Enterprises should conduct sufficient investment analysis and evaluation of feasibility, economy, technology and safety and reliability. The selection of cranes should be based on the busyness of the enterprise's lifting operations and load changes to correctly select the type and level of crane work. Its main technical parameters should be Meet the needs of enterprise safety production.
1. The shell of the electrical equipment protected by the leakage protector of the single-girder gantry crane must be grounded, and the grounding generally has the following requirements:
(1) The metal casing of the protected electrical equipment should be grounded separately.
(2) The grounding of the metal casing of the electrical equipment protected by the single main girder gantry crane should be separated from the grounding of the neutral point of the power supply as much as possible.
2. When the above requirements cannot be met and a common grounding method must be adopted, the following requirements shall be met:
(1) When the electromagnetic leakage protector is used, the shell of the protected electrical equipment can be connected to the protective ground wire (PE wire) or the protective neutral wire (PFN wire). In this case, the automatic switch can not be checked, but the dynamic stability and thermal stability of the leakage protector (zero sequence transformer) must be checked.
(2) When an electronic leakage protector is used, the metal casing of the protected electrical equipment can also be connected to the protective ground wire. In this case, in addition to checking the dynamic stability and thermal stability of the zero-sequence transformer, it should also check whether the auxiliary power supply voltage of the leakage protector is within the allowable voltage range when a single-phase grounding occurs, so as to Ensure that the leakage protector can operate reliably.
(3) The grounding resistance should be able to ensure the reliable operation of the leakage protector.
(4) When the power distribution system adopts the classification protection of leakage protectors, in order to make the protectors at all levels of the single main girder gantry crane operate selectively, the breaking time of each level should be different. At this time, if the protective grounding of all levels cannot be separated, the breaking time should be readjusted to meet the requirements of the grading protection.