Millions of electronic devices are damaged in China every year due to poor grounding

Many people know that when using expensive equipment, the shell must be grounded, such as using a three-core power plug. But few people know why it is necessary to ground. Below we use the working principle of the three-phase generator transmission line to illustrate the importance of equipment grounding.

By observing Figure 1, you will soon understand what the main function of the ground wire is, that is: the main function of the ground wire is to protect against lightning.

In Figure 1, the red lines A, B, and C represent high-voltage transmission lines. High-voltage transmission lines are generally supported by iron towers to transmit hundreds of thousands of volts of alternating current over long distances. In this way, it is inevitable that they are often struck by lightning. In order to avoid lightning strikes, a ground wire is generally erected above the high-voltage line in parallel. This ground wire is generally called a lightning protection ground wire. The so-called ground wire is a wire connected to the earth. When thunder strikes, lightning will first hit the lightning protection ground wire. The lightning protection ground wire can lead lightning into the earth, preventing the high-voltage transmission line from being punctured by hundreds of millions of volts or even billions of volts of lightning, and preventing other electrical equipment connected to the line from being damaged by instantaneous high-voltage shocks. Therefore, the lightning protection ground wire in Figure 1 is completely different from the ground wire in general electronic circuits.

In addition to the lightning protection ground wire, the outer shell of the generator and transformer must also be grounded. This kind of grounding is called protective grounding. The protective ground wire and the lightning protection ground wire are different. The biggest difference between the protective ground wire and the lightning protection ground wire is that the ground wire of the protective ground generally has no current passing through it, while the ground wire of the lightning protection ground has a very large current passing through it when thunder strikes, and the current can be greater than hundreds of thousands of amperes. The main function of the lightning protection ground is to introduce the high voltage of lightning into the earth to reduce the impact of the high voltage of lightning on electronic equipment; while the protective grounding makes the potential of the equipment shell the same as that of the earth, avoiding the internal circuit of the equipment from induction charging and generating displacement current under the strong electric field, and preventing the human body from being electrocuted when touching the outer shell of the electronic equipment. Therefore, the functions of the two are completely different.

The neutral line grounding of the three-phase generator is also a protective grounding, and its function is to introduce the electrostatic high voltage induced by the coil in the generator into the earth. When the load is completely balanced, there is no current flowing through the neutral line of the three-phase generator and the ground wire connected to the ground. However, the neutral line grounding of the three-phase transformer is not a protective grounding, but a lightning protection grounding, because the neutral line of the three-phase transformer not only supplies power to the user in parallel with the live line, but also serves as a lightning protection. When thunder strikes, the neutral line can introduce most of the energy of the lightning into the earth through grounding, and only a small part of the energy finally becomes a differential signal and is mixed with the transmission voltage and transmitted to the user terminal.

At present, people do not have a deep understanding of the generation of lightning and the disasters it causes.

We know that due to the strong electric field between the earth and the ionosphere, clouds in the sky must first be polarized and charged. Then, under the action of wind, polarized and charged clouds can easily separate into two (or more) parts, making them charged bodies, one with positive charge (usually the lower layer) and the other with negative charge (usually the upper layer). Therefore, charged clouds at the same height (i.e., clouds with the same charge properties) can easily combine with each other under the action of wind, making the energy of the cloud body more and more powerful, that is, the potential is getting higher and higher. When two clouds with opposite charges approach each other, or when a charged cloud body approaches the ground surface, discharge will occur, that is, thunder. Therefore, as long as there are clouds and wind, thunder will often occur, and the first buildings to be struck by lightning are mostly high-rise buildings.

According to statistics:

On average, there are more than 100 lightning strikes on Earth every second, and the energy generated by each lightning strike is enough to light a 100-watt light bulb for three months; during the rainy season, one person is struck by lightning every six minutes, and tens of thousands of people are injured by lightning strikes every year; Shanghai TV suffers an average of 33 major lightning strikes each year, and the most recent one was on April 13, 2010. Each lightning strike causes varying degrees of damage to electronic equipment; on June 22, 1992, several computer interfaces at the Beijing National Meteorological Center were destroyed by induced lightning, resulting in a loss of more than 20 million yuan.