3. Timer Design Examples 3.8 Star-Delta Reduced Voltage Starter Control KM1 Reduced Voltage Starting Main Circuit PLC External Wiring Control Purpose: z Usually the starting current of the three-phase AC asynchronous motor is 5 ~7 times larger than the rated current. To reduce the effect of the starting current on the electrified wire fence, a star-delta reduced voltage starter should be applied. z Starting process of a star-delta reduced voltage starter: When the switch is turned on, the contactors of both motor starter and “Star Reduced Voltage Starter ” will be enabled first. After a 10 sec delay, the contacto r of “Star Reduced Voltage Starter ” will be disabled.
Finally, the contactor of “Delta Reduced Voltage Starter” will be enabled after 1 sec, which operates the main motor circuit normally. The control purpose in this process is to assure the contactor of “ Star Reduced Voltage Starter ” is disabled completely before the contactor of “ Delta Reduced Voltage Starter ” is enabled. Devices: DVP-PLC Application Examples 3-11 KM0 KM2 M 24V Y0 24G Y1 SS Y2 X0 COM X1 KM0 KM2 Device Function X0 X0 = ON when START is pressed. X1 X1 = ON when STOP is pressed. T1 10 sec timer. Time base: 100ms T2 1 sec timer. Time base: 100ms Y0 Motor starting contactor KM0 Y1 “Star Reduced Voltage Starter” contactor KM1 Y2 “Delta Reduced Voltage Starter” conntactor KM2