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 is caused by energised power lines running in a parallel with or crossing over de-energised lines. Induced voltage may also be caused by climatic and ground conditions. The presence and magnitude of induced voltage is influenced by the distance between the lines, the voltage of the energised line, the length of parallel run and the switching and loading of the energised line. Due to the multiplicity of influencing factors and the inability to control the effects of induced voltages, line workers and ground workers are in constant danger from its effects
The presence of induced voltage may vary from day to day, hour to hour or minute to minute and its magnitude and effect is also influenced by changing climatic and ground conditions.
INDUCED VOLTAGES CREATED BY CAPACITANCE:
Grounding induced voltage does not eliminate it, it merely transfers its effect to ground level creating ground potential rise (GPR). If ground resistance level is low the effects are not so serious, however, if ground resistance level is high there is a serious threat to ground workers. Values of 20kV and 1-2 amps have been recorded from capacitive induction
INDUCED VOLTAGE CREATED BY MAGNETIC FLUX:
Values of 1.5kV and 20 amps have been recorded for magnetic flux induction. In addition Induced voltage created by magnetic flux may create ‘earth loops’ allowing dangerous currents to circulate through the earthing conductors. (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 practicefor 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.
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