Need help troubleshooting a Mentor DC Drive for an extruder

[allandesignusa]

I have a Mentor Drive 6MS200, Single Quad, for a max 200kw DC motor, Max continuous rating AC 460, 3 phase on 380 V that is powering the motor of twin screw extruder.

I am having the following problem:

Upon start at lowest possible RPM, huge sparks occur on the carbon brushes and an "over current" error is displayed on the mentor drive.

I have meanwhile replaced the brushes, but as winter and rain is upon us, the problem seems to become worse.

What seem to help, is warming the room and then starting the drive - Once ON, there are no apparant issues.

However, it has rained a lot recently, and it could be more moisutre in the control room.

Also, I don't have an oscilloscope, which does scare me to attach to the unit. As I mentioned the moment power starts, and overcurent occurs instantly, so I don't think I would see anything!!!

I am a Mechanical Enginer with basic electircal background. I know my way around 3phase AC motors and the use of the Voltmeter and understand the dangers at this high power levels.

Unfortunately, Mentor is not cooperative and is simply saying " just replace everything".

Any ideas what the problem could be? There are the 6 trysystors, inside the Mentor drive as well as Field Controller FXM2 by KTK Newtonw Limited.

In addition there are some resistor network and the potentionmeter for the speed setting with a tachometer for speed measurement on the shaft of the motor in a closed loop feedback control system.

I would appreciate any feedback and help and would gladly compensate for it.

Sincerely,

Allan

 

[duke37]

I have used a KTK drive some years ago, supplying both field and armature.
My uncle had his car run away down Vastre hill and arrived in Newtown at high speed. Luckily he hit nothing and the sheep in the trailer went to market as intended.

I presume that you have cleaned the commutator of carbon debris.

The field must be energised before the armature. The field is highly inductive so will take some time to get energised.
The armature drive should have a current limit to stop excess current but the commutator will not like high current when stationary.

It is a good thing that you know how to work with high voltages but the power level has no effect on danger.

Do you have details of the two drives? We had circuit diagrams of the KTK drive.

 

[allandesignusa]

Hi Duke,

Thanks for your quick reply.

I have attached a link for the electrical diagrams to download:.
http://www.haytak.com/KTK.pdf
http://www.haytak.com/Circ.pdf
http://www.haytak.com/Men.pdf
Thanks,

Allan

 

[duke37]

I have had a look at the data you sent. The KTK supply which we had just had a 0-10V signal for speed and another for torque, non of this computer nonsense.

It seems strange that KTK can't spell their address !

I would think that there is too much armature current and looking at the data

LED #9 current limit

Parameters
#08 Current feedback 0 to 1.6V
#10 as #08 amplified to 6.66V
#31 Current limit
#51 sets rate of change of speed (accelleration) #02
#61 Current slew rate limit
"If the armature current were allowed to change too fast the inherent lag of the interpoles fux could, in extreme cases, result in a flashover"

Motor sparking, check
#30
#31
#61

My eyes have given up !
Does allendesignusa mean you are in the states although frequency should not matter?

Duke

 

[allandesignusa]

Thanks,

The machine is running off of a generator 50hz 380V 3 phase.
The question, how could I identify if the problem is the mentor or the KTK?i
Given the fact that seems to be temperature / humidity dependent, this could indiate a loose connection or crack on a board.
Also, the part I don't understand what is the purpose of the armature field from the KTK? I haven't started by reducing any of the settings on mentor, but that would be the next choice. What about a way to tell if the 6 thrysistors are working correctly?

Yes, Motor is sparking and fuse is tripping on startup. Motor shaft can easely be turned by hand.!!

 

[duke37]

If the equipment works correctly at speed, then the power side is likely to be correct and the fault is in the control side.

The KTK only controls the field and the voltage across the field should be measured. If there is a poor connction, then this does not necessarily give the current but the current may be low enough to measure with a meter.

What fuse is blowing?

Humidity will affect resistances if the board is dirty.

 

[allandesignusa]

The fuse on the generator, which is rated to 800 Amp is blowing sometimes.
If not, then only the Mentor drive, switching to FAULT mode and inicating "overcurrent"

Also, at full load the system does not run more than ~250 Amp at runtime.

Therefore, it seems that the problem might be more on the KTK side and not the Mentor (power). The field the KTK generates, does that change during the startup of the motor?

What can I exactly measure on the KTK before startup? Armature Voltage? on F1 / F2 between 350 and 370 Volt? Fig 1 on KTK.pdf

Could there be a fault on the F1 and F2 cable connections to the motor. For example, the insulation of one of these calbes is slightly damaged and since, these cables are sitting in a grounded cable metal tray leading to the motor, the short could not be measured unless there is a load?

What about the F1 / F2 values on the Motor? With power off and If I disconnect the two form the motor, could I measure the resistance between the two on the motor?

 

[duke37]

Where are you located?
What are you extruding?

Without looking back at the diagrams, I think the field has a controlled curent, thus any leakage in your cables will give less current at the motor. As I said previously, you can get an idea of the field exitation by measuring the voltage and if the current is not too high you could measure the current.

The resistance of the motor field can be measured by disconnecting one connection only.
Measuring the resistance betweeen the feed cables MAY give an indication of cable leakage.

The field current should be constant unless you are using field weakening for high speed.

There should be current limiting in the armature, this is not working, maybe not set corectly.

If you have damaged cables sitting in a metal trough, you are living dangerously, particularly when it is damp. In this case, high power is more dangerous than low power since the supply will not notoce some leakage.