Dear all,
Can anyone help me to diagnosing the below problem?
As maintenance engineer in a sugar factory, I have been having problem with induction motor 37Kw driven by variable frequency drive (VFD), type Vacon NXS, this motor is running normally at 1200 rpm with draw current about 8.5A, the thing is that this motor was stopped working the drive HMI shown “Saturation Trip” which was indicating the drive is gone, we changed the drive & fuses with a new one and the motor restarted.
The same problem happened yesterday for the same other motor 37Kw, I found the drive main breaker was tripped and there is abnormal sound internal the drive, I turned it ON for control supply to what is HMI showing to locate the fault and keep the drive ready for start, then the drive’s HMI was ceased to function and did not shown the parameter, after checking I found the 3-F fuses 63A was blown, motor & power cable meggering was in GO .
The question is:

• Why the fuses was blown while this motor is running normally?
• why the drive component defective when the fuses blown? while there is no over-current or
short-circuit coming through the motor or power cable.
• What is the “Saturation Trip” cause to drive?

I’m wishing hearing from you dears.

Drive is showing a defective component according to the manual. Best to have a local repair shop check drive boards and power components. If you want to send to US we work on a lot of these Vacon drives. Do you have a linear reactor or any other protection on drive? What is distance from drive to motor? You monitor incoming power?

Dear Danial,
thanks for your comment, as you said the manual shown the drive defective component, we don't have filters/chokes for voltage spikes or linear reactor just the essential protection for the drive and motor, the distance between motor & the drive about 45m, incoming voltage 690v

check the power circuit .some component in either the coverter(rectifier)circiut or the inverter circiut should be shorting.carry out some tests.

motor is not inverter rated.

Saturation refers to voltage applied to motor is more than the required voltage to produce sinusoidal magnetic field density. so might be having problem in control module for switching inverter.

Please suggest me for improvement.

Have a capable Rewind shop test the motor with an All Test Meter. I believe that the motor could have been spiked by high voltage Thus the resistance and phase angle are out of sync. The motor probably needs a rewind with VFD compatible wire. By changing the VFD the problem went away for a short time until it received another spike perhaps.If the control module is having a problem try switching to constant torque mode instead of automatic switching if it is possible with that model of inverter,

Well abo

• Why the fuses was blown while this motor is running normally? drive can run with one fuse blowen because the have a bridge rectifier where all 3 input come together and dc is made. regardless of the motor if the first drive had a blowen bridge then the fuse was taken out then.

• why the drive component defective when the fuses blown? while there is no over-current or
short-circuit coming through the motor or power cable.

over current and short circuit is monitored on the back end of the drive not the front end.


• What is the “Saturation Trip” cause to drive?

With our Nexdrive product we can increase the torque level. if this is too high you can over saturat the motor. Perhaps this value in the vacon drive is set too high.

Hello Abo, saturation trips in NXS means that gate firing circuit for IGBT's was saturated, mos likely not able to turn off at high load spike or short circuit. Source could be in inverter itself or external. Could well be you have nasty problem in cable or motor with spike short circuit at ver short intervals as you lost 2 inverters already on ne motor. Megger test will not always show, if i.e. short is rotor position or vibration related (loose winding inside motor). Anyway reading you last notes indicates drive is broken now as well, as display went off.

What voltage is the Drive and motor rated for? You stated you had 690 volts on the input. This is higher than most drives can handle, even the 575 Volt drives. The distance between the motor and drive is too long. You will need to used a line reactor/filter on the output of the drive, and may have to add Shielded cable on the output of the dirve. You may also have to lower the Carrier Frequency on this drive. The voltage the motor is actually seeing is much higher than the 690, because of the distance and the high input voltage.

Hello Abo,
A few points
1) In case you are using 690VAC VFDs, you should have an output du/dt filter to protect the motor from voltage stress. This is true for all VFDs.
2) The first drive has tripped on Saturation Fault which indicates that there could be a component defect in the drive. For the second case, fuses are blown which could indicate blown input rectifier bridge or short in DC Bus due to IGBT failure.
3) In the second failure, you mention that you heard a noise and the Main Breaker tripped. Main breaker has tripped due to high current. You should always check power components before turning on mains supply if the main breaker has tripped.
4) As you have had two failures in quick succession, I would recommend that you have a look at the input voltage also.
In any case, please send your reply to me directly on vacon.uae@vacon.com

Is the INCOMING voltage 690 or BUS voltage 690? Big difference.

I would have a reputable motor shop test the motor while warm and under running conditions. Many winding issues will not show up in a cold state.

For a 37kw (50hp) motor, 8A is a VERY low draw. I assume that you are probably using a gearbox. Do not operate the VFD in "Sensorless Vector" mode but instead switch to v/hz operation. The tuning algorithms used for sensorless vector performance are too "hot" for low motor loading.

The Vacon VFD units are pretty robust and failures so quickly would indicate an outside issue (defective motor or power quality).

Good Luck!

690vac.... sounds like a mining operation? is this what the drive is rated? Our 1000vac input mining drives are a LOT different than our 230, 460, & 575vac drives....

when something breaks like this it, it is good to have all the information, like:
- did it used to work? for how long?
- is this a new application that has never worked long yet?
- what is the power source? Delta? open delta? wye? grounded? Does your vicon work with the type of input you have?

Obviously it is not a motor or motor cable issue as you meggered them and they passed, so first 'guess' w/o real info, is look at the input power. BTW, it is fairly easy in some cases to short the input diodes (causing the large input fuses to pop) on a vfd if you have a loose connection on any power wire (input or output).

Bottom line here - ensure that the control/power system of this motor is properly designed. After that, check that every component from power supply down to motor is not broken.

Othervise, you'll be spinning around in circles, spending money, time and chief's nerves and not providing a solution.

Good luck!

hello.. in the case of dc voltage it would be approximately 1.35 input voltage so it's no matter, you need to check the dc bus and the IGBTs when the main breaker is tripping because the fuse is almost tripping due to short circuits, also you need du/dt filter because of the distance between the drive & motor.