Robert Blum and I discussed this last summer and I had forgotten all
about it until I got a call last night from a fellow SWL who was
experiencing some sudden onset RFI. He had been bragging about his new
Panasonic variable speed heat pump
and how much it had saved him this summer. I asked him to take a MW
transistor radio near his fancy new heat pump and to let me know the
results.

Surprise surprise. The noise was most intense at the exterior heat
pump.
..
We had a very odd situation at work in that the bearings in the vari-
speed motor that drives the ventilation system, a very big motor and
fan, kept going through bearings at a frightful rate. The bearings are
supposed to be good for 10K hours. we were getting as little as 6
weeks.

In one of my searches I had found a reference to the longitudinal
currents induced in the rotating shaft. This current wants to flow
from end to end and must punch it's way through the lubrication. This
destroys the lube and eats tiny wholes in the bearing surface. A very
bad situation. I gained permission to go into the service area, an
area off limits to even engineers with my trusting DX398 and the 19uH
noise probe. There was an intense amount of static coming from the
motor. Our electrician didn't call me an idiot, but he stiffly agreed
to check the voltage from end to end on the shaft. It was well over
100 volts. After he pried the dust caps off, and when we turned out
the lights, you could see a million little arcs at each end in the
bearing!

The solution was to use ceramic coated steel bearings. Noise gone, And
no more bearing replacements.

The only HF reception gear where I work is a WWV clokc backup, 3rd
level redundancy, that I monitor at my bench. I had noticed periods of
noise strong
enough to unlock the WWV derived clock, but hadn't been able to locate
the
noise source.

The audio guys were very happy because their long AES digital audio
liines
were experiencing serious, as in unusable, noise issues.

I wonder how many of the new high efficiency heat pumps and air
handlers are
going to have some rather odd problems.

My friend is trying to figure how to explain what is happening to the
warranty people. I don't envy him. If work was a valid example, his
bearings ought to fail
pretty soon.

And before you ask, reducing the RFI from this unit was a nightmare.
It took several hundred dollars of heavy duty RFI filters, a lot of
ferrite and
a lot of bypass caps with a local grounding rod and 4AWG bond back to
the home's NEC ground.

Terry

In article
,
wrote:

Robert Blum and I discussed this last summer and I had forgotten all
about it until I got a call last night from a fellow SWL who was
experiencing some sudden onset RFI. He had been bragging about his
new Panasonic variable speed heat pump and how much it had saved him
this summer. I asked him to take a MW transistor radio near his
fancy new heat pump and to let me know the results.

Surprise surprise. The noise was most intense at the exterior heat
pump. . We had a very odd situation at work in that the bearings in
the vari- speed motor that drives the ventilation system, a very big
motor and fan, kept going through bearings at a frightful rate. The
bearings are supposed to be good for 10K hours. we were getting as
little as 6 weeks.

In one of my searches I had found a reference to the longitudinal
currents induced in the rotating shaft. This current wants to flow
from end to end and must punch it's way through the lubrication. This
destroys the lube and eats tiny wholes in the bearing surface. A very
bad situation. I gained permission to go into the service area, an
area off limits to even engineers with my trusting DX398 and the 19uH
noise probe. There was an intense amount of static coming from the
motor. Our electrician didn't call me an idiot, but he stiffly agreed
to check the voltage from end to end on the shaft. It was well over
100 volts. After he pried the dust caps off, and when we turned out
the lights, you could see a million little arcs at each end in the
bearing!

The solution was to use ceramic coated steel bearings. Noise gone,
And no more bearing replacements.

The only HF reception gear where I work is a WWV clokc backup, 3rd
level redundancy, that I monitor at my bench. I had noticed periods
of noise strong enough to unlock the WWV derived clock, but hadn't
been able to locate the noise source.

The audio guys were very happy because their long AES digital audio
liines were experiencing serious, as in unusable, noise issues.

I wonder how many of the new high efficiency heat pumps and air
handlers are going to have some rather odd problems.

My friend is trying to figure how to explain what is happening to the
warranty people. I don't envy him. If work was a valid example, his
bearings ought to fail pretty soon.

And before you ask, reducing the RFI from this unit was a nightmare.
It took several hundred dollars of heavy duty RFI filters, a lot of
ferrite and a lot of bypass caps with a local grounding rod and 4AWG
bond back to the home's NEC ground.

You post about the strangest stuff. I have never heard of this kind of
problem. One or more of the rotor windings must be some how shorted to
the shaft.

Ceramic bearings are not the solution as the current can go through
whatever gear train and mechanical load to which it is connected. The
motor shaft should not be electrically hot. That would be a shock
hazard. That motor is either built wrong or designed wrong.

--
Telamon
Ventura, California

Telamon wrote:


You post about the strangest stuff. I have never heard of this kind of
problem. One or more of the rotor windings must be some how shorted to
the shaft.

Ceramic bearings are not the solution as the current can go through
whatever gear train and mechanical load to which it is connected. The
motor shaft should not be electrically hot. That would be a shock
hazard. That motor is either built wrong or designed wrong.


It's a conductor in a changing magnetic field. A difference of
potential is created.

In article ,
David wrote:

Telamon wrote:


You post about the strangest stuff. I have never heard of this kind of
problem. One or more of the rotor windings must be some how shorted to
the shaft.

Ceramic bearings are not the solution as the current can go through
whatever gear train and mechanical load to which it is connected. The
motor shaft should not be electrically hot. That would be a shock
hazard. That motor is either built wrong or designed wrong.


It's a conductor in a changing magnetic field. A difference of
potential is created.

It's a conductor that is supposed to be in a net neutral magnetic field
so no potential is created.

--
Telamon
Ventura, California

On Dec 2, 7:52 pm, Telamon
wrote:
In article
,



wrote:
Robert Blum and I discussed this last summer and I had forgotten all
about it until I got a call last night from a fellow SWL who was
experiencing some sudden onset RFI. He had been bragging about his
new Panasonic variable speed heat pump and how much it had saved him
this summer. I asked him to take a MW transistor radio near his
fancy new heat pump and to let me know the results.

Surprise surprise. The noise was most intense at the exterior heat
pump. . We had a very odd situation at work in that the bearings in
the vari- speed motor that drives the ventilation system, a very big
motor and fan, kept going through bearings at a frightful rate. The
bearings are supposed to be good for 10K hours. we were getting as
little as 6 weeks.

In one of my searches I had found a reference to the longitudinal
currents induced in the rotating shaft. This current wants to flow
from end to end and must punch it's way through the lubrication. This
destroys the lube and eats tiny wholes in the bearing surface. A very
bad situation. I gained permission to go into the service area, an
area off limits to even engineers with my trusting DX398 and the 19uH
noise probe. There was an intense amount of static coming from the
motor. Our electrician didn't call me an idiot, but he stiffly agreed
to check the voltage from end to end on the shaft. It was well over
100 volts. After he pried the dust caps off, and when we turned out
the lights, you could see a million little arcs at each end in the
bearing!

The solution was to use ceramic coated steel bearings. Noise gone,
And no more bearing replacements.

The only HF reception gear where I work is a WWV clokc backup, 3rd
level redundancy, that I monitor at my bench. I had noticed periods
of noise strong enough to unlock the WWV derived clock, but hadn't
been able to locate the noise source.

The audio guys were very happy because their long AES digital audio
liines were experiencing serious, as in unusable, noise issues.

I wonder how many of the new high efficiency heat pumps and air
handlers are going to have some rather odd problems.

My friend is trying to figure how to explain what is happening to the
warranty people. I don't envy him. If work was a valid example, his
bearings ought to fail pretty soon.

And before you ask, reducing the RFI from this unit was a nightmare.
It took several hundred dollars of heavy duty RFI filters, a lot of
ferrite and a lot of bypass caps with a local grounding rod and 4AWG
bond back to the home's NEC ground.

You post about the strangest stuff. I have never heard of this kind of
problem. One or more of the rotor windings must be some how shorted to
the shaft.

Ceramic bearings are not the solution as the current can go through
whatever gear train and mechanical load to which it is connected. The
motor shaft should not be electrically hot. That would be a shock
hazard. That motor is either built wrong or designed wrong.

--
Telamon
Ventura, California

Try
http://www.rema.uk.com/pdfs/Report%20No%202.pdf
-- -- -- -- -- -- -- -- -- -- --
http://www.hpac.com/Columns/Equipmen...Article/32111/
Specifying_VariableFrequency_Drives
About half way down:
"Eddy currents induced in the laminations and shaft of a motor,
causing pitting and premature bearing failures."
The link they give is now dead but I may have it archived.
-- -- -- -- -- -- -- -- -- -- --
http://ecmweb.com/mag/electric_mating_new_variable/index.html
"Other undesired side effects
You also should be aware of other potential side effects caused by
high frequency.
These include undesirable audible noise, harmful vibration, and
bearing problems."

"Bearing problems. Another possible problem, which still isn't fully
understood, is
the slow disintegration of the roller/ball (antifriction) bearings
that support the shaft.
It appears this is caused by bearing current and static discharge.
What happens is
that pitting occurs on the roller/ball surface and, when accumulated,
causes the
bearing to make noise. If not addressed, vibration will begin to
develop."
-- -- -- -- -- -- -- --


Shortly after the "vibration' is noted the bearing will fail. We had
at least three have
the actual bearing disintegrate. The sudden 1/4" play was very
interesting.

I think the main problem is adding a variable speed control to a
standard 60Hz 3 phase
motor, Unwanted eddy do unexpected things. However the efficiency
boast suggests
that many or even most, AC and air handling motors will be retrofitted
where possible,
and that most new designs will use this technology. I hope they solve
the eddy current
issues.

An commercial electrician friend says several motor makers are voiding
the warranty of
any of their 60Hz motors used with variable speed drives. He says the
vari speed drive
makers are suggesting a conductive grease. He is very happy to be
retiring and hopes
to be out of here before the first snow flies.

I do wish people would credit me with having at least a minimal amount
of technical skill.

Terry

On Dec 2, 7:52 pm, Telamon
wrote:
In article
,



wrote:
Robert Blum and I discussed this last summer and I had forgotten all
about it until I got a call last night from a fellow SWL who was
experiencing some sudden onset RFI. He had been bragging about his
new Panasonic variable speed heat pump and how much it had saved him
this summer. I asked him to take a MW transistor radio near his
fancy new heat pump and to let me know the results.

Surprise surprise. The noise was most intense at the exterior heat
pump. . We had a very odd situation at work in that the bearings in
the vari- speed motor that drives the ventilation system, a very big
motor and fan, kept going through bearings at a frightful rate. The
bearings are supposed to be good for 10K hours. we were getting as
little as 6 weeks.

In one of my searches I had found a reference to the longitudinal
currents induced in the rotating shaft. This current wants to flow
from end to end and must punch it's way through the lubrication. This
destroys the lube and eats tiny wholes in the bearing surface. A very
bad situation. I gained permission to go into the service area, an
area off limits to even engineers with my trusting DX398 and the 19uH
noise probe. There was an intense amount of static coming from the
motor. Our electrician didn't call me an idiot, but he stiffly agreed
to check the voltage from end to end on the shaft. It was well over
100 volts. After he pried the dust caps off, and when we turned out
the lights, you could see a million little arcs at each end in the
bearing!

The solution was to use ceramic coated steel bearings. Noise gone,
And no more bearing replacements.

The only HF reception gear where I work is a WWV clokc backup, 3rd
level redundancy, that I monitor at my bench. I had noticed periods
of noise strong enough to unlock the WWV derived clock, but hadn't
been able to locate the noise source.

The audio guys were very happy because their long AES digital audio
liines were experiencing serious, as in unusable, noise issues.

I wonder how many of the new high efficiency heat pumps and air
handlers are going to have some rather odd problems.

My friend is trying to figure how to explain what is happening to the
warranty people. I don't envy him. If work was a valid example, his
bearings ought to fail pretty soon.

And before you ask, reducing the RFI from this unit was a nightmare.
It took several hundred dollars of heavy duty RFI filters, a lot of
ferrite and a lot of bypass caps with a local grounding rod and 4AWG
bond back to the home's NEC ground.

You post about the strangest stuff. I have never heard of this kind of
problem. One or more of the rotor windings must be some how shorted to
the shaft.

Ceramic bearings are not the solution as the current can go through
whatever gear train and mechanical load to which it is connected. The
motor shaft should not be electrically hot. That would be a shock
hazard. That motor is either built wrong or designed wrong.

--
Telamon
Ventura, California

I knew I had a good link"
http://www.motionsystemdesign.com/Issue/Article/47423/
Diffusing_current_trouble.aspx

This problem is not imaginary or all that odd. An example of a new
technology that is widely
adopted and applied before all the bugs are worked out. There are
solutions. But the best
solutions start with a motor designed for variable speed operation,
and by installing the
inverter very close to the motor.

And yes, under some conditions even ceramic bearings aren't an
effective solution.
They worked for us, but other steps were also taken:
Inverter moved to within inches of the motor.
Some very heavy duty LC and RC 'snubbers' where installed.
Serious RFI filtering was installed between the inverter and the
motor.
And even more serious heavy duty RFI filtering was installed on the AC
mains.
The AC mains cable size, especially the neutral, was upgraded several
wire sizes.
A kelvar fiber insulated "V belt" has to be used because standard
rubber was too conductive.
And the who rig has a special rail around it to keep people from
touching the pulley.

That area was off limits before and it is doubly so now. Everyone who
enters must be
on a approved list, log in and out, have training and no one can go
their alone. I wonder
if the energy saving are worth the extra heartaches.

Terry

On Dec 2, 8:37 pm, Telamon
wrote:
In article ,



David wrote:
Telamon wrote:

You post about the strangest stuff. I have never heard of this kind of
problem. One or more of the rotor windings must be some how shorted to
the shaft.

Ceramic bearings are not the solution as the current can go through
whatever gear train and mechanical load to which it is connected. The
motor shaft should not be electrically hot. That would be a shock
hazard. That motor is either built wrong or designed wrong.

It's a conductor in a changing magnetic field. A difference of
potential is created.

It's a conductor that is supposed to be in a net neutral magnetic field
so no potential is created.

--
Telamon
Ventura, California

In the real world, there is not a net neutral field at the motor
shaft. In smaller motors, with sinusoidal wave forms, the amount of
current is tiny and many bearings can handle it pretty well.

This has been a well known problem with large motor and generator sets
for many years. Typically, these units have three bearing pedestals,
one at the motor end, one at the generator end, and one in between.
The bearings are sleeve type bearings, and all but one pedestal is
isolated from ground to prevent the destructive circulating currents.

With the advent of variable speed drives, this type of problem is now
being seen more in smaller motors, due to the "interesting" resulting
waveforms.

Bob

In article
,
wrote:

On Dec 2, 7:52 pm, Telamon
wrote:
In article
,



wrote:
Robert Blum and I discussed this last summer and I had forgotten
all about it until I got a call last night from a fellow SWL who
was experiencing some sudden onset RFI. He had been bragging
about his new Panasonic variable speed heat pump and how much it
had saved him this summer. I asked him to take a MW transistor
radio near his fancy new heat pump and to let me know the
results.

Surprise surprise. The noise was most intense at the exterior
heat pump. . We had a very odd situation at work in that the
bearings in the vari- speed motor that drives the ventilation
system, a very big motor and fan, kept going through bearings at
a frightful rate. The bearings are supposed to be good for 10K
hours. we were getting as little as 6 weeks.

In one of my searches I had found a reference to the longitudinal
currents induced in the rotating shaft. This current wants to
flow from end to end and must punch it's way through the
lubrication. This destroys the lube and eats tiny wholes in the
bearing surface. A very bad situation. I gained permission to go
into the service area, an area off limits to even engineers with
my trusting DX398 and the 19uH noise probe. There was an intense
amount of static coming from the motor. Our electrician didn't
call me an idiot, but he stiffly agreed to check the voltage from
end to end on the shaft. It was well over 100 volts. After he
pried the dust caps off, and when we turned out the lights, you
could see a million little arcs at each end in the bearing!

The solution was to use ceramic coated steel bearings. Noise
gone, And no more bearing replacements.

The only HF reception gear where I work is a WWV clokc backup,
3rd level redundancy, that I monitor at my bench. I had noticed
periods of noise strong enough to unlock the WWV derived clock,
but hadn't been able to locate the noise source.

The audio guys were very happy because their long AES digital
audio liines were experiencing serious, as in unusable, noise
issues.

I wonder how many of the new high efficiency heat pumps and air
handlers are going to have some rather odd problems.

My friend is trying to figure how to explain what is happening to
the warranty people. I don't envy him. If work was a valid
example, his bearings ought to fail pretty soon.

And before you ask, reducing the RFI from this unit was a
nightmare. It took several hundred dollars of heavy duty RFI
filters, a lot of ferrite and a lot of bypass caps with a local
grounding rod and 4AWG bond back to the home's NEC ground.

You post about the strangest stuff. I have never heard of this kind
of problem. One or more of the rotor windings must be some how
shorted to the shaft.

Ceramic bearings are not the solution as the current can go through
whatever gear train and mechanical load to which it is connected.
The motor shaft should not be electrically hot. That would be a
shock hazard. That motor is either built wrong or designed wrong.


I knew I had a good link"
http://www.motionsystemdesign.com/Issue/Article/47423/Diffusing_current_trouble.aspx

This problem is not imaginary or all that odd. An example of a new
technology that is widely adopted and applied before all the bugs are
worked out. There are solutions. But the best solutions start with a
motor designed for variable speed operation, and by installing the
inverter very close to the motor.

And yes, under some conditions even ceramic bearings aren't an
effective solution. They worked for us, but other steps were also
taken: Inverter moved to within inches of the motor. Some very heavy
duty LC and RC 'snubbers' where installed. Serious RFI filtering was
installed between the inverter and the motor. And even more serious
heavy duty RFI filtering was installed on the AC mains. The AC mains
cable size, especially the neutral, was upgraded several wire sizes.
A kelvar fiber insulated "V belt" has to be used because standard
rubber was too conductive. And the who rig has a special rail around
it to keep people from touching the pulley.

That area was off limits before and it is doubly so now. Everyone who
enters must be on a approved list, log in and out, have training and
no one can go their alone. I wonder if the energy saving are worth
the extra heartaches.

That's a very interesting problem. This quote from the link you posted
sums it up "A normal ac power supply is symmetrical, so that its
three-phase vectors sum to zero. But variable frequency drives turn that
into dc current, and then chop it into power at rates to 20 kHz. At
those high frequencies, constant, perfect phase balance is impossible ‹
and the phase vectors sum to a nonzero voltage."

There still could be an solution in the controller that could balance
the fields and eliminate the shaft currents but you might end up losing
some of the efficiency.

--
Telamon
Ventura, California

That's a very interesting problem. This quote from the link you posted
sums it up "A normal ac power supply is symmetrical, so that its
three-phase vectors sum to zero. But variable frequency drives turn that
into dc current, and then chop it into power at rates to 20 kHz. At
those high frequencies, constant, perfect phase balance is impossible ‹
and the phase vectors sum to a nonzero voltage."

There still could be an solution in the controller that could balance
the fields and eliminate the shaft currents but you might end up losing
some of the efficiency.

There are always very slight differences in each phase of a three
phase winding, and the currents are always slightly different, even if
the supply is symmetrical. One of the tests for winding integrity for
new and in service motors is to place different frequency voltages on
the three phases and compare the current waveforms. They will be
slightly different, but the differences can be indications of where
problems are.

The circulating currents caused by the differences have only been an
issue in the past with larger (say over 300-500 HP) motors. Now, with
these nasty waveforms, the problem shows up in much lower HP.

This is only one of the motor problems with these drives. I'm sure
manufacturers have changed and are continuing to change their designs
to handle the added voltage stresses and heating problems caused by
these drives as well.

Similar "growing problems" occurred in the 60's-80's when industry
changed from DC drives that used DC generators to solid state DC
drives.

Bob

On Dec 4, 6:49 am, Bob wrote:
That's a very interesting problem. This quote from the link you posted
sums it up "A normal ac power supply is symmetrical, so that its
three-phase vectors sum to zero. But variable frequency drives turn that
into dc current, and then chop it into power at rates to 20 kHz. At
those high frequencies, constant, perfect phase balance is impossible ‹
and the phase vectors sum to a nonzero voltage."

There still could be an solution in the controller that could balance
the fields and eliminate the shaft currents but you might end up losing
some of the efficiency.

There are always very slight differences in each phase of a three
phase winding, and the currents are always slightly different, even if
the supply is symmetrical. One of the tests for winding integrity for
new and in service motors is to place different frequency voltages on
the three phases and compare the current waveforms. They will be
slightly different, but the differences can be indications of where
problems are.

The circulating currents caused by the differences have only been an
issue in the past with larger (say over 300-500 HP) motors. Now, with
these nasty waveforms, the problem shows up in much lower HP.

This is only one of the motor problems with these drives. I'm sure
manufacturers have changed and are continuing to change their designs
to handle the added voltage stresses and heating problems caused by
these drives as well.

Similar "growing problems" occurred in the 60's-80's when industry
changed from DC drives that used DC generators to solid state DC
drives.

Bob

Another issue, according to a retired commercial electrician friend,
is the
newer high efficiency motors run from slightly hotter to much hotter.
The
weigh from ~10% to ~30% less. I suspect these motors will not last
nearly
as long as the older ones, and when you add a variable speed drive I
would
guess the service live will be much shorter.

I know that transformers from the 50's and 60's are heavier and run
much
cooler then most "modern" transformers.

I have a 1940 vintage 3 phase 30HP motor that when spun by a "motive
source", think lawn tractor, makes a nice genset. Very clean AC
waveform.
I can pull about 2KW from each phase. A similar modern motor produces
a very nasty pseudo/quasi sine wave and will generate a lot less
power.
Even most EEs don't understand that the common AC motor will make a
very useful genset. You can't draw as much current as the motor would
draw, but the simplicity is hard to beat.
Here is one way to do it.
http://www.qsl.net/ns8o/Induction_Generator.html

Terry