Motor high amps

[Abualnassr]

Hi.

In our plant DCS there's always current (amps) icon associated with each motor. What does this current value gives me ?
And, how can i know the max and min amps for any motor ?

Regards,

 

[dpc]

Not sure what you are asking. The motor nameplate will provide the maximum amps allowed. Minimum is not generally a concern for the motor. Very low current could indicate a problem with the driven equipment - this is specific to the application.

"Theory is when you know all and nothing works. Practice is when all works and nobody knows why. In this case we have put together theory and practice: nothing works... and nobody knows why! (Albert Einstein)

 

[davidbeach]

In addition to what dpc said, if you are questioning what information your DCS provides, you need to find someone there to answer your question. Nobody here knows your DCS system.

 

[waross]

In our plant DCS there's always current (amps) icon associated with each motor. What does this current value gives me ?

It will show you whatever it has been programmed to show. Both the primaries and secondaries of the CTs monitoring the actual motor current may be over-wound or under wound.
I remember a scheme where the CTs were over or under wound as required so that 150% of motor current corresponded to 5 Amps in the secondary circuit of the CT. The software was then set up so that a 100% on the monitor indicated 150% of rated current. But, what your DCS indicates may depend on the philosophy of the engineer who designed it.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Abualnassr]

Ok guys, I think I phrased my question in a bad way. What I need to know is what does high or low amps indicates.

I mean, if the maximum allowed current is 60 amps, and it showed in the DCS that it is 40 amps, does this indicate a problem in the driven equipment ?
If, yes what is the possible causes for this.

And, vice versa, if the current in the DCS is like 70 amps, what does this indicate ?

 

[dpc]

If the motor current exceeds the nameplate rating, that is a concern. Lower currents are not generally a problem.

But as David Beach said, we have no idea how the DCS was configured and what current values were programmed into it. The DCS knows nothing about the motors except what someone told it.

"Theory is when you know all and nothing works. Practice is when all works and nobody knows why. In this case we have put together theory and practice: nothing works... and nobody knows why! (Albert Einstein)

 

[itsmoked]

You 'can know what the MAX amps are' by going to the motor and looking on the required metal plate that will have the Full Load Amps("FLA") or "kW" listed on it.
If you exceed that number of amps you are reducing the motor's life by some rate depending on how much you exceed it by.

That said, your DCS system better be accurately showing the current. At some point in time someone should have used a clamp-on ammeter to confirm that the DCS is correctly reporting the current. The DCS should be showing 100% when the MAX current is reached.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Abualnassr]

So having a current below DCS programmed minimum doesn't mean a problem ?

 

[itsmoked]

If you are seeing unexpected numbers on a DCS, YOU MUST INVESTIGATE.

It is trivial to have crappy, wrong, non-valid numbers showing on a DCS. If you use a separate tool to determine the motor's current then go to the DCS and find they agree then you can start investigating why your motor really is drawing less current than expected.

In some cases a low reading indicates a serious problem in others it means no load. We can't tell you based on the scant information you've coughed up.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[electricpete]

I haven't followed the whole logic, but it is possible that current is monitored because it tells something about the load on the driven equipment. The limits programmed into the DCS may have been developed by knowledge of the process and have nothing to do with the motor. Without knowing the process there is nothing anyone here can tell you about that. On the other hand we can make some judgments about the motor from the current in relation to nameplate ... that may or may not be the intent of your "limits".

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[sparky970]

We used the indication in our plant so the operators could tell if there was flow present.

 

[DickDV]

First, the motor nameplate Full Load Amps is not the maximum amps but rather the highest continuous allowable amps at a 40degreeC ambient temperature. Short term amps may be as high as eight to ten times that especially when starting.

Second, as to minimum amps, the motor completely unloaded will still draw somewhere between 20 and 50% of nameplate FLA. So, I would doubt that displayed minimum amps have anything to do with the motor. Instead, the minimum amps is probably being used to indicate loading conditions in the connected load. To know what the significance of that indication is, you would have to know how the load uses torque and what operational limits to torque exist. It would not be possible to say much more about it from here since we know essentially nothing about the load (except that it is some kind of pump).