Simoreg DC Master drive problem

[cjd1965]

Wow, just read this whole thread and talk about things going sideways!


A good DC drive guy on site would have had this straightned out long ago. I'd string up whoever decided putting in a new simoreg was a good idea. DC motor drive control isn't something you want to mess around with if you don't know what you are doing.

This is why i said earlier i would have got a eurotherm/SSD/Parker tech in to check the drive and let them 'handle it'. I know it is $$$ but at least they are competent to diagnose issues like this on site . More so if they dont have inhouse people on the printing site

Cheers

 

[allscott]

I don't see anything out of the ordinary here. The shunt field can be hooked up in either series or parallel. The "french" electrician was almost certainly right and the motor field was hooked up in parallel for who knows what reason.

The field on the Eurotherm was probably set up as a current regulator. When set up as a current regulator is doesn't particularily matter if you have the field in series or parallel because the voltage will be adjusted to provide the setpoint current. The Siemens drive should have been set up the same way, however if it wasn't and the field was simply set up as a voltage source and the nameplate data was used and assumed a nameplate current of 5.4A with a 360V source, then I can see where this could all go downhill very quickly.

The nice thing about the eurotherm is that as long as the OP didn't throw it out he can check the current setting of the old drive without powering it up as the field current setting is a series of rotary switch on the front of the drive.

 

[DickDV]

The speculation about the field wiring doesn't make sense to me for the following reasons: first, the nameplate does not indicate a dual voltage field so I would expect to find only F1 and F2 leads in the junction box.

Second, it is possible that the field is wound in two coils and is connected internally. But, if the total resistance is 60 ohms, each of the two coils would have to be 30 ohms. Put them in parallel and you have 15 ohms, not 30! They could be in parallel with one burned open. That would give 30 ohms but the field would be way weak and the motor would run too fast with too little torque.

So, none of this field stuff makes any sense to me.

All of you are correct in saying that the solution here is to get a good DC drive/motor tech on site and get it fixed properly. I said that at the beginning and it still is the right course. There isn't any reason to wait for the motor data either. The nameplate says enough for a good tech to work with.

And, there are excellent DC techs close by the OP's location. I've given him some names.

For me, this thread has no chance of solving the OP's problem. I've tried to use it to be a little informative on DC systems for those that are interested but, fix it!??? Nah! The OP is going to have to pay someone for that.

Finally, leitmotif, CEMF is the internal motor generator producing voltage that bucks the armature supply voltage. It is a direct function of shaft speed and field intensity. It has no effect on the field current and, at zero speed, would be zero volts anyway.

 

[leitmotif]

Finally, leitmotif, CEMF is the internal motor generator producing voltage that bucks the armature supply voltage. It is a direct function of shaft speed and field intensity. It has no effect on the field current and, at zero speed, would be zero volts anyway.[/quote]

Thank you Dick for confirming my wrong thinking. Been too long since DC theory class

Dan Bentler

 

[garmar]

The Frenchman is right. You will get half the ohm readings at full temperature. That is because it is tied internally. The reading you get now is called half set. When the motor is cold the shunt will draw more amps until it gets to operating temp.
The shunt is always at full voltage and speed is adjusted by armature voltage. Your shunt is what gives the motor torque.
I have been reading this tread and it all sounds like improper drive parameters. I hope this helps.

 

[DickDV]

garmar, I've never seen a motor winding go down in resistance as the temperature goes up.

Just what kind of copper is that wire made of?

 

[cjd1965]

hi i found a link to a few pages about DC motors that may interest someone

http://zone.ni.com/devzone/cda/ph/p/id/46

it is a preview section from a book

 

[allscott]

The Frenchman is right. You will get half the ohm readings at full temperature. That is because it is tied internally. The reading you get now is called half set. When the motor is cold the shunt will draw more amps until it gets to operating temp.
The shunt is always at full voltage and speed is adjusted by armature voltage. Your shunt is what gives the motor torque.
I have been reading this tread and it all sounds like improper drive parameters. I hope this helps.

?????????????????????????

I don't know where to start, most of what you said is either dead wrong or not necessarily true.

 

[garmar]

The temperature that copper doesn't have any resistance to flow is around -410 F. The general rule is "the higher in temperature the wire is, the higher the resistance to electrical flow. Most metals increase their electrical
resistivity by about 0.005 per degrees. So, if the resistivity of copper at 25 C is, say, 1, then at 500 C it will be 1+500x.005=3.5! This means if you heat your wire to 500 C, then its resistance increases 3.5 time! The current through it then drops by 3.5 times.

 

[garmar]

All copper electrical wire is 99% pure copper.

 

[allscott]

Thanks for the metalurgical lesson LOL. In a nutshell the resistivity of copper goes up as the temperature increases correct, is that what you are trying to tell us? I think thats what DickDV was refering too.

The field flux in the shunt winding of a DC motor is directly proportional to the current flowing through it. The current and therefore flux/torque of the motor would decrease as the temperature rises in the motor if the field voltage were to be kept constant.

Modern drives almost exclusively use current control on the shunt field. The reason for this is that despite the temperature of the motor and the resistance of the field windings the current (which is what matters) and therefore field flux can be held constant as the motor heats up.

You are partially correct in stating that the field remains constant and armature voltage is varied to control speed. The field is constant because the current is regulated up until base speed, If more speed is required the field is weakened (less current) in order to obtain more speed when the armature is at full voltage. There is an obvious drop off in torque if the field is weekend.

While an interesting discussion, I don't think were helping the printing of books in michigan by discussing the conductivity of copper.