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Join Date: Aug 2008
Location: TN, India.
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Motor name plate misleading

09/09/2008 6:59 PM

I had come across a motor which is used for ATT ( Automatic turbine test ) in NTPC power plants, supplied from germany has the name plate of,

230/400 V, 0.18 KW, 50 HZ, 1.15/0.67 A - Star/ Delta, 0.73 pf.

These values are not tallying with power calculations.

B's 1.732x400x0.67x0.73=1.732x230x1.15x0.73=334 KW.

Actually this motor was taking no load amp of 1.01 A ( wye conn ), and according to name plate, the over load relay was set at 0.75 A. So even at no load operation it trips on overload. There is any solution to this dilemma?

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Guru
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#1

Re: Motor name plate misleading

09/09/2008 8:16 PM

First off, you do not apply the 1.732 when calculating kW if it is a 1 phase motor, and you have to factor in efficiency. So the kW is:

400 x 0.67 x .73 = .19564kW, then assuming 92% efficiency, the output power is .1799kW

OR

230 x 1.15 x .73 =.193 kW, x .92 = .178 kW

In both cases, that is close enough. Are you sure it is a 3 phase motor? If it is, then the nameplate is wrong in one way or another

By the way, that would be 334W or .334kW, not 334kW.

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Guru
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#2

Re: Motor name plate misleading

09/09/2008 11:16 PM

I doubt that a motor this size is a 3 phase motor so the 1.73 factor is not needed.

230 x 1.15 x .73 = 193 watts or 0.193 kw 400 x .67 x .73 = 195 watts or 0.195 kw.

Close enough.

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Participant

Join Date: Sep 2008
Posts: 2
#3

Re: Motor name plate misleading

09/10/2008 4:53 AM

what is really your problem is it the computation? or the actual setting of your overload relay? I can only give you guide answere...

1. Wye and Delta is for Three phase source. not for single phase....

2. your problem with the name plate and computation is a separate thing. when dealing with the actual current reading of the motor versus the name plate rating you have to consider the operation of the motor thus it run well did you check if you have a problem in your motor? Name plate are really ment there as a guide, it is for the purpose not to mislead the endusers.

3. Overload reley selection and setting is another case if the motor works well you have to just reset it. to solve problem.

If you have more question post it well go direct to your point friend.

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Guru

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#4
In reply to #3

Re: Motor name plate misleading

09/11/2008 12:21 AM

Light Tower,

You did a good job of pointing out that a wye/delta motor is three-phase.

When you say, Name plate are really ment there as a guide, do you mean "guide" as information you can ignore? I hope not. The tables in the code books are the guide for typical motors, whereas the nameplate is the actual design values for this motor. In setting the overload relay, the nameplate is to be followed.

I am wondering if the problem with readings is an incorrect voltage or frequency. The original post does not say what these are, so I am curious. Also the original post speaks of a wye current draw when the motor is running, but that is when the starter should have the motor connected delta. Can we get more information?

Regards--JMM.

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Power-User

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#8
In reply to #4

Re: Motor name plate misleading

09/12/2008 5:10 AM

Dear Jmueller,

"Also the original post speaks of a wye current draw when the motor is running, but that is when the starter should have the motor connected delta. Can we get more information?" - this motor would be connected up as either Star (WYE) or Delta i.e. it would not have the star/delta change over that you are referring to.

Kind Regards

Mr. W.A Snow

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Guru

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#13
In reply to #8

Re: Motor name plate misleading

09/16/2008 11:14 PM

I appreciate your correction and the kindness in how it was worded!

--Jmueller

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Power-User

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#14
In reply to #13

Re: Motor name plate misleading

09/17/2008 1:27 AM

Dear Jmueller, It does not cost anything or take longer to be polite.

Thank you.

Regards

Mr. W.A Snow

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#5

Re: Motor name plate misleading

09/11/2008 4:18 AM

In Germany you can feed 400 V as single phase with the help of small transformer, we have vaccum pumps on german m/c rating 240 v , but m/c manufacturar provide voltage stpe down transformer in side the m/c for ...

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Guru

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#6

Re: Motor name plate misleading

09/11/2008 9:21 AM

Assuming you have connected in Y configuration where did you get the third wire ? did you use by chance the ground wire as the third one and hence tripped the starter (instead of burning off the grid) the calculations are clear that it is a 1Φ motor

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#7

Re: Motor name plate misleading

09/12/2008 2:54 AM

230/400 V, 0.18 KW, 50 HZ, 1.15/0.67 A - Star/ Delta, 0.73 pf

The one thing missing here is the efficency. For three phase motors of this size a typical efficency would be in the order of 0.5 - 0.6 rather than the 0.92 as point out in one of the previous posts. For the purpose of this calculation I will use an effeciency of 0.55.

Motors above 1KW or 2KW (typically) will have effeciencies in the order of 0.8 -0.9.

The fact that Star/Delta is mention would mean that it is 3 phase motor.

Therefore:-

Power = √3·V·I·cosφ.η

where

P = power in watts

V = applied voltage

I = current in amps

cosφ = power factor

η = motor efficiency

Therefore:-

Star Calculation:-

√3 x 230 x 1.15 x 0.73 x 0.55 = 183 watts (0.18KW)

Delta Calculation:-

√3 x 400 x 0.67 x 0.73 x 0.55 = 186 watts (0.18KW).

Therefore the conclusion would be that this is a 3 phase motor, 0.18KW, cosφ = 0.73 and η = 0.55. Therefore the name plate is infact correct.

Kind Regards

Mr. W.A Snow

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Power-User

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#9
In reply to #7

Re: Motor name plate misleading

09/12/2008 10:53 PM

G.A.

You've filled it. Not the hole, the blank in the question.

AC Wing.

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Commentator

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#10
In reply to #7

Re: Motor name plate misleading

09/13/2008 6:55 PM

Hi HoleInTheSnow:

i have one doubt.

In 3 phase power calculations we have to use line voltage & line current if the formula is

Power = √3·V·I·cosφ

so the line voltage for star & delta would be same.Here 230v given for star.

line current in star should be less than delta.

Motor winding designed according to full load current rating. So in star line current is equal to phase current. In delta line current is √3 times phase current.If 0.67 is line current, then phase current 0.386.

In star phase current = line current = 1.15. So is it right?

Star Calculation:-

√3 x 230 x 1.15 x 0.73 x 0.55 = 183 watts (0.18KW)

Delta Calculation:-

√3 x 400 x 0.67 x 0.73 x 0.55 = 186 watts (0.18KW).

Kindly clear my doubts.

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#11
In reply to #10

Re: Motor name plate misleading

09/15/2008 3:54 AM

Lspraba,

The original post stated the nameplate to be:

230/400 V, 0.18 KW, 50 HZ, 1.15/0.67 A - Star/ Delta, 0.73 pf.

Upon re-reading I think this should have read:

400/230 V, 0.18 KW, 50 HZ, 0.67/1.15 A - Star/ Delta, 0.73 pf.

Just to be sure I double checked this against a number of motors here with a similar KW and the name plates were typically as follows:

400/230 V, 0.6/1.05 A, 0.18KW, pF 0.69 Star/Delta - this is very similar to the nameplate posted by k. dhana but the star/delta parameters are in the reverse order to the original post. It would appear that k.dhana posted the nameplate parameters in the incorrect order. Can anyone shed some light on this ?

Therefore based on this, I should have posted :

Star Delta Calculation:-

√3 x 230 x 1.15 x 0.73 x 0.55 = 183 watts (0.18KW)

Delta Star Calculation:-

√3 x 400 x 0.67 x 0.73 x 0.55 = 186 watts (0.18KW).

Please accept my apology, I should have read what I was actually writing.

"so the line voltage for star & delta would be same.Here 230v given for star" - this is incorrect. If you have a 230V (line voltage) supply then the motor should be connected in Delta and if you have a 400V (line voltage) supply then the motor should be connected in Star i.e. the motor would not start in Star and then change to Delta. In both cases (Star or Delta) the voltage across each motor winding is 230V (400/√3 = 230V).

If you connected the motor in Delta to a 400V (line voltage) then you probably should expect some smoke along with a rather irate boss/customer .

Kind Regards

Mr. WA Snow

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Commentator

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#12
In reply to #11

Re: Motor name plate misleading

09/15/2008 6:55 PM

Hi HoleInTheSnow,

No need for apology. But by means of this, I saw your kindness & sweetness.

You are correct. If we apply 400V for delta connection definitely smoke will be observed. Sorry for my mistake.

Since in our industry (india),we don't have 230v line voltage system, i never seen motors having this type of name plate details. We are having 400v system. For example, a 3 phase squirrel cage induction motor name plate detail,

2.30 kW, 415V, 5.57A, Connection-Delta.

We can get the rated power in name plate only in delta. In star it is 1/ √3 times.

I learnt one new thing by you.

Thank you.

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Power-User

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#15
In reply to #11

Re: Motor name plate misleading

01/28/2009 5:13 AM

agree....

"beside that if you connected the motor in Delta to a 400V (line voltage) then you probably should expect some smoke along with a rather irate boss/customer "

fyi, i have bad experience, when i bought motor. motor has came is 400/230, start/delta. And my line voltage is 400 V.

Our panel(starter) is already ready and already installed in site(in the forrest, far away from store).the case is motor running at the star condition but when process transfer from wye to delta happen, Thermal Overload Relay always Trip.even we have adjusted TOR untill max range.

Investigation result show us that our motor is wrong. but because of some work that cannot be delayed. we decide to not use (star/delta starter) and connect motor directly at wye connection (DOL conection).

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AC Wing (1); Anonymous Poster (1); elect-ok (1); HoleInTheSnow (4); jmueller (2); JRaef (1); light tower (1); Lspraba (2); sb (1); wareagle (1)

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