How To Troubleshoot Crane Leakage?

Hoisting machinery belongs to special equipment and is widely used in factories, enterprises, mines, road construction and other fields. There are many driving methods for cranes: pneumatic, electric, hydraulic, etc. The electric drive mode is used for lifting. Once a leakage fault occurs, it will cause electric shock to the operator.
This article will take a 10 ton bridge crane as an example to describe how to check and deal with the leakage process.

If in the daily use of the equipment, the operator reflects that the lifting machinery often has "electric shocks" and the equipment is in a relatively dangerous working state, it should be stopped and comprehensively inspected and troubleshooted.

1. Focus on checking the hand operator for manipulation and the hook for lifting heavy objects.

Most of the bridge cranes are installed high in the sky, and most of the mechanical devices and electrical components are not in contact with people, so they will not be electrified.
Only the handheld operator for manipulation and the hook for lifting heavy objects may come into contact with personnel, so the two are the key objects of investigation.
 

First of all, check the portable handheld terminal. After disassembling the shell, use a multimeter to measure the working voltage of its internal components. If it is lower than the safe voltage, the handheld terminal can be considered safe, and the possibility of leakage can be ruled out.
 

The next step is to check the hook: first turn on the main power switch to electrify the hoisting machinery, and then use a multimeter to measure the voltage between the hook and the neutral line of the main power box. If the data can be detected, it means that the hook is accidentally charged. , At the same time, this is also the direct cause of the accidental electric shock of the lifting machinery.

2. Check all electrical parts (assuming that the hook is leaking electricity)

The hoisting machinery is used to lift goods, and it will not be charged under normal conditions. It is initially suspected that there is a short circuit between the phase wire of the power supply and the ground or between conductors. Careful inspection of all electrical components is required.
 

The inspection found that in the junction box of the lifting motor, the insulation layer on one lead had been damaged. The insulation resistance of one phase power supply to the ground was measured by an insulation resistance tester. It was precisely because of the leakage of the motor casing that the hook was accidentally electrified.
 

Lifting machinery should be equipped with a grounding protection function, which can act as a short circuit in the event of leakage to prevent electric injury.
This failure can be inferred as the failure of the grounding protection, and it is necessary to conduct a comprehensive inspection of the entire grounding system.

3. Different systems have different protection principles

Generally speaking, the grounding protection of hoisting machinery mainly includes TN, TT, IT and other systems. We need to check and judge the grounding protection mode of the crane.
 

The first is to check the external general power supply transformer. There are four terminals on the low-voltage side, which are a neutral wire and three phase wires, which can rule out the possibility of an IT grounding system. It should be a TN or TT grounding system. Then check the main power box of the hoisting machinery. According to the relevant specifications of the hoisting machinery, the resistance of the repeated grounding of the TN system should not be greater than 10Ω, but the measured value has reached 50Ω, which obviously exceeds the standard value. Further inspection found that The resistance between the ground wire and the neutral wire is very large, indicating that the protective ground wire has not been grounded repeatedly, and the actual grounding effect is only for the TT system.
 

Because the grounding resistance is too large, the grounding system cannot play the role of leakage protection, resulting in leakage failure of lifting machinery.

4. Summary
Combined with the above inspection and analysis, we believe that the external cause of the accidental electrification is the leakage of the electrified metal structure (motor) of the hoisting machinery. The internal cause is that the proper grounding protection fails to

provide short-circuit protection, and there are two reasons for the failure of the protection:
(1) The easy-to-charge metal structure is not connected to the neutral point of the power supply;
(2) The short-circuit current is much smaller than the set value of the automatic circuit breaker.
 

According to this judgment, the improvement of the electrical protection circuit can be proposed:
(1) Connect the easy-to-carry metal mechanism of the lifting machinery with the neutral point of the TN system power supply;
(2) Set up one or more repeated grounding points.

Note: The above operations need to be performed by professionals! ! !