Problems with the IEC 60909 Calculation Method (And ENA G74) in CFG Dominated Networks
The IEC 60909 standard is well established, and used across most of industry to calculate the maximum fault currents that can occur on a system. The primary use of the standard is to select switchgear fault ratings. In recent years, problems have been encountered using the standard when calculating fault levels on networks with a […]
High EPR Sites and Hot / Cold Classification
Introduction When we carry out an earthing study for a site, one of the key questions we try and answer quickly are ‘Is the site a Hot Zone?’ and ‘Is the site a high EPR Zone?’. Back in the olden days (Pre 2020), these questions in the UK regulatory framework really meant the same thing. […]
Earthing Studies: Fault Return Current – ENA S34 Calculations vs Detailed Models
Introduction In earthing studies, one of the most important steps to undertake is to calculated the fault current actually injected into the ground grid vs fault current that will return via metallic paths such as cable sheaths, as it is only the ground grid injection that causes an EPR and associated touch and step voltages. […]
Soil Resistivity Testing
Introduction Measuring soil resistivity by direct electrical measurement is fundamental to designing a safe and cost-effective earthing system. It is the foundation on which good design is built on. If the soil resistivity input data is wrong, then the entire earthing design will usually be wrong and this can lead to costly delays and rework. […]
ENA P28 – Point On Wave Switching for Large Sites With Multiple Transformers
A few weeks ago now, our MD (Steve Sommerville) gave a short presentation in Distributed Energy Resource (DER) Forum in relation to energisation of transformers on large generation sites with multiple transformers. The current P28 standard does not have a provision of how to consider these sites, and requires that all transformers are considered using […]
Network Curtailment Costs and a Way Forward?
An interesting article below from the BBC discussing the ongoing issue with constraints, and the overlap to zonal pricing. It is a hot debate, with a certain amount of heat on both sides, and as is often the case on contentious issues, the important detail often gets lost in the soundbites. These issues are a […]
NESO – Sub Synchronous Oscillations
Introduction NESO have been pushing for the majority of developers to carry out Sub Synchronous Oscillation (SSO) studies for all new generation systems connected to the network. This has always been the case for HVDC links, but now includes, Storage, Wind and Solar PV. Note this only applies to sites that fall under the Grid […]
Navigating NESO Grid Code Compliance
Obtaining an ION from NESO is becoming a more and more challenging task. Historically this was driven primarily by construction completion and testing. In more recent years this is being driven by meeting the paperwork and simulation studies requirements. Power system studies and analysis have moved from being a side issue to construction, to a […]
Ramp Rates for BESS Units and Voltage Change Limits – What is Credible?
Background A key question that has been causing some disagreement between DNOs and BESS operators is how to consider BESS units in terms of ramp rates, and the impact to the Step Voltage Change (SVC) and Rapid Voltage Change (RVC) for P28 compliance. This is not a simple / clear answer and needs some detailed […]
