First, the street lamp power supply has only short circuit and overload protection without leakage protection. The reason is not to use the leakage circuit breaker, the key is to get into the misunderstanding. Some people think that the three-phase leakage circuit breaker has the dead zone of operation, and it can not be used for reliable protection of personal electric shock. It is better to use it; some people think that the normal leakage current may cause the leakage circuit breaker. Misoperation, reduce the reliability of street lamp power supply; some believe that due to irregularities in the installation of street lamps, such as only the street lamp phase line is taken and the neutral line is borrowed from elsewhere, resulting in the leakage circuit breaker not working properly.
In fact, the leakage circuit breaker is a safety appliance whose main function is to provide indirect contact protection. When a single-phase ground fault occurs, the contact voltage of the lamp post can be lowered, which is beneficial for protecting personal safety. If the rated leakage current (I△n) of the earth leakage breaker is 200 mA and the grounding resistance Rd is 200 Ω, the contact voltage = Rd * I Δn = 200 * 0.2 = 40 V, within the specified voltage range. Taking the author's area as an example, the soil resistivity is 110Ω on average, and the measured average value of the single-pole grounding resistance Rd is 58Ω. If there is no leakage protection and single-phase ground fault occurs, the contact voltage=Un*Rd/(Rd+R0)= 220 × 58 / (58 + 4) = 206V, close to the phase voltage, which is obviously very dangerous. After the leakage circuit is broken, it can prevent the cable from overheating due to the long-term leakage current, shortening the service life and causing the leakage arc current to burn the electrical equipment.
Second, the street lamp electrical appliances, especially the ballast quality is not good, the heat is serious, the insulation is easy to be broken and the pole is charged. Once the pedestrian touches, the consequences are unimaginable.
Third, the circuit breaker is not tested for sensitivity check, and the rated trip current is too large. Some select the circuit breaker, only consider the short circuit protection, but ignore the overload protection and single-phase end short-circuit sensitivity check. The rated trip current of the circuit breaker is too large. Regardless of the nature of the load, it is selected as 100A or even 150A. . This tends to cause the circuit breaker to not jump and lose the function of the circuit breaker when the grounding short-circuit current is large and the cable is hot.
Fourth, the use of cable metal skin as the PE main trunk process is complex and low reliability. The construction process of the metal sheath of the cable as the PE main trunk is complicated. Each base lamp must be welded with two solder joints. Each solder joint should be stripped, polished, tinned and welded. The operation is cumbersome and the quality of the solder joint is difficult to guarantee. There are so many The series solder joints, the reliability of the PE main trunk connection can be imagined. In addition, it is almost impossible for the cable to be completely protected from moisture. As long as moisture collects inside the cable, rust corrosion of the metal sheath is inevitable. Under normal circumstances, after 3-5 years of low-voltage cable of street lamp, the metal sheath will have rust breakpoint and lose the protection of PE main trunk. In this way, although the grounding protection of each street lamp is actually “independentâ€, in the event of a single-phase ground fault, the dangerous voltage will exist for a long time.
VFD power cable
Product Name: 0.6/1kV low smoke halogen free VFD power cable
Model: TFOU(C)-VFD
Specification: 3×1.5+3×1.0/3mm2~3×185+3×95/3mm2
Executive Standards: IEC60092-350, Q/321001KLA089-2007
Application: The cable is cable specifically engineered for use in variable frequency AC motor drive (VFD) applications.
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