identifying the voltage rating of electric motor with out a name plate 1

[ni1o]

How will you identify the voltage rating of an existing motor if it doesn't have nameplate?

 

[7anoter4]

You have to know:
what kind of motor[dc,induction,synchronous] and at least no. of poles,frequency,stator length and bore diameter.
For induction motor the electromagnetic force E=.95*Voltage [approx.]
Within 20% precision:
E=4.44*frq*w*kform*Fi [frq=frequency 50 or 60 Hz]
Fi=2/pi()*tau*li*B
B=7000-9000 gauss [0.7-0.9 Wb/m^2] Magnetic flux density in air gap
kform=0.8-0.9 depends on ratio Y/tau
Y=coil[loop] width
w=no.of turns in series per stator phase.
tau=Dstator*pi()/no.of poles

 

[jraef]

Simple eh?

I've often wondered why people remove nameplates from electric motors? When they do it are they thinking this is no big deal?

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[waross]

A partial answer to your question Jeff.
A long time ago a foreign student asked me for a quick way to determine the HP of a motor with no nameplate. During the discussion he shared that in his home country the utility charged a flat rate for motors based on the HP. (This was a long time ago and I'm older than I look.) People removed the nameplates so that they could lie about the HP.
We have both seen motors where the nameplate has been half removed by abuse, either during removal or installation or possibly by using the motor as a fulcrum for nearby work. I have assumed that sometimes the plate comes completely off.

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

 

[petronila]

Hello ni10

I will supouse is a low voltage motor (< = 600 V)
1.Take a look of the connection block and you can have an idea, (6 wires connected in star= High Voltage, connected in Delta= low Voltage)Ej: 380/690, 380(D), 690(Y) or maybe 230/400, 220(D)-400 (Y), if the motor is with out block terminal then take a look of the end wire quantity (12, 9 or 6)and how are wired.

2. Then estimate the power output (by taking all sizes of shaft gross, Frame bolt distances and shaft center height, then you can estimate the frame.
3. Uncouple the motor (If it is), perform a Megger, if is OK , connect the motor in low voltage connection (D) and run then read the no load current and speed.
4. The full load current will be 3* that current(aproach)

With frame, no load and rated current and speed go to catalog and find the match motor.

Regards

Carlos

 

[LionelHutz]

I suppose you could try every common utility voltage starting at the lowest. When you find the first voltage where the no-load current is abnormally high then you have likely gone up by one too many voltage steps. So, go back to the previous voltage and hope that is correct.

 

[ozmosis]

If it is a small motor, I wouldn't bother looking too deeply. You will spend a lot of time on something that will possibly still leave you with a lot of questions and potential problems if you connect.
I'd just buy a new one if small and scrap this one with no nameplate.
"small" to me would be <15Hp(11kW).

 

[mls1]

7anoter4 - An excellent post but I have to ask, what is the basis of 0.7-0.9 tesla? Is this so that the rotor density does not exceed ~1.7 tesla and start saturating? Is there a standard air gap to peak density ratio used in motors? Thanks!

 

[7anoter4]

Thank you, mls1.
No standard in Electrical Machine Design. I saw motor with 0.55 T in air gap and 2.2 T in the rotor teeth. Depends on lamination material quality,
cooling system and other. But usually on a modern induction [asynchronous] machine air gap magnetic flux density is 0.7-0.9 T.