Abstract : This paper introduces the working principle of common inverter starting circuits, analyzes the causes of frequent tripping, elaborates on the working principle and wiring method of three-wire starting control of inverters, and explains the advantages of three-wire starting control. Keywords : Inverter, Three-wire starting control, Fault 1 Common Inverter Starting Circuits In locally operated inverter control circuits, inverter starting is usually achieved by connecting a pair of self-holding contacts on both sides of the start button. The wiring is shown in Figure 1. KA is generally the auxiliary contact of the power circuit contactor or the contact of the intermediate relay. Most inverters in the transportation department of the Shanxi branch of China Aluminum Corporation use this starting method. Operators reported frequent tripping of the inverter. The inverter model is FRN160P9S-4. The recent fault records show OC1 and OC2, i.e., acceleration overcurrent and deceleration overcurrent protection activation. There are generally three reasons for this: short circuit at the output, increased load, and excessively short acceleration/deceleration time settings. Inspection revealed that the inverter, external power supply circuit, and load were all normal. The inverter had been in normal use for over a year, so there should be no issue with low parameter settings. The inverter started normally upon restarting, but tripped again 30 minutes after the technician left, with the same fault indication. During a no-load test of the control circuit, the "RUN" indicator light on the display panel was found to be flashing during frequency adjustment. Careful inspection revealed that the KA contact was oxidized and not properly engaged. The cause of the fault was determined to be poor engagement of the KA contact, causing the running command to be intermittent. The inverter, operating at a certain frequency, appeared to receive a rising or falling frequency pulse, triggering the acceleration/deceleration overcurrent protection to trip. [b][align=center]For more details, please click: Simple and Practical Three-Wire Starting Control for Inverters[/align][/b]