## electrical motor power factor & efficiency

## electrical motor power factor & efficiency

(OP)

hello,

I want to know where each figure recorded from the LCD panel of the power feeder of an AC motor driving a machinery goes.

in other words, I have the reading at one instance reads in the panel at electrical room:

KW = 700

KVAr = 800

AMP = 70

and this is on a 11KV feeder.

so what is the 700 over here in a power triangle?

how do I relate to power factor ?

how do I get my electrical efficiency? can I say eff= data sheet kw / reading kw from panel?

Thanks & Regard,

I want to know where each figure recorded from the LCD panel of the power feeder of an AC motor driving a machinery goes.

in other words, I have the reading at one instance reads in the panel at electrical room:

KW = 700

KVAr = 800

AMP = 70

and this is on a 11KV feeder.

so what is the 700 over here in a power triangle?

how do I relate to power factor ?

how do I get my electrical efficiency? can I say eff= data sheet kw / reading kw from panel?

Thanks & Regard,

## RE: electrical motor power factor & efficiency

KVAr = 800

KVA = sqrt(700^2+800^2) = 1,060

I = 1,060kva/(sqrt3*11kv) = 55.6A

but you said amps = 70

Unless I made an error (and that's very possible that I did) it seems your data does not add up quite right.

Setting that aside, power factor could be calculated from kw and kva. I'm going to stop short of telling you exactly how to calculate it, that is something you should be able to figure out.

You don't have enough information to calculate motor efficiency because you don't know the actual motor shaft output power. If you have motor factory data you might be able to estimate motor efficiency from that by adjusting for your operating point. Of course there is likely also an efficiency associated with the driven equipment.

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(2B)+(2B)' ?

## RE: electrical motor power factor & efficiency

Input kW divided by input kVA gives power factor.

Generally speaking, motor data sheet includes power factor and efficiency information at different load points.

If the voltage at the motor terminals is lower than rated (11kV), motor draws higher currents for the same kW. This is to be kept in mind.

## RE: electrical motor power factor & efficiency

## RE: electrical motor power factor & efficiency

@LionelHutz : it does, however for some reason (or a misunderstanding of some part of the triangle) , I am not getting the number corresponding to what I am reading from the panel when manually calculating PF ...

## RE: electrical motor power factor & efficiency

datasheet says @100 load , the current is 92 Amps

I read in electric room 76 Amps only ...

quite weird to me ...

## RE: electrical motor power factor & efficiency

## RE: electrical motor power factor & efficiency

the 76A measured when the motor shaft is 100% loaded, i.e. reading taken when machine @ 100 load.

## RE: electrical motor power factor & efficiency

If the data sheet says that the full load current is 92 Amps, then at 76 Amps, the motor is not at full load.

Bill

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Ohm's lawNot just a good idea;

It's the LAW!## RE: electrical motor power factor & efficiency

Muthu

www.edison.co.in

## RE: electrical motor power factor & efficiency

## RE: electrical motor power factor & efficiency

A few other lower likelyhood possibilities:

## RE: electrical motor power factor & efficiency

as for @bacon4life questions

the first post was what I read that day in electrical room through the feeder panel, the other numbers I mentioned 92A is the rated current at full load in the data sheet of the motor,

as of the questions, i will try to answer:

1- here is a new full set of readings

I1 = 77A

I2= 75

I3 = 77.7 A

U = 10.8 KV

P = 1.01 MW

q= 1.01 MVAR

i trust those as I took them myself

2- it is a standard motor yes

3- none noticed , nor reported

4- it is ..

Do the readings look consistent?

thanks again

## RE: electrical motor power factor & efficiency

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(2B)+(2B)' ?

## RE: electrical motor power factor & efficiency

so now what is the pf ?

efficiency?

thanks

## RE: electrical motor power factor & efficiency

efficiency unknown, same reasons as above

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(2B)+(2B)' ?

## RE: electrical motor power factor & efficiency

the motor rated power in the data sheet is 1200 kw

so whats the efficiency here ?

## RE: electrical motor power factor & efficiency

Estimated KVAR = 1010 KVAR

kW based on KVAR estimate = 1433 kW

Estimated efficiency at full load = 84% efficiency.

Estimated load at 77 Amps. (77A/92A) = 84% load.

Judgement call;

1. 84% efficiency seems unreasonable low. I would expect 90% or better efficiency.

2. Neither the real current nor the reactive current are linear with respect to the per unit load.

3. The efficiency will be close to the efficiency at 75% load as shown by the data sheet.

4. The efficiency at 75% to 85% is typically better than the efficiency at 100% loading.

Bill

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Ohm's lawNot just a good idea;

It's the LAW!## RE: electrical motor power factor & efficiency

you didn't provide enough information. Efficiency is power out divided by power in. Power in is 1.01MW. What is the shaft or output power?

## RE: electrical motor power factor & efficiency

and regarding point 4 , this 11kv motor has its highest efficiency & pf at 100% load as per its datasheet !!

## RE: electrical motor power factor & efficiency

What does the data sheet show for efficiency at 100% and at 75% loading?

Bill

--------------------

Ohm's lawNot just a good idea;

It's the LAW!## RE: electrical motor power factor & efficiency

@75% 93.5%

power factor

@100 its 73%

@75 its 67%

afaik that power factor drops badly if you are operating way below the rated point

## RE: electrical motor power factor & efficiency

## RE: electrical motor power factor & efficiency

so for my readings provided here ,

I1 = 77A

I2= 75

I3 = 77.7 A

U = 10.8 KV

P = 1.01 MW

q= 1.01 MVAR

how is power triangle gonna look like?

## RE: electrical motor power factor & efficiency

## RE: electrical motor power factor & efficiency

My last quote (so just grow up.) was directed at somacast.

Like "Back at you!"

I am sorry if I was not clear.

Bill

--------------------

Ohm's lawNot just a good idea;

It's the LAW!