During the use of bridge cranes, especially double girder bridge cranes, some customers have discovered that all interlocking control switches are working normally and the main contactor coil is suddenly cut off. This situation will cause the main circuit and control circuit of the bridge crane to lose power. In order to ensure the continuation of production, some operators artificially put the main contactor on top and forcibly connect the main circuit and the control circuit. This approach, although the bridge crane can continue to work, but there will be a big hidden danger.
The main contactor coils of bridge cranes are cut off due to the following reasons:
(1) The vibration generated during the operation of the cart makes the sliding iron and the guide rail not firmly combined, and the power supply has problems, which causes the main contact of the main contactor and the normally open auxiliary contact to be disconnected at the same time, and the main contactor coil fails to lock itself. Causes a power outage.
(2) The partial contact of the sliding iron is poor, which causes the bridge crane to lose phase instantaneously when it reaches a certain section of the sliding rail. If the missing phase happens to be connected to the control circuit, the coil of the main contactor will be de-energized and automatically If the lock fails, even if the bridge crane is re-energized after slipping through the poor contact due to inertia, the main contactor coil will not be able to pull in by itself, and the start button must be pressed again.
(3) The vibration generated when lifting heavy objects makes the main contactor 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 fails to lock and loses power.
The control circuit of the bridge crane is connected to the bridge crane from the three-phase 380V power supply through the switch QS, and two phases are taken from the three-phase power supply as the power supply of the control circuit, and the main contactor coil KM of the bridge crane is supplied with power. The overcurrent relay normally closed contacts KI, KI1, KI2, KI3 are connected in series to protect each motor of the bridge crane; the zero starting protection contacts Q1, Q2, Q3 are connected in series for zero starting protection; the series is connected to safety The protection switch SA is used for emergency stop in unexpected situations; 3 limit switches SQ1, SQ2, SQ3 are connected in series for the chain protection of the crane; the button SB is used for the start of the crane, and the 2 normally open auxiliary contacts of the main contactor KM completes the self-locking of the main contactor; the following groups of limit position limit switches and the corresponding two pairs of contacts of each cam controller work together to complete the limit of the bridge crane.
A power outage accident in a bridge crane should first be handled by professionals while ensuring safety.
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