208 3 phase 1.5 h.p. motor rotational change 3

[sambullion]

Ok guys the equipment is a 155 ton split chiller.
as described 3 phase 208 voltage 1.5 H.P. motor ,
some of the fans will change rotation or rather run backwards at start up and then the next startup will run in the proper rotation,

Notes current checks are ok so far. motor ohms out ok .
voltsge checks good never had this type of problem, am i lossing my mind are is it so simple i cant see the forest for the trees.

Thanks Sambullion

 

[waross]

Look for a single phase condition. Small fans will sometimes be turned by air currents. The direction at start then depends on the wind direction. I would expect that there is little motor protection on these fans.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[edison123]

waross

air currents vs electric currents ?

Seriously though, wouldn't single phasing act as a brake on an idle 3 phase motor and prevent the driven fan from spinning at all due to air currents ?

 

[waross]

Hi, edison.
I have seen this happen. There are always exceptions but although single phasing developes quite a bit of force, the force is at right angles to the direction needed to produce torque. Because of the lagging phase angle of the rotor current producing the force, any rotation will allow the force developed by the single phase condition to develop torque. It is common to see cooling fans on transformers turning gently in the breeze. If single phase power is applied, the fans will accelerate in the same direction that they were being turned by the breeze.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[sambullion]

Yes but i havent found any single phase state... all fuses are good... voltage is good...motors ohm. out good , as well as amp draw, motors are now 12 years old and yes these fans come on in stages due to a oil pressure or also know as head pressure, and the fans will run backwards some times, but not everytime.

I do suspect that the fans counter rotation prior to, being energised is casuing a problem , This circut has a total of 5 fans, the fans spin in counter rotation due to the first stage of the circut being placed in operation...

Thhanks again , Sambullion

 

[roydm]

Sounds very strange indeed. If the fans are 3 phase and all phases present I don't see how they can run backwards. Is it possible you have lost a phase and one of the larger motors is running backwards generating the 3rd phase in the wrong rotation. When you see one running backwards are the others also going backwards?
If you stop the fan and let it re-start does it still go backwards.
You need a phase rotation indicator to help you troubleshoot this I think.
Good Luck, keep us posted.
Roy

 

[itsmoked]

If all 3 phases are really there I can't see any theoretical possibility.

I've even built 6 channel head pressure fan controllers from scratch to do exactly this and never seen that occur with 3 phase fans.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Skogsgurra]

Absolutely. No way it can do that if all phases are there. Check every phase on every motor with a clamp-on ammeter. If currents are there and have reasonable values, it shouldn't happen.


Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[sambullion]

To all of you who have responded to my POST


THANK YOU ,

makes me wish i would have brought home the schematic where i could have been more concise in my description of the circut, and the sequence of operation,.

Though i am convinced i simply have a bad motor i suppose the thing that baffle me most is the interment behaviour,

I suspect i will find a fuse blown, when i go back to it on Monday...

But i will post again when i do find the Gremlin that has caused me to scratch my old bald head....

Best Regards
Sambullion

 

[itsmoked]

That will likely be the case. Only a fan would let a motor get away with single phasing and not utterly toast, rapidly.

Another example of why fuses are lousy for quality motor protection.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Marke]

One of the things to be wary of, is that if you make the measurements when the fans are running, you can get fooled into thinking that the three phases are there when only tow are actually there. If you loose a phase and a motor is operating, it will regenerate that missing phase and with a volt meter, it will appear that all is well. You should find a major difference in current however, so I recommend doing both voltage and current checks.

Best regards,

Mark Empson
L M Photonics Ltd

 

[waross]

We had some issues a long time ago with blast freezer fans when a fan tripped on overload. The static pressure from the others would backspin the unpowered fan. If a reset was preformed the overload heater elements could be seen heating up red hot before they radiated enough heat to the bimetal strips to trip out. Sometimes an overload heater would fail open and the motor would run backwards on single phase the next time a reset was preformed. Occasionally a contact in the starter would burn off.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[DickDV]

When checking for all three phases on a motor, it is important to check for all three phase CURRENTS since it is possible to have an open phase inside the motor. In that case, you could have all three phase voltages on the motor but it would still be single-phasing due to no current flowing on one of the phases.

 

[sambullion]

Hello Gents,
Thought you might like to know wher i got to today ,
Well lets start this way i did not win....
But for those of you who would like to know a tad bit more.

The fuse was blowed as expected so i ordered me a mtr. they are rather proud of them.. So i install a new fuse and begin my checks , I must degress a bit this circut for whatever reason which consist of 2 fan mtr. sharing the same contactor,,, so which mtr. is failing shouldnt be a problem ,

Pull all leads from contactor for both mtrs.
All legs ohm out ok to grd. all legs give consistent ohm values and are similar very close , using a digital fluke meter.,
What to do right , Hook every thing back up and lets get some current readings
all legs within 1/10 of a amp of each other. Remember i got got a bunch off these fans and gee you would think this would be straight forward. NOPE NOT TODAY...

So while i have my men cleaning the coils and regular PM,
And i still know i got a bad mtr. just dont know which one,
So i check the circut wiring look at every inch looks good,
Physcialy look at mtr terminations still ok
OHm out at the terminial at the mtr again ok.


Well the motor want be here till tuesday ,so what do i do

I move the leads for one of the mtrs to another contactor and hopefully i will have a blown fuse in the morning..

Yep i turned the chiller back on both circuts and well if it holds overnight them boys will have icicles hanging off of ther toes....

 

[waross]

When one fuse blows it is good practice to replace all three. The surge that took out one fuse may have compromised one or both of the other fuses. Check the fuse holder of the blown fuse for signs of heating or looseness.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[sambullion]

I will change out those fuses Bill ,and thanks..
I know its a waste of money but i am going to send this mtr to a rewind shop , I JUST GOT TO KNOW what in the heck going on in i've seen all kinds of things that have baffled me over the years but this takes the cake,

And fellers thank you one and all

Best Regards
Greg

 

[LionelHutz]

It's very possible that the fuse just blew, especially if these fans freewheel backwards when they are not running. The start-up current is much higher when trying to start a motor that is turning backwards and this current might not have been accounted for in selecting the fuse.

 

[Marke]

Hello LionelHutz

The start-up current is much higher when trying to start a motor that is turning backwards

I can't say that I have experienced this. From my experience, in most cases with low slip induction motors, the start current is the same, but because the starting slip is higher, the start time is longer and this will operate protection etc.

Best regards,

Mark Empson
L M Photonics Ltd

 

[LionelHutz]

You're right Mark, the current stays high much longer. Still, you'll likely need a bigger fuse starting a motor that is freewheeling backwards compared to starting a motor that is stopped.