Troubleshooting electrics on a borehole pump

[mellwaters100]

Firstly, apologies if this is the wrong board - found a similar thread in here so that I would start here!!

So, I have a borehole pump that is causing me problems. Forgive me if I use the wrong terms, I am kind of learning as I go along, but hoping to get some contrustive advice.

I have a Lowara 2GS05T pump with corresponding motor down a 50m well. There are a total of 4 wires going down the well: Earth, Brown, Blue and Black. This cable connects into a switch (a Tech Nova 008) which is feed from a regular ring main (through a pressure switch that is connected to a header tank).

Some things to note:
- This arrangement has been working perfectly fine for over 10 years.
- Couple of weeks ago, the pump got clogged, which burnt out the old motor. First I knew was waking one morning and all the electric was off. Traced it to the motor tripping everything off.
- I replaced the old motor with same make and model, wired everything up as before. It is a 0.55kw pump and I *believe* it is a 3 phase pump, and the switch is the invertor converting single phase to 3 phase?

Unfortunately, the Lowara motors are only supplied with a short lead, so the connection to the power supply is in the well. At this time, I believe the connection is water tight.


The fault "seems" to be occurring when the pump has not kicked in for about an hour - but this is pure gut feel at this point in terms of time. Each time, the pressure has dropped in the tank and the switch is thrown as expected, but the thermal cut out has kicked in. BTW, the motor is in at least 40 metres of water and the well is not dry.

However, I can stand over the pump for hours on end, cycling the pump and everything works fine!

I have tested the circuits with a voltimeter, and everything checks out. All circuits check out as complete. When powering the pump, I see an increase on one of the wires - suggesting the 430v motor start, and the pump runs properly.

My only suspicion is that the motor I have put on is at least 10 years old (was here when we moved in). On the surface, the spindle felt a little stiff when first starting. However, on the surface, started every single time without fail.

As it is a pain to drag the pump so wondering if there are any checks that I can perform before resorting to that. Could it be that the switch itself is not giving enough initial power?

On this - when I go and look and the thermal switch has kicked in, if I re-set it there is often a pause of about 3 seconds before water starts flowing. However, if I flick the power switch off and on quickly a couple of times, it starts immediately.

What readings should I expect on a healthy invertor?

Any help on this would be much appreciated. As a new pump is £500, a bit reluctant to make a speculative purchase.

Also, the pump house has a QMC75 Lowara switch on the wall. Wondering whether to give this a go but there's a hell of a lot of wires in there, all the instructions are in Italian and I don't want to wire this thing up and blow the motor!!

Thanks all!

 

[Lectrician]

Photos of control gear and the 'thermal trip' which operates?

 

[mellwaters100]

Hi Lectrician,

Thanks for responding.

Images as follows:
1.

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• mellwaters100
• 15 Jun 2012
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• mellwaters100
• 15 Jun 2012
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• mellwaters100
• 15 Jun 2012
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The thermal trip switch is to the left of the main switch in the first picture. The red switch does light up when power is going through.

Thanks!

 

[Lectrician]

The pump should be changed with that top capacitor box.

You don't have a three phase pump, it is single phase, but it's capacitor (as with all bore hole pumps) is mounted in the control box and not in the pump - this is more for maintenance purposes than anything else. The capacitors fail and require replacement ocasionally. The capacitor and trip will be sized to the pump they correspond to.

The pumps are matched to the top box and should not be interchanged (due to their ratings).

 

[conny]

Also ensure pump is rotating in the correct direction. If not you will have to change over either the run winding leads or the start winding leads but NOT both sets. If you have a multi-meter the start winding will have the higher resistance.

 

[bernardgreen]

Couple of weeks ago, the pump got clogged, which burnt out the old motor.

Are you sure the pump clogged and that burnt out the motor or did the motor burn out and you assumed the pump was clogged as no water was being pumped.

How often has the pump been starting and stopping in recent months ?

Is (was) the motor oil filled ( as a coolant ) and has that oil been lost ?

From the data sheet

• Maximum number of starts per hour evenly distributed: 30 (4OS), 40 (L4C).

Submersible pump motors have to be very compact ( less than 4 inches diameter in this case ) and as a result would run very hot if not for the cooling effect of the water. When the motor starts it takes a lot more current than its rated current until it has reached normal operating speed and therefore frequent stopping and starting can cause the motor windings to over heat.

If the control is just a pressure switch sensing the depth of water in the header tank then I would consider changing that as well. It might be the pressure switch is starting and stopping the motor too often and that has led to the motor burning out. A better control would be achieved with two float switches, a low level on that turns the pump on via a latching contactor when the water level is low and an upper one that de-latches the contactor when the tank is full. This means the pump runs for longer each time but has far less starts and stops which will prolong the life of motor and pump.

Also consider supplying the pump from its own RCD and MCB so the rest of the house does not lose power when the pump has a fault.

It might be cheaper to have the motor re-wound and new bearings fitted than to buy a new one. Many submersibles do have re-windable stators as burn outs are not un-common.

 

[mellwaters100]

Thanks, everyone, for your replies - been very helpful.

Are you sure the pump clogged and that burnt out the motor or did the motor burn out and you assumed the pump was clogged as no water was being pumped

Could actually have been both - when extracting the old pump I found the remains of a rat skeleton at the intake for the pump (will teach me to make sure the well hole is covered in future!). Am assuming a bone has been sucked into the pump itself and jammed it as the pump was quite hard to turn manually. However, if the pump did jam, guessing the motor would have thrown the thermal trip. I do know that when I re-wired this motor on the surface, it tripped the power and not the thermal switch - so guessed it's fried itself - somehow.

With the motor that is in now - it is the same make and model as the fried motor - and that arrangement had been running for 5 years. The pressure switch checks water pressure in a vertical pressure vessel - I have the upper limit set to 45PSI and the lower as around 25PSI. I have seen some recommendations to have this set as around 65/45, but lowered wondering if the motor was over-heating getting up to the higher pressure.

Overall - starts per hour are well within the range, guess no more than 6 during normal operation.

UPDATE: This morning I have done a few multimeter readings for resistance and voltages.

Common / Blue:
- Resistance = 19.2
- Volts during starting phase = 250
- Volts during running phase = 400

Common / Black:
- Resistance = 13.2
- Volts during starting phase = 40
- Volts during running phase = 280

I may be measuring the wrong things (!) but are these expected values?

With the thermal switch - the motor tripped around 10pm last night - I went and looked at around 9.30am this morning. I reset the switch and it then tripped after about 5 seconds - without water getting pumped. You have to wait about 1 minute to reset it, which I did. Water got pumped for a few seconds then it tripped again - suggesting overheating? I reset the switch, and then it's been working fine for the last hour, cycling correctly.

I do wonder if the motor itself is seizing up a little after an hour or so of not cycling; however, if this was the case, I would of thought it would never get kick started again?

Guess at this point, wanting to check if the control box and readings are as expected - fix the easier things first!! I have even considered getting a cheap water timing value to run water back into the well once every hour, just to make sure the pump gets at least 1 cycle an hour!!

Thanks for reading and any advice - really appreciate it.

 

[timtheenchanter]

Guess at this point, wanting to check if the control box and readings are as expected - fix the easier things first!! I have even considered getting a cheap water timing value to run water back into the well once every hour, just to make sure the pump gets at least 1 cycle an hour!!

Thanks for reading and any advice - really appreciate it.

IMO, it sounds like the motor is getting on a bit, you said it was 10 years old, its possible that its sticking, and a few movements get it running again.

presumably the motor is sealed with it being in a borehole pump (not had experience of these, so an assumption here) otherwise a strip and clean would probably solve it.

the water timer is only delaying the inevitable IMO.

 

[magnicon]

For what they cost,I would replace that capacitor and see where you go from there.Can you borrow a 'tongtester'?,current readings would be far more useful as a diagnostic.
As you found debris around the pump are you sure the pump itself is ok?
because they are multistage with many internal passages,also all the ones I have dealt with have a built in non-return valve,does that work?.
Why is the ground wire in the panel disconnected?.
Is the cable from the pump to the panel sized correctly as we came a cropper on that once,and it was 220 M down!.