Using a Power Quality Analyzer to rule out "dirty power"

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GoldDigger said:
Regardless of the nature of the pump mechanism, any motor with a rotating component will have more angular momentum while spinning that while stationary. That means that a torque must be applied to the entire pump/motor assembly to get the rotor spinning. \
The only exception would be a motor assembly with two counter rotating rotors or with a reversing gear between the motor rotor and an equally massive pump rotor.
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Angular momentum can be put to a user's advantage with a sizable flywheel to counteract inertia. This is not readily available to one's advantage especially in a scroll pump.

Not only that the pump could not develop usable momentum for such small disk in the pump/motor assembly, it is also subjected to a relentless counter force caused by back pressure. . . you stop the motor it will come to dead stop—no coasting.
Although momentum is the product of mass multiplied by velocity, this Newtonian Law hardly applies in scroll pump because of the reason above.

P=MV

Where:
P=Momentum
M=Mass
V= Velocity


This law is very useful in some applications.
Let's take the oilfield pump. It does have its flywheel, counter balance and the pitman arm.

All of the above combined-- along with gravity can really be efficient and energy saving . . . that guy Isaac is pretty smart:)

With the correct rotation of the prime mover, the position of the pump piston. . . and while it is on its upward stroke (the horse head), this position is where the most work being done by the motor.

The pitman arm where the counterweight is mounted operates the walking beam so that it is on its way down using gravity to help bring the oil up.
Works like a titter-tatter.

Reversing the rotation of the prime mover would cause an energy saver to become an energy hog contraption.
 
markebenson said:
People can debate all day. If they think thats the problem just use a recent model oscilliscope and provide the facts.
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This is an irascible comment.

OP is soliciting ideas that would hopefully help with his dilemma. Not an specific idea that he can put into action. You as member is free to contribute what you have in mind. I think that each post has its own merit.
Don't assume that your idea is the one that would “save the world”.

Look at his conclusion:

“What are you thoughts”

Interestingly enough, what would you be looking at the oscilloscope if it were a slowly developing mechanical failure.
 
A couple of things-
The 'kick' of motor only helps determine rotation if that's marked on the case; I'd be surprised of it was (on a sealed compressor).

We only have the HVAC company's supposition that the compressors failed from reverse rotation. We don't know if they're actually rotation-sensitive, would have to ask the manufacturer.

It's possible that they all came from a bad factory lot (is the mfg involved?).

Anyway, for PQ, a Fluke 41 analyzer or even a carefully-connected 'scope will tell you a lot about the PQ now, but not about what it was when the compressors failed; unless they're still failing, that is.
 
11bgrunt said:
The HVAC thinks EC closed main and sent power to roof unit disconnects that were closed before HVAC startup checks.
The 13 compressors have failed and 13 compressors were replaced.
Voltage balance is very good.
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Given that statement you are now convinced that the failure was not caused by dirty power.

You can still hook up the oscilloscope and keep us posted if your power still need scrubbing.
That will allow those who stand by "hook up oscilloscope and search for dirty power" a good night sleep.
 
myspark said:
You can still hook up the oscilloscope and keep us posted if your power still need scrubbing.
That will allow those who stand by "hook up oscilloscope and search for dirty power" a good night sleep.
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Nobody has suggested "searching" for dirty power. It was voiced as a possibility. A simple observation with a scope would put that to bed at a stroke.
Why do you have a problem with that?
 
Besoeker said:
Nobody has suggested "searching" for dirty power. It was voiced as a possibility. A simple observation with a scope would put that to bed at a stroke.
Why do you have a problem with that?
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Why would that be a problem for me?
You are simply supporting my statement when I suggested to hook up the scope. And all others' thoughts are distinct possibilities.

HVAC replacement have just been installed and the jury still out whether the 13 motors that failed were a bad lot.

Why is that eating your guts?
 
Most scrolls over a certain size have phase monitors with lock out circuits. I'm a little surprised at what I'm hearing here.

Wrong rotation will result in suction and discharge pressures being close to equal. Amp draw and cooling will be nill. There will be inadequate compressor lubrication.

The difference is great enough that even the most basic of checks would uncover the condition. Not like they have an arrow on them and something one can compare it with. Nor can one say A, B, C clockwise rotation is good to go. Any decent HVAC guy knows it has to be verified. Gross negligence IMHO.

I never buy the "power quality" thing when only one piece/type of equipment in entire complex has a problem.
 
Besoeker said:
Nobody has suggested "searching" for dirty power. It was voiced as a possibility. A simple observation with a scope would put that to bed at a stroke.
Why do you have a problem with that?
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My analyzer has a scope. I get more information than needed to conclude that the compressor motor failures are not power related.
The original question is about measuring current on one wire, multiply by the number of wires in the run and agree that is an approximate total similar if all conductors could be measured at one time with a Flex CT.
All the HVAC guys I polled said a scroll will not pump when rotating backwards, will not produce cold air in the building and will overheat because no refrigerant is being pumped. They say it should have tripped out on thermal before the motor died.
I said "You are an air guy, I am a power guy." I am sure someone will have an answer eventually. Too much money involved.
 
myspark said:
This is an irascible comment.

OP is soliciting ideas that would hopefully help with his dilemma. Not an specific idea that he can put into action. You as member is free to contribute what you have in mind. I think that each post has its own merit.
Don't assume that your idea is the one that would “save the world”.

Look at his conclusion:

“What are you thoughts”

Interestingly enough, what would you be looking at the oscilloscope if it were a slowly developing mechanical failure.
Click to expand...

My suggestion was to eliminate the possibility of faulty power.
 
Considerations

Considerations

myspark said:
Scroll compressors can be run in either direction. It is inconceivable to have these things running in reverse and subsequently destroy the motors as others had theorized.

Perhaps the HVAC guy needs a brush up on scroll compressors when he said it was running in reverse. Not only that it's impossible to check rotation of a hermetic AC motor, the two spiral scroll mechanisms don't rotate.

The movable half of the two spiral compressor element wobbles, that generate the compressing action caused by the eccentic cam that is coupled to the motor shaft.

All of these things are enveloped in one " seamless" casing and welded throughout--no serviceable part, just the refrigerant ports ( low and hi pressure) and the motor picker head.

If these are capacitor- run motors, using the wrong capacitance value would cause the motor to run hot and noisy-it may also vibrate.
.
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Compressors Typically fail one of 3 ways:
Locked Rotor
Grounded
Weak or No Pumping efficiency

While the percentage may be small, the HVACR Techs who have worked across the Commercial to Industrial range of systems for more than 20 years successfully and risen to Master Levels with that trade are VERY savvy with Electricity as it concerns not only HVAC, but beyond. They full well know their limits and know when to call for expert assistance regarding matters that are not the " every day."
Scroll compressors are Return gas cooled. While they will run in reverse, they will definitely overheat quickly and will then cycle the internal overload protection device indefinitely until they either die or the fault is corrected. The service life of said units is damaged every time the compressor motor is cycled in internal.
Scroll comprssors give a definite incorrect and loud sound when run in reverse, and also they will not COOL in reverse rotation.
They will give a bad harmonic vibration that is not seen in forward rotation. ITS LOUD.
If the space is unoccupied when the supposed damage is incurred this is double trouble.
Modern HVAC units are SUPPOSED to have all 3 phase motor loads phased the same from the factory, so it is possible to have phase reversal on a property that affects RTU systems that is not " caught " by the HVACR Foreman supervising the install if the line voltage is reversed for any reason after it was KNOWN to be correct.

I have been on a jobsite that had all reciprocating units and one newer Scroll RTU that was running backwards when I hit the roof.
Of course everyone involved was claiming negative knowledge.

We have been progressively going deeper into an age when these types of systems are Engineered right on the wire. In former times they were much more rugged.
This is because everything has been monetized and also weaponized and the society is based on debt which can only lead to a very bad situation regarding the future.
Everything has become volume driven and there is not much incentive for newer Techs in the light commercial sector to be want to be the best or even be motivated to be really good at what they do. The people who really have the edge are self motivated and self actualized types, and gauranteed they are not electrical slouches.
They also will not deliver volume over quality of workmanship.
Nothing will destroy a marriage quicker than being an HVACR Tech.
There are lot of new generation systems at large that have design flaws, so among other investigations I would look into the units in question and see if anyone else is having problems.
The exact failure of the compressors needs to be known, and it needs to be determined if the refrigerant was burned in any of those cases.
A lot of the better Engineered gear for the Industrial level will come with Phase protection installed from the factory.
ICM makes a decent small, line side phase monitor for cheap. They have solved all kinds of problems with the " definite ' dirty power we have in this locality which includes regular dropping of one phase and brown outs etc.
For sure the line disconnects to the RTUs should not have been closed before startup for any reason.
That should have been a glaring mistake to any savvy HVAC guy walking that roof before the units were brought on line.
The next thing that needs to be watched like a hawk is any subsequent failures on the replacements that were installed.
With more details and photographs I can offer more insights possibly.
 
StarCat, nice post.

Compressor’s need to be sent back and failure mode determined. If it is electrical burn out then acid in the system will ruin replacement compressor’s. Perhaps even coils over time.

To fix it right requires a lot of labor and some knowledge. Typically you add a special suction line filter with removable core. You pull oil samples and check for acid. It isn’t unusual to change filter core and compressor oil half a dozen times over a few week period. On most scrolls, an oil change means un-brazing the compressor and turning it upside down to drain the oil. Very time consuming.

Sadly many HVAC guys will throw in a new compressor, maybe acid neutralizer if you are lucky, and figure it will last long enough for them to be long gone. Building owner will wonder why he has to replace compressor every couple/few years.

Stuff happens and it might not be anyone’s fault. Still someone should step up and let building owner know what needs to be done to fix this mess the right way. If it is what I think it is it’s going to be costly, and painful, as all units are affected even if they haven’t failed yet.
 
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