In collaboration with Outram Research Ltd, SP Energy Networks & UK Power Networks

Please note: SP Energy Networks’ RTFLM image © Scottish Power Ltd 2021. See original article.

In 2010, SP Energy Networks and Outram Research Ltd (ORL) undertook an innovation project to develop a Natural Disturbance Fault Level Monitor (PM7000FLM), capable of predicting through measurement, the worst case fault levels (short circuit current) on distribution networks. This has been successfully utilised at 132kV, 33kV, 11kV and LV network voltage levels. Due to reliance on naturally occurring disturbances within the network, although portable and straightforward to deploy, the response time served as a drawback of the PM7000FLM for the purpose of using it in real-time, Active Network Management scenarios.

To overcome this, another innovation project was instigated by SP Energy Networks and later joined by UK Power Networks (UKPN) developing the Real-Time Fault Level Monitor (RTFLM), which incorporated a built-in disturbance generator to apply very small pulses of its own artificial load to the network. This reduces the fault level prediction time from weeks/days to seconds.

Motivation for PNDC testing

The RTFLM was field-trialled in SP Energy Network’s network in Chester, with results giving a positive outlook for future deployment. However, whilst both relevant and useful, there were limitations to these trials which collaborative work with PNDC has managed to overcome.

SP Energy Networks were unable to put a real fault on their network, so the only result comparison has been detailed network models rather than the actual fault value. Furthermore, there was a limit on the number of scenarios that could be reproduced/emulated, with limited repeatability of scenarios. Extreme/corner cases could not be effectively evaluated.

PNDC role

Testing of the RTFLM at PNDC was identified as a potential route to a comprehensive evaluation. Given the capabilities of PNDC in real-time simulations and hardware-in-the-loop experimental evaluations, the performance of the RTFLM algorithm could be effectively characterised for all cases of interest in a flexible and safe experimental environment.

PNDC evaluated the performance of the RTFLM under a number of network operating scenarios (e.g. radial and interconnected) and measurement locations using an SP Energy Networks’ network model in the RTDS. The RTFLM generated peak and RMS fault level estimates were compared for accuracy against the actual fault level in the RTDS model.



The testing was successful with the RTFLM exhibiting less than 1% error in fault level estimation when connected directly to the 11kV node of interest. Furthermore, its performance was evaluated under other connection arrangements giving the DNOs a guide in terms of suitable locations for RTFLM installation, as well as demonstrating the accuracy of fault level values generated at higher voltage nodes (1.3% at 33kV). These PNDC test results gave confidence to the DNOs to proceed with further field trials on their own networks as well as supplementary hardware testing in a European test house applying 3 phase bolted faults at 10.7kV and 37kV for direct Fault Level result comparison.

SP Energy Networks has directly embedded £42.8m of benefits within their RIIO-ED2 business plan submission, from deployment of Real Time Fault Level Monitoring and Active Fault Level Management, by reducing or deferring the need for traditional network reinforcement.
Full details can be found here: SP Energy Networks RIIO-ED2 Innovation Strategy

The RTFLM is much smaller than previously trialled iterations of active fault level monitoring equipment, creating less of a disruption to the wider environment and reducing deployment costs significantly.

Impacts all 14 licence areas in UK as well as having worldwide implications therefore having a positive impact across all electricity consumers.

Once we had all the tests set up the RTFLM responded as well as anticipated. Now, thanks to the RTDS set up in PNDC we have a clear, independently validated picture of the different interconnected network scenarios the RTFLM can be used for and importantly those it cannot. This technology has been dubbed a ‘gamechanger’ by those in the electricity industry and we are eager to get more units on the network where it can become a key enabler for future renewable generation connection.

John Outram,

Managing Director, Outram Research Ltd
Outram Research Ltd


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