Induced Voltage and the Transformer effect.
Remember..
The presence of induced voltage may vary from day to day, hour to hour or minute to minute, it is impossible to eliminate, difficult to manage and does not go away.
Caution...
The effects of induced voltages, often overlooked, whether created by capacitance or magnetic flux can be lethal for power line workers and has caused many fatalities and injuries.
INDUCED VOLTAGE
Induced voltage may be caused by capacitance, inductance or climatic and ground conditions. It is pervasive, unpredictable, uncontrollable, difficult to manage and it doesn’t go away. Its magnitude and effect, may vary from day to day, hour to hour and minute to minute.
Induced voltage is facilitated by incorrect earthing arrangements and may be created when energised high voltage power lines cross over or run in parallel with denergised power lines. Values of 20kV at 1-2 amps for capacitive induction and 1.5kV at 20 amps for magnetic flux induction have been recorded.
Grounding induced voltage does not eliminate it, it merely transfers its effects to ground level where it creates ground rise potential (GRP). Due to the multiplicity of influencing factors and the inability to control induced voltage, line workers and ground workers are in constant danger from its effects.(Scroll down for images)
Earth loops are sometimes formed unintentionally and may occur as a result of the following:
- Station Earths being applied at both ends of the de-energised line
- “Boxed-in” / bracket grounding earthing arrangement on the de-energised line
- More than one set of earths on the de-energised line.
Current International best practice for worker protection:
Check if circulating currents are facilitated in earthing arrangements. Closely monitor induced voltage levels using GRP monitoring equipment and evacuate the worksite when hazards reach dangerous levels.
