Japanese utilities have a particular concern when it comes to lightning-induced problems on their networks. First of all, lightning activity in Japan is comparatively high by international standards. Secondly, Japanese customers have very high requirements for reliability and even residential customers are not prepared to accept power interruptions in general and particularly any which might exceed one hour
duration. Finally, the high population density of Japan makes utilities in that country especially focused on safety issues since conductor drops on distribution networks due to lightning strikes are perceived to present a real threat to the public.
Distribution networks in Japan are primarily overhead due to the rapid scale of development within the country during the past fifty years. Very high urban growth and spiraling land costs have made construction of underground systems far more costly than overhead systems. Similarly, overhead networks have been seen as allowing greater flexibility in terms of being more easily re-located whenever necessary to accommodate continued urban expansion.
Chubu Electric Power Corp., based in Nagoya, is an example of how one Japanese utility has dealt withlightning-related problems on its distribution network. The utility serves a total of more than 9.5 million customers with a 125,000 km distribution network consisting of some 2.6 million mostly concrete poles and about 1.4 million pole-mounted transformers. Chubu Electric’s distribution system is more than 95 per cent overhead and, like most in Japan, is basically of the loop type but with switches
normally left in the open position.
According to Kazuo Iizuka, Assistant Manager of Planning at Chubu Electric’s Distribution Department, network design to deal with lightning-related problems has been made with three priorities in mind: first of all safety; secondly reducing the service area affected by an outage; and thirdly, minimizing the time of any power interruption.
Between 1968 and 1982, Chubu Electric converted all of its 6.6 kV overhead distribution conductors to the insulated type, with a cross-linked polyethylene (XLPE) covering having a thickness of 2.5 mm. Iizuka explains that after installation of these covered conductors, whenever there was a surge on the network due to lightning, thepower arc tended to be concentrated at one spot along the conductor typically less than 50 cm from the insulator. This generally led to complete burn down and dropping of the conductor.
