Name plate data on induction motors

[sinnadurai sripadmanaban]

In induction motors details like kW,rpm,FLA,V,Hz,SF,design code,insulation class,amb temp etc are normally given. Why they do not include the no load current,locked rotor current too so that engineers need not refer tables for same?.

 

[Smart $]

Good question... but I don't know the answer. Perhaps so it doesn't get confused with FLA by non-qualified personnel.

 

[iceworm]

In induction motors details like kW,rpm,FLA,V,Hz,SF,design code,insulation class,amb temp etc are normally given. Why they do not include the no load current,locked rotor current too so that engineers need not refer tables for same?.

The NEC is a set of minimum specs that the "wise men of Gotham" believe are required for an installation meeting NEC90.1,
"... installation that is essentially free from hazard but not necessarily efficient, convenient, or adequate ..." And Nema MG-1 has similar requirements. None of these agencies has your convenience as a priority.

ice

 

[sinnadurai sripadmanaban]

nameplate details of induction motors complying NEMA design code

nameplate details of induction motors complying NEMA design code

In induction motors details like kW,rpm,FLA,V,Hz,SF,design code,insulation class,amb temp etc are normally given. Why they do not include the no load current,locked rotor current too so that engineers need not refer tables for same?.

What I want to know is a comparison of those parameters(values) for different design codes of motors of a given kw/rpm(how they vary with design code or are they same for all design codes)After rewinding a motor to test it on no load you need the no load current of the new motor before it burnt. Why should one search for manufacturers literature?. Similarly for across the line starting LRA should be given in name plate to verify whether it has changed after rewinding and within limits. The values will guide for study purposes for a proper understanding of NEMA design codes and their value.

 

[Smart $]

What I want to know is a comparison of those parameters(values) for different design codes of motors of a given kw/rpm(how they vary with design code or are they same for all design codes)After rewinding a motor to test it on no load you need the no load current of the new motor before it burnt. Why should one search for manufacturers literature?. Similarly for across the line starting LRA should be given in name plate to verify whether it has changed after rewinding and within limits. The values will guide for study purposes for a proper understanding of NEMA design codes and their value.

Suggest you obtain a copy of NEMA Standards Publication MG-1 ($305).

You can download a condensed version for free. I do not know if it contains the information you require.

 

[weressl]

What I want to know is a comparison of those parameters(values) for different design codes of motors of a given kw/rpm(how they vary with design code or are they same for all design codes)After rewinding a motor to test it on no load you need the no load current of the new motor before it burnt. Why should one search for manufacturers literature?. Similarly for across the line starting LRA should be given in name plate to verify whether it has changed after rewinding and within limits. The values will guide for study purposes for a proper understanding of NEMA design codes and their value.

There is extensive data available for each equipment. The motor nameplate data is there as the basic neccesity for the operation and simple troubleshooting, not for the design or detailed analysis of the drive system. Experience and necessity are the determining factors how these things are established as industry practice. If you feel strongly about it, I suggest you start lobbying the various industry and user groups and perhaps in a mere 50 years you MAY accomplish SOME results.

 

[Besoeker]

In induction motors details like kW,rpm,FLA,V,Hz,SF,design code,insulation class,amb temp etc are normally given. Why they do not include the no load current,locked rotor current too so that engineers need not refer tables for same?.

Perhaps they are not altogether useful in normal operation?
Beyond short term starting conditions, how often do you encounter a locked rotor?
What use would you make of no load current?

 

[weressl]

What use would you make of no load current?

Underload protection such as broken belt, or coupling and deadheading centrifugal pumps.

 

[GeorgeB]

What I want to know is a comparison of those parameters(values) for different design codes of motors of a given kw/rpm(how they vary with design code or are they same for all design codes)After rewinding a motor to test it on no load you need the no load current of the new motor before it burnt. Why should one search for manufacturers literature?. Similarly for across the line starting LRA should be given in name plate to verify whether it has changed after rewinding and within limits. The values will guide for study purposes for a proper understanding of NEMA design codes and their value.

Go to www.baldor.com, then literature. Search for PR2525 and download the "Cowern Papers". There is more useful and practical information there about induction motors than I've seen anywhere.

 

[jdsmith]

Underload protection such as broken belt, or coupling and deadheading centrifugal pumps.

A power factor relay would be the preferred solution for detecting deadheaded centrifugal pumps or broken belts. Undercurrent relays work, but if a motor is swapped for a spare or rewound an undercurrent relay should be adjusted or it may misoperate.

 

[jdsmith]

In induction motors details like kW,rpm,FLA,V,Hz,SF,design code,insulation class,amb temp etc are normally given. Why they do not include the no load current,locked rotor current too so that engineers need not refer tables for same?.

As others have indicated, the data required on a motor nameplate is given by NEMA MG-1. Manufacturers of NEMA frame motors typically supply the minimum data required because it keeps the nameplate itself smaller which saves cost. The condensed version is free and is around 75 pages long - it will give you the general flavor of the standard. The full $305 version is 670 pages long and is much more useful if you are interested in above NEMA motors.

The locked rotor current is given on the nameplate with the kVA code. I don't like kVA codes, I would prefer locked rotor current given as a percentage of full load amps. When I buy medium voltage motors I make the manufacturer list the locked rotor current as % of FLA.

Typical values of no load current are available for different size ranges, speeds, and efficiencies of motors. I would guess that the Cowern papers that GeorgeB referenced might include typical no load currents. Your favorite motor supplier should also be able to provide this information.

 

[weressl]

A power factor relay would be the preferred solution for detecting deadheaded centrifugal pumps or broken belts. Undercurrent relays work, but if a motor is swapped for a spare or rewound an undercurrent relay should be adjusted or it may misoperate.

A power factor relay would be subject to the same course. But please do read what I actually responded to and it was: what use the No Load Amperes on the nameplate would have?

 

[ActionDave]

Go to www.baldor.com, then literature. Search for PR2525 and download the "Cowern Papers". There is more useful and practical information there about induction motors than I've seen anywhere.

R2525, Cowern Papers- neither of these worked in the search bar. Can you link to the page you are referencing?

 

[Smart $]

R2525, Cowern Papers- neither of these worked in the search bar. Can you link to the page you are referencing?

Direct link: http://www.baldor.com/support/literature_load.asp?LitNumber=PR2525