The electrical protection equipment of cranes mainly includes control devices, protection panels (distribution boards), collectors (power supply slide lines), motors, resistors, lighting, various limiters, interlock switches, lightning protection and grounding and other safety protections Device. The safety technology of the electrical control system of bridge cranes is to prevent malfunction or loss of control due to operating errors or electrical faults such as controllers and protection panels, and biological fall or impact accidents; the second is to prevent touching bare contact wires or insulation (insulated) Electric shock caused by damage or poor grounding.
1. The safety technology of the controller
The controller is one of the important electrical equipment on the crane. Its main purpose is to control the start, stop, reverse, speed change and safety protection of each motor. It is required to work in conjunction with the limit switch to limit the position of the mechanical operation driven by the motor, prevent offside accidents, protect the zero start, and prevent the control handle (bǐng) from being cut off when it does not return to the zero position. ) After the power is turned on again, the motor suddenly rotates and an accident occurs.
There are start button, zero contact, end switch (limiter) contactor coil and auxiliary self-locking contact, emergency switch, hatch switch, and normal closed contact of overcurrent (Electron flow) relay (relay) in the control circuit First class. Single-girder cranes usually refer to single-girder bridge cranes. The main beams of single-beam crane bridges mostly use I-shaped steel or a combined section of steel and steel plates. The hoisting trolley is often assembled by chain hoists, electric hoists, or hoists as parts of the lifting mechanism.
The zero protection is that only the handwheel is opened and closed when the zero position is in the zero position. If the zero contact point in the control circuit is not closed, the control circuit cannot be connected, so that the handwheel must be pulled back to the zero position after the crane is finished. It runs normally during a job to prevent accidents caused by the sudden movement of the crane after the handwheel does not return to the zero position after stopping the work, so it is called the zero position protection.
The end switch (limiter) is connected in series in the control circuit. The forward contact is closed, and the upper end switch is active; the backward contact is closed, and the lower end switch is crane. The single beam crane has two operation modes: ground and air. There are two types of ground operation: wired handle operation and remote control handle operation; aerial operation refers to operation in the driver's cab. The driver’s cab has two types: open and closed. It can be divided into two types for installation on the left or right according to the actual situation. There are two types of entry directions: side and end to meet the needs of users. When the crane reaches the end point, the limit switch is opened, the control circuit is cut off (cut; cut off), the contactor coil (winding) is de-energized, the contactor is off (zhá), the motor stops rotating and reaches the limit effect.
The emergency switch and the hatch interlock switch all use this principle for protection.
2. Safety technology of protection board (distribution board)
After the power supply is introduced, it first goes to the protection board (distribution board), and then distributes it to each motor. The single beam crane has two operation modes: ground and air. There are two types of ground operation: wired handle operation and remote control handle operation; aerial operation refers to operation in the driver's cab. The driver’s cab has two types: open and closed. It can be divided into two types for installation on the left or right according to the actual situation. There are two types of entry directions: side and end to meet the needs of users. The electrical protection device protection panel of the crane is installed in the cab, and its function is to protect the motor and the main circuit from overload or short circuit (the current does not pass through the electrical appliance and directly connect the power poles), protect the short circuit of the control circuit and make each limit switch , Emergency switch, cabin door switch, etc. play a safety protection role. In the protection panel, there are protective electrical appliances such as total switch, main contactor (contactor), overcurrent (Electron flow) relay (relay), fuse (fuse), indicator light and button. During operation, first push on the main switch, and then press the main contactor button. At this time, the indicator light is on, indicating that the main power supply has been connected. When you stop using it or when there is a failure, you need to cut off (cut; cut off) the power supply, just pull down the knife.
3. Grounding protection and zero connection (using IT system or TT system)
In order to prevent electrical equipment insulation (insulated) damage to make the metal parts of the equipment live and electric shock accidents, according to the requirements of the TT system, crane electrical equipment metal shells, wire protection metal pipes, metal structures, etc., according to electrical requirements, reliable grounding, or according to TN system The requirements for protection are connected to zero. If the crane’s track, metal structure, and metal structure of the factory building have been connected to zero and have reliable contact with the crane, the crane may not be provided with a special grounding (zero connection).
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