Hidden fire hidden in LED display

Recently, incidents evoked by LED display screens have frequently occurred, causing great losses to people's lives and property. The causes of these accidents are often attributed to the aging of the line, short circuit, internal high temperature and other factors. As the frequency of accidents increased, people began to conduct more in-depth analysis and finally opened the truth of the problem.

Reflections caused by a report

In May 2010, the engineers of Aerospace Green Power received a report that when a new building in Zhengzhou was inspected, it discovered that the neutral current of the LED display installed on it was very high. Further measurements show that the currents on the three phase lines are almost equal, about 250A, and the current on the zero line reaches 450A. The acceptance personnel refused to accept the project. The LED screen installation company found Aerospace Green to seek answers to the questions and solutions.

This issue has attracted the attention of aerospace green engineers. This phenomenon is contrary to the common sense of electricians. Conventional electrical theory tells us that when the three-phase load balancing, zero line current is zero, the "zero line" is a term thus probably come. So is the phenomenon in this report accidental or inevitable? If it is inevitable, it means that more and more LED screens will bring huge security risks. Because the zero line is not equipped with an overcurrent protection device , if the neutral current exceeds the phase current, the neutral line will have a high temperature due to overcurrent when the phase line has not yet reached the protection threshold, accelerating the aging of the line, and finally May cause fire.

Shocking conclusion

Aerospace Green's engineers began in-depth and meticulous research. First, consult a large amount of foreign materials. It was learned from the data that the phenomenon mentioned in the report did exist. When the load is a rectifier circuit, this is an inevitable phenomenon.

As early as the 1990s, Europe and the United States began to popularize information equipment and energy-saving equipment. One of the serious consequences of the heavy use of these devices is the frequent occurrence of electrical fires. After an in-depth analysis, people finally discovered that the culprit that caused these problems was the rectifier circuit. The rectifier circuit causes the current on the zero line to exceed the phase current. In older buildings, the cross-sectional area of ​​the zero line is often smaller than the cross-sectional area of ​​the phase line. As a result, the zero line will be overheated, thereby inducing fire.

The LED display is powered by a switching power supply. The switching power supply includes a rectifier circuit. This led to the strange phenomenon mentioned in the report.

In fact, the electrical load in modern buildings includes rectifier circuits, ranging from cell phone chargers to elevators and air conditioners. Therefore, it can be foreseen that the zero line current exceeding the phase current in modern buildings will be a common phenomenon.

This conclusion is truly terrifying because it means that with the prevalence of modern electrical loads, there will be a huge hidden security risk in our buildings.

The disaster caused by excessive zero current

Excessive zero-line current brings a huge security risk. Because of the provisions of the traditional electrical construction specification, no overcurrent protection device is allowed on the zero line. When the zero line current is too large, no protection action will occur and the zero line can only be overheated.

In modern buildings, the cross-sectional area of ​​the zero line is the same as the cross-sectional area of ​​the phase line. In older buildings, the cross-sectional area of ​​the zero line may be only 1/3 of the cross-sectional area of ​​the phase line.

The basic physics knowledge tells us that when a current flows through a conductor, it causes the conductor to generate heat. The amount of heat is proportional to the resistance of the conductor and is proportional to the square of the current flowing through the conductor. Therefore, if the cross-sectional area of ​​the zero line is the same as the cross-sectional area of ​​the phase line (which means the same resistance), when the neutral current reaches twice the phase current, the zero line's heat generation is four times that of the phase line. If the cross-sectional area of ​​the neutral line is 1/3 of the phase line (meaning that the resistance of the neutral line is 3 times the resistance of the phase line), when the neutral current reaches 2 times the phase line current, the amount of heat generated by the neutral line is 12 times of phase line!

Through the above analysis, we know that when the current on the zero line exceeds the phase current, it will inevitably lead to overheating, which may cause fire.

Prevent problems

We found that LED screens have this feature and we can take measures to prevent them. Someone may think that this problem can be solved by bolding the zero line of the LED. But this is not a good solution. Because, although we have bolded the zero line of the LED screen, the LED screen has partially eliminated the issue of zero line overheating, but the current on the zero line is still very large. These currents flow into the neutral line in the building, causing similar problems in the building. Unless the entire zero line of the entire distribution system is bolded.

NBF is a solution that has been launched to fully address this issue. The Chinese name of NBF is called "neutral harmonic current blocker." This equipment has been widely used in Europe and America since the 1990s. Aerospace Science and Industry Corporation 706 exerted its advantages in power quality control technology and independently developed NBF products. Its performance indicators have reached the advanced level of similar foreign products.

The installation of NBF is very simple. If it is installed on the neutral line in series , the harmonic current generated by the electronic device can be reduced by more than 80% . It takes only half a day's construction time, and the power-off time can be controlled within one hour .