|
Posted by Robert Wilson on June 17, 2008, 7:01 am
Please log in for more thread options
Andrew Bishop wrote:
> what sort of maximum frequency can I run a 3 phase 3 hp motor at
> running 240 3 phase without killing motor
>
> Thanks Andrew Bishop
Hi,
Sorry to top post, but frankly those if you who are overspeeding a motor
on a VSD are insane. Motors are designed to operate at the frequency on
their rating plate,no higher. You are risking a motor explosion. I
have seen the after effects of a motor letting go and I promise you it
is like a bomb going off. You don't have to go a lot higher to be in
the dangerous region.
Just so you know my background is motor speed controllers and control
systems and have seen the results of endeavours like this.
Most sincerely,
Robert.
|
|
Posted by Tony Jeffree on June 17, 2008, 7:59 am
Please log in for more thread options
On Tue, 17 Jun 2008 12:01:00 +0100, Robert Wilson
>Andrew Bishop wrote:
>> what sort of maximum frequency can I run a 3 phase 3 hp motor at
>> running 240 3 phase without killing motor
>>
>> Thanks Andrew Bishop
>Hi,
>Sorry to top post, but frankly those if you who are overspeeding a motor
>on a VSD are insane. Motors are designed to operate at the frequency on
>their rating plate,no higher. You are risking a motor explosion. I
>have seen the after effects of a motor letting go and I promise you it
>is like a bomb going off. You don't have to go a lot higher to be in
>the dangerous region.
>
>Just so you know my background is motor speed controllers and control
>systems and have seen the results of endeavours like this.
>
Hi Robert -
As it happens, the installation I have was supplied pre-wired and
pre-configured to those settings by Newton-Tesla, so I presume they
checked that the motor theuy supplied was good for 2.4 times
over-speed. However, I take your point that in general, you can't rely
on a motor being safe at more than its name-plate RPM unless you have
other information from the manufacturer that tells you different.
Regards,
Tony
|
|
Posted by on June 17, 2008, 8:08 am
Please log in for more thread options wrote:
> Andrew Bishop wrote:
> > what sort of maximum frequency can I run a 3 phase 3 hp motor at
> > running 240 3 phase without killing motor
>
> > Thanks Andrew Bishop
>
> Hi,
> Sorry to top post, but frankly those if you who are overspeeding a motor
> on a VSD are insane. Motors are designed to operate at the frequency on
> their rating plate,no higher. You are risking a motor explosion. I
> have seen the after effects of a motor letting go and I promise you it
> is like a bomb going off. You don't have to go a lot higher to be in
> the dangerous region.
>
> Just so you know my background is motor speed controllers and control
> systems and have seen the results of endeavours like this.
>
> Most sincerely,
>
> Robert.
Well Robert I do a lot of work on electric motors, in fact three of my
biggest 4 customers are rewind and motor people.
Presumably you have never heard of VDF rated motors ? Why do VDF
manufacturers make them able to go to 120 Hz on the normal range
because although I have seen special motors that run on 200 Hz and 400
Hz I have never seen a 120 Hz motor.
[ Quick phone call to one of the motor people and he's not got a clue
what I'm talking about ]
The rotor of a 2 pole motor is identical to a 4 pole rotor, it's the
stator that's different so if a 4 pole runs at 1425 and 2 pole runs at
2800 how do you differentiate what rotor of the two identical ones to
fit.
Last item have you seen a rotor off a modern metric framed motor
lately ?
Gone are the helical grooves filled with cast alloy. They are still
there but it's all internal, the outside is one complete smooth
surface with nothing to snag or cause centrifugal force to act on it.
Want proof ?
I have converted 6 or 7 3/4Hp 2 pole motors to run at 12,000 with
the expert help of the motor people.
These run 8 hours a day 4 -1/2 days a week continuous and have done
for the last 4 or 5 years.
Only one has given problems and that was caused by crashing the head
into the frame of the machine which bent the spindle.
I have seen motors that have exploded but not for many years and it's
usually been another fault that caused the problem. Like someone
dropping a length of chain into a fork truck motor so they can get off
work early [ true ]
Most applications that will come into use here is on machine tools
which also need a low speed so the norm is to use 4 pole motors to get
the low speed [ many shaper etc even use 6 pole motors for the low
speed application ] and over speed to get higher which still doesn't
exceed fitting a 2 pole motor anyway.
Personally and from many years hands on experience I think you are
over reacting.
John S.
|
|
Posted by Robert Wilson on June 17, 2008, 8:29 am
Please log in for more thread options Hi John,
I agree with you that i'm probably over reacting but I thought it
important to make the point because no-one else had. If you have the
blessing from the manufacturer then it's a different game as you say,
but I doubt many of the other contributirs have gone to that kind of
lengths to be sure about what they're doing.
Am I being naive here?
Sincerely,
Rob.
john@stevenson-engineers.co.uk wrote:
> wrote:
>> Andrew Bishop wrote:
>>> what sort of maximum frequency can I run a 3 phase 3 hp motor at
>>> running 240 3 phase without killing motor
>>> Thanks Andrew Bishop
>> Hi,
>> Sorry to top post, but frankly those if you who are overspeeding a motor
>> on a VSD are insane. Motors are designed to operate at the frequency on
>> their rating plate,no higher. You are risking a motor explosion. I
>> have seen the after effects of a motor letting go and I promise you it
>> is like a bomb going off. You don't have to go a lot higher to be in
>> the dangerous region.
>>
>> Just so you know my background is motor speed controllers and control
>> systems and have seen the results of endeavours like this.
>>
>> Most sincerely,
>>
>> Robert.
>
> Well Robert I do a lot of work on electric motors, in fact three of my
> biggest 4 customers are rewind and motor people.
> Presumably you have never heard of VDF rated motors ? Why do VDF
> manufacturers make them able to go to 120 Hz on the normal range
> because although I have seen special motors that run on 200 Hz and 400
> Hz I have never seen a 120 Hz motor.
> [ Quick phone call to one of the motor people and he's not got a clue
> what I'm talking about ]
>
> The rotor of a 2 pole motor is identical to a 4 pole rotor, it's the
> stator that's different so if a 4 pole runs at 1425 and 2 pole runs at
> 2800 how do you differentiate what rotor of the two identical ones to
> fit.
>
> Last item have you seen a rotor off a modern metric framed motor
> lately ?
> Gone are the helical grooves filled with cast alloy. They are still
> there but it's all internal, the outside is one complete smooth
> surface with nothing to snag or cause centrifugal force to act on it.
>
> Want proof ?
>
> I have converted 6 or 7 3/4Hp 2 pole motors to run at 12,000 with
> the expert help of the motor people.
> These run 8 hours a day 4 -1/2 days a week continuous and have done
> for the last 4 or 5 years.
> Only one has given problems and that was caused by crashing the head
> into the frame of the machine which bent the spindle.
>
> I have seen motors that have exploded but not for many years and it's
> usually been another fault that caused the problem. Like someone
> dropping a length of chain into a fork truck motor so they can get off
> work early [ true ]
>
> Most applications that will come into use here is on machine tools
> which also need a low speed so the norm is to use 4 pole motors to get
> the low speed [ many shaper etc even use 6 pole motors for the low
> speed application ] and over speed to get higher which still doesn't
> exceed fitting a 2 pole motor anyway.
>
> Personally and from many years hands on experience I think you are
> over reacting.
>
> John S.
|
|
Posted by Charles Ping on June 17, 2008, 12:37 pm
Please log in for more thread options
Robert Wilson wrote:
> Hi John,
> I agree with you that i'm probably over reacting but I thought it
> important to make the point because no-one else had. If you have the
> blessing from the manufacturer then it's a different game as you say,
> but I doubt many of the other contributirs have gone to that kind of
> lengths to be sure about what they're doing.
>
> Am I being naive here?
>
> Sincerely,
>
> Rob.
>
>
> john@stevenson-engineers.co.uk wrote:
> > wrote:
> >> Andrew Bishop wrote:
> >>> what sort of maximum frequency can I run a 3 phase 3 hp motor at
> >>> running 240 3 phase without killing motor
> >>> Thanks Andrew Bishop
> >> Hi,
> >> Sorry to top post, but frankly those if you who are overspeeding a motor
> >> on a VSD are insane. Motors are designed to operate at the frequency on
> >> their rating plate,no higher. You are risking a motor explosion. I
> >> have seen the after effects of a motor letting go and I promise you it
> >> is like a bomb going off. You don't have to go a lot higher to be in
> >> the dangerous region.
> >>
> >> Just so you know my background is motor speed controllers and control
> >> systems and have seen the results of endeavours like this.
> >>
> >> Most sincerely,
> >>
> >> Robert.
> >
> > Well Robert I do a lot of work on electric motors, in fact three of my
> > biggest 4 customers are rewind and motor people.
> > Presumably you have never heard of VDF rated motors ? Why do VDF
> > manufacturers make them able to go to 120 Hz on the normal range
> > because although I have seen special motors that run on 200 Hz and 400
> > Hz I have never seen a 120 Hz motor.
> > [ Quick phone call to one of the motor people and he's not got a clue
> > what I'm talking about ]
> >
> > The rotor of a 2 pole motor is identical to a 4 pole rotor, it's the
> > stator that's different so if a 4 pole runs at 1425 and 2 pole runs at
> > 2800 how do you differentiate what rotor of the two identical ones to
> > fit.
> >
> > Last item have you seen a rotor off a modern metric framed motor
> > lately ?
> > Gone are the helical grooves filled with cast alloy. They are still
> > there but it's all internal, the outside is one complete smooth
> > surface with nothing to snag or cause centrifugal force to act on it.
> >
> > Want proof ?
> >
> > I have converted 6 or 7 3/4Hp 2 pole motors to run at 12,000 with
> > the expert help of the motor people.
> > These run 8 hours a day 4 -1/2 days a week continuous and have done
> > for the last 4 or 5 years.
> > Only one has given problems and that was caused by crashing the head
> > into the frame of the machine which bent the spindle.
> >
> > I have seen motors that have exploded but not for many years and it's
> > usually been another fault that caused the problem. Like someone
> > dropping a length of chain into a fork truck motor so they can get off
> > work early [ true ]
> >
> > Most applications that will come into use here is on machine tools
> > which also need a low speed so the norm is to use 4 pole motors to get
> > the low speed [ many shaper etc even use 6 pole motors for the low
> > speed application ] and over speed to get higher which still doesn't
> > exceed fitting a 2 pole motor anyway.
> >
> > Personally and from many years hands on experience I think you are
> > over reacting.
> >
> > John S.
Robert
I don't think that you're over-reacting. Just expressing the caution
that an expert professional would be expected to deliver. Thankfully
I'm not an expert professional but you've said more forcefully what I
suggested earlier - Beware the basic meachanics of the arrangement.
By the way about a year ago I took your advice on running a 415volt
three phase inverter on single phase 415volt. Your rule of thumb of 3
times the rating was spot on. It took a 10HP inverter to run a 3HP
motor in this fashion.
Regards
Charles
|
| Similar Threads | Posted | | 240v 3 phase in 415v 3 phase motor | April 17, 2008, 6:03 am |
| 3-Phase Distribution from Phase Converter | June 14, 2008, 3:50 am |
| Re: Anyone knowledgeable about BTH motors? | October 4, 2006, 6:28 pm |
| Anyone knowledgeable about BTH motors? | August 28, 2006, 4:00 pm |
| Servo motors | May 12, 2008, 8:59 am |
| Free electric motors | October 10, 2006, 10:07 pm |
| Re: Recommend sources for DC motors | August 11, 2006, 8:03 pm |
| Reducing noise from cabinet mounted motors | May 2, 2008, 5:04 am |
| Big 3 phase motor | August 15, 2006, 1:18 pm |
| 3 phase motor as a generator ? | August 9, 2006, 12:50 pm |
|
|
Yahoo! 
Google 
Windows Live 
del.icio.us 
digg 
Netscape 
XML Sitemap
> running 240 3 phase without killing motor
>
> Thanks Andrew Bishop