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Impressed voltage

Impressed voltage

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Impressed voltage (IV) is an umbrella term used by many in the electrical power industry to encompass the following: 1. Capacitive coupling (arising from the electric field and voltage source) 2.Inductive coupling (arising from the magnetic field and current source) 3.Conductive coupling (arising from current flow through a connection with earth) 4. Trapped charge (arising from residual charge left on the capacitance of an item of equipment). The term IV relates to the existence of a voltage on an item of equipment, or metallic object, which is not directly connected to the energised power system, but which has arisen as a result of either an electrical coupling mechanism, or a residual charge at the time of circuit de-energisation. Such voltages can be dangerously high and a source of danger and therefore must be eliminated before contact is made with the equipment/metallic object. IV is a significant safety hazard to be managed and controlled on any electrical construction site.

Chapter Contents:

  • 11.1 Impressed voltage — composition
  • 11.2 Permanent and temporary works
  • 11.3 Impressed voltage — principles
  • 11.3.1 Capacitive coupling — principles
  • 11.3.2 Inductive coupling — principles
  • 11.3.3 Conductive coupling — principles
  • 11.3.4 Trapped charge — principles
  • 11.4 Inductive coupling — analysis
  • 11.4.1 Current transformer analogy
  • 11.4.2 Inductive coupling — position of induced emf
  • 11.5 Physiological effects of electricity
  • 11.5.1 Electric shock
  • 11.5.2 Impedance model of the human body
  • 11.5.3 Electric shock — current thresholds
  • 11.5.4 Electric shock — voltage thresholds
  • 11.5.5 Touch potential — safe voltage threshold
  • 11.5.6 Single phase to earth fault — inductive coupling safe voltage threshold
  • 11.5.7 Balanced load current — inductive coupling safe voltage threshold
  • 11.6 Capacitive coupling — IV magnitude calculations
  • 11.6.1 Conducting plane images
  • 11.6.2 Three-phase coupling
  • 11.6.3 Example of capacitive coupling
  • 11.7 Inductive coupling — IV magnitude calculation
  • 11.7.1 Conducting plane images
  • 11.7.2 Three-phase coupling — balanced load current
  • 11.7.3 Single phase to earth fault inductive coupling
  • 11.7.4 Example of inductive coupling
  • 11.8 Practical considerations
  • 11.8.1 Combined effect of capacitive and inductive coupling
  • 11.8.2 Capacitive vs inductive coupling — severity
  • 11.8.3 Working in an air-insulated substation
  • 11.8.4 Rules and guidance for controlling IV
  • 11.8.5 Microshocks
  • 11.8.6 Overhead lines
  • 11.8.7 Long metallic objects
  • 11.8.8 Operational considerations
  • 11.8.9 HV cables
  • 11.8.10 Electric field shielding
  • 11.8.11 Magnetic field screening
  • 11.8.12 GIS enclosures
  • 11.8.13 GIS switchgear — trapped charge
  • 11.8.14 Air cored reactors
  • 11.8.15 Electric and magnetic field design limits
  • 11.9 The management of impressed voltages

Inspec keywords: electrical safety; electricity supply industry

Other keywords: electrical construction site; inductive coupling; capacitive coupling; impressed voltage; trapped charge; residual charge; circuit deenergisation; safety hazard; electrical power industry; power system; IV; electrical coupling mechanism; conductive coupling

Subjects: Power system management, operation and economics

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