text: <s>[INST] PF 400 tripping in Undervoltage Fault Summary: Fault Code 4In our Plant Cooler section we have 13 nos. PF 400 Drives ( Cat No. 22C-D260A103 132 KW MFD 2007 JUL 30 China). Out of them 3 Drives are often (After 2-3 day’s) tripping in UNDER VOLTAGE FAULT F4. After every fault i have checked Advance Display Parameter d326 Fault Bus Voltage which was 560-580 VDC (Normal) I have enabled Flying Start & Bus regulation parameter but problem not rectified. Any Suggestion PLZ ? [/INST] Are there any line reactors installed with the drives? With this many large drives together there's a good chance the harmonics cresated could be causing DC bus ripple, which the drive could interpret as an undervoltage condition. Cheers \\n </s>