M aintenance experts agree that excessive heat causes rapid deterioration of motor winding insulation. The common rule states that insulation life is cut in half for every 10 C of additional heat to the windings.

As an example, if a motor that would normally last 20 years in regular service is running 40 C above rated temperature, the motor would have a life of about 1 year.

pump motor over amping

Leading standardization organizations have concluded that 30 percent of motor failures are attributed to insulation failure and 60 percent of these are caused by overheating. Articles have been published stating that a significant cause of bearing deterioration is overheating.

There are typically five main reasons for overheating—overload, poor power condition, high effective service factor, frequent stops and starts, and environmental reasons.

Overload conditions Stator current is frequently used to measure load level, but load level can easily be masked by an overvoltage condition. A common mistake is made in operating at an overvoltage to reduce the stator current and to reduce the introduction of heat.

Why is my motor over amping?

It has been shown that for motors ranging from hp, operating at a 10 percent overvoltage would typically decrease losses by only percent. Even though the motor current may vary when applying overvoltages, the excessive damaging heat in the motor will not improve.

A load error of more than 10 percent can be introduced by relying on stator current readings to access probable load and heat levels. Under full load conditions, this is the difference between life and death to a motor. For example at a coal-fired power plant in the United States, a hp 6.

Two identical applications had undergone unscheduled outages in the previous 12 months. A mild overload was identified by examining the stator current of this motor. However, after looking at the true load to the motor, an overload of nearly 20 percent was discovered.

This explains why these motors were failing. The repair for each of these three motors ran into the hundreds of thousands of dollars. In industrial applications, perfect voltage conditions are rare. Losses, not current levels alone, are the true source of heat. These losses are a destructive factor to windings and a significant reason for bearing damage.

This justifies the need for accurate knowledge of operating load level. Only accurate load level calculations can give reliable measurements of excessive losses and overheating in the motor.

Power condition Electric motors in manufacturing plants generally need to be derated because of poor power conditions in order to maximize their useful life.Log In. RE: Motor over amping when discharge valves are closed Thanks for the link. I am hoping it is axial flow as that would explain the overamping.

I will no more tomorrow regarding what the pumps are. As for the shafts, I agree, something else is happening. We are going to do VA signatures to see what is up there.

Thanks again! If pumps are radial type there is still a good chance they could be running on the right side of the curve despite the pinched valves. The fracture would show signs of fatigue in bending. If the shaft was under-designed for the loads or the design was changed without accounting for shaft size, it could be failing from overload. The fracture would show signs of torsional failure. This can be very difficult to diagnose. The radial vibration may show very little sign of a problem.

The fracture would show signs of fatigue in torsion. The last one seems to match up to the fact that you run with a pinched discharge. If the pump is pinched back too far, you could be seeing vane pass frequency vibration from suction recirculation. This could be exciting the torsional resonance. I am no expert on rotor dynamics, but there are simple methods available to calculate the torsional criticals that might indicate if this is an issue.

Save a sample of the fracture surface of a broken shaft and have a metallurgist look at it. They can tell you why it failed.

High Amperage problem with centrifugal pump motors | AMP Maintenance Forums

We use a lab called Materials Evaluation and Engineering, Inc. We have a standing contract with them and send them samples regularly.

RE: Motor over amping when discharge valves are closed I assume that electricpete meant to say: Axial flow pumps have highest BHP at low flow. Mixed flow are somewhere in between. Mixed flow pumps sometimes have a humped BHP curve that drops at low flow and at high flow. RE: Motor over amping when discharge valves are closed Yup, that's what I meant.

RE: Motor over amping when discharge valves are closed Single stage pumps are quite often mixed flow type.Centrifugal pumps are said to be overloaded when the driving motor draws excess current resulting in excess then normal power consumption. This overloading of the pumps can be caused by various reasons as discussed in one of the following sections. Centrifugal pumps that are driven by AC induction motors should be started with minimum load on them so as to limit the starting current.

Care has to be taken and certain procedures have to be followed while starting specific types of pumps to avoid high current being drawn by the motor at pump start-up. Therefore, it is recommended that radial impeller pumps be started with discharge valves closed whereas propeller pumps are started with discharge valves fully open.

Centrifugal pumps with radial impellers, consume more power with an increase in flow rate. Thus, when the system resistance to the pump drops, more and more liquid is pumped resulting in increased power consumption. In such cases there is a tendency for the motor to trip on account of motor overload as shown in the following curve figure Requirement of hydraulic power for operating a pump can be calculated using the following equation. Centrifugal pump operation to the right of the BEP has different set of problems as cavitation may occur, shaft may undergo deflection, mechanical seals and bearing can be stressed.

This can cause a drop in pump efficiency and an increase in power consumption by pumps, which may cause the motor to trip. The characteristic curves of the lower specific speed pumps indicate that such pumps have overloading features. Centrifugal pumps having low to medium specific speeds have P—Q curves which rise upward curves 1 and 2 in figure For higher specific speeds, the P—Q curves maybe approximately flat and horizontal. In case of propeller axial flow pumps, which have very high specific speeds, the power for the pump falls as the flow rate increases curves 4 and 5 in figure This implies that for low specific speed pumps, the power requirement of the pumps keeps on increasing which ultimately leads to tripping and overloading of the motor.

Pump suction specific speed Nss is commonly used as a basis for estimating the safe operating range of capacity for a pump. The higher the Nss is, the narrower is its safe operating range from its best efficiency point BEP. Most users prefer that their pumps have Nss in the range of —11 for optimum and trouble-free operation.

Based on two basic types of circulation commonly used, high pressure HP steam producing boilers can be classified as: - Natural or thermal circulation Insufficient NPSH leads to lower liquid pressure in the pump and if The gas liquid separation can be modeled using Stokes law. Where gas bubble terminal velocity is expressed as. Sign up for free if you are not a member already.

Share This! You may also like. Process Equipment Boiler circulation systems: natural circulation and forced circulation. Where gas bubble terminal velocity is expressed as, The subscripts L and G stand for liquid phase Common types of pump mechanical seal piping plans — Double dual seals.

Cause of pump overloading. Login Username or Email:. Remember Me. Advertise with us Advertise directly with us. Get links to your website. Reach out to our reader base of engineering professionals. Email - admin enggcyclopedia.Can some one guide us in carrying out the investigation for resolving the high amperage problem for some of our newly installed centrifugal pumps? Presently some of the pumps are operating in parallel to avoid tripping due to overload on motors.

Will highly appreciate suggestions Original Post. S svanels Messenger. Do they rotate freely? What type of product? We definitely need more information Was this the engineer? Images 1. The pumps rotate freely. The product is hydrocarbons. The motor sizing is already checked by the pump vendor for undersizing. The product specific gravity has been checked and found according to the pump design. The pumps performance is OK.

The only problem we are facing is that the motors are taking high amperes, i. We need to know what else should be checked to find out the root cause? J Josh Leader. Have you checked the motor overload trip setting? G GregG Member. If the pump was sized right. And the rotation is right and the voltage is right. Then it's the load. The elec. Is the panel set up right with the overloads.

Just because the imperler fits dosen't mean that it's right. Try ajusting the out put and checking the amps. As an old electric motor shop owner it looks like the load is to much. The question is why. What about oversizing? E electricpete Leader. The top suspects would be : sorry if I'm repeating earlier items actual mechanical overload, low voltage, unbalanced voltage, trip setting incorrect, trip device malfunction. Measure current on all three phases.After operating for a varied amount of time, pumps turn off.

CAUSE Between the main power buss, where power comes into the chiller, and the pump motor there will typically be several places in the electrical circuit where power can be interrupted. These are: Wires, fuses, motor starters and internal motor winding protectors.

Any of these can cause a pump shutdown. With power off at the chiller main service disconnect, perform the following checks:. Make a note of the pumps SF amps indicated on the pump motors nomenclature sticker. If your chiller is equipped with a motor starter, make sure the amp setting on the motor starters overload adjustment is set to match the pumps SP amps.

If it is not, lift the plastic dust cover and adjust using the proper sized screwdriver. Using an amp clamp, check the running amp draw pump s. If the running amp draw is greater than SF amps, reduce fluid flow through the pump until your running amp draw is at or below SP amps.

Search for:. You are here:. With power off at the chiller main service disconnect, perform the following checks: 1.

Check tighten as needed all wire connections between the main power buss and pump. Restart the chiller and pump s. Make sure your pump s are turning the correct direction. Share on. Chiller Problems — Water Heating Up.

Upgrade to new remote micro.Centrifugal pumps are said to be overloaded when the driving motor draws excess current resulting in excess then normal power consumption. This overloading of the pumps can be caused by various reasons as discussed in one of the following sections. Centrifugal pumps that are driven by AC induction motors should be started with minimum load on them so as to limit the starting current. Care has to be taken and certain procedures have to be followed while starting specific types of pumps to avoid high current being drawn by the motor at pump start-up.

Therefore, it is recommended that radial impeller pumps be started with discharge valves closed whereas propeller pumps are started with discharge valves fully open. Centrifugal pumps with radial impellers, consume more power with an increase in flow rate.

Thus, when the system resistance to the pump drops, more and more liquid is pumped resulting in increased power consumption. In such cases there is a tendency for the motor to trip on account of motor overload as shown in the following curve figure Requirement of hydraulic power for operating a pump can be calculated using the following equation. Centrifugal pump operation to the right of the BEP has different set of problems as cavitation may occur, shaft may undergo deflection, mechanical seals and bearing can be stressed.

This can cause a drop in pump efficiency and an increase in power consumption by pumps, which may cause the motor to trip. The characteristic curves of the lower specific speed pumps indicate that such pumps have overloading features. Centrifugal pumps having low to medium specific speeds have P—Q curves which rise upward curves 1 and 2 in figure For higher specific speeds, the P—Q curves maybe approximately flat and horizontal. In case of propeller axial flow pumps, which have very high specific speeds, the power for the pump falls as the flow rate increases curves 4 and 5 in figure This implies that for low specific speed pumps, the power requirement of the pumps keeps on increasing which ultimately leads to tripping and overloading of the motor.

Pump suction specific speed Nss is commonly used as a basis for estimating the safe operating range of capacity for a pump. The higher the Nss is, the narrower is its safe operating range from its best efficiency point BEP. Most users prefer that their pumps have Nss in the range of —11 for optimum and trouble-free operation. Pipe pigs are used for performing following types of tasks 1. Cleaning of pipeline and displacement of sludge 2.

Separation between batches of different This can also occur due to poor heating of steam network before the steam enters into the system.Forum Rules.

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Results 1 to 19 of Thread: OT: High amperage on cased well pump motor.

pump motor over amping

Thread Tools Show Printable Version. OT: High amperage on cased well pump motor Have been working with cased well pumps for many years. Never actually found one that would show normal continuity levels across the coils in the motor, bearings feel good, no shorts the case, yet FLA is about 3. This is a 3 wire, 2HP pump. Normal amperage should be in the 10A range.

pump motor over amping

It is pulling 35A. I did find some shaft seal damage from age. My thought was that the motor filled up with water but this one is filled with oil to retard that. The oil I sampled coming out of the motor was crystal clear. I am just at a total loss here and always like to know the cause of a failure. For testing, I decoupled the pump from the motor and motor is still over amping.

Motor also showed excess heat. To make sure the start winding starter was not causing this, I pulled the start wire once running so only the two motor leads were running it.

Still not right. Any thoughts on this? Neither of these seem to be the case but I did note while still in the hole that the pump was not moving water like it should.

If I had to guess, I would say the motor was not coming up to full speed, even unloaded. I should note that voltage was tested going to the motor and all looked good. I don't know what a "cased well pump" is but I'm familiar with a unit called a 'jet pump'


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