Effects of Voltage Drop in Submersible Pump

Your wire size must be too small. Voltage drop should be at most 5%. IF the pump motor can still run without overheating, it will still turn at nearly full speed; thus little effect on flow. Does the pump have thermal protection built in?

That question was already answered in post 1. Please reread.

Do you have a thermal sensor actually in the motor? (That is not the same as overload protection.)

You're assuming that the pump motor is an induction motor. The only motors that make sense to attach to a pump are an induction and universal brushed motor. An induction motor would be more likely. It would certainly be strange to use a servo or stepping motor for this but I've seen weird designs before. I agree that the voltage drop is too much but to know what this lower voltage at the motor will do to the speed of an induction motor will require knowing the torque curve or the NEMA rotor selection. The Steinmetz motor model calculation could then be applied in iteration to discover the new slip but this is rarely needed to be done.

In the realm of a universal motor, it might be that the motor itself is undersized for the mechanical load present. Thus the current draw would be higher than anticipated making a larger voltage drop for the wires. This could be a bearing problem in the impeller, motor, or any transmission between the two.

what is the rating of sub motor-pump and size of cable from MCC to starter and starter to pump-motor?. Did you check with the pump manufacturer?.

Dear Mr. rubeshkrishna,

You have not mentioned the following.

1. H.P or KW of the Pump Motor, or Name Plate Data

2. The Cable Size used.

3. Whether, you have connected Capacitor for the Motor, if so how much KVAR.?

Motor H.P. or KW or Name Plate will tell us what is the Full Load Current. Capacitor will reduce the Line Current and hence reduce Voltage Drop, besides Improving Power Factor, and Heating Effect of the Motor winding. 100 Metre Distance from Panel Board to Motor appears to be Very high, Normally it will be 15 Metres (approx)

Select the CORRECT Cable Size properly i.e at the rate of 1000 Amps/Sq. Inch, for Copper Cable i.e 1.5 Amps/MM^2 and if it is Aluminium Cable, at the Rate of 625 Amps/Sq. Inch or 1 Amp/ MM^2. and this is for ambient Temp. of 40 Deg.C.

If Ambient Temp. is high, the DE-RATING FACTOR for the CABLE is TO BE DULY CONSIDERED. OR use CABLE SELECTION CHART, for deciding the Cable Size. Hence Check up the Cable Size, what has been used, and if it is under sized, Replace the Cable.

Alternatively Select the Cable Size in such away, the Voltage Drop at Full Load DOES NOT EXCEED 5%. and add Capacitors.

H.P.(of the Motor) x 0.4 = Capacitors, in KVAR is to be connected.

DHAYANANDHAN.S

Dear sir,

Thank you for valuable reply .I am giving you the data as per your need

Motor detail

kw=5.5

FLA=14.5 Amps

Voltage=415 +6%

-15%

Pump details:

Discharge=1.94 LPS/94 mm dia

H=210-77 mtr

No of stages:35

Cable size used from starter to motor=50 mtr/2.5 Sqmm cu cable (Depth of submersible pump placed)

cable used from MCC to starter=100 mtr/16 Sqmm Al cable

No we are not connected the capacitor

RK

You likely have a bad connection between starter and motor. The anticipated voltage drop for 50 mtr of 2 Sqmm of cu with 14.7A of current is only 6.2V.

When you don't know what is happening, you should provide every bit of information you do have.

Dear Mr rubeshkrishna,

Thank you for your posting. You have replied:

"Cable size used from starter to motor=50 mtr/2.5 Sqmm cu cable (Depth of submersible pump placed)

cable used from MCC to starter=100 mtr/16 Sqmm Al cable

No we are not connected the capacitor,

RK"

Pl. refer my Point No.2, CABLE SIZE. Now you your self can understand the Problem, WHY VOLTAGE DROP IS MORE.

MY SUGGESTION - Your problem is very simple. Pl. DO THE FOLLOWING:

1. Replace the Cable - from STARTER to MOTOR by 10 MM^2 COPPER CABLE. If you use 16 MM^2 Copper Cable from Starter to Motor, IT WILL BE THE BEST OPTION, since 10 mm^2 Copper Cable is JUST SUFFICIENT.

2. Pl. provide Capacitor of 3 KVAR as close as possible to the Motor, through a contactor, to ensure, when the motor is stopped the Capacitor should trip and after starting the motor, Capacitor SHOULD BE SWITCHED ON. Do not directly connect the capacitor, to the Panel Board.

3. Pl. post the INFORMATION after attending to this and inform the Voltage Drop, noticed after changing the cable and adding capacitor.

DHAYANANDHAN.S

I Replace the Cable from STARTER to MOTOR by 10 Sqmm COPPER CABLE.Now the problem get reduced

thank u sir.

RK

Is this problem completely solved, or just reduced?

British Standard 7671.

Voltage Drop Calculations

Sounds like someone didn't follow the local electrical standards and regulations regarding voltage drop for cable sizing.

The calculation is in the electrical standards and commonly available off cable manufacturer's websites. A qualified electrician (which you are not) should be performing this industrial (3 phase motor) work for legal and safety reasons.

Please get in an electrician to fix your site issues.

Pump discharge will get affected if the frequency (i.e speed) changes. Lower voltage will reduce the torque developed by the motor in proportion to square of the voltage. Since pump is generally considered as a low inertia drive, there may not be problem in starting of the motor. However due to less voltage at the motor terminal the motor will draw more current, hence more copper loss. But magnetisation current will be less, hence iron loss will be less. Thus there may not be appreciable change in motor heating.

Fits I think you cable is way to small to have a volt drop of 50volts over 100meter. Are you sure it's 100meters and not 1000meters?

Second, please let me know the following, motor HP, motor type (2 or 4 pole), supply Hz, FLA & voltage, pump type, number of impellers, HP required per impeller, depth of pump in well or hole, size of cable.

Quickly, if your voltage drop does not drop below 80% of NPV then you should be ok, providing that your motor is not fully loaded to start with. While many of the answers given are good, and can be applied to surface motors, submersible pumps have a different set of rules, which once you have provided the information I asked for, I will explain.

This looks like a homework question to me........

Or possibly he bought a cable that is too small for the load.

If the second one, to Quote an old German saying "He saves money no matter what it costs!"

With such a volt drop, the motor will run much warmer than normal (already mentioned by others), whether this is a problem or not depends upon many factors - motor type, cooling (internal & external), mechanical load to name but a few....

This is all an exercise in futility if the OP cannot answer the basic question of what the motor nameplate (or mfr specification) says that the motor design voltage is. If the motor is designed for 380V, I fail to see any problem with the motor getting.... 380V! If it is designed for 480V and can accept +-10%, that gives him an acceptable lower limit of 360V. Again, where is the problem here? If the motor is designed for 415V, then the lower limit is 373.5V and without knowing the further distance from the motor starter to the bottom of the well, it MIGHT be right on the ragged edge of acceptable.

But my crystal ball is on the fritz today, I cannot see across space and time to the OPs motor to devine any further data.

But most CR4 respondents seem to prefer making a WAG. Look at the OT I got for asking what type of motor was being used. You want the whole design specification... Good Luck :)

I still find it odd how many induction motor devotees on this thread seem to have never heard about "slip" or that the produced torque depends on both EMF and slip.

• "Look at the OT I got for asking what type of motor was being used."

If I had to guess (which is a competitive sport around here), I'd say you drew the OT Flag because of introducing a Universal Motor into the discussion. Non-sequitur to a discussion on a submersible pump in my opinion (but not worthy of flagging either). I know you mentioned it was unlikely, but you should also know that people only read about 35% of any post that contains more than 12 words.

Really!!! That much, I would have thought less........:-)

(My CR4 emoticons have stopped working....!!)

If anyone from CR4 is reading this, why no smileys anymore.....?

If you get to snarky they take them away form you.

Del and I just got ours back yesterday.

CTRL + R seems to temporarily fix the issue.

Hi, lets try that.

Good tip, many thanks.

You are dead right!!!!

The submersible pump manufacturer should give cable size and length for each of their product.