Learnings

Outcomes

D2.4 and 3.2 Both these deliverables and the summary are the results of the electric field measurements on the full-scale test rig against the FEA simulations.  This deliverable will also report the UAV influence on the electric field.

This deliverable investigated the application of compact, non-contact electro-optic (EO) probes for measuring electric-field (E-field) distributions along high-voltage cap-and-pin suspension insulator strings. The primary objective was to identify defective insulator units, particularly shorted units that had completely lost their insulation capability, while supporting the development of future drone-based live inspection systems for overhead transmission networks. Initial studies demonstrated that EO probes could successfully detect defects by analysing E-field variations in both sweeping and point measurement modes. In sweeping mode, probes measuring the E-field component parallel to the string axis identified defective units through a reduction in field magnitude near the fault locations, while radial component measurements provided supplementary indications through profile crossing points. In point mode, radial measurements showed superior defect-localisation capability, accurately identifying faulty units using characteristic peak-and-valley patterns between insulator sheds. Experimental observations were validated using finite element analysis (FEA) simulations in COMSOL, confirming the reliability of the measured E-field distributions.

Building upon these findings, a full-scale 400 kV insulator string was subsequently investigated. The study demonstrated that defects could be identified using measurements taken only along the direction parallel to the string axis. Measured E-field profiles were processed using cubic smooth spline detrending and normalisation to align local minima with insulator pin positions. The second derivative of the splined profiles was then compared with simulated healthy-string profiles, where defective units appeared as distinct crest jumps at pin locations. For more challenging cases, particularly defects near the high-voltage end, the measured profiles were compared with a library of simulated defect scenarios to determine the best match based on profile shape and trough characteristics. The results confirmed that reliable defect identification can be achieved using only simulation-based references and a single EO probe, significantly simplifying future drone-integrated inspection systems for live high-voltage transmission assets.

To understand the impact of the drone on the e-field itself, a simplified UAV geometry representing the dimensions of a DJI Matrice 350 RTK platform was incorporated into the model as a floating-potential solid body. The UAV was positioned at different locations along the insulator string through a parametric sweep to emulate practical inspection movement during operation. Electrostatics physics and an extremely fine mesh were employed to ensure accurate field calculations. The vertical E-field component, denoted as Ev, was extracted along a representative measurement line corresponding to the probe location used in experimental studies.

Comparison of the Ev profiles obtained with and without the UAV demonstrated that both the overall profile shapes and E-field magnitudes remained highly consistent regardless of UAV position. Only negligible variations were observed as the UAV traversed the string. These results indicate that the physical presence of the UAV has minimal influence on the surrounding E-field distribution and therefore is unlikely to compromise defect detection or E-field measurements during live aerial inspection. The findings provide important validation for the feasibility of future drone-integrated EO probe inspection systems for high-voltage transmission assets. 

This comparison is reassuring to NGET, knowing that once this technology is adopted into business as usual, the insulation measurement readings will be accurate, reflecting the true values of the HV asset being tested. 

D4.2 Report summarising laboratory testing of UAV system in laboratory environment

Based on the feedback and design requirements learnt from the lab-based experimentation, and desktop version of the sensor, a compact drone-based device requirements were provided to the sensor manufacturer. The manufacturer, on the basis of the research and information provided in the requirements capture, has now developed a compact unit that is mountable on a drone. 

This new unit design will assist NGET to integrate the system on to existing NGET drones, keeping integration costs low, removing the requirement to subsequently purchase a purpose-built drone and the associated staff training.

D3.3 Software tool to record and monitor UAV measurements.

The drone capture requirements led to a simplification of measurement capture via the drone mountable version of the device. This device is now undergoing testing within the University of Manchester to understand if the data capture mechanism is compatible with both the drone system and also capable of capturing faults.

Depending on the results from this, it may allow for in-flight measurement display to the NGET drone crew. This would streamline data capture, with assurance the system is working as intended, through a live readout display.

Lessons Learnt

The electric field probe performance was tested on three different electrode geometries that provided distinct electric field profiles on which sensing performance can be evaluated. The fibre optic probes were used in experiments to measure electric fields within these electrode geometries, and hence test the sensitivity, usability and repeatability of e-field measurements. In parallel with experiments COMSOL FEA models of tested geometries were developed to obtain predicted localised electric field data for the considered geometries. The obtained COMSOL predicted e-field magnitudes were compared to the corresponding probe measured data for practical assessment of sensing performance. In all three geometries, the two probes yielded repeatable results and magnitudes. With increase in the voltage magnitude and associated electric field increase, the measurements formed a linear response for all electrode geometries. Differences between the COMSOL magnitudes and those recorded using the probes were observed, however these were associated with the placement of the probe within the electrode geometries, and variations within the actual COMSOL models. The results contained in this report provide sufficient evidence to deploy the sensors for the next stage of this project, which is the small-scale insulator string measurements. Detailed results of the sensor tests against electrode geometries are provided within the report/Document “D1.3 Report on sensor performance against standard electric field profiles, sensitivity and usability”. 

The future projects following the technical findings are highlighted below,

1. Improving the deployment process and associated vehicle for the E-field sensor will be required to ensure that measurements can be replicated reliably across different overhead line insulator configurations, including tension strings, suspension strings and multiple-string arrangements. In addition, the approach will need to be benchmarked for composite insulators; this should form part of the next phase of work, with a focus on understanding and validating the electric field profiles of composite insulators.
2. The E-field sensor has demonstrated the capability to detect anomalies within high-voltage assets associated with failures, ageing mechanisms of dielectric material degradation and integrity issues. This indicates that the sensor could be used to identify faults in assets such as bushings, sealing ends, post insulators and other equipment where electric-field distribution is an important design or condition-assessment parameter. Although the sensor has initially been developed for overhead line applications, there is potential to adapt and deploy it on other asset types, depending on business need. A further top-down assessment of vulnerable assets would therefore be useful to identify where the sensor could provide the greatest operational value and where future deployment should be prioritised.
3. A key area for further assessment is the development of digital twins that can integrate E-field sensor measurements with other relevant performance indicators, such as thermal distribution. This should begin with the development of high-fidelity finite element analysis models using established software, such as COMSOL, before comparing real-time sensor data with the corresponding digital twin outputs. The existing SIF project, FoSMo, is already exploring the integration of large datasets and the development of digital twin models. The E-field sensor data and recordings generated through this project could therefore be adopted within FoSMo to increase the value, impact and wider applicability of the project learnings.

Dissemination 

1. The project has its first conference paper accepted at IEEE ICD in Jul. 2024. The paper titled “Electric Field Mapping by Electro-optical Probes in known Geometries under High Voltage”.
2. The project has its first journal paper submitted to IEEE Trans. on Power Delivery in Jan. 2025, under review currently, titled ‘Condition Monitoring of Cap and Pin Insulator String by Electric Field Mapping using Electro-optical Probes with FEA Model Validation’
3. The project has two conference papers which will be shown at IEEE CEIDP in Sep. 2025. ‘Evaluation of the Impact of UAV Vibration on Defect Recognition of a Cap and Pin Insulator String’
4. ‘Condition Assessment of Composite Insulators-Based Electric Field Measurement Using Electro-Optic Probe’ Condition Monitoring of Cap and Pin Insulator String by Electric Field Mapping Using Electro-Optical Probes With FEA Model Validation (IEEE TRANSACTIONS ONPOWERDELIVERY,VOL.41,NO.1,FEBRUARY2026)
5. Evaluation of the Impact of UAV Vibration on Defect Recognition of a Cap and Pin Insulator String ( 2025 IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP)
6. Electric Field Mapping by Electro-Optical Probes in Known Geometries Under High Voltage ( 2024 IEEE 5th International Conference on Dielectrics (ICD) - Toulouse, France)