Whilst not directed at the public supply network, could the situation set out in figure 44.1 in BS7671 2018 cause damage to equipment on a LV installation connected to a DNO supply?
Whilst not directed at the public supply network, could the situation set out in figure 44.1 in BS7671 2018 cause damage to equipment on a LV installation connected to a DNO supply?
That is a very interesting question. It looks like the common N or PEN will have a Voltage rise on it above true earth with whatever consequences. This may be serious if the substation Re is high. The regs. suggest that the common system is to link the high Voltage and Low Voltage earthing systems together. I suppose then that local earth electrodes come into their own at installations along with equipotential bonding.
There surely must be automated disconnection apparatus to disconnect if this fault occurs.
During the bad wet windy weather a few months back, we had a problem here in Norfolk. Overhead lines on wooden poles carry H.V. Below them are L.V. cables. An H.V. porcelain insulator broke down and H.V. tracked down to an L.V. cable. The top of the pole caught fire. The event continued for some time, and many sparks were seen emanating from the top of the pole as well as flames.
Many electrical appliances were destroyed during the incident in a holiday chalet park. Many just exploded.
This was more of a line to line fault, but just shows what H.V. can do if it lifts a L.V. up to dangerous levels.
P.S. The fault took out one of the 200 Amp. H.R.C. main fuses of the three phase supply at the holiday chalet park.
