The solar activity and the casualties from electrical current
One of ends of the metal screens of the 20 kV cables is connected to ED of the 110 kV substations, and the other – to ED of the transformer station. The neutral of the 20/0.4 kV transformer and the neutral conductors of the consumers are connected to it. In this way the neutral terminals of the consumers turn out to be galvanically connected to ED of the substations. They in turn, owing to the lightning protection cables, turn out to be connected to ED on the entire continent. As a result of that, upon a fatal solar flare the voltage on ED of some substation may reach hundreds of kilovolts. Although for the consumers this value reduces, it may not pose a real risk to their lives.
Here are some more accidents with terminal outcome, which happened at the end of the 80s and the beginning of the 90s of the previous century in Bulgaria during abnormally high solar activity (fig. 1а). The real reason still remains unexplained because no one guessed to relate them to the solar flares preceding the fatal date.
In the town of Vidin parents who returned home after a storm found their five-year-old son dead, lying behind the washing machine. According to the news in the newspaper, the child somehow managed to touch the input terminals of the washing machine, as a result of which he died. The explanation is absurd as the terminals are located under the back lid of the washing machine and the access to them is impossible without special tools. But what else could they think about, after an investigation established that the body of the machine had been earthed, i.e. 100% secured according to the rules. And to the fact that it was connected to the water supply tap with a plastic hose, i.e. it was insulated from the water main, nobody paid attention. And to no avail, as at a certain moment during the storm high voltage occurred in the ED of the110/20 kV substation. The occurring difference in the potentials between the body of the washing machine, which was galvanically connected to the ED of the 110 kV substation and the water supply tap, which the child seems to have touched, proved fatal.
The second case happened in the town of Septemvri. A television technician climbed on the roof of a multi-storey block of flats to connect a television cable to the group aerial. “A storm was approaching,” an Electricity Supply Company representative told me, “and we called him to get down. A few minutes later he really descended, but he was pale and shaking all over and said electrical current had hit him. We exchanged glances – what current, there isn’t a single cable there. In the ambulance car he got worse and he died on route to the hospital, repeating an electric current had hit him”. Yes, everybody knew the television cable screen is connected to the television set chassis, but they also knew it had been reliably earthed through the neutral conductor and were absolutely certain of the impossibility for occurrence of a difference in the potentials between the neutral and the building armature. To imagine any voltage occurred in the neutral for them is equal to imagine the sun rose in the west.
The history of energetic knows a number of similar cases, but I would like to suggest three more, which I am sure would help even Doubting Thomases to understand the extent to which Bulgaria’s distribution network can be dangerous or people’s life.
Here is how the press described one of them. In the town of Gabrovo a mother went to the train station together with her son to have a cup of coffee. While the mother was having her coffee, the boy managed to climb on the roof of a goods wagon in the sidetrack. The spark that flashed between the child’s head and the contact conductor was not visible at daytime and only when people got to the child that had fallen to the ground, they understood what had happened. Here is how the station master in Ezerovo commented what happened, “As the distance between the contact conductor and the wagon roof is 2.5 m, this means the boy for some unknown reason held some wire which he used to reach the conductor”.
The second case gives us the opportunity to realise how preposterous this explanation is, although it is in line with the level of the modern science. I was told about it by the chairman of the commission investigating the accident, Associate Professor Ushev – a lecturer at the Technical University of Varna. At the train station in Povelyanovo a worker climbed for some reason on a tank wagon that had also stopped on the sidetrack. Naturally, he knew all safety regulations by heart. However, here we should give a small explanation. Maintenance workers with long years of experience know that the safety clearance to the conductive parts is 2.5 m. They are also aware that the spark gap under voltage of 35 kV equals 150 mm, and under 110 kV – 650 mm. They never breach clearances close to these values. Most of them successfully retire, without even knowing they walked through a “mine field” all their life. Some of them, however, are not that lucky, and this is confirmed by the case in Povelyanovo – a spark flashed and the worker fell dead to the ground. As the case did not fit into any rules, it remained unsolved.
Everyone here should know that if a spark flashes over an air gap of a metre – metre and a half, the voltage pulse should have a value of several hundred kilovolts. Consequently, just like in the previous case, reverse overlapping of the air gap from the “earth” to the contact conductor occurred.
A solar flare caused the occurrence of the enormous potential in the Earth’s mantle, but at the identified place it occurred only thanks to the power engineers, who installed an ED in the substation and connected it through the lightning protection cables of the 110 kV OPL to the ED of a number of other substations.
The height of the failure to understand the reasons for occurrence of overvoltages in the electrical grids can be the fatal accident with Dimitar Vasilev – head of substation at the Electricity Supply Company in Varna. Mitko, as his friends used to call him, was an expert of a high class. On 8.8.1996 he, for some reason which was known only to him, climbed using a ladder to the base of a bus bar circuit breaker at the Lazur 110/20 kV substation which was live. Owing to a fatal coincidence, just like in the previous cases, despite the theoretically safe clearance to the circuit breaker knives, reverse overlapping of the air gap occurred, which developed into earth fault. Vasilev suffered significant burns and died a few days later in hospital. The most remarkable thing is that the very participant in the accident could not understand what had happened. As the person on duty at the substation told us, after he fell to the ground where the arc had thrown him off he repeated several times, “What happened?”
Compared to the tragic cases described above, frequent failures of domestic appliances are nothing special, but naturally they cause their owners enough troubles. Guided by that, in 2003 I wrote a letter to the Bulgarian Minister of Energy, in which I suggested a simple and reliable way out of the situation – the screens and armor of the 20 kV cables at the 110/20 kV substations should not be earthed, and the earthing of the existing cables should be removed. To observe the respective rules for technical operation, it is quite sufficient to earth the screens and armour of the said cables on their other end. I received a reply that, to say the least, stunned me. In brief, its contents can be reduced to the following: everything is fine and in order with us, the failures of domestic appliances are caused by electric shocks (although nobody knows what this is), and people died through negligence. Moreover, the forthcoming introduction of the potential equalization system would render electric current shocks to people impossible.
Yes, it is true that the equalization of potentials removes the immediate danger to people, but when will this happen? Ten years have passed, but nothing has changed. Yes, the number of failures in the grids decreased, and there is no news of dead people in the press, but is this due to the efforts of the power engineers? According to NASA announcements, they have nothing to do with that as the typical minimum of the solar activity is 486 days, and since 2004, when the next minimum of the solar activity started, 821 days have elapsed with no spots on the solar disk. The occurrence of the next maximum is quite late, but sooner or later it will come and then again at least half of Bulgaria’s population will find themselves in conditions of increased danger not only to the good working order of the domestic appliances but also to their life.