Previous in Forum: DC Motor 3rd Wire Use?   Next in Forum: LED Wings Project
Close
Close
Close
17 comments
Power-User

Join Date: Mar 2010
Location: Islamic Republic of Pakistan
Posts: 115
Good Answers: 14

Motor Nameplate Missing: How to Determine Motor kW and rpm by Physical Inspection Only

01/05/2021 10:53 AM

Respectable Electrical Engineers,

Is there any rules of thumb by which we can determine LV three phase squirrel cage induction motor kW and RPM by doing motor physical inspection only ( Without energizing it )?

For Standardization of inventory description of LV induction motors, four most critical information i-e KW, RPM, type of Mounting and FRAME SIZE are required against each motor. All this data is available on the nameplate of the motor.

Example : Motor 11 KW, 2915 RPM, IM B3, 160M, TYPE: 1LA5163-2CA60-7, SR # EH567 1524 01 002, SUPPLY : 380 ~ 420 V, 50 HZ, D, 50 HZ, PF 0.85, IP55, INSL: F, MAKE: SIEMENS

We are facing issue since there are number of motors having nameplate missing ranging from 0.18 kW up 355 kW.

Physical inspection clarify about type of mounting whether it IM B3, B5, B14, B35 etc.

Foot , shaft and Flange measurement clarify about frame size of the motor. i-e 80 M, 90S, 90 L, 100 L , 112 M, 132 S etc

Frame size also give somewhat idea about the kW range of the motor.

As far as RPM are concerned, by doing physical inspection, it is very difficult to determine whether it is 2 pole, 4 pole or 6 pole machine.

So

Is there any rules of thumb / method by which we can determine LV three phase squirrel cage induction motor kW and RPM by doing motor physical inspection only ( Without energizing it )?

Looking forward for valuable comments . . . . .

Login to Reply
User-tagged by 5 users
Interested in this discussion?
You can "subscribe" to this discussion to be notified of new comments.
Click on the Subscribe menu at the top of the page.
Anonymous Poster #1
#1

Re: Motor Nameplate Missing: How to Determine Motor kW and rpm by Physical Inspection Only

01/05/2021 11:27 AM
Login to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 29931
Good Answers: 808
#2

Re: Motor Nameplate Missing: How to Determine Motor kW and rpm by Physical Inspection Only

01/05/2021 11:31 AM

One way is to use maintenance records. The plant item should have a maintenance record stating what was done to it, when, by whom, what was bought to do it, when, what parts were used, etc., etc.

It would be a disservice to the facility were that information not contained therein. Talk to others in the <...we...> to locate and inspect them.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Login to Reply
Power-User

Join Date: Mar 2010
Location: Islamic Republic of Pakistan
Posts: 115
Good Answers: 14
#6
In reply to #2

Re: Motor Nameplate Missing: How to Determine Motor kW and rpm by Physical Inspection Only

01/05/2021 10:34 PM

My question was not about keeping maintenance record and suggestion for improvement.

Login to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 29931
Good Answers: 808
#10
In reply to #6

Re: Motor Nameplate Missing: How to Determine Motor kW and rpm by Physical Inspection Only

01/06/2021 7:27 AM

Response #2⇑ was not intended to attract critique.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Login to Reply
Associate

Join Date: Dec 2020
Location: Dayton Ohio
Posts: 36
Good Answers: 2
#3

Re: Motor Nameplate Missing: How to Determine Motor kW and rpm by Physical Inspection Only

01/05/2021 12:39 PM

You didn't state if the motor was mounted or loose. Assuming it is mounted but not running, I would look up the machine it is mounted on. If not able to do that, look at the overload settings and voltage. If not mounted, look at the motor wiring in the pecker head. The number of wires and wire size can tell you a few things. If the motor is loose and a small size, it's not worth the effort. Replace with new. If you really want to know, take it to a motor repair facility. They can look at the construction and determine who made it and from there can narrow the choices by size. Another possibility is to send pictures and measurements to a motor salesman. They might know some information just from that.

Now consider the squirrel cage itself. That is the most important thing when it comes to RPM and the required HP. It should have some identification on it.

Now ask yourself if it is worth your time/effort in the first place. If this motor is running a squirrel cage blower and is three phase, consider putting a VFD on it for better performance.

__________________
Don't follow in the footsteps of someone who you wish to emulate. Instead, seek what they sought.
Login to Reply
Power-User

Join Date: Mar 2010
Location: Islamic Republic of Pakistan
Posts: 115
Good Answers: 14
#7
In reply to #3

Re: Motor Nameplate Missing: How to Determine Motor kW and rpm by Physical Inspection Only

01/05/2021 10:36 PM

Don't understand the logic why to put VFD . . . Please re-read. Motors are placed in store.

Login to Reply
Associate

Join Date: Dec 2020
Location: Dayton Ohio
Posts: 36
Good Answers: 2
#9
In reply to #7

Re: Motor Nameplate Missing: How to Determine Motor kW and rpm by Physical Inspection Only

01/06/2021 5:42 AM

When a motor starts up it tries to immediately go to full speed. This creates a large inrush of current and also over time can put additional stresses on squirrel cages. Of course this depends on the size also. Larger ones can have more issues. A VFD allows the motor to start slower and ramp up to speed. This reduces the inrush current and can increase the life of both motor and squirrel cage. A soft starter can also do this but VFDs aren't that much more cost and give better control.

__________________
Don't follow in the footsteps of someone who you wish to emulate. Instead, seek what they sought.
Login to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 29931
Good Answers: 808
#11
In reply to #7

Re: Motor Nameplate Missing: How to Determine Motor kW and rpm by Physical Inspection Only

01/06/2021 7:33 AM

If the <...Motors...placed in store...> are from only one supplier, as does happen with some facilities, than if may be possible to use the manufacturer's catalogue information to determine their rating, stock holding records, or even purchase order records.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Login to Reply
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 29823
Good Answers: 1665
#4

Re: Motor Nameplate Missing: How to Determine Motor kW and rpm by Physical Inspection Only

01/05/2021 1:43 PM

https://www.generatorjoe.net/html/motorformula.html

https://www.engineeringtoolbox.com/electrical-motor-calculator-d_832.html

http://www.drivesandautomation.co.uk/useful-information/frame-sizes-power-current/

__________________
Break a sweat everyday doing something you enjoy
Login to Reply
Guru
Engineering Fields - Electrical Engineering - Been there, done that. Engineering Fields - Control Engineering - New Member

Join Date: Dec 2008
Location: Long Island NY
Posts: 14850
Good Answers: 913
#5

Re: Motor Nameplate Missing: How to Determine Motor kW and rpm by Physical Inspection Only

01/05/2021 4:50 PM

Somehow you will have to find out the number of poles exist in the stator and rotor assembly in order to determine the synchronous RPM rating. You might be able to determine this by looking into a ventilation opening and applying some knowledge of geometry to identify the pole ratio. If the case is sealed then no, you cannot identify the shaft rotation from just an external inspection.

__________________
"Don't disturb my circles." translation of Archimedes last words
Login to Reply
Power-User

Join Date: Mar 2010
Location: Islamic Republic of Pakistan
Posts: 115
Good Answers: 14
#8
In reply to #5

Re: Motor Nameplate Missing: How to Determine Motor kW and rpm by Physical Inspection Only

01/05/2021 10:38 PM

Agreed. Thinking on same line too

Login to Reply
Guru

Join Date: Oct 2006
Location: 44.56024"N 15.307971E
Posts: 6004
Good Answers: 240
#12

Re: Motor Nameplate Missing: How to Determine Motor kW and rpm by Physical Inspection Only

01/06/2021 1:05 PM

I was always told that the most important part of a motor was the data plate.

Protect it at all costs.Without it,it is very hard to determine a replacement.

Here is a low tech method that will put you in the ballpark for the info you need.

What is the voltage/frequency supplied to your facility?

Look for other similar frame sizes,and check their name plate data.

Apply the lowest of the voltages determined this way,and test the motor for response.

Check the motor amps.

Do they seem reasonable for the motor size?.

Compare this to the data plate amps on similar motors.

Change voltage if appropriate.

When you have a close match,check and compare to the data previously determined.

Check the RPM of the motor.

A low rpm will indicate low voltage,if it is far out or range by comparison.

Frame sizes vary for different HP motors.

Here is a chart to help you reference the possible HP for different frame sizes:

https://www.kellerelectrical.com/pdf/NEMA%20Frame%20Chart_KEI.pdf

If all else fails,take the motors to a motor repair facility and they can determine the voltage,frequency,rpm and other info about the motor by checking the stator wire size,number of poles,shaft size,etc.

__________________
"A man never stands so tall as when he stoops to help a child." "Ignorance does not consist of what a person does not know,but of things he knows that just aint so"
Login to Reply
Power-User

Join Date: Mar 2010
Location: Islamic Republic of Pakistan
Posts: 115
Good Answers: 14
#13
In reply to #12

Re: Motor Nameplate Missing: How to Determine Motor kW and rpm by Physical Inspection Only

01/07/2021 12:10 AM

It is stated earlier that out of 04 Nos critical parameters, 02 nos are determined via physical inspection i-e Mounting & Frame size.

Get approximate idea about kW from frame size of the motor.

As far as RPM are concerned, provide supply and run motor or open end shields and see poles configuration.

Supplied voltage and frequency is 3 phase 400 V 50 Hz for LV system.

Question is about how to determine motor kW & RPM by doing physical inspection only ( not to energize and not to open end shields ) whereas ur response solely related to energizing of motor and then note down RPM.

Login to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 29931
Good Answers: 808
#14
In reply to #13

Re: Motor Nameplate Missing: How to Determine Motor kW and rpm by Physical Inspection Only

01/07/2021 2:28 AM

Well, there are enough ideas above to provide directions of travel in solving the immediate problem, if not prevention of recurrence.

Do let the forum know how it all goes.

<unsubscribes>

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Login to Reply
Guru

Join Date: Oct 2006
Location: 44.56024"N 15.307971E
Posts: 6004
Good Answers: 240
#15
In reply to #13

Re: Motor Nameplate Missing: How to Determine Motor kW and rpm by Physical Inspection Only

01/07/2021 6:12 AM

Based on the constraints of your question,I recommend the link below:

Very cheap and reliable for just such questions.

https://weluvsale.com/products/3d-laser-solar-system?utm_medium=cpc&utm_source=bing&utm_campaign=Bing%20Shopping&msclkid=437ca6c92ccb109fe14ef93fc7d957de

(When in doubt,the answer is always 42.)

https://www.independent.co.uk/life-style/history/42-answer-life-universe-and-everything-2205734.html

Good luck determining detailed info within your constraints.

__________________
"A man never stands so tall as when he stoops to help a child." "Ignorance does not consist of what a person does not know,but of things he knows that just aint so"
Login to Reply
Guru

Join Date: Oct 2006
Location: 44.56024"N 15.307971E
Posts: 6004
Good Answers: 240
#16
In reply to #13

Re: Motor Nameplate Missing: How to Determine Motor kW and rpm by Physical Inspection Only

01/08/2021 10:12 AM

OK.I see.You want to determine the EXACT RPM,KW, and Voltage from a group of motors that have no data plate.
Since you asked for a "rules-of-thumbs" method,and you have been given them,yet you object because they are not precise enough,here is a method that has been used for many Kyears:
Suspend a N50 magnet,50mm diameter on a .004" tungsten wire exacly 200 MM +-.0000000001MM in length .This has to be the pendulem length,not the wire itself.
The distance above the motor external case has to be EXACTLY 4MM when the pendulum is at rest.
Pull the pendulum back exactly 150MM+-.000001MM,measured along the radius of the arc of the pendulum, and release using an electronic release mechanism to avoid the variable stickiness of human fingers.
The release must be precisely centered on the center line of the motor shaft when released.
Count the number of times the pendulum swings before coming to a total stop,and the total length of each arc,along the radius of the arc.Add the lengths together and record this value.
Repeat this by releasing the pendulum from the opposite direction.
Record these numbers.
They will be used in a later calculation.
Then release the same pendulum in a precise 90 degree angle to the motor shaft from the exact same distance.
Perform the release in the same manner as above,from both directions.
Record these numbers also.
Now you must weigh these motors in water to determine the exact weight of the copper vs iron in the motor.
Consult a table for the specific gravity of copper and iron.
Measure the volume of water displaced by the motor.
Use this to determine the ratio.
Now you know how much copper is in the motor.
Take the previous data from the pendulums and email them to this expert in such matters,and he will provide the answer based on your original request constraints.

Link below:

https://www.istockphoto.com/photos/merlin-the-wizard?phrase=merlin%20the%20wizard&sort=mostpopular

As always,I wish you the best of luck in your pursuit of knowledge,within the constraints of the original post.

__________________
"A man never stands so tall as when he stoops to help a child." "Ignorance does not consist of what a person does not know,but of things he knows that just aint so"
Login to Reply
Guru

Join Date: Dec 2010
Posts: 1618
Good Answers: 111
#17
In reply to #13

Re: Motor Nameplate Missing: How to Determine Motor kW and rpm by Physical Inspection Only

01/09/2021 1:19 PM

It is my opinion that you are expecting the impossible to sort all these motors solely by visual inspection, without dismantling.

You appear to be sure that the motors are 400V 50 Hz. With frame & shaft sizes, that narrows the possibilities to several powers.

If you could add a resistance test, not an invasive act, just remove terminal cover [suitable ohm-meter for low resistance essential] this would narrow the powers. You could at least sort those motors which look/measure identical - resistance value could then narrow rating.

Inside terminal cover, the terminals may have links for star/delta of six winding ends or just 3 studs - are they linked star or delta [for 400V] - additional information.

Do motors already in your plant look/measure similar, have data sheet or nameplate, driven load with rating/speed?

I suggest you energise the smaller motors with a motor starter panel, to get speed - colour banded discs, as used to check vinyl record player disc speed use the strobe effect of a simple neon lamp - a good white paint dot on shaft end key will appear at two places for 3000 rev/min [50Hz , neon flash is twice per cycle = 100 Hz; night & room lights off!!], four for 1500 rev/min etc. N.B. very small round 230V 50Hz LED light bulbs I have tested had 100% 100Hz flicker. The easy way is use a calibrated strobe gun.

Finally, you can use a small motor of lowest rev/min to spin the bigger ones, some kind of belt coupling is probably easiest. The residual magnetism of the rotor is probably enough to give volts from driven motor to operate frequency measure mode of a professional grade digital multimeter. If not dab a car battery onto one phase winding - best done with a car starter solenoid for safety. You can check the procedure with two small motors belted together.

67model

Login to Reply
Login to Reply 17 comments
Interested in this discussion?
You can "subscribe" to this discussion to be notified of new comments.
Click on the Subscribe menu at the top of the page.
Copy to Clipboard

Users who posted comments:

67model (1); Aghvel Niazi (4); Anonymous Poster (1); EBrown (2); HiTekRedNek (3); PWSlack (4); redfred (1); SolarEagle (1)

Previous in Forum: DC Motor 3rd Wire Use?   Next in Forum: LED Wings Project

Advertisement