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LC03-3.3 SOP8 TVS Static Protection 3.3V

The protective grounding in the elevator not only prevents electrical equipment leakage, so as to avoid electric shock accidents, but also is necessary for the "logical place" of computer-controlled elevators, and its importance is obvious. Therefore, whether the correct use of protective grounding measures in the elevator installation will directly affect personal safety and equipment safety. In the past few years, I have found that some installation units (or installers) have incomplete understanding of the protection grounding, and the connection is not standardized, which causes hidden dangers to personal safety, and often causes elevator failure or even breakdown of integrated circuits. The situation happened. Several phenomena are listed below.

1 Pay insufficient attention to the neutral and ground wires used in the elevator

Some people think that the zero line and the ground line have no voltage. They are more perfunctory when laying and connecting. It is often found that the laying is not in place, the connection is loose, and the multi-strand line does not adopt the transition joint form. According to the provisions of GB50182, the exposed conductive parts of all electrical equipment should be reliably grounded or connected to zero. Fixed connection bolts for electrical equipment are generally not considered to be reliable ground connections, but should be in the form of jumpers. The connection of the grounding wire shall not be loose. In the place where there is vibration, anti-loose measures shall be added. For the three-phase four-wire system, the power supply system with zero-connection protection (TN-C) shall not be loosened at the separation point of the equipment room, and the point shall be The grounding resistance should be ≤ 4Ω.

2 The connection to the elevator power supply is not standardized

According to the provisions of GB50182, the elevator power supply should be dedicated and should be sent directly to the equipment room by the building distribution room. Therefore, not only the three-phase power line but also the neutral and ground lines should be sent directly to the equipment room. There was an installation unit that led the power supply from the first-floor rental room. Although the lock was added to the three-phase power supply, the working neutral line and the ground line were shared (the power supply was the TT system). When the renter retired the rent, the work zero line was removed, and the work zero line was hit on the ground line. Therefore, the lighting system was still working normally and no hidden dangers were found. In fact, a certain voltage drop appeared on the ground line. . (Click on the picture as shown in Figure 1.) EL1 and EL2 are the car's 25W illumination, EL3 to EL9 are the hoistway 60W illumination, and Rd is the grounding resistance. The measured value is about 10Ω (the standard specification should be ≤4Ω). The potential of the point is about 21.4 V, and as a result, a communication board malfunctions.

3 The understanding of the protection grounding is not comprehensive. For the protection grounding, not only the protection grounding form of the power distribution system should be understood, but also three concepts should be clarified, namely zero-connection protection, grounding protection and repeated grounding. According to the provisions of GB9089.2, there are three types of protection grounding methods for power distribution systems: TN, TT and IT.

The power distribution is a TN system (that is, a power supply network with a user having a separate transformer). The power system is directly grounded. The exposed conductive part of the electrical device should be connected to the grounding point through a protection line. The so-called protection zero system This is the most commonly used distribution grid in elevators. TN system can be generally divided into TN-S (three-phase five-wire power supply) system, TN-C and TN-CS (three-phase four-wire power supply) system, as shown in Figure 2 (please click), Figure 3 (please click) And Figure 4 (please click). In this system, it is strictly forbidden that the exposed conductive part of the elevator electrical device is grounded separately, because when the grounded electrical equipment is damaged by the insulation and the shell is hit, the protection switch or the protection fuse cannot be disconnected due to the large resistance of the earth, so the power neutral The point potential is raised so that all zero-connected electrical equipment is energized. This increases the risk of electric shock and poses a hazard to weak current systems in the elevator.

The power distribution is the TT system (that is, the power grid of the user generally uses a common transformer), and the power system is directly grounded at one point. The exposed conductive part of the electrical device should be connected to the grounding pole independent of the grounding point of the power system through the protection line, so-called Protective grounding system (also three-phase four-wire power supply), please click on it as shown in Figure 5. The neutral line in the system is only used for working the neutral line, and the exposed conductive part of the elevator electrical device is strictly prohibited from being connected to the neutral line. Because if the zero-connecting measures are adopted, if the insulation of the electrical device is damaged and the shell is short-circuited, a serious imbalance will occur in the utility grid power supply system, posing serious damage to the equipment.

The power distribution is an IT system (three-phase three-wire power supply grid), and the exposed conductive part of the electrical device should adopt the same direct grounding protection as the TT system. The elevator generally does not use this power supply grid.

The so-called repeated grounding, only for the zero-protection system. In order to improve the safety performance of the zero-connection protection, the neutral line should be grounded repeatedly, that is, the neutral line of the power distribution system should be connected to the earth again through the grounding body or natural joint at the specified location (the grounding resistance should be ≤10Ω), generally The power distribution cabinet has been processed.

4 The correct handling method of "logically" the use of computer-controlled elevators should be handled in accordance with product requirements. When the product is not required, according to the provisions of GB50182, the TN power supply system can be connected to the protection line (PE); it can also be connected to a separate grounding device, but the ground resistance of the device must be ≤ 4Ω; The "logically" approach is handled.