Autotransformer starts the main circuit of multiple motors

The main circuit design uses one autotransformer to start multiple motors as shown in the figure. The starting circuit is composed of
autoswitch QFO, contactor KMO, autotransformer T and contactors KM01~KMON. Each motor The rated voltage operating circuits
are independent of each other. Taking the motor Ml as an example, when the motor Ml is running normally, the circuit composed of QF1, KM1 and thermal relay KR1 supplies power.
    It should be pointed out that the coil of Tongxiao autotransformer is designed for a relatively short operating time. Generally, it is only allowed to be started 2 to 3
times in a row. When starting again, it needs to wait for it to cool down before starting. One autotransformer is used to start multiple motors, and the number of starts is relatively frequent. Therefore, in addition to considering the capacity of the autotransformer based on the motor, maximum starting load and starting time, an autotransformer
with a larger capacity can also be used in special places.
Also consider the configuration of a backup autotransformer .
    (3) Control circuit design In order to achieve the above purpose, PLC is used as the controller to realize automatic and interlocking control of the starting of multiple motors
. PLC selection is mainly based on the number of controlled motors to select the number of I/O points. To meet the control requirements, you can choose sorting type, medium or low-
end PLC to meet the production requirements.
    According to the requirements of the control system, each motor should be equipped with a start button and a stop button. At the same time,
the signal of the motor overload protection thermal relay should also be fed back to the PLC. In order to save the number of input points of the PLC, the overload protection thermal relay of each motor can be After the normally open contact of the stop
button is connected in parallel with the normally open contact, it is used as an input signal and then sent to the PLC, so that the cost of the control system can be reduced. Therefore, each
motor only requires two input points from the PLC. Similarly, it can be seen from the main circuit that each motor is controlled by two main contactors, so two
PLC input points are required to control the contactors. In this way, according to the number of motors to be controlled , the number of l/o points required by the PLC can be determined
, and then the specific configuration of the PLC can be determined.