Possible for Motors of Same kW to Have Different HP?

75KW = 100.53HP

There's got to be something else in the motor spec that's different, or you've got a mechanical problem that is taking excess power.
Have you determined what caused the original burn out?

What do you say about the internal connection of the motor?star,delta.How is the mechanical coupling,any gears?

Check to see what HP the motor is actually using. I could be that something is causing it to use more than it can deliver. That may have been what caused the previous one to go bad. You may have another problem, such as a bad bearing.

What is the Eff. and SF of the two motors.

For the input at both motors to be same as 75 kW, there can be distinct change at the output (shaft power) attributable to various motor design factors such as; selection of flux densities in core, Design for minimum cost or good power factor or good efficiency.

Most of the on-shelf motors in the market are designed for minimum cost to remain price wise competitive however renowned manufacturers readily deviate from this pattern.

I'd like to know what the amperage is on the new motor compared to the previous one under the same load. Is that stuff available?

To be honest I'd still look at the mechanics of the drive, you're loosing 20% throughput for the same power used. You haven't replied as to the cause of the burn out.

You don't say what type of mill the drive is for. I've had a 2200HP horizontal ball mill use up 15% of power chewing it's pedestal bearings apart. The mill control kept reducing the burden loading as the mill used more power to rip it's self-apart.

When the motor burnt out and was taken for repair, the repairer said it looked like the windings on one end

had been bumped at some stage. The motor had just been in to them for checking during our annual shutdown about 2 weeks before it burnt out. It burnt out right on one end or the windings. I will get some info on the other questions today.

I have to ask. Is it possible your repair guy is sabotaging your motors to keep work coming in. Seems kind of odd that he checked out the original, and 2 weeks later it burned up. Did he also supply the replacement? Of course, whoever installed it may have bumped or dropped it also. Looks like the windings may have been dinged somehow.

That burnout looks suspiciously like ones I have seen that have resulted from too much moisture accumulating in the windings, resulting in a breakdown of the insulation capabilities of the wire coating. Humidity can do this, and dust or other airborne contaminants can accelerate the problem. If one uses a solvent to clean the windings, one can also damage the insulation. When the motor was overhauled, were the windings dipped and baked? Was it dried thoroughly before firing it up?

Of course, that doesn't explain the lower output for the new motor...

<...Any suggestions if its not a HP thing?...>

Yes. Fit a motor overload device and set its trip setting to the full load current as stated on the motor nameplate. Throughput falls to zero while a new motor is being sourced and installed!

Well, that makes a lot of sense. GA

GA JRaef and Trevor.

Given the fact that the motor was stripped for inspection by you repairer, he/they are the most likely culprits for causing the damage. It still doesn't explain the 20% loss of throughput for the mill.

Must that burn out causes of the previously installed 75kw be identified/analyzed. Problem seems to be at the mechanical aspect since I'm sure electrical protection was anticipated. Supply voltage too are possibilities that lessen its HP.

This is the correct answer. When you talk about the "grunt" of the motor, that speaks to torque. Check the torque curve of the motor at various rpms.

Sorry for the tardy reply. Still waiting on some info on the original burnt out motor.

The new motor is a TECO. EFF is 95.5, 4 pole 50Hz 1480 RPM IP 56. It drives a hammer mill crushing bone. The old motor was definitely 4 pole 1480 RPM. Not sure on the Hz though.

The mill is like a flywheel, so it does have some momentum.

If it turns out that the Hz figure is correct then your best bet is probably, as per TonyS in an earlier reply, to review/check that the first motor failure (and all subsequent failures) might be caused by increased load. Bearing failure and other factors could cause this.

If there is not a mechanical explanation for the problem, then look for some sort of (recent) compromise in the power supply.

Pl ascertain the gauge of the copper wire he has used for winding. Compare with the original wire and check whether both are same. In case he has compromised it is likely that it under performs. In no case motors can have different HP with same KW. This has already been explained by other readers.

Vasgosun.

There is a difference in Horse Power and Break Horse power (BHP). BHP is distinctively less than HP depending on the amount of losses in motor accordingly shaft torque relates to BHP and not HP of the motor.

Take into consideration speed torque curves for suitable motor replacement.

Does anyone else think that motor ratings have gone optimistic a bit since the mandated efficiency standards (EISA) have come to be?

In the past year I have seen two motor/pump combination failures because the motor HP chosen would not drive the pump as required. These are new installations and designed by experienced pump engineers. The HP chosen should have been enough, but weren't. Both had very high efficiency rated motors.

Had I done the calculations, I would say human error, but these were experienced pump engineers making the error, or was it an error? I am starting a new conspiracy theory here - motor manufactures are selling us lowered HP motors (i.e. 20HP is really 18HP) to show a drop in FLA, thereby increasing apparent efficiency. They get away with this most of the time because of the usual safety factor (25% over sizing) built in by most engineers. Border line applications point out the truth when a 20HP motor won't do the work it should. Any takers to this theory?

LOL! You are accusing motor manufacturers of a conspiracy and a cover up. I'm not a big fan of conspiracy theories, I think the world is generally too complacent and/or lazy to pull something like that off. It would take an enormous amount of effort to keep every person involved quiet, including testing authorities, workers, engineers etc. etc. etc.

AC motor energy efficiency improvements come from a handful of areas in combinations that vary from manufacturer to manufacturer. Lower winding resistance by using larger magnet wire, smaller air gaps, better quality steel in the laminations, better QC on the winding methods, less air flow required for cooling etc. etc. etc. One drawback of using energy efficient motor designs is that some of these methods leave the motor more susceptible to power quality issues in the systems they are connected to and in particular voltage unbalance. As a result, you can end up with more of an effect being noticed from Negative Sequence Currents, which produce negative torque and essentially rob the motor of usable shaft torque. If you have had problems with EE motors, that's the first thing I would look at.

Very useful document on the subject.

I haven't - our customers have. The motors I refer to were on water pumping skids. We were only building duplicates of what had been done in years past. The 20HP motors on one skid had to be replaced with 30HP units to do what 20HP units had done before all the concern over efficiency ratings. On another, a 5HP motor had to be replaced with 7.5HP to do what 5HP had done in the past. And, there is no over driving them. With a VFD I have run motors on pumps up to 120HZ with no problems. Similar, but newer motors are refusing to be driven much over 60HZ.

The original motor burned out and now the new motor does not seem to have enough power?

Have you checked that all three phases are drawing the correct amperage? A missing phase will give reduced power and the motor may run hot enough to burn out.

Check the amperage under full load.

Problem become very easy if it is well communicated

First mention the nameplate of the motor Like that

For Example :75 KW,400 V, 50 Hz, D, 134 A, P.F 0.86, 1480 RPM (VEM)

Now if you have any load record then mention that load record.

After that mention the nameplate of the motor (New One)

Like : 75 KW, -- V, --Hz, Connection Type, --- A, Power Factor, --- RPM (Male - - )

Now mention its load

Now start writing what problem U are facing.

Hoping for Ur reply

Well checked all the phases and they were OK. Got the person who checked the original burnt motor and showed him the trend graph (of power useage) on our computer, before the burnout. He blamed it on amps drag and said that is why it burnt out. Our sparky disagreed, so they agreed to disagree.

Replaced the screen underneath the Mill, and lo and behold it was back to normal

We put this down to the cradle holding the screen in place. There is a small gap between the hammers on the rotor and the screen. This gap may have been larger and was causing a lot of drag as there would have been a lot more product in there than normal. It has jacking bolts to push the cradle into place, and we think the jacking bolts may not have been screwed home when we did the overhaul.

The new motor is going as well as the old.

Still doesn't explain why the old motor suddenly burnt out as it didn't trigger the overload prior to the event.

Dear whezmabeer

Guest is correct .

You might be supplying 2phase to the motor due to starter circuit problem.

Related to magnetic contactor. ( contact welded )