Reasons Why The Main Contactor Coil of The Crane is Powered Off

单梁桥式起重机

双梁桥式起重机

During the operation of an electric single-girder crane, sometimes the various chain control switches are working normally, but the main contactor coil suddenly loses power due to various unexpected reasons, causing the main circuit and control circuit of the working crane to lose power. In order to ensure production, lifting operators sometimes artificially push the main contactor with wood or other objects to forcefully connect the main circuit and the control circuit. Although the crane can continue to work, all the limit switches lose their control function. It may cause the lifting to exceed the limit, and in severe cases, it may even cause serious accidents such as the wire rope being broken and the hook falling.

The main reasons for the power outage of the main contactor coil of the crane are as follows:
(1) The vibration generated when the cart is working makes the slide iron and the guide rail not firmly combined, causing problems with the power supply, causing the main contact and the normally open auxiliary contact of the main contactor to be disconnected at the same time, and the main contactor coil self-locking failure. causing a power outage.
(2) The partial contact of the slide rail is poor, resulting in an instantaneous phase loss when the bridge crane reaches a certain section of the slide rail. If the missing phase happens to be connected to the control circuit, the coil of the main contactor will be powered off and automatically If the lock fails, even if the bridge crane is re-energized after sliding over the poor contact due to inertia, the main contactor coil will not be able to close on its own, and the start button must be pressed again.
(3) The vibration generated when lifting heavy objects causes the main contactor to not close tightly, the main contact and the normally open auxiliary contact are disconnected due to vibration at the same time, and the main contactor coil self-locking fails and the power is cut off.

Emergency treatment of bridge crane power failure:
1. Insert the normally closed contacts KI, KI1, KI2, and KI3 of the overcurrent relay into the control circuit in sequence to provide overload protection for each motor of the bridge crane. Once the current of the motor exceeds the set threshold, the overcurrent relay contacts will Opens, interrupting the circuit to protect the motor from overload damage;
2. Connect zero starting protection contacts Q1, Q2, and Q3 in series for zero starting protection. If the motor does not reach the zero position, the zero starting protection contacts will open and starting operation is prohibited.
3. Connect the safety switch SA in series for emergency stop in unexpected situations;
4. Insert three limit switches SQ1, SQ2, and SQ3 in series for the chain protection of the crane. They are installed on the bridge or other locations to monitor the position of the crane and trigger action when the preset limit is reached to prevent the crane from continuing. Moved or exceeded limits.
5. The following sets of extreme position limit switches and the corresponding 2 pairs of contacts of each cam controller work together to complete the limit position of the bridge crane. By detecting the position of the crane, corresponding actions are triggered to limit the range of movement of the crane.