VFD Phase Loss Fault?

A customer has two AB Powerflex 753 VFD running on two identical powdered metal presses. Both where installed about two years ago. One is running fine. The other has had a problem during decel where it gets a loss of phase fault (#17), and they have to power down the unit. They report that they have prevented this by speeding up the decel from 180s to 120s and using dynamic braking, although the brake resister is getting extremely hot.

They may need a larger brake resistor to handle the load, but their question and mine, is why on this press would the motor be causing a loss of phase fault on the one VFD (High DC Bus Ripple). We work on, and install a large number of VFD's in the area, and I have never encountered this.

Note (Brake Resistor normally are installed on larger PM presses. Not for stopping time, but to absorb the energy after compaction/ejection. Would load reactors help? I have been leaning toward a problem in the drive, but wanted to see if someone could explain this to me.

Also, we set the inPhase LossActn to either ignore or alarm, and still encounted a fault, that required the drive to be reset.

From A-B:

Fault Number : 17

Fault Display : Input Phase Loss

Fault Name : Input Phase Loss

Fault Type : None

Fault Description : The DC bus ripple has exceeded a preset level.

Corrective Action : The most common cause of this fault would be a loss of a phase on the incoming line. This will cause the bus ripple to increase going beyond specifications. This can also be caused by extremely noisy utility power, or disturbances being induced on the line. An example would be a punch press on the same transformer line as the drive. These presses put large spikes on the power line, and can wrachet the voltage on the bus quite dramatically.

If a noisy power supply line is inevitable, then an isolation transformer or a line reactor may be necessary.

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I've dealt with a lot of drive problems, and every time when the drive was giving me grief over incoming power, the problem turned out to be with the drive itself. Usually what I do to troubleshoot drive issues is to disconnect the motor from the drive and try to run it. If you still get a fault when no load is connected, odds are the drive is malfunctioning. But I would try doing what A-B suggests here first, depending on how you've installed it.

I believe that AB has chosen to leave out the input reactors in their Powerflex series so the addition of a 3% reactor would be the first response. At rated load, you will loose 3% of your input voltage across the reactor so this would not be suitable for an application that already has an input voltage on the low end of the range, say 470VAC or less.