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Motor Upgrade

Motor Upgrade

Motor Upgrade

(OP)

I have a 480V 200hp motor used on a screw pump application that I am looking to upgrade.  This motor is currenlty being overloaded by the process and management wants to upgrade it.  

This particular motor is constantly overloaded and as a result we keep tripping on overload.  Production folks simply go and reset the overloads (against my reccomendation) and keep restarting the motor after trips.  We have smoked this motor three times in the last month.  We keep sending it out for repair put it back in service and the the same thing happens.  Mechanics say that they have gone through all mechanical part of the application and there is nothing wrong, so it simply leds to the process loads.

We have taken several amp readings on the motor and see that it is pulling about 300A when the rated FLA is only 226A.  

Management has asked me how we can get about 10% more capacity out of this motor.  They have asked me weather we had to buy a larger motor (next standard size is 250hp) or if we could have this one rewound to a larger hp.  Is it possible to have this motor rewound to give a larger hp maybe an additional 10% or so? Motor data is:

3-Phase
6 Poles
1190 rpm
60hz
FLA = 226A
S.F. =1.15
Alt S.F. = 1.0
Ambient = 40deg C
PF = 86.5
NEMA B

The one constraint we have is that if we upgrade to a 250hp motor then we will need to upgrade the starter size to a size 6 for the size 5 that we have is only rated up to 200hp.  I'm assuming that this would be the same case even if we rewound the motor and upgraded the hp some?

I'm going to put a power logger on this motor.  Other than power kW is there anything in particular I can look for as a red flag to say that there is a problem other than the process overload.  Could power factor be a problem?  Starting current?

RE: Motor Upgrade

I doubt if you can upgrade this motor to suit your load, which seems to require 270 hp. Buying a new motor to suit the load is more economical than rewinding/upgrading the old motor.

RE: Motor Upgrade

(OP)

Thanks Edison, I'm not seeing how you arrived at the 270hp though.  I'm guessing you calculated this based of the 300A current measurement that I provided you with?

RE: Motor Upgrade

Yes. 226 A = 200 HP. 300 A = 265 HP.

RE: Motor Upgrade

The 300amp loading indicates more than 250hp and certainly more than 10% upgrade.

To cover the load represented by 300amps you will need a 300hp motor.  Keep in mind that the motor frame size is going to change and the shaft elevation will be greater.  That will require that the motor mounting be lowered or the pump mounting be raised if this is a coupled power train.  Not so much an issue if the power train is belted.

If belted, you will need to look at the belting for 300hp rather than 200hp.

RE: Motor Upgrade

You might be able to cheat a little bit depending on what your motor terminal voltage is.  If it's a little low (450-460V), and if you have taps available on the upstream distribution, you can adjust the taps to raise motor voltage (480-500).  You may still pursue this option as an interim solution until a longer term approach could be implemented if applicable.

RE: Motor Upgrade

Sorry, I neglected to explain my response.

The motor's current doesn't really tell the whole story in the context you posted because you don't mention the motor's actual operating voltage, or the HP (KW) it's operating at.  If the operating voltage is low, then the motor is pulling extra current drive the load.  Raise the voltage, and current will go down.  How much depends on where it is operating.  If it is below nameplate voltage, then you can feasibly increase to around 485V and have operating current in the range of its service factor rating.  Hope that helps.

RE: Motor Upgrade

Ultimately the rating is determined by the motor's ability to reject heat to the environment. If you have an environment cooler than the temperature the motor is rated at then you will be able to squeeze a little more than nameplate rating out of it. I guess this is probably the reason why you have been able to overload your motor and get away with it.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: Motor Upgrade

Don't know this for sure, but can a 200HP motor be rebuilt to have a 1.25 service factor without changing the frame size? That's about what you need here.

I know the use of SF as a continuous HP increase is controversial, but is the overloading situation continuous or occasional?


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln  
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RE: Motor Upgrade

Can you reduce the load? I know that the first answer is going to be no way!
Then after adding up the price of a 300 HP motor, a larger starter, possibly new cabling, new mounts to accommodate the higher shaft, and labor to put it all together, ask again if the load may be reduced.
On the other hand, how many rewinds will it take to equal the cost of a 300 Hp installation.
Of course if it's belted, a sheave change will be quick and cheap.

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

RE: Motor Upgrade

Could a multi-HP blower be put on the motor to force down the temperature?

Can an additional motor (75hp) be coupled onto the drive system and actually share the load correctly?
If it could a much less expensive addition of switch gear could be added.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Motor Upgrade

I would check the torque speed curves on both motors before coupling them. A bad mismatch in curves may result in the smaller motor hogging the load and overloading badly at slight overloads or not picking up its share of overloads. If the curves are matched, the motors will probably share the load correctly. Beware if the smaller motor has a slightly different rated speed than the larger motor.

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

RE: Motor Upgrade


    If the motor is so acted from the beginning when it is installed, then you definitely need to get a new one with more power.
    But if it is not the case, then cause is in motor. What is the state of the motor, it can say only in rewind shop. You need to find the most important examination-detail:
" no load" current with run at full voltage.
In this case the current should not be greater than 70 -80A , if motor is intended for S1
(S1 - continuous duty: the motor works at a constant  load for enough time to reach temperature equilibrium).
If " no load"current is significantly higher, can be two causes:
-        inadequate winding-details or
-    core-iron insulation damage, due to frequent burns of motor and (maybe) inappropriate heating the motor before removing the old windings (see attach.)
Power of the motor you can not increase just like that. This can be done only in case the motor works, for example, in S2 – duty (S2 - short-time duty: the motor works at a constant load, but not long enough to reach temperature equilibrium, and the rest periods are long enough for the motor to reach ambient temperature.)
Power of the new motor you can not specify only from the current that old motor now has, because you dont know „no load" current. What to do if the „no load" current  is 150 or 200 A? The only correct way is to calculate the necessary power, torque etc, by professional or the manufacturer.
   Zlatkodo

RE: Motor Upgrade

Increasing the motor size may only be pushing the problem elsewhere.  If the blower cannot reliably handle 300 hp, then increasing the motor HP might just start causing failures of the blower instead of the motor.  Before changing motors, I would check and see what the blower was designed for to see if the shafts, bearings, etc can handle the increased torque.

RE: Motor Upgrade

Excellent point ischgl99!  I've seen that phenomena carried out up thru 5 steps.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Motor Upgrade

Why would a higher rated motor damage the blower, pump or whatever is the load ?

RE: Motor Upgrade

because a 300 hp motor produces 50% more torque then the 200 hp motor running at the same speed.  If the shaft was designed for 200 hp, adding that much more torque could reduce the safety factor enough that the shaft fails prematurely.  

The bearings are also selected for a given speed and load.  Since the torque has increased, the load on the bearings could also increase resulting in reduced life of the bearings.  Increasing the load 50% on the bearings results in a reduction in life of about 70%.  Another issue is the lubricant was selected for a certain loading on the bearings, a higher load may require a different lubricant.

RE: Motor Upgrade

(OP)

Just trying to think outside the box, is there anything that can be done with a VFD to provide the required torque but limit the current to the motor thus preventing it from overheating?  Can you possibly use a VFD to drive a motor over base speed and provide more hp for a given touque?  Can any kind of torque control be used?

I should have all the power readings tomorrow from a 3-day data log to look at.

RE: Motor Upgrade

Yes but then you will be increasing the actual load at possibly a faster rate.  You would have to increase the voltage over your base and reduce the gearing.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Motor Upgrade

ischgl

A 300 HP motor is capable of producing 50% more torque only if the load requires it. It won't dump the torque on the load just because it can. The motor is reactive component not a proactive one.

rockman

Why would you want to run your pump above the base speed, which would not only increase the load on the motor but affect the pump flow as well ? The bottom-line here is that if a load requires a certain torque and power at a given speed, your motor must match it. In your case, the motor getting burnt thrice within a short period indicates the existing motor is undersized.

A 300 HP motor doesn't necessarily mean an increase of shaft center height of the motor frame. It all depends on what is the frame size of the existing motor. Normally motor OEM's use the a variation of basically the same frame (with same shaft center height and across bolt center holes) for different outputs by varying the length i.e. along the axis. This is done so that the same diametered core can be used to produce a wide range of motors since core punching tools are expensive.

RE: Motor Upgrade

(OP)

I just retrieved the information from a 3-day power log on this motor.

The voltage which was logged stayed at about 265V L-G.  This is about 4% lower than the nominal 277L-G voltage.  Does this 4% seem o.k.  I dont see from the results that increasing this voltage would give enough headroom to reduce the current on the motor.

I looked at all three line currents and they average about a 3-4% current imbalance between phases.  I dont think this is much cause for alarm.

Attached you will see the power log for this motor.  The first sheet shows the motor kW on the bottom and the PF at the top.  PF seems to stay above .8 which seems o.k.  The second plot shows the individual phase kW plots with the total kW plot at the end.

As you can see from the plot the motor kW is well over 150kW which corrosponds to a 200hp motor.  For the first 18hrs the motor seems to average about 180kW which corrosponds to about 241hp.  There is also a timeframe of about 9hrs where the motor appears to average about 200kw which is equivelent to about 268hp.

The highest peak that was recorded was 226kw or about 302hp. Based off all of this information I am thinking that we need somewhere between a 250hp to 300hp for this application.

We never had any problems with this 200hp motor in the past, however due to more efficient productin increases we are now putting more of a load on this pump and thus obviously overloading it.  

RE: Motor Upgrade

Yup. You need a higher rated motor. May be you can put some caps while you are at it to improve pf closer to 0.95.

You also need to look at switchgear, protection, CT's, cables etc.

RE: Motor Upgrade

edison, I understand that completely, and if you read the first post again, you will see that the motor is drawing more amps then the 200 hp motor is designed for indicating the plant is already overloading the pump and it could be operating at or near 300 hp if the plant installed that motor.  My experience is if there is available HP, someone will try to use it all.

My point was and still is, don't install a larger motor if the driven equipment is not designed to handle that load, the motor might survive, but the pump most likely will not.  I work in the reliability field and see this all the time, someone who does not understand the whole picture trys to "fix" the problem and creates a new one.    

RE: Motor Upgrade

No, the motor wouldn't ... survive. Often, the motor is the weakest link due to that damn insulation.

RE: Motor Upgrade

I suppose that you have checked and determined that the pump is capable of the increased through-put.
I would consider a 300 Hp motor with a 1.15 service factor. I would also evaluate the pump capacity and consider a 350 HP motor if there is any possibility that the load may increase in the future. If you have any problems with a 300 HP motor, the extra cost of a 350 may be small compared to possible plant down time.
But, check the pump. If the pump is maxed out, consider either a larger pump and motor or a second pump, if that is feasible in your layout.

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

RE: Motor Upgrade

(OP)

O.k. so it sounds as if I would need at least a 300hp motor (Assuming pump is capable of handeling)

As I stated earlier this motor is fed from a 480V size 5 starter.  My question now becomes if I upgrade this motor weather or not to leave it at 480V or increase the motor to a 4.16kV.  All other motors in the plant are 480V for 200hp and below and all motor above 200hp seem to be at 4.16kV.  This may be because above a 200hp requires a size 6 starter.

If I install a new motor at 300hp at 480V then I have to install a new size 6 motor starter in the MCC which we do not use elsewhere in the plant.  I would also have to run a new branch circuit to the motor due to the fact the the existing one is only 350MCM and would not be large enough for a 300hp motor.  I would probably need 750MCM or pull a parallel pair of 350's.

In the same electrical room there is a spare 5kV starter that is no longer in use.  If I were able to utilize this starter (verifying CT's etc..) I would probably only need to pull a #2 branch circuit out to the motor which would be much cheaper than the 480V size cable.

What do you guys think about 480V vs 4.16kV?  Any other things to consider?

RE: Motor Upgrade

There are a lot of safety and training issues to be addressed before installing the first MV motor in the plant. If you already have MV motors installed in the plant, those issues will have been dealt with, (hopefully).

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

RE: Motor Upgrade

(OP)
Waross

We have several other MV motors in the plant, so this would not be the first.  These training issues have been adressed and are done so on a continuing basis.

RE: Motor Upgrade

The part that seems to be a bit hidden here is that, at the overload conditions on the 200hp motor, there already is 300hp being drawn from the electrical system and poured into the pump.  It's really too late to ask if the pump can handle it.  It already is!

Asking for 300hp from the electricals involves overloading most of the components obviously so they would have to be changed out to get back inside their design limits.  If MV is an option, I think I would take it.

It's worth observing that a NEMA B motor's nameplate rating is really set by thermal conditions.  At peak overload, that same 200hp motor is somewhere just over 400hp.  If that motor was located in a deep-freeze it probably could go on making 400hp all day long but certainly not at its rated ambient temp of 40 degrees C.

My point is that today's NEMA motors are amazing machines, capable of huge overloads and lots of abuse.

RE: Motor Upgrade

Rockman

What about the pump, has someone adjusted the butterfly valve on pump head to tweak more vacuum out of the pump causing it to overload?

Are there leaks in the system, requiring the pump to move more atmosphere than necessary, or are too many machines down on set up leaking vacuum?

We had the same problem with our pump and after vibration analysis, several tune ups, KW logs, and system audit basically were going to need an additional pump in the system.

In my experience if the system requires a lot of flow, the blower type pumps work better, but have a history of double the maintenance such as bearing replacement. Screw pumps are good in closed systems.

I'm just a Tech and these things were not mentioned, so I am curious about your findings on the pump side of the problem.

  

RE: Motor Upgrade

(OP)

I made a mistake and had my power logger set up for a 3-phase wye configuration when the motor is wired in a Delta configuration.  

I'm not sure exactly what this would do to my kW results but I'm sure it would skew them.  I'm going to set up the meter for a three element delta configuration and take another set of measurements.  

If my new measurments are fairly close to the ones posted above (not sure how far off they will be) then I think i am more inclinded to lean towards a MV setup.

RE: Motor Upgrade

Quote (DickDV):


The part that seems to be a bit hidden here is that, at the overload conditions on the 200hp motor, there already is 300hp being drawn from the electrical system and poured into the pump.  It's really too late to ask if the pump can handle it.  It already is!

Bingo !
 

RE: Motor Upgrade

(OP)

I went back and set the meter up for the correct configuratin.  I did not see much of a change (only a few kw) between the wye and delta configuratin methods for measuremnt.  I'm thinking that my previous measurments will then be o.k. to use.


Will the actual kW calculated to the input of the motor be greater than that calcuated on the output of the motor.  I belive it will be because of motor efficiency.

In other words if I calculate the ouput kW by using motor hp * .746 this will differ from a kw calculation using motor V * FLA * 1.73 * PF.  This difference will be the efficieny of the motor?

I'm assuming that the cauculation on the elctrical motor input will be larger that that used for the motor output.  However I guess motor hp * .746 is a good aproximation to use when doing comparisons as I have been doing in this thread?

RE: Motor Upgrade

Supply to the motor does not care whether the motor is wye or delta connected. Power input to the motor is Sqrt (3) x Line to Line Voltage x Line Current x pf x Efficiency.

So I do not undertsand what you mean by setting your power analyzer to correct configuration.

RE: Motor Upgrade

(OP)

Edison

You are correct.  I was just getting confused with some information that someone had given me in regards to my data logger.  Power is power so the measurements that I have are valid.

Going back to the 480V vs. 4.16kV discussion, I see that the maximum size motor a size 5 starter can handle is a 200hp.  If I go to a 250hp motor can I push the limitations of a size 5 starter or must I go to a size 6?

RE: Motor Upgrade

No, go to a size 6.
I saw a 400 HP motor running on a starter rated for 250 HP. I made a lot of money changing out a 400 HP motor with a bent shaft. The contactor flashed phase to phase trying to open under full load current. Faced with a phase to phase short on the supply the motor became an induction generator with a short on the terminals. The motor slowed down quicker than the fan and the coupling exploded. That's probably when the motor shaft bent. There are reasons for contactor ratings.

300 HP, 4160V is better.

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

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