- HIOKI headquarters building, 3-phase 4-wire, 6.6kV receptacle, Secondary of PT
- 1 year from June 2003 to May 2004
Problem & Analysis
While measuring for 1 year at the receptacle of a 3-phase 6.6kV circuit, a voltage dip is detected only during a lightning strike. This voltage dip occurred 6 times in 3 consecutive days (August 5th to 7th, 2003). The residual voltage is very low and a long voltage dip period is detected on CH3 (T-R phase) as 4.708kV for 109ms.
The instantaneous high voltage is generated by a lightning strike which shorts the distribution cable and tower. Then, the fault current flows and the voltage drops. To remove this fault, the circuit breaker trips, but the voltage drops continues until that time (approx. 0.07s to 2s). This represents an instantaneous voltage drop (voltage dip) caused by a lightning strike.
Source : Guidebook for Power Quality Measurement, HIOKI E.E. Corporation