152 kw Motor HP

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A-1Sparky

Senior Member
Location
Vermont
I've got a chiller compressor motor with a nameplate rating of 152 kw. This is a 460v 3 phase motor. I'm thinking it's a 200 hp motor, but wanted to make sure. Is this the correct formula to put me in the ballpark?


(I X E X Eff. X 1.73 X PF)/ 746
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Doesn't "close enough" usually end up getting you in trouble? ;) Just kidding...thanks for the confirmation. :)

I don't see that you much choice but to proceed as if it is a 200HP motor.

What is the nameplate voltage on the motor?

I have never seen a motor marked in kW that is rated for 480V. I have seen some that are dual rated in HP/480V and 400V/kW. siemens makes a line of motors that are rated this way. the nameplate seems to vary sometimes though. you might have to get the instruction sheets out. you might also have to get an auxiliary nameplate from the manufacturer to placate the inspector when he looks at it and wonders what it is.
 

Besoeker

Senior Member
Location
UK
I've got a chiller compressor motor with a nameplate rating of 152 kw. This is a 460v 3 phase motor. I'm thinking it's a 200 hp motor, but wanted to make sure. Is this the correct formula to put me in the ballpark?
The conversion is as Jraef has given.
A further thought. Motor nameplates with a kW rating is standard in the EU bit of the world (and elsewhere). But 152kW seems like a special rather than a standard machine - 150kW would be and rather closer to your 200hp rating. What is the frequency and/or shaft speed?
 

A-1Sparky

Senior Member
Location
Vermont
I don't have a whole lot of info. on this motor. We are in the data collection phase of an arc-flash study, and just have the nameplate spec of 152 KW. No HP rating is given. The engineer that I'm working with asked for the HP, so I figured I could give it to him by doing the calculation.
 

beanland

Senior Member
Location
Vancouver, WA
Arc Flash

Arc Flash

If you are gathering data for an arc flash study, and are considering the generation contribution from motors, you need to know is this chiller uses a VFD or not. Many newer chillers use VFD which cannot backfeed power into an arc. So, as a load, it may be 152kW but as a source for arcing current, it may be zero.
 

A-1Sparky

Senior Member
Location
Vermont
I was talking with a tech last week, and he was telling me that while he was working on a drive, a fault at the motor caused a fireball to shoot out of the vfd and pass right by his head. :eek:hmy:
 

Besoeker

Senior Member
Location
UK
I love the way the power is stated in kW for 50 Hz and HP for 60 Hz since it assumes that the specification standards go with the frequency.
I think its with nation rather than frequency.
The vast majority of the countries in the world use SI. Regardless of frequency. So, a kW rating would be appropriate for the vast majority of countries.
But the US is a big market. And still embraces Imperial units. It makes business sense for multinationals to recognise that and to offer products rated in Imperial units for that one market.
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
I was talking with a tech last week, and he was telling me that while he was working on a drive, a fault at the motor caused a fireball to shoot out of the vfd and pass right by his head. :eek:hmy:

I have heard versions of this kind of story over and over again, they are generally myths or exaggerations fostered by the fact that most people do not understand what a VFD is, so they attribute all sort of magical thinking to them, including mysterious "fireballs" and such. Much more likely versions:

1) He witnessed an Arc Flash event having nothing whatsoever to do with it being a VFD, but because there was a VFD in the box, it was automatically to blame in his mind.
2) Someone dropped a tool across the DC bus connections and the tool vaporized, causing the arc flash event to be in the drive. I had a 25 year veteran drive technician killed by that once, very tragic.
3) He energized a VFD in sub-zero temperatures and the capacitors were frozen, which can sometimes cause them to rupture somewhat catastrophically. I have witnessed some very violent versions of this, it can scare the bejeebus out of someone who doesn't know what's happening. But there is no "fireball", just a loud popping sound and occasionally some goo coming out of the caps.

Back to the motor sizing: Motor HP is a relatively meaningless term in the chiller industry. Chiller mfrs rarely list a HP value, because the motor is custom made for the chiller and it is not a COTS motor. So the chiller mfr specifies a speed and torque requirement tailored to operate their chiller design, the motor mfrs respond to exactly what they need and the nameplate for the motor is created after testing on the chiller to provide the necessary relevant information. That's why you don't see the term "FLA" on the nameplate, there is no operation at anything less than what it was designed for, or more than what it is designed for. So what you see is the RLA, LRA and MCA or MOCP.

Usually the only time you need a HP value is when you are using something like SKM software to calculate Arc Flash energy contributions, and in that software you apparently have to chose HP or KW for the entire study, you cannot mix them. If all of the other motors are HP and the chiller is only shown with kW, just use the formula to convert and plug the nearest HP value into the software, the tiny differences will have no real effect on the outcome. And if there is a VFD, it's a moot point anyway.
 

A-1Sparky

Senior Member
Location
Vermont
I have heard versions of this kind of story over and over again, they are generally myths or exaggerations fostered by the fact that most people do not understand what a VFD is, so they attribute all sort of magical thinking to them, including mysterious "fireballs" and such. Much more likely versions:

1) He witnessed an Arc Flash event having nothing whatsoever to do with it being a VFD, but because there was a VFD in the box, it was automatically to blame in his mind.
2) Someone dropped a tool across the DC bus connections and the tool vaporized, causing the arc flash event to be in the drive. I had a 25 year veteran drive technician killed by that once, very tragic.
3) He energized a VFD in sub-zero temperatures and the capacitors were frozen, which can sometimes cause them to rupture somewhat catastrophically. I have witnessed some very violent versions of this, it can scare the bejeebus out of someone who doesn't know what's happening. But there is no "fireball", just a loud popping sound and occasionally some goo coming out of the caps.

Back to the motor sizing: Motor HP is a relatively meaningless term in the chiller industry. Chiller mfrs rarely list a HP value, because the motor is custom made for the chiller and it is not a COTS motor. So the chiller mfr specifies a speed and torque requirement tailored to operate their chiller design, the motor mfrs respond to exactly what they need and the nameplate for the motor is created after testing on the chiller to provide the necessary relevant information. That's why you don't see the term "FLA" on the nameplate, there is no operation at anything less than what it was designed for, or more than what it is designed for. So what you see is the RLA, LRA and MCA or MOCP.

Usually the only time you need a HP value is when you are using something like SKM software to calculate Arc Flash energy contributions, and in that software you apparently have to chose HP or KW for the entire study, you cannot mix them. If all of the other motors are HP and the chiller is only shown with kW, just use the formula to convert and plug the nearest HP value into the software, the tiny differences will have no real effect on the outcome. And if there is a VFD, it's a moot point anyway.

From what I was told, the motor was not inverter-rated, but had been in use with a vfd for about two years. When this unlucky guy went to start it up, the windings shorted and caused the arc flash. Sounded plausible to me, but I am by no means a vfd expert.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
From what I was told, the motor was not inverter-rated, but had been in use with a vfd for about two years. When this unlucky guy went to start it up, the windings shorted and caused the arc flash. Sounded plausible to me, but I am by no means a vfd expert.

If the windings shorted the arc would have been inside the motor.
 
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