this approach benefits most of our Clients. Stages can be broken up over time, or completed sequentially. If you would like to know more, please get in touch.

We also have a handy flow chart detailing the stages and process.

Stage 1 – Core Studies

These studies are the key studies that need to be carried out as early as reasonably possible. These are needed to fix the design and equipment specification. The aim of these studies is to make sure the site can meet the required power delivery and quality requirements, and if not identify any mitigation measures like shunt MVAr compensation, additional inverters, harmonic filters or Point on Wave switching controllers.

Note that the short circuit study is not actually required by NESO, but is a key study needed to prove the system is safe.

Stage 2 – Detail Studies

These studies are used to finalize the design and confirm the settings of all necessary controllers for the PPC and Inverter and carry out tuning to get an acceptable response for the voltage and frequency response. These studies tend to attract a high level of review from NESO and form the backbone of the compliance process.

Common issues at this stage are problems with manufacturer / OEM models not correctly implementing all the required NESO functionality – such as lack of fast de-load functions in storage modules, and associated ramp rate limiters.

Stage 3 – Protection

A protection study will need carrying out before an ION is issued. Note that NESO do not formally review this study as such, but they need to be satisfied that one has been carried out and the protection settings are reasonable.

An arc flash study is sometimes carried out at this stage. Although this is not required by NESO.

Stage 4 – GC 0141 RMS & EMT Studies and SSO Study

This section is the ‘hard yards’ and where a lot of projects begin to struggle. We have provided a detail post on this process already which can be found here. The key to success at this stage is to plan ahead and make sure the vendor / OEM models are good.

The SSO requirements from NESO are very new and not well developed. There are a number of different strategies that can be adopted here, and it needs careful discussion with NESO before starting. Note that once the SSO studies are started no other changes should be made to the system or its control settings, as it would invalidate the whole SSO results.

This stage is the final hurdle in getting an ION. Do not underestimate how long this stage can take – it is recommended to allow at least 3 months.

Stage 5 – Validation

This stage occurs usually several months after the ION has been released and requires close out of all remaining points. A simulation study is carried out to validate the site settings and final values used and the DIgSILENT RMS and EMT PSCAD models.

Flow Chart

A flow chart of the process is shown below. You can download the flow chart from our website. If you would like to know more, please get in touch.