text: <s>[INST] Intermittent F12 HW overcurrent and F36 SW overcurrent faults I have a customer who installed a PF700 (20BD077A3AYNANC1) in place of a bulletin 1392 ac spindle drive. the original 1327- spindle motor remained, and the 1392 was removed.the machine after start up has run now for about 1 year. Intermittently the customer will experience F12 and F36 faults one or two times and then the system will operate fine. During the faults the drive which is running a dressing wheel is running at a constant speed before the fault. the customer recorded the following at parameters during the fault:Fault amps Par 225 59.3 (this appears to be ok as it is below the rating if the drive)Fault Bus volts 762.3 (This appears high if running at a set speed. Typically it is 652 VDC.)Status 1 at Fault Par 227 0000111000011111. ( Bit 4 says it was accelerating but i was told it was running at a constant speed.) the unit firmware is Rev 4.01 Ser B Any ideas on what might be the cause of the intermittent trips? [/INST] It could be a configuration problem.How is the drive controlled (Hard Wired or Digitally)?What Dynamic Control Mode has been chosen?Is there any feedback device attached to the motor?Is it a direct drive application or there is a gear reducer between the motor and the wheel?How long the load side of the drive wiring is and how old? From my personal experience, since we've been extensively involved in replacing tens of 1336 and 1392 Legacy VFDs with Architecture Class PF70s and 700s, we've also experienced quite a few nuisance trips on F12.Same scenario. The Fault Time Parameter Snapshot seemed to be okay.Tweaking the application files helped to some extent but didn't solve the problem.What did end the trips, and I know it sounds counterintuitive, too easy and pretty expensive, was the replacing of the drive's load side old field wiring and some of the motors!!!:smileysurprised.It was a last resort measure since the numerous electrical measurements of the physical electrical circuits never returned but normal readings.Further investigations led us to conclude that the length and age of the existing wiring couldn't withstand the new generation VFDs output form. A default PWM (Pulse Width Modulation) of 4kHz could very easily penetrate the adjacent phase weak insulation, combine with the existing modulator and generate a Hardware Overcurrent Fault. As for the high DC Bus voltage, you might want to invest into an isolation transformer. A line reactor (which I hope it is present on the line side of the drive) will filter drive generated EMI from the upstream feeder branch of the distribution system but it will not protect the VFD when experiencing high-voltage transients, brownouts or any other power supply temporary problems. \\n </s>