Inspection precautions for emergency power-off swi

Inspection precautions for emergency power-off switch of hoisting machinery

as an important electrical protection device of hoisting machinery, emergency power-off switch plays a very important role in safe operation. Because the inspectors have different understanding of the connotation of the switch after entering the experimental interface, there are also certain differences in the judgment criteria of whether the switch is qualified in the daily inspection process. 3. Taking the breaking load test of safety belt as an example, it is stipulated in the supervision and inspection procedures for cranes: "the crane must be equipped with an emergency power-off switch, which can cut off the main power supply of the crane in an emergency. The emergency power-off switch should not be reset automatically, and should be located in a place convenient for the driver to operate."

some inspectors judged that the emergency power-off switch was qualified only by "the emergency power-off switch cannot be reset automatically". Such a determination method will make some unqualified emergency power-off switches be misjudged as qualified, which will bring hidden dangers to safety production. At present, the structures of emergency power-off switches on the market are diverse, and the methods of locking and resetting are also different. Therefore, the judgment of whether the emergency power-off switch is qualified or not should not only meet the requirements of automatic reset, but also check its reset mode and relevant requirements according to relevant national standards

Article 4.4.4 of GB "design principles for mechanical safety emergency stop" stipulates: "after operating the emergency stop device to generate an emergency stop command, the command must be maintained through the engagement (locking) of the driving device until the emergency stop device is reset (disengaged)." Paragraph 4.4.5 stipulates: "the reset (disengagement) of the emergency stop device shall only be carried out manually on the emergency stop device. When resetting the emergency stop device, the restart command shall be generated by the emergency stop device itself without its distance being the track width of the two wheels of the front axle."

1. Correct inspection sequence and method

(1) inspect each control point, especially for dual control systems. In addition to setting interlock protection for each control system, each control device should be set with emergency power-off switch, including flashlight and portable control device

(2) check whether there is a main power contactor on the crane, and the power supply of all mechanisms must be led from the outgoing end of the main power contactor

power on test: operate the emergency power-off switch, the main power contactor acts, cut off the main power supply of all mechanisms, and the operation of all mechanisms stops

(3) check the structural form of the emergency power-off switch, which should comply with the provisions of the non automatic reset and reset mode of the emergency power-off switch, and the main power supply of the mechanism should not be connected at the same time when resetting

2. Operation test

the emergency power-off switch shall be maintained by engaging or locking after operation, and cannot be reset automatically; The reset action should be generated by touching the emergency power-off switch itself, rather than touching other buttons. After resetting, give the mechanism an action command, and the mechanism should not act. Only after the start button is touched and the power is turned on, the mechanism can accept the command and generate action

if the above requirements can be met at the same time, the emergency power-off switch can be judged as qualified

in the process of inspection, everyone will notice whether the emergency power-off switch can be reset automatically. It is easy to ignore the two requirements that the main power supply should not be connected after the reset mode and reset of the emergency power-off switch. The common structural forms of the emergency power-off switch roughly fall into the following three categories:

a. mushroom head switch

b. lockable set button switch, reset can be carried out by triggering and interlocking start button

c. ordinary (not lockable) button switch

for type C switch, it cannot be locked, and the main power supply is connected while the emergency stop is released, so it is easy to judge as unqualified

for type B switch, it can cut off the main power supply of the mechanism and cannot be reset automatically. Many staff of using units, including some inspectors, often make wrong conclusions and think it is qualified. However, the reset mode of this switch does not meet the requirements, which has a great trend to replace the conventional coal-fired steam turbine motor station, and the main power supply is connected at the same time of reset, so it is unqualified

for type a switch, it can cut off the main power supply of the mechanism and cannot be reset automatically. The reset is generated by the touch switch itself. These requirements are met, but it cannot be judged that the switch is qualified. It is also necessary to test whether the main power supply can be connected while the switch is reset. If it cannot be connected, it is qualified, and if it can be connected, it is unqualified

in a word, as an important inspection item, the qualification of the emergency power-off switch is directly related to the judgment of the overall conclusion of the crane, which is closely related to the safe use. We must understand the relevant provisions in the national standard in detail, and make a correct conclusion through careful observation and a series of tests during the inspection