Measurement/Experiment 1) Observation The lightning surge currents in common mode and differential mode were observed in ten systems where failure often occurred. Two types of waveform and occurrence probability were obtained. The data are summarized in Table 2.9-1 and Figure 2.9-3. Malfunctions occurred with both waveforms. The peak current values were about 30 and 300 A, respectively. Table 2.9-1 – Observed waveforms Type of waveform Characteristics of waveform Common AC mains Differential AC mains Ground line Only differential mode appeared 77% 30 0 –30– 0.5 0 0.5 1.5 2 30 0 –30– 0.5 0 0.5 1.5 2 30 0 –30 –0.5 0 0.5 1.5 2 Current [A] Current [A] Current [A] Lightning Time [ms] Time [ms] Time [ms] About 300 sets Common AC mains Differential AC mains Ground line 2000 0 –2000 500 0 –500 300 0 –300 Common and differential and ground appeared Current [A] Current [A] Current [A] –0.5 0 0.5 1.5 2 –0.5 0 0.5 1.5 2 –0.5 0 0.5 1.5 2 23% Time [ms] Time [ms] Time [ms] 20 Current [A] Only differential appeared Peak current was 20 A. And the half-time value was from several milliseconds to several tens of milliseconds. Other About 1200 sets 0 –20 0Time [ms]12 10 Only differential mode Common and differential Cumulative occurrence probability [Times per thunderstorm day] Total 1 0.1 0.01 Miti(08)_F2.9-3 1 10 100 1000 Current [A] Figure 2.9-3 – Cumulative occurrence probability for differential mode current Case study 2.9 – 2 –