Failure aspects of electronic watt-hour meters due to direct lightning strikes to distribution lines - Electromagnetic disturbance caused by lightning current flowing through watt-hour meters and its countermeasure-

Recently, advanced "smart meters" have been introduced widely to electric power distribution lines. Since smart meters consist of many low-voltage electronic devices, their vulnerability to disturbances such as lightning surges is a matter of concern. Therefore, to establish an effective lightning protection countermeasure against these disturbances, we have been investigating the lightning failure aspects of electronic watt-hour meters (WHMs), which have a function similar to that of a watt-meter section in smart meters. In this paper, we explored countermeasures for improving the performance of WHMs against the lightning transient magnetic fields. At first, we examined the performance of WHMs by lightning impulse current tests. As a result, it has become clear that the increase in distance between a bus conductor and a processing unit and magnetic shield of a processing unit are effective in reducing the probability of failures caused by the transient magnetic fields. Next, we proposed a calculation method of the lightning failure rate of WHMs based on a lightning surge analysis. The calculation results indicate that the failure occurs more frequently by subsequent strokes than by first strokes or if the grounding resistance of a pole transformer is higher.