Voltage Uprating

An increase of the voltage level allows for a significant increase of the transmission capacity in the existing right of way. The feasibility of voltage upgrade depends on the detailed assessment of the air clearances, required tower adaptation, the further use of existing conductors and also permissible electromagnetic emissions (E- and H-Feld and audible noise).

Technology Types

Essentially, there are two methods for voltage uprated in the existing right of way:

  • Use of the existing towers with smaller adaptation of the tower layout and insulators.
  • Removal of old towers (e g. 220 kV) and the erection of new towers for a higher voltage level (e.g. 380 kV). Thereby, the 220 kV right of way is kept.

Components & enablers

  • New insulators
  • Conductor bundles
  • Tower reconstruction or new tower
  • Transmission line surge arresters (TLAs)

    • Non-gapped line arresters (NGLA)
    • Externally gapped line arresters (EGLA)

Advantages & field of application

A voltage uprating of the existing OHL is an efficient way to increase the capacity. In particular, the use of existing towers and conductors minimises investment costs. Although the larger required air clearances can be solved by some technical adaptations, the increase of electro-magnetic fields and noise emissions is a much more challenging issue. For this reason, this option is particularly suitable up to 220 kV and in areas with low population density.

The second option is to use the existing right of way, remove old towers and replace them point-on-point with new towers that are suitable for higher voltages. To fulfil the requirements related to the air clearance, audible noise and electromagnetic fields, the new tower designs (typically higher compared to the old line) and arrangements of the conductors must be used. For this option, many technical solutions exist. Some examples are:

  • Use of V-Insulation string for reduction of conductor swing out
  • Single level arrangement of pure aluminium conductors that hang on low sag steel wires
  • Application of surge arresters

Technology Readiness Level

TRL 9 up to 170 kV

TRL 7 ≥ 245 kV

Research & Development

Current fields of research:

New tower designs and conductor arrangements, that allow boundary conditions to be fulfilled.

Best practice performance

Depends on specific grid configurations.

Best practice application


[1] S. Venkatesan, A. Haddad, H. Griffiths, N. Harid and M. Albano. Reducing air clearance requirements for voltage uprating of overhead line by use of line surge arresters. [Link]

[2] Siemens. Line surge arresters. [Link]

[3] Pterra Consulting. Why not voltage uprating as a planning option? [Link]

[4] B. Zemljaric and M. Jerele. Experience with uprating 35 KV overhead line to 110 KV voltage level using post line insulation. [Link]

[5] S. Venkatesan, R. Bhattarai, M. Osborne, A. Haddad, H. Griffiths and N. Harid. A case study on voltage uprating of overhead lines-air clearance requirements. [Link]

[6] Berlijn S M, Halsan K, Lundquist J.. Voltage Uprating of Statnett's 300 kV Transmission Lines to 420 kV. [Link]

[7] K. Niall und A. Walsh. Maximising benefits from distribution losses management - An ESBN perspective. [Link]