I was called upon to diagnose interesting problem that occurred earlier this week that is inverter related.
A 20yr old Mazak Lathe displayed a over current fault on an Inverter drive, if the motor is disconnected the fault is usually the IGBT transistors.
Upon opening the cabinet containing the controller and inverter, I saw right away that one of the ground conductors to the large brass ground plate had burned all the insulation off the wire for a distance of around 20" from the ground plate, continuing from there to its destination, it was in perfect shape.
The Ground wire was loosely bundled with 3ph hyd pump and chiller and the Inverter motor wires, no flexing or moving of the cables would normally occur, the heat had burnt some of the Hyd pump and chiller cables and inverter cables, these are heavily insulated wires.
The excess current in the ground wire had obviously originated 20" from the Gnd point.
The copper wire composition had changed so much that the 14g wire could be snapped easily, obviously some heavy current had been passed.
The 3ph motors were megger'd to Gnd and were OK.
One of the inverter wires was burnt through to the conductor in around a 3" length.
All conductors were repaired and replaced and the machine came on with no fault.
The only explanation I have is somehow there was punch through from the VFD wiring to the Ground wire. It appeared to have occurred over a period of time.
See this ref: http://www.belden.com/pdfs/Techpprs/Evaluating VFD.pdf
M.
A 20yr old Mazak Lathe displayed a over current fault on an Inverter drive, if the motor is disconnected the fault is usually the IGBT transistors.
Upon opening the cabinet containing the controller and inverter, I saw right away that one of the ground conductors to the large brass ground plate had burned all the insulation off the wire for a distance of around 20" from the ground plate, continuing from there to its destination, it was in perfect shape.
The Ground wire was loosely bundled with 3ph hyd pump and chiller and the Inverter motor wires, no flexing or moving of the cables would normally occur, the heat had burnt some of the Hyd pump and chiller cables and inverter cables, these are heavily insulated wires.
The excess current in the ground wire had obviously originated 20" from the Gnd point.
The copper wire composition had changed so much that the 14g wire could be snapped easily, obviously some heavy current had been passed.
The 3ph motors were megger'd to Gnd and were OK.
One of the inverter wires was burnt through to the conductor in around a 3" length.
All conductors were repaired and replaced and the machine came on with no fault.
The only explanation I have is somehow there was punch through from the VFD wiring to the Ground wire. It appeared to have occurred over a period of time.
See this ref: http://www.belden.com/pdfs/Techpprs/Evaluating VFD.pdf
M.