The effect distances, from aerial HV energized conductors, have on electrostatic coupling to vehicles and machinery: CIRED 2025 Paper
When working within the vicinity of energized Over Head Lines (OHLs) the risk of induced voltages is present due to electrostatic and electromagnetic coupling between the live aerial conductors and machinery/vehicle/plant item below. As per UK legislation GS6, persons operating within a work area must manage health and safety. UK network operators require that Impressed Voltages are identified, and mitigation actions implemented where needed. In this blog post, we will analyze the induced voltage onto unearthed machinery in the vicinity of OHL circuits (400kV-11kV).
Modeling of work activities
A range of HV OHLs (400kV – 11kV) were modeled for this study. Each circuit was given worst-case parameters. For the voltage ranges 400kV-132kV, both transposed and untransposed circuit arrangements were modeled. Two types of machinery have been modeled within CDEGS to analyze the voltage induced due to adjacent OHLs. These are a crane and small plant item; it was assumed that no field earths were applied.
With these assumptions in place, this allowed the HIFREQ module of CDEGS to study the induced voltages onto the machinery and compare the estimated values against tolerable limits. The 50V SELV limit was applied based upon the assumed human resistance of 1000Ω (hand – feet) and fatal current of 50mA.
Key results of study
From the comprehensive simulations conducted the following minimum safety distances could be observed using the 50V SELV limit.
| Circuit Voltage Level | Minimum Distance from Centre Line Inducing <50V | |
| Crane | Small Plant | |
| 400kV – Untransposed | 100m | 90m |
| 400kV – Transposed | 60m | 60m |
| 275kV – Untransposed | 80m | 70m |
| 275kV – Transposed | 50m | 45m |
| 132kV – Untransposed | 50m* | 45m* |
| 132kV – Transposed | 30m | 18m |
| 33kV | 16m | 16m |
| 11kV | 10m | 10m |
* Induced voltage lower than 50V at 14m due to phasing arrangement, however, exceeds SELV limit at 16m.
As previously stated GS6 states hazard management is to be carried out up 10m away from the closest aerial conductor measured at ground level. However, the results of this study have shown that the induced voltage due to electrostatic coupling can exceed the 50V SELV limit up 90m away depending on the voltage level the circuit. It is worth noting that worst case information for the conductor height and current flow per phase has been utilized for this study, and these situations may be present for some UK systems; Therefore, it would be recommended that where work is carried out within the calculated minimum distances, Impressed Voltage studies are conducted to identify whether mitigation actions (such as field earths being used) are required to ensure safety of workers.
How PSC can help
At PSC, we understand the critical nature of compliant and safe work practices for your project.
Our specialists combine deep industry knowledge of impressed voltages with the power of SES CDEGS to provide a comprehensive analysis that turns technical challenges into reliable, effective solutions.
By partnering with us, you gain a trusted partner committed to ensuring the personnel work effectively and safely during all projects conducted near live systems.
Contact our specialist team to learn more about our services and how we can help.
