Learnings

Outcomes

Deliverable 1.3: Report of E-field sensor performance 
 
The work within this deliverable highlighted the electric field sensor performance, such as usability, sensitivity and reproducibility, against standard electric field profiles including plane-plane, sphere-plane, sphere-sphere geometries.  
The three considered test geometries provided examples of uniform and non-uniform electric field profiles, with repeatable results. The simple geometries were also simulated within Comsol, to provide a baseline electric-field profile, which was used to verify the measurements obtained using the electric field probes. Measurements were performed within the HV labs, with voltages up to 15 kVrms across the geometries, and generating electric fields up to 12 kV/cm. The voltages were increased in 1 kV steps, to understand the sensitivity of the sensors to change in electric fields. The sensor probes were placed within the field in the tests, and were stationary throughout the voltage application.  
The results highlighted a difference between 0.2 and 20% between the measured and simulated results, with the largest margin observed for the case of non-uniform geometry. This difference can be explained by the nature of the simulations, and also the difficulty in accurately mapping the locations of the probes in a 3D space for comparison with idealised scenario simulations. Despite the observed difference in the measured/simulated values, the sensor itself responds to small changes in fields, highlighting the capability to be able to develop electric field profiles of more complex geometries. The current exercise also allowed the team to understand the use of the probes, with significant learnings in data interpretation, repetition and positioning of the sensor.  

The research team also identified problems with one of the three sensors, and recognised that erroneous measurements were being recorded by one of the probes. This was identified during the above testing exercises and later sent for replacement from the parent company. However, the two working probes provided evidence to enable progression to the next part of the project, and start measuring electric field profiles of insulator samples. 

Deliverable 2.1: Bespoke rig building with design documentation and CAD drawings (Month 12) 

The key tasks of this deliverable were to build a complex rig, that could hold onto a small number of cap and pin insulators (currently set at 6 sheds). 
 
The idea behind such a system was to employ an actuator stand capable of holding an insulating arm "rod"  on which the electric field sensors’ probes would be installed. To measure the electric field on the surface of healthy and unhealthy "faulty" insulators from various angles, the actuator stand can be moved vertically (up/down) to position the probes at each cap and pin unit. The original idea also involved a motorized head, which would hold onto the small-scale samples. This motorized head would rotate the insulator along the central axis.   
 
However, without suitable tension within the system, the motorised head would only rotate the first cap and pin section, leaving the subsequent pins stationary. To avoid this, a circular track was designed, along which the vertical actuator system would move. This would provide the rotational aspect of the sensor. enabling the electric field probes to measure the electric field at each unit with distinct coordinates. However, further analysis of the initial design highlighted some challenges that made the system difficult to implement and construct. Some of the challenges are highlighted below:

• The framework and stand included significant metal components. The large metal framework could potentially cause electric field interference, which could possibly skew the results of the insulator samples.
• Whilst the vertical movement of the actuator was not an issue, the horizontal movement provided challenges. A simultaneous control of both these axes required significant precision, highlighting the need for a complex automated system and adding further risk with component failure (and delays in the project). 
• The sheer complexity of the rig required several suppliers to provide different components to be brought and assembled (and automated) at the University. This added further delays and costs to the rig.  

In order to overcome the above challenges, it was decided to move to an automated robot arm, which was capable of performing all the complex measurements and actuations required for probe manipulation along the small-scale insulators.  
 
The insulators itself are now held using an engine block, as the robotic arm provides the necessary actuation around the circumference of the sheds. 
Initial results have highlighted positive feedback between the arm and the controller, allowing for more accurate readings to be performed within a 3D space.  
 

Recommendations for further work 
The electric field measurement system could also be applicable to other HV assets. However, the assessment of the sensor is yet to be done on full-scale assets, and this is the future work within the current project. 

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 is provided within the report/Document “D1.3 Report on sensor performance against standard electric field profiles, sensitivity and usability.  
 
Dissemination  
The project has it’s first conference paper accepted at ICD 2024. The paper titled “Electric Field Mapping by Electro-optical Probes in known Geometries under High Voltage”.