Diagnosis and treatment of man-made electrical faults in WD-400 excavator
WD-400 type excavator (4m3 excavator) is the main mining bureau of Xiaolongtan mining equipment, the electric control system than conventional relay control is much more complicated, so the diagnosis and elimination of the electrical fault is the primary problem affecting the normal operation of equipment. Through years of trial and error, although most of the general diagnosis and treatment skills have been mastered, some special electrical faults still make it impossible for the maintenance staff to start. Therefore, it is necessary to make further analysis and Discussion on this kind of fault, in order to improve the ability to deal with the fault. The so-called special fault refers to the general troubleshooting train of thought diagnosis difficult to deal with.
Fault phenomenon:
One morning 15 shovel driver according to the conventional sequence starting F-D generator, the bucket automatically and quickly filed, scared the driver emergency stop repair.
Fault diagnosis:
The control principle shows that if the unit is started without the master command operation, then the operating mechanism should not have any action. Even if the adjustment is not ideal, there may only be slow parts crawling, this fault is clearly not crawling problem. If the power supply phase sequence does not meet the requirements of this machine, the whole system will be out of order and turn the negative feedback into positive feedback. Remanence voltage positive feedback effect will make the generator low dramatically rise, if the hoisting mechanism brake has been opened, the motor will rotate rapidly and the failure of the above, but the phase sequence indicator shows that the phase sequence is correct, auxiliary to prove the correctness of the sequence. So far, the search for the fault point seems to be out of the question. What is the special cause of this strange fault? The equivalent circuit of the part is shown in figure 1.
The basic principle of the mechanism is in the unit after the start, open the excitation switch, operation master controller handle (forward or reverse) to a given winding magnetic trigger 1ZF (not shown in the figure) provide about -15~15mA (change with the position of the handle) given current makes the trigger output trigger pulse. The positive or negative half controlled bridge rectifier to guide hoist excitation windings of the generator 1F provides excitation current, so as to produce a -460~460V DC voltage between the output end of the generator, the S101 S102, so that the motor forward or reverse rotation. The voltage and current of the 1ZF in Figure 1 are set up to stabilize and improve the working conditions of the generator, and the control action is opposite to the given winding. When the master controller is in the zero position, the positive and negative excitation components do not have output because of no triggering pulse, and the motor is not enough to rotate. To explore new ideas to find the fault must therefore consider whether, due to line aging damage and 220V DC control power on magnetic trigger given winding excitation resulting in half controlled bridge rectifier conduction output, and the generator drive motor rotation? But the instrument test shows that the lines are well insulated and have no strings. During further inspection, it is found that the inner winding potentiometer 1W33 of the control cabinet is hot, and the resistance wire is red. So far, it is sure that the DC control power is connected into the current negative feedback winding. Disconnect the S112 line on the 1W33 and measure that there is a 220V DC voltage between the potentiometer and the potentiometer. In order to avoid blind search, according to the electrical diagram of the whole machine, the logic analysis method is used to determine the suspicious part and the instrument is used for detection. It was finally found that the two strands of the lead wire of the lift motor were in error with the 501 and S112 lines from the control cabinet, as shown in the dotted line at the fork in figure 1. The processing method is to re approve the wiring, and the fault can be eliminated after the test.
