DC motor and drive problem

[mohamed]

hi to all :waving:,
am new in the forum
i have a problem with a dc drive
let me start with the application
it's a centrifugal force pump runs with a dc motor without a gearbox , the operation speed is 1300 rpm working 24/7
the problem is the speed drops from 1300 rpm to 200 rpm instantaneous and back to 1300 rpm without any user interfere . happens at random times like 5 times / h and could be 1 time /day but happen every day
we made some solution but the problem is still on ( until step 5 )
1- change speed reference pot ( 10k ohm , 5k ohm all 10 turns )
2-change start stop push buttons , control relays , power and control cables from panel to motor and from panel to operator panel
3-change speed reference from pot to push button ( option in drive )
4-change motor :38:
5-last changed the control card on the drive
but this made the 1st problem gone and a new one appear
the drive stop without any fault as if someone press stop push button so we change it but the problem still on
can someone help

 

[Marvo]

Can you give us some specific details? Make and model numbers of pump and drive please.

What is the exact application? What is being pumped and why? You say the pump is working 24/7, is it running continuous or is there an external control that switches it on and off?

 

[mohamed]

thanks ,
the drive is sprint electric PL/PLX 315 ( but i can't find the type on the drive )
the motor is 428 kw , 1800 rpm , 440 va , 1040 ia , 330 vf , 7.5 if
the pump used in tissue stock ( pulb ) called fan pump and works 24/7 continouse

 

[Besoeker]

thanks ,
the drive is sprint electric PL/PLX 315 ( but i can't find the type on the drive )
the motor is 428 kw , 1800 rpm , 440 va , 1040 ia , 330 vf , 7.5 if
the pump used in tissue stock ( pulb ) called fan pump and works 24/7 continouse

Sounds like a paper mill application.
If it's a compound wound machine, and many DC motors are, it could be loss of the shunt field. I've seen that problem a few times in paper mills. The damp atmosphere can cause corrosion of terminals.

Does the drive have field loss protection?
I think the same drives were marketed by Eurotherm and others.
We installed a few but had problems with reliability.

Some information here.

http://www.sprint-electric.com/products/plx

 

[Darkwood]

We could do with establishing if there are any indicators coming on the drive cards to suggest tripping etc, you may be correct here Besoeker regarding output protection, the initial fault could have seen the demise of the original drive card and thus a new one exposes the underlying issues although I'm a little reserved about the OP's methods to resolve the problem, it appears this could have been an expensive exercise to locate the problem probably at the firm/customers expense for what I see as some unecessary work.

@mohamed - What testing has been done here?
Is the speed control closed loop?
Are there any indicators/leds on the drive card when the motor now stops without obvious command?

 

[mohamed]

thanks again for the answers and let me respond to both of you in one reply ,
@Besoeker
yea it's a paper mill
i think i say we changed the motor with the one i last say it's ratings ( the 1st one was greater in kw ) both motor have problem of winding ?
about The damp atmosphere can cause corrosion of terminals the drive in a room with a central air condition and the atmosphere kept to 27 c
@darkwood
the seller support here and the manual ( what i know from my little experience ) say that if the drive tripped it should give a message on the screen defining the fault and could not be removed till i reset it and i check the fault history there was no data stored on it
if you ask about programming outputs of drive to indicate the fault so what faults should we program ?
the way we solve the problem was not expensive for us this problem cause waste product and a lot of stop time
What testing has been done here?
i don't know what you mean but we check every single aspect of the system ( drive , motor , wiring )
Is the speed control closed loop?
if you speak about this motor it dose not depend on machine speed ( machine is set to about 800 rpm ) if you speak about speed feedback of this motor yea it's closed loop with tacho ( and we try to change to emf and have the same problem of speed down and up )
Are there any indicators/leds on the drive card when the motor now stops without obvious command ?
no just the word stop on the drive screen and relay of start stop light go and not energized ( i say we change stop push button and we change the control cable from drive room to operator panel )

 

[Darkwood]

@darkwood
the seller support here and the manual ( what i know from my little experience ) say that if the drive tripped it should give a message on the screen defining the fault and could not be removed till i reset it and i check the fault history there was no data stored on it
This would suggest it is receiving a stop command or the stop circuit is failing at some point and opening or going high resistance, also dependant on the control circuit a fault somewhere could be pulling down the voltage and the either some control relay drops out or the voltage could be below the drives threshold to remain with a run command. The fault of intermittent stopping with no trip codes or logs could be many things and an indepth knowledge of control systems or and understanding of how to read the wiring schematics will be needed otherwise you will be guessing and spending money that on parts that are working fine.
if you ask about programming outputs of drive to indicate the fault so what faults should we program ?
No I was just on about intregral indicators or trip messages.
the way we solve the problem was not expensive for us this problem cause waste product and a lot of stop time
What testing has been done here?
Before commiting to buying parts, replacing wiring looms,drives and motors which can be expensive if not required, I would have expected you to test the motor windings and voltages present when running, drive outputs, Tacho signals, control signals etc etc - this is how to isolate the issue/fault and eliminate suspect parts and wiring. i don't know what you mean but we check every single aspect of the system ( drive , motor , wiring )
Is the speed control closed loop?
if you speak about this motor it dose not depend on machine speed ( machine is set to about 800 rpm ) if you speak about speed feedback of this motor yea it's closed loop with tacho ( and we try to change to emf and have the same problem of speed down and up )
When the motor slows down you need to check current demand and voltage present at motor terminals to assess where the issue lies, if the voltage present is only asking the motor to run slow then obviously the issue lies upstream.
Are there any indicators/leds on the drive card when the motor now stops without obvious command ?
no just the word stop on the drive screen and relay of start stop light go and not energized ( i say we change stop push button and we change the control cable from drive room to operator panel )

Can you not eliminate external controls and use as a temp' option the input terminals direct with a little hand held controller which is known to be ok ... this would again rule out problems with your external controls if the fault persists...
What is the control voltage out of interest and are you using PNP NPN derived from the drive or external to the drive?..

TBH - there are too many what/why/when etc for us to give you any real solid leads, you need to get your meters out and figure out what is happening when the motor slows or it stops without any real obvious cause.

 

[Besoeker]

@Besoeker
yea it's a paper mill
i think i say we changed the motor with the one i last say it's ratings ( the 1st one was greater in kw ) both motor have problem of winding ?
about The damp atmosphere can cause corrosion of terminals the drive in a room with a central air condition and the atmosphere kept to 27 c

It could be at the drive panel rather than the motor.
Has the shunt field voltage been tested at the motor?

 

[mohamed]

thanks guys ,
while i was posting last reply , seller support in the area just made and indication ( not in control system ) relay energized when the drive current reach 700 A ( the drive as he say 750 A ) and after he leave , the drive stop and didn't give any fault message and the relay was energized :6: . when we say that to him , he say that the problem is mechanical ( a load happen in the pump ) and say an information which i can't check if it's true or false , any drive dc or ac when the current approach to it's max rate it try to vary the speed ( down the speed ) to limit the current
1-if this variation didn't reduce the current the an error appear with drive over current
2-if the variation limits the current it will rise up to operation speed
can someone say it's true or false

 

[Darkwood]

thanks guys ,
while i was posting last reply , seller support in the area just made and indication ( not in control system ) relay energized when the drive current reach 700 A ( the drive as he say 750 A ) and after he leave , the drive stop and didn't give any fault message and the relay was energized :6: . when we say that to him , he say that the problem is mechanical ( a load happen in the pump ) and say an information which i can't check if it's true or false , any drive dc or ac when the current approach to it's max rate it try to vary the speed ( down the speed ) to limit the current
1-if this variation didn't reduce the current the an error appear with drive over current
2-if the variation limits the current it will rise up to operation speed
can someone say it's true or false

It would all depend on drive, the motor and and job its doing, having this parameter active would only suit certain applications and if it is part of the drives program then it suggests you originally had no control issues and the drive was reacting to a load increase and as the tech' help suggest it is a mechanical issue which could be anything from bearings seizing up to load increasing beyond motor capability, as you also mentioned the original motor may have been larger in KW which may have been sized for the task in hand.

This is why I said you need to do tests and take readings, as you say you have a new drive then I assume the info' you received will have been in the installation and set up manual unless like some drives they are just shipped out with basic set-up and diagnostic info, now the task here is to understand the motors job itself and see if anything has changed that could increase the load demand if not a direct mechanical issue like bearings or foreign material clogging up the lines.

I work on wire drawing lines and one option on the drive is to put the system in torque mode that tries to compensate any variation in torque by adjusting the speed until it hits its set point, although this is a different scenario and drive set-up it has similarities to what your drive seems to be doing in that it see's max current set as a limit and tries to reduce speed if this line is crossed until the motor recovers then it reverts back to normal speed.

 

[PEG]

It would all depend on drive, the motor and and job its doing, having this parameter active would only suit certain applications and if it is part of the drives program then it suggests you originally had no control issues and the drive was reacting to a load increase and as the tech' help suggest it is a mechanical issue which could be anything from bearings seizing up to load increasing beyond motor capability, as you also mentioned the original motor may have been larger in KW which may have been sized for the task in hand.

This is why I said you need to do tests and take readings, as you say you have a new drive then I assume the info' you received will have been in the installation and set up manual unless like some drives they are just shipped out with basic set-up and diagnostic info, now the task here is to understand the motors job itself and see if anything has changed that could increase the load demand if not a direct mechanical issue like bearings or foreign material clogging up the lines.

I work on wire drawing lines and one option on the drive is to put the system in torque mode that tries to compensate any variation in torque by adjusting the speed until it hits its set point, although this is a different scenario and drive set-up it has similarities to what your drive seems to be doing in that it see's max current set as a limit and tries to reduce speed if this line is crossed until the motor recovers then it reverts back to normal speed.

This part sprung to mind as i read this...all testing results + a careful hand on bearings and stuffing boxes,which can lock-off any motor,and free-off after the process stall issues are attended to.

It is surprising how many times,and for just how long,such an issue with a bearing,can repeat itself,before a catastrophic failure,identifies the culprit.