Brand AVX TPSE226M035R0125 Low impedance tantalum capacitor AVX 22

LC03-3.3 SOP8 TVS Static Protection 3.3V

Practice has proved that the use of protective grounding is an effective safety protection measure in China's low-voltage power network. Since the protective grounding is divided into grounding protection and zero-connection protection, the objective environment used by the two different protection methods is different. Therefore, if improperly selected, it will not only affect the protection performance of the customer, but also affect the power supply reliability of the power grid. Then, as a power customer in a public distribution network, how can we properly and reasonably select and use the protective ground?
First, we must understand and understand the grounding protection and zero-connection protection. Master the differences between the two protection methods and the scope of use. Grounding protection and zero-connection protection are collectively called protective grounding. It is to prevent personal electric shock accidents and ensure the normal operation of electrical equipment. An important technical measure. The difference between these two protections is mainly manifested in three aspects: First, the protection principle is different. The basic principle of grounding protection is to limit the leakage current of the leakage device to the ground so that it does not exceed a certain safety range. Once the protection device exceeds a certain setting value, the power supply can be automatically cut off. The principle of zero-connection protection is to use the zero-connecting line. When the device is damaged by the insulation and forms a single-phase metallic short circuit, the short-circuit current is used to prompt the protection device on the line to operate quickly. Second, the scope of application is different. According to relevant factors such as load distribution, load density and load nature, the Rural Low Voltage Power Technical Regulations divides the scope of use of the above two power grid operating systems. TT system is generally applicable to rural public low-voltage power network, which belongs to the grounding protection mode in protective earthing; TN system (TN system can be divided into TN-C, TN-CS, TN-S) is mainly suitable for urban public low voltage A dedicated low-voltage power network for power customers such as power grids and factories and mines. This system is a zero-connection protection method in protective earthing. At present, China's current low-voltage public power distribution network usually adopts TT or TN-C system, and implements single-phase and three-phase hybrid power supply modes. That is, three-phase four-wire 380/220V power distribution, while supplying power to the lighting load and the power load. Third, the line structure is different. The grounding protection system has only phase and neutral lines. The three-phase power load can be used without a neutral line. As long as the equipment is well grounded, the neutral line in the system must have no ground connection except the neutral point of the power supply. The zero-connection protection system requires that the neutral line be protected in any case. If necessary, the protection neutral line and the zero-connection protection line can be erected separately. At the same time, the protection neutral line in the system must have multiple repeated grounding. .
The second is to correctly select the grounding protection and zero-connection protection according to the power supply system where the customer is located. What kind of protection should the power customer take? First, it must depend on the power distribution system that the power supply system is in. If the public distribution network where the customer is located is the TT system, the customer should adopt grounding protection in a unified manner; if the public distribution network where the customer is located is the TN-C system, zero-connection protection should be adopted uniformly.
The TT system and the TN-C system are two systems with their own independent characteristics. Although both systems can provide customers with 220/380V single and three-phase hybrid power supplies, they can not only replace each other, but also protect them. The requirements above are completely different. This is because, in the same power distribution system, if the two protection modes exist at the same time, the phase-to-ground voltage of the neutral line will rise to half or higher of the phase voltage in the case of a ground-protected device. At this time, all devices on the zero-protection (because the metal casing of the device is directly connected to the neutral line) will carry the same high potential, so that the metal parts such as the device casing exhibit a high voltage to the ground, thereby endangering the user. Security. Therefore, the same distribution system can only use the same protection method, and the two protection methods must not be mixed. Secondly, the customer must understand what is called protective grounding, and correctly distinguish the difference between grounding and zeroing protection. Protective grounding refers to the fact that household appliances, electrical equipment, etc. may be charged with metal casing due to insulation damage. The grounding provided to prevent such voltage from endangering personal safety is called protective grounding. The grounding protection of the metal casing with the protective earthing wire (PEE) directly connected to the grounding pole is called grounding protection. When the metal casing is connected with the protective conductor (PE) and the protective neutral conductor (PEN), it is called zero-connection protection.
The third is to according to the different setting requirements of the two protection methods, standardize the design and construction process standards to standardize the distribution line design and construction process standards and requirements in the customer's power receiving end building, through the indoors of newly built or renovated customer buildings. The power distribution part is implemented by a three-phase five-wire system or a single-phase three-wire system instead of the three-phase four-wire or single-phase two-wire power distribution mode in the TT or TN-C system, which can effectively realize the protection grounding of the client. The so-called "local three-phase five-wire system or single-phase three-wire system" means that after the low-voltage line is connected to the customer, the customer has to change the original traditional wiring mode, based on the original three-phase four-wire system and single-phase two-wire system wiring. On the top, each additional protection line is connected to each of the customer's grounding wire terminals that need to implement the grounding protection electrical socket. In order to facilitate maintenance and management, the intersection of the indoor lead-out and the outdoor lead-in end of the protection line shall be installed on the power distribution board that the power supply is introduced, and then the access method of the protection line shall be separately set according to the power distribution system where the customer is located.
1. Setting of TT system grounding protection line (PEE) When the customer's power distribution system is TT system, the customer must take the grounding protection method. Therefore, in order to meet the grounding resistance value of the grounding protection, the customer should bury the artificial grounding device in the outdoor according to the requirements of the "Technical Regulations for Rural Low Voltage Power". The grounding resistance should meet the following requirements:
Re≤Ulom/Iop
Where: Re ground resistance (Ω)
Ulom is called the voltage limit (V). Under normal circumstances, the operating current of the residual current (leakage) protector of the adjacent upper stage of Iop can be considered according to the AC rms value of 50V (A).
For the average customer, as long as 40×40×4×2500 mm angle steel is used, it can be driven into the underground 0.6 m vertically by mechanical driving, which can meet the resistance requirement of the grounding resistance. Then, it is welded with a round steel with a diameter of ≥ φ8 and then led out to the ground for 0.6 m, and then connected to the protection wire (PEE) of the switchboard with the same material and type of wire as the imported power supply phase.
2. Setting requirements for zero-protection line (PE) of TN-C system Because the system requires customers to adopt zero-connection protection mode, it is necessary to add a special one on the basis of the original three-phase four-wire system or single-phase two-wire system. The protection line (PE) is taken from the protective neutral (PEN) of the customer's power distribution panel and is connected to the original three-phase four-wire or single-phase two-wire system. In order to ensure the safety and reliability of the whole system, special attention should be paid in the use. After the protection line (PE) is taken out from the protection neutral line (PEN), the neutral line N and the protection line (PE) are formed on the client side. The two wires cannot be combined into a (PEN) line during use. In order to ensure the reliability of the repeated grounding of the protection neutral line (PEN), the first and the end of the TN-C system main line, all the branch T terminal rods, the branch end rods, etc. should be equipped with repeated grounding lines, and three-phase The four-wire system should also be grounded repeatedly at the entrance bracket of the subscriber line, before the (PEN) line is divided into the neutral line (N) and the protection line (PE). The wire cross section of the protective neutral (PEN), neutral (N) or protective wire (PE) is always selected according to the wire type and section standard of the phase line.