L68B2 Mast SectionSafety technology explanation of tower crane grounding and zero connection
Tower crane grounding and zero connection
L68B2 Mast Section：
http://www.towercranesupply.com/product/l68b2-mast-section-for-tower-crane-masts
1. Single protective grounding measures can't guarantee safety in the three-phase four wire system neutral direct power grid. If a single grounding is adopted, when the tower crane metal structure leaks electricity, the current will return to the power supply through the tower crane grounding resistance and neutral grounding resistance. Because the two grounding resistance values are basically equal, the partial voltage is also basically equal, so there is one 220V on the tower crane grounding resistance Half of the voltage, because the current is not large, the voltage can exist for a long time. If a person standing on the wet ground contacts the leakage tower body, he or she will wait for the grounding resistance of the tower crane to bear the similar voltage in parallel, which may cause electric shock.
2. Although protective zero connection measures can play a protective role, there are still potential safety hazards. In the three-phase four wire neutral grounded power grid, the tower crane adopts the protective measures of metal structure connecting the working zero line. When the metal structure of the tower crane leaks electricity, the leakage current directly returns to the zero line, forming a phase zero short circuit. Because the line resistance is small and the current is large, the safety device on the leakage line will be disconnected soon, so the leakage power supply will be cut off, which plays a protective role. However, due to the current flowing through the working zero line when the power consumption is unbalanced, and there is a certain resistance on the zero line, a certain voltage can be generated on the zero line. When the metal shell of the equipment is connected to zero, a certain voltage will also be generated, and at the same time, a potential safety hazard will be caused. To sum up, in the same power grid, it is not allowed to connect some equipment to neutral or some equipment to ground. Because when the earth equipment leaks electricity, the zero line also produces voltage to the earth, all the earth equipment will be electrified, causing a wider range of security risks.
L68B2 Mast Section：
http://www.towercranesupply.com/product/l68b2-mast-section-for-tower-crane-masts
3. The three-phase five wire system can play an ideal protective role. The so-called three-phase five wire system is based on the three-phase four wire system, plus a special protection zero line, often called PE line, the first end is connected with the working zero line of the power supply end, the middle is not connected with the working zero line, the end is repeatedly grounded, because the special protection zero line usually does not have any current flow, the equipment shell is connected to the protection zero line, and no voltage will be generated, so it can be compared Reliable protection. The reliability of overload and short-circuit protection device must be guaranteed by adopting protective zero connection measures. When selecting fuse protection, the insurance capacity cannot be increased blindly to ensure the fuse function.
