Grounding, Electromagnetic Interference and the Power System Industry

Most electric power engineers must regularly deal with design and operational problems whereby portions of the phase currents following along undesirable paths result in various effects ranging from minor annoyances to spectacular failures. A significant number of these problems are related to grounding and electromagnetic interference. A good understanding of these subjects and appropriate engineering software tools is critical to every power utility which is concerned with the safety and reliability of its system and its responsibility towards the public and its employees. The following discussion underlines the importance of grounding and electromagnetic interference.

1. Power system networks, ideally, should carry balanced three-phase power currents on the network. Typically then, currents are restricted to flow along predetermined metallic paths or earth. In practice, however, there is always an unbalance due to unsymmetrical system components and loads. This results in current flows in so-called "unenergized paths" and earth. The result of this varies from imperceptible effects and minor annoyances, to significant equipment damage and safety hazards. In addition to these "steady-state" unbalance conditions, one must regularly deal with abnormal conditions ranging from naturally triggered fault conditions (such as lightning) to equipment malfunctions or failures and vandalism.

2. Although three-phase balanced normal and abnormal power flow analysis techniques are well understood and perfectly predictable, current flows outside the three phase network (i.e., earth, skywires, neutral wires, metallic sheaths and various conductive structures) are extremely difficult to estimate using conventional circuit theory or approximate methods, mainly because neutral currents are no longer constrained to flow along dedicated paths (such as skywires) but can freely flow in soil along complicated three-dimensional paths.

3. The effects of such current flows are numerous and encompass many power system specialities such as:

  1. Grounding and all its ramifications which range from:
    • safety issues (touch, step and transferred potentials).
    • conductive coupling to pipelines and metallic structures.
    • ground potential rise (GPR) and its effects on telecommunication equipment and phase neutral shifts.
    • protective system malfunctions due to circulating currents and voltage stresses on electronic circuitry.
    • transient problems involving lightning and switching of power system equipments such as breakers and capacitor banks.
  2. Electromagnetic interference problems such as:
    • induction to gas, oil or water pipeline systems.
    • audio noise in telephone and communications circuitry.
    • coupling to fences and elongated metallic structures.
  3. Magnetic and electric fields and related public issues which involve:
    • magnetic fields from residual currents in distribution systems.
    • magnetic fields generated by buried neutrals and pipes carrying "residual" currents.

4. Accurate computation of such effects was virtually impossible (except for very simple generic cases) before the advent of the "computer" and "software" era. Nowadays, specialized software coupled to powerful computer platforms allow accurate predictions of these effects. The complexity of the phenomena however, requires not only engineering specialization and commitment but genuine management awareness and support in order that the benefits of this new knowledge acquisition result in significant returns on the investment. The direct and indirect benefits, however, can be phenomenal: typically 10 to 100 times the investment within the next five years and more than 1000 times within ten to twenty years. These benefits are summarized hereafter.

5. The benefits which result from investing in state-of-the-art accurate engineering analysis solutions to grounding and electromagnetic interference problems can be categorized as follows:

  1. Benefits to the power system utility:
    • accurate, realistic engineering designs which provide optimum performance at economical cost. Potential problems are identified at the design stage and costly operational mitigation additions or modifications are avoided.
    • lengthy discussions and conflicting arguments and opinions are eliminated because authoritative trusted methods are used to generate the design.
    • standardization based on comprehensive modelling is made possible.
    • court cases involving incidents, prospective problems, and environmental issues can be fought or settled out-of-court with great confidence and understanding of the events, topics and responsibilities.
    • the quality and superiority of the designs will have significant long term effects on the reliability of the network and will result in substantial reduction of power system faults and failures resulting from power frequency and transient voltage stresses generated by grounding conduction and electromagnetic interference.
  2. Benefits to the public as a result of:
    • more economical and more reliable power supply as a consequence of less power system faults and reduced equipment failures.
    • safer power system installations and less inductive interference problems.
    • better mitigation or elimination of environmental electromagnetic fields.
    • increased trust and confidence in the electric power utility through the perception of leadership in accurately assessing public concerns.
  3. Benefits to the utility engineer who:
    • is no longer helpless when faced with complicated engineering problems and who no longer is subjected to the frustration of suggesting designs or mitigation based on unreliable, incomplete methods.
    • acquires significant knowledge and understanding of a difficult but highly challenging engineering subject.
    • feels useful, respected and appreciated by his colleagues and his management.
6. The following publications and papers provide a written testimony of the direct benefits which have been derived by a number of utilities currently using the CDEGS software, a leading package specializing in grounding and electromagnetic interference and developed by SES & technologies ltd.