overloaded pump 1

[adviavan]

hello everybody...
I have problem with motor pump in my factory.
I utilized Teco motor 11kW 2 pole 3 phase. this motor overloaded for unknown reason.

this motor is currently replaced because the previous has unstable electrical current. after the replacement, electrical current was good until yesterday, the motor started to overloaded and shut off automatically. and i have no idea what's going on.
FYI, when I try to maximize water flow, electric current is going up to 24.7A and when minimized it's decrease to 22.7A. is it normal?
Another engineer said that it was because of the impeller. but I think it's because of the motor or something related to the motor.

does anyone know how to fix this problem since I am lack of water for production?

Thanks in advance for your help. big appreciation for you..

Sincerely

 

[waross]

FYI, when I try to maximize water flow, electric current is going up to 24.7A and when minimized it's decrease to 22.7A. is it normal?

You can't get something for nothing.
The more liters of water the pump delivers at a given head pressure, the more work the motor has to do.
The more work the motor has to do, the more current the motor draws.

does anyone know how to fix this problem since I am lack of water for production?

Bigger pump.
There may be other issues but based on the information provided, bigger pump.
However, how is the voltage? If the incoming phase voltages are unequal the phase currents will be unequal and the motor may overload on one or two phases.
Has production been changed in any way lately?
For example:
Opening a valve that directs water to a closer storage tank with less pressure drop in the line may overload a pump.
Opening a valve that allows the pump to deliver more volume may cause the pump to overload.

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

 

[flexoprinting]

Likewise with a vacuum pump and atmosphere, there may even be an FAQ (Frequently asked questions) on this subject. It sure comes up often enough.

 

[electricpete]

FYI, when I try to maximize water flow, electric current is going up to 24.7A and when minimized it's decrease to 22.7A. is it normal?

I'm assuming we are talking about fixed speed pump pumping incompressible fluid and the flow is adjusted by changing position of a valve.
It may be normal. We don't have enough information.
#1. What kind of pump. Axial flow pumps will tend to draw more power at low flow than at high flow. Mixed flow pumps may act this way over portions of their range. See faq237-1543
#2. Is the flow that you're observing the pump flow or system flow? These can go in opposite directions if you are throttling a recirculation valve to control system flow.

You can't get something for nothing.
The more liters of water the pump delivers at a given head pressure, the more work the motor has to do.
The more work the motor has to do, the more current the motor draws.

I'd offer a different slant. The above quote carries an assumption of constant pump head pressure. However the pump curve tends to have decreasing head pressure with increasing flow. So as we increase flow by adjusting a throttle valve to move along the pump curve, the fluid power (which is proportional to flow rate times head) might either go up or down. Also variations in pump efficiency can play a role when translating fluid power to shaft power.

The most common pumps are simple single stage radial flow pumps which increase bhp with flow and this is what most people are familiar with. But there are other pumps (mixed and radial flow pumps) that do not act exactly this way.


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

 

[electricpete]

Most likely in this size range it is a simple radial flow centrifugal pump. In that case, my comments are a sidetrack.

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

 

[jraef]

Much more simplified: load = flow in a centrifugal pump. More flow = more load. A very common issue unfortunately, is that someone may have attempted to cut costs by selecting the pump motor based on an exact amount of flow required at the time of purchase. The pump itself was obviously capable of DELIVERING more flow, but the MOTOR selected for that pump was not. So when you discovered that the pump had additional capacity and tried to utilize it, you then also discovered the design flaw; you were not allowed to use it.

So being that your pump is apparently capable of delivering your desired flow, in theory you could just install a larger motor. But be careful, there may be efficiency curves in play here, so doing so may give you more flow, but at the expense of higher energy input per unit of flow to get it. So rather than think of this as a purely electrical problem with the motor, I would get a Mechanical Engineer with hydraulic expertise involved to investigate all of the hydraulic issues first. You don't want to fix one thing and create a new problem.

"Will work for (the memory of) salami"

 

[electricpete]

"more flow = more load" applies to radial flow rotodynamic pumps
It does not necessarily apply to mixed flow or axial flow rotodynamic pumps.

Hopefully it is evident in my FAQ linked above that the phrase "centrifugal pump" can be ambiguous. Specifically the meaning used in pump standards (which includes radial flow, mixed flow and axial flow rotodynamic pumps) is different than many would conclude based solely on the meaning of the individual word "centrifugal" (radial directed). That is why I put quotes around the phrase "centrifugal pump" in the FAQ… to highlight this common and surprising usage of the phrase.

Pretty much all multiple-stage rotodynamic pumps are mixed flow …. and yet 90% of people at my plant (and probably on this forum) walking by such a pump would call them a centrifugal pump without a second thought (unless/until someone started talking about the direction of flow). And P&ID symbols do not distinguish flow direction. The distinction of flow direction is not particularly important to us electrical engineers unless/until we start talking about change in current with flow. Then it becomes important.

So my clarification would be that "more flow = more load". applies to radial flow centrifugal pump.


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

 

[adviavan]

bigger pump can be considered as solution for this problem.

i haev another information, on the pump nameplate, it shown that voltage is 380V and current is 21 A.

i think 21 A is the maximum current that this motor can handle. heat generation may occur when electric current above this level. so i was referring to this current. at minimum flowrate, the lowest possible current is measured at 21.3A. when it comes to high flowrate, electric current going up to 24.7A, that means pump is current overloaded. is it possible to solve the problem if i use bigger motor?

i have electrical safety equipment, i called it "termis", it automatically shut off the motor when current comes and going up to specific value. i have set it to shut off at 25A but at any current, the motor shut off automatically at stable current.

i confuse with this 2 possibility. is "automatic shut off" caused by smaller motor (that means need bigger motor to compensate bigger current) or the motor have thermal sensor (bigger current than the motor can handle) that works as safety instrument before the motor burnt?

thank in advance dude...

 

[Parchie]

Can you give more info on your load side? How much fluid is it pumping compared with your flow requirements? What @jraef said earlier, the more water your motor flows out, the more amps your motor experiences. If you can limit your valve opening (throttle) up to the 21 amps level, then your good. If you can't live with a lower pump output, you really need to replace the motor with a bigger one.

 

[adviavan]

@Parchie it pump the required flow but at higher amp than it should be.
for example,
1 m3/h --> 21.3 A required
4 m3/h --> 22.5 A required
8 m3/h --> 24.4 A required
11m3/h --> 25.1 A required.
i can't limit the valve opening to achieve 21A. the lowest possible amps was 21.3A. it only pump 1m3/h of fluid.

someone said that the problem because of the impeller. he said that the installed impeller was incorrect size, I dont know whether it was oversize or under size. he suggest me to lathe the impeller. is it make-sense argument?

another engineer said to give additional speed variable control to control the amp required. is it make sense? I think this solution cant work well. it does reduce not only the amps but also pressure and flowrate.

 

[waross]

You are correct on both issues.
Lathing the impeller, will reduce the pressure and the current.
Throttling a valve will reduce the pressure and the flow and the current.
and
Slowing the motor with a Variable Frequency Drive, will reduce the flow rate as well as the current.

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

 

[Pumpsonly]

Post the pump performance curve and everything will be clear.Looks like a over sized pump with an under sized motor.

 

[djs]

A very common issue unfortunately, is that someone may have attempted to cut costs by selecting the pump motor based on an exact amount of flow required at the time of purchase.

This is very likely the case. The system was specified for a certain head pressure which reduces the Hp required. A solution is not necessarily to change the pump but rather replace the motor that drives the pump.

 

[Parchie]

someone said that the problem because of the impeller. he said that the installed impeller was incorrect size, I dont know whether it was oversize or under size. he suggest me to lathe the impeller. is it make-sense argument?

That someone is correct, he's just too vague! The affinity law for a centrifugal pump that is run at the same speed as the original setup but the impeller diameter is changed (shaved by way of machining) states that the change in flow is directly proportional to the change in the impeller diameter and that horsepower changes with the cube of the diameter change.

E.g, if you reduce the impeller diameter to 98% of its original diameter, your hp draw(hence, your motor amps) will reduce to (0.98)^3 = 94%. In your case, that will be equivalent to 20.05 amps but the flow will be 0.98 m3/h; 21.18amps for a reduced flow of 3.93m3/h, etc.

Hope that helps.

 

[waross]

If you reduce the pressure you will reduce the current but then you won't have enough pressure.
If you reduce the flow rate you will reduce the current but then you won't have enough flow.
Most solutions will reduce both the flow and the pressure at the nozzles.
Your pump seems capable of both the flow and the pressure that you require.
Your motor is not capable.
Bigger motor.
The next issue is the 380 Volt motor. Not a good fit for a 208 Volt circuit. Is it also 50 Hz?
You should post all the nameplate data, there may be issues with voltage as well as power.

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

 

[adviavan]

@pumpsonly unfortunately, i dont have the pump performance curve.. it was not the pump that i wanted to use but my boss change it without my permission.

@djs but if i change to bigger motor, i have to change all piping system since the equpment has fixed piping and made of stainless steel pipe. when i change to bigger motor, it has different dimension and different size of impeller (cmiiw). it will cause alteration on piping system. and it will cost much.

@parchie thanks so much, that's really helps. is it rule of thumb of pump calculation?

@waross what i remember from the nameplate was 380v 3phase 2pole 21A 50Hz has a star and delta wiring. but when i measure the voltage for all the 3 phases, it has stable voltage.. around 389V. is there any issues with that?

 

[waross]

By far the best solution will be to put a bigger motor on the existing pump. Sometimes that is possible and is worth exploring.
Another solution may be to combine two previous suggestions.
The motor is rated at 21 Amps, it produces the flow and pressure at 25 Amps. We need to gain 25/21 in motor power or about 20%.
Step one, use small transformers to raise the voltage up to about 450 Volts.
Step two, use a VFD to raise the nominal speed up to 3600 RPM. (60 hz)
Now the motor should produce enough power at 21 Amps to develop the flow and head that you need. Unfortunately at the higher speed the motor would be even more overloaded. solve this issue by:
Step three, now trim the impeller to bring the flow and pressure back down to the values you need.
If you go this route the cheapest way to raise the voltage is with two small dry type transformers connected as an open delta auto-transformer.
You will now have a non-standard, specially modified pumping system that will be a disaster if someone else in the future changes any settings or needs replacement parts.
Changing the piping and using a larger pump may be the better solution in the long run.
The other solution may be to plug off 20% of the spray nozzles.

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

 

[iop995]

If changing to a bigger motor is difficult, maybe it's easier to add cooling to existing one. With 20% current overload need to remove about 40% more heat; try external cooler with eventualy, if not too hard and/or too expensive, some water pipes between cooler flow and motor. Move overload setting accordingly and check motor temperature.

 

[adviavan]

Thank you so much for all your assistance

I really appreciate it, such a great honor to be helped by you.
It seems that the problem almost solved. i explain everything based on all your explanation and my boss think that it make sense. i suggest him to get a bigger motor and granted. just waiting for the new bigger motor and see what will happened then.. hahaha

once more, thank you so much it really helps me will stay on this thread to see if there are any comment or opinion come to this thread.

 

[waross]

Thank you for the update adviavan.

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