Crane hoist phase error accident

　　Due to the use of three-phase asynchronous conical brake motors as the power device in the hoist crane, the operating direction of the three-phase asynchronous motor is related to the phase sequence of the power supply. When the phase sequence of the power supply changes, the running direction of the motor is opposite to the original direction. At this time, when the "lower" button of the operator switch is pressed, the lifting appliance rises, and the limit position limiter for the rise is not working, which is prone to accidents. Every year, lifting accidents such as crushing of the drum, squeezing deformation of the hook group, and breaking of the steel wire rope caused by phase error occur.

　　At present, the CD1 and MD1 electric hoists produced and widely used in China do not have phase fault protection measures (which are required to be installed in the electric hoist standard), which poses certain hidden dangers. In our survey feedback statistics, it was found that 203% and 171% of faults and defects were caused by rope guides and fire limit switches. In addition, in the follow-up of the use of newly installed electric hoists in the past year, it was found that 305% were caused by the lack of phase sequence protection.

　　To prevent the occurrence of lifting injury accidents caused by phase error, a human phase error protection device should be installed in the control box of the electric hoist. When the power supply is out of phase or out of phase, the phase error protection device will work, causing the main power contactor to disconnect. The crane can only continue working after the power supply is restored to normal. This can not only prevent the power supply from being out of phase and causing winding, but also prevent the motor from being burned out during phase loss operation.