XQB1 type protection box circuit b

The protection box is an important part of the electrical circuit of the bridge crane . Its function is to protect the the bridge crane
. It ensures the power supply for all electrical equipment on the crane, and has over-current protection, under-voltage protection, and zero-position protection. ,
limit protection and emergency protection and other protection functions.
    The XQB1 type protection box circuit is shown in Figure 8-2. Among them, SAi, SA2, and SA3 are all linkage switches, and SA is an emergency stop
switch.
    In the figure, osi is the main power switch, KM is the line contactor, KI1~KI4 are the overcurrent relays of each motor of
the crane . Each motor has two phases protected by the overcurrent relay. KI is the total overcurrent relay, sQJ~SQ3 are hatch
safety switches, SQ4-SQ8 are limit switches. When the operating mechanism (large, trolley or lifting mechanism) reaches the limit position, it
is disconnected, causing KM to be released and the motor to stop. to avoid accidents.