Overhead crane in the work process sometimes various interlocking control switching state is normal, and the main contactor coil due to various causes of accidents sudden power outage, the overhead crane is working in the main circuit and control circuit energized . Then bridge crane will not stop due to inertia, is likely damaged the workpiece and the machine, and even cause serious personal injury or death, there is a serious hidden dangers. Operatives in order to ensure the production, sometimes artificially made of wood and other objects on top of the main contactor, forcibly connected to the main circuit and control circuit, so although the crane can continue to work, but all the limit switches have lost control action , it may cause lifting over the limit, even when serious cause rope to pull off, hook falling vicious accident.
Analysis of the main contactor coil power is due mainly to the following aspects:
(A) the vibration generated when the work carts make Waterloo rail combined with strong, power supply problems, causing the main contactor main contacts and auxiliary contacts while disconnected, the main contactor coil failure caused by self-locking power.
(2) Waterloo local poor contact, resulting in a certain overhead crane rail line to the instantaneous phase, if the missing phase which happens to be connected to the control line, it will make the main contactor coil power, self- lock failure, even due to inertia glide overhead cranes poor contact at the re-energized after the main contactor coil is also unable to pull, you must re-press the start button.
(3) lifting heavy vibrations generated when the main contactor is not strong, the main contact and normally open auxiliary contacts while disconnected due to vibration, the main contactor coil is self-locking and power failure.
2 failures
Bridge crane control circuit schematic diagram shown in Figure 1 as shown by the solid line portion. After switching from a three-phase 380V power supply QS access bridge crane, removed from the two-phase three-phase power control circuit as the power to overhead cranes KM main contactor coil supply, followed by the string into the control circuit overcurrent relay normally closed contact KI, KI1, KI2, KI3, for each crane motor overload protection; series with zero starting protection contacts Q1, Q2, Q3 for zero starting protection; string into the safety switch SA is used for accident in case of an emergency stop; string into three limit switches SQ1, SQ2, SQ3 for crane interlock protection; button SB used cranes start, the two main contactor normally open auxiliary contact KM completion of the main contactor The self-locking; following several groups and each limit position limit switch cam controller corresponding to two pairs of contacts with the work, completed bridge crane limit.
Overhead crane at work in order to solve the power failure problems occur, the original line has been improved. The time relay access control circuit, the use of time delay relay break contact, so that the main contactor coil in an instant loss of power after power is restored quickly, the main contactor remained energized, ensure that the main circuit to work properly.
Improved circuit shown in dotted lines in Figure 1. The time relay JS20 a D (delay time is 0 ~ 60s) in parallel with the primary coil KT KM contactor coil ends, JS20 a group of D 2 instant-on, delay off contacts were connected in parallel Main contactor 2 normally open auxiliary contact on KM. Delay time can be used according to the actual situation JS20 an adjustable resistor on D adjusted so that the delay time is greater than line momentary power failure time, instantaneous power failure in KM coil, JS20 a delay D groups remain open contacts control circuit is closed until the re-energized, thus solving the main contactor momentary power failure problems. Time relay contacts in the form of access to the circuit had no impact on the rest of the circuit, the limit switches can work, thus ensuring the normal operation of crane safety and avoid accidents caused by equipment and personal injury.
Through the bridge crane to improve, to good effect, does not reappear crane runaway phenomenon, to achieve the desired objective, to ensure the safe operation of the crane.
