Project at a glance:

Client ABB
Project PadihamSuper Grid Transformer (SGT) 4 Replacement
Location 400kV Substation

Impressed Voltage Study

Project Brief

ERM was approached by ABB to carry out an impressed voltage survey to ensure safety during a planned Super Grid Transformer 4 (SGT4) replacement at National Grid Padiham400kV Substation.

Our Approach

ERM acquired a comprehensive understanding of the works and activities that would take place in the substation and assessed these to identify possible impressed voltage hazards. ERM provides a detailed and thorough approach, analysing all aspects of the work with the aim of identifying and where possible eliminating risks from impressed voltage within the work area.


The unique nature of each impressed voltage study requires a large variety of approaches and recommendations in order to calculate and mitigate hazards. Numerous techniques are used which entail a variety of challenges including the following:

  • Gathering information on a wide range of work activities.
  • Gaining a holistic understanding of the electrical environment and the possible sources of impressed voltage.
  • Simplifying the environment to determine worst case sources and carrying our calculations to quantify the hazards.
  • Compiling practical, innovative engineering solutions to reduce impressed voltage hazards.

Project Outcome / Deliverables

The complex substation electrical environment was analysed by ERM and sources of impressed voltage were analysed and the risks quantified. A report and drawing were provided, which thoroughly described the hazards with guidance on methods of work or ways to reduce / eliminate the hazards where possible. The report was provided in the agreed time period, which enabled the works to be mobilised with no delays.

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