75HP Motor Problem

[behradk]

Hi Everyone,
I have a problem with a 75 HP motor and I hope someone could help me with that. We have installed a 75HP Gould pump in one of our car wash facilities. The model# is 66SV-6/2. Our voltage is 208V and the wiring configuration is DELTA. Our operating pressure is 275 PSI which is a normal operating pressure. The FLA for a 75 HP motor at 208V is 211A. We did measurements at various pressure and got the following results:

Line----Amperage@ No Load--------Amperage@10 psi-----------Amperage@55 psi-------------Amperage@150 psi---------------Amperage@200 psi-----------Amperage@275 psi
L1-------------40.5---------------------------99.8---------------------------127-------------------------------205--------------------------------283----------------------------314
L2--------------43----------------------------102.2---------------------------129-------------------------------205-------------------------------288----------------------------314
L3-------------41.5---------------------------99.5---------------------------127-------------------------------205--------------------------------287----------------------------314

The Line to Line voltage of the terminals @ 275 PSI is: 201V , 200V, 200V
As you see, the amperage is way too high at 275 PSI and it trips the overload every time. The manufacturer has mentioned that the Full Load Amps should be 185-Amps at 208-Volt for this Motor & at No Load, Amps should be around 50-Amps. Does anyone knows why we are getting such a high amperage? Please let me know if you need any more information and I will supply that.

Thank you all in advance.

 

[DRWeig]

You're pumping too much water?

Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

 

[behradk]

YEs, I'm pumping about 338 GPM.

 

[itsmoked]

Classic 208V that isn't.. I would consider putting boost transformers in to get it back up to 208 or more if that pump runs for more than a few minutes at a time.

A pump is a mass-flow device. That means the more material that runs thru it the more work it does. If you are pumping too much volume you are overloading the motor. You need to put in restrictions be they nozzles, smaller nozzles, orifice plates, or a flow limiting valve.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[behradk]

On the discharge side of the pump I have many nozzles that they are supposed to spray on the car. The current operating point is almost in the middle of the pump and I think the motor should be able to handle this load.... If I close the downstream valve it will increase the pressure after the pump. How does this affect my amperage? Does it reduce my amperage? Besides increasing the voltage, is there any other solution?

 

[itsmoked]

Looking at the curve for your pump it appears your 338gpm and 275psi are right where they should be. This points back at the motor side. I believe you are seeing over current because the motor is undervoltaged.

Has anything changed since the system has been running? Or is this a new installation?

Is the volume you're stating actually a measured value you have?


Keith Cress
kcress -

http://www.flaminsystems.com

 

[behradk]

This is a new installation. The GPM is the calculated GPM. I believe the actual GPM should be almost the same.

 

[itsmoked]

Whoaaaaa wait a minute. I take it all back. Not the motor side. The values you're giving us as your operating point is fine for the '6' version. You actually have the '6/2' version which is less capable. You are using too much volume which IS requiring more hp. At 275PSI you can only have 290GPM NOT 338GPM.
So you need to reduce the flow or reduce the head at which your flow is occurring at down to 250PSI.

T'wer me I would close a valve slowly while watching the ammeter until you hit nameplate. Try it briefly and see how the current responds. Some pumps won't drop current with restricted flow.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[itsmoked]

We cross-posted. Calculated.. Ugh. Too bad as that doesn't help with diagnosis.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[behradk]

You are right. Basically the design pressure is 251 PSI @ 338 GPM. When I move my nozzles (It is a huge Gantry with lots of nozzles), due to movement of they rubber hoses the pressure ramp up to 275 PSI or drops to 251 PSI. Either way, my operating point is moving on the pump curve and I'm not out of the curve. That's why I think the motor itself should be able to handle the load. I have a specific demand (Pressure and flow rate) that I have to meet at the nozzles. Do you think that if I close the discharge valve a little, it helps me to reduce the amperage ?

 

[itsmoked]

Yes! If you have the valve give a try while looking at the pressure and the amperage. That will quickly show if it's going to work. A lot of motor loads are in-constant and allow overloads that are short and sporadic however some loads like yours, air compressors, and refrigeration can be nearly continuous. In these continuous cases slight overloads can make BIG differences in operational reliability. Likewise low voltage can be very problematic in continuous situations. You may need to reduce your pump's load even down from the curve as that low voltage will put your motor at increased amp-draw continually. Again in some cases it wouldn't matter but in continuous application it can and does.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[itsmoked]

Looking at your pressures and currents you listed it really does look like you are FLOWING way too much. Definitely try the valve.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[dpc]

Just out of curiosity, what is the actual nameplate voltage for the motor? There are a lot of "triple rated" motors out there that are listed as 208/230/460. These motors will not perform well when operated at 208 V. It will run, but not at rated efficiency or power factor (or torque).

A motor actually intended to operate on a 208 V system will have a nameplate voltage of 200 V.

 

[waross]

Try plugging off some nozzles.
Throttling a valve will drop the current but it will also drop the pressure at the nozzles.
You may get some increase in performance with a higher voltage but not enough.
By the way, do you have positive pressure on the suction side of the pump?

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

 

[electricpete]

It seems like this is a positive displacement pump, isn't it?
Then it is expected that current goes up as pressure (I assume dp) goes up.

338 psid * 150 gpm = 22 KW fluid power
sqrt(3)*208V&205a = 74 KW electric apparent power
A surprisingly low product of pf* EffMotor* EffPump..most likely EffPump is the problem somehow.

How is the pressure adjusted?
Do you have link to this pump curve?


=====================================
(2B)+(2B)' ?

 

[electricpete]

Do you think that if I close the discharge valve a little, it helps me to reduce the amperage ?

Not if it is positive displacement pump. Unless I am misunderstanding something about the system..

=====================================
(2B)+(2B)' ?

 

[itsmoked]

Pete check the pump out.

It's a 3 stage centrifugal.


Pump PDF

Keith Cress
kcress -

http://www.flaminsystems.com

 

[electricpete]

Thanks Keith. Your link doesn’t seems to work for me.
I did find this with pump curve on 2nd page of pdf (page 41) which sure looks like centrifugal.

http://blumenauerpumps.com/commercialpressure/esv/66eSV.pdf

So, going back to op, pressure is changing and currrent going up - what is being adjusted?


=====================================
(2B)+(2B)' ?

 

[behradk]

@itsmoked: I will definitely try using a globe valve downstream of the pump and see the effect.

@dpc: The name plate just shows 230/460V. I talked to the manufacturer and they said this motor also works with 208V, but it is a very minimum voltage. When we ordered the pump, we indicated that out voltage is 208V. I don't know why they sent us a motor that they know it barely works with 208V.

@waross: Yes, I have a positive pressure on the suction side. This pump is drawing the water from a 4000 GAL tank, so I have enough static head on the suction side.

@electricpete: No, this is a multi-stage centrifugal pump. Here is the link to the curve:

http://blumenauerpumps.com/commercialpressure/esv/66eSV.pdf

you should use curve 6/2. I adjust the pressure by using a globe valve downstream of the pump.

 

[ScottyUK]

ePete,

Here's Keith's link in a form that works:

http://media.wix.com/ugd/391cd0_5b6fb3f23f1d3bead1ea21c08560f67f.pdf