Below in conjunction with accompanying drawing the utility model embodiment is described in further detail: as shown in the figure, single speed three-phase asynchronous motor with multiple powers M is a YCHD280M-10 high starting torque high-slip threephase asynchronous, have single speed (540 rev/mins) three power grades (37/27/17kW), it derives from design on standard laid down by the ministries or commissions of the Central Government YH serial motors basis, can be by (for example changing the motor stator winding mode of connection

Reach the purpose that has level to regulate power grade.Microprocessor 5 is an EASY412-AC-R type PLC microcomputer, is the center processing computer.Transformer TC, bridge rectifier 3,7824 type three terminal integrated voltage stabilizers 4 constitute the power circuit of giving microprocessor 5 power supplies.Wherein, one group is the output of 24V direct voltage, and another group exchanges output for 36V.Microprocessor 5 constitutes the current detection sensor circuit with current detection sensor 1,2.The current detection sensor circuit is a custom circuit, and current detection sensor only can be designed to 1-3, is designed to 2 in the present embodiment, and its output is connected with input I7, I8, the N of microprocessor 5 respectively.Microprocessor 5 and output Q thereof
1-Q
44 A.C. contactor KM that connect
1-KM
4Constitute power of motor grade conversion control circuit, A.C. contactor KM
1-KM
4Three set of connections U with motor M
1V
1W
1, U
2V
2W
2, U
3V
3W
3, and power line A, B, C be connected into three kinds of power supply states, i.e. A.C. contactor KM
1, KM
2Motor M is the 37kW power level status during adhesive, A.C. contactor KM
1, KM
3Motor M is the 27kW power level status during adhesive, A.C. contactor KM
2, KM
4Motor M is the 17kW power level status during adhesive.A.C. contactor also can select 2-5 only.Microprocessor 5 and current sensor 1,2, A.C. contactor KM
1, KM
4, and microprocessor internal software constitute overload, phase shortage, starting and detect time-delay, short circuit, motor overheating protective circuit.4 button SB
1-SB
4An end be connected with the 24V DC power supply, the other end is connected with input I1, I2, I3, the I4 of microprocessor 5 respectively, has startup respectively, stops, manually debugging and debugging and reset function automatically.Constitute instruction control circuit.
Present embodiment operation principle and process are as follows: after power line A, B, C energising, press start button SB
1,, select maximum power level to drive A.C. contactor KM automatically if microprocessor 5 does not have last time electrical fault memory
1, KM
2Adhesive makes dragging motor M in the operation of 37kW power grade, lags 6 seconds, and the current signal of 5 couples of current detection sensor 1,2 detected dragging motor M of microprocessor carries out analyzing and processing, judges at any time whether overload, short circuit, phase shortage, overheating fault exist.If there is fault to disconnect A.C. contactor KM
1, KM
2, stop the moving row of motor; If fault-free judges at any time then whether current electric current is less than or equal to the load current value of 27kW.If be less than or equal to the load current value of 27kW, continue to detect 5-50 minute no change, disconnect A.C. contactor KM
1, KM
2, stop the 37kW power grade, postpone 0.5 second connection A.C. contactor KM
1, KM
3, dragging motor is operated on the power grade of 27kW, whether the load current that this moment, microprocessor 5 was still judged dragging motor M at any time is greater than the rated current of 27kW or smaller or equal to the rated current of 17kW.If return the running status of 37kW after 20 seconds greater than the rated current of 27kW; If the rated current smaller or equal to 17kW postpones 5-50 minute disconnection A.C. contactor KM
1, KM
3, delay time and connect A.C. contactor KM after 0.5 second
2, KM
4, dragging motor M is operated on the 17kW power grade.If no-load current changes, dragging motor M operates on a certain power grade all the time.