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Behaviour of Borewell submersible pump electricity consumption with changing water tables

Let us take a given installation of a borewell with single/multistage fixed discharge submersible pump - i.e. the pump is fixed at a certain depth and the output end of the borewell is connected to a given overhead tank.  This would mean the total dynamic head of the borewell is fixed.  

The pumping electricity consumed (units) for such a borewell would of course depend on the quantum of water pumped out of the borewell. 

However if the static water table level in the borewell changes (for example during or just after the monsoon the water table may be high and in the peak summer it may be lower)

a) Does the pumping electricity consumed in units change or remain constant ?

b) If there is a change in the consumed electricity what is the reason - is it due to pump behaviour or some other reason ?

Avinash Krishnamurthy

avinash@biome-solutions.com

9341324692

 

 

 

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1. Dear Avinash

Dear Avinash Krishnamurthy,

 

The pumping unit cost would be more during the summers would be high as compared to that of monsoon period of water levels. The KWH energy would be more when the static water level is deep. In general, 1 m drop of water level consumes 0.4 KWH of extra energy.

 

With regards,

 

D. Chakraborty

Scientist

Central Ground Water Authority (CGWA)

New Delhi

2. Dear Avinash

 

 

Let us take a given installation of a borewell with single/multistage fixed discharge submersible pump - i.e. the pump is fixed at a certain depth and the output end of the borewell is connected to a given overhead tank. 

This would mean the maximum and not total dynamic head of the borewell is fixed.  

The pumping electricity consumed (units) for such a borewell would of course depend on the quantum of water pumped out of the borewell.  -

The quantum of water pumped is dependant on the inflow into the well which when matches the pump discharge results to steady state conditions, unless of course the well goes dry due to over pumping

However if the static water table level in the borewell changes (for example during or just after the monsoon the water table may be high and in the peak summer it may be lower) The current drawn by the pump changes and this also leads to the pump consuming more electricity.

for every submersible pump there is an upper and lower limit of the ideal  working head, if the water level is above or below this level the motor will draw more current and will lead to increase in pumping cost.

In summer, this is  usually not a problem as the working head is well within the optimum range, but many a times in the rainy season due to the unconfined system being saturated the pumping water level is way above the minimum required limit, in this case the pump draws up to 15-20% more current  for eg. a 1 hp submersible pump which should draw about 6.5 to 7 amperes, draws 8 amperes

 

I think this should answer your query

Regards

Anil Lalwani

www.wellwaterworks.com

contactus@wellwaterworks.com

 

 

 

 

3. Behaviour of Borewell submersible pump electricity consumption w

Dear Sir,

Your assumption that the the dynamic head is fixed if not a correct statement.  

I?n bore wells irrespective of season when you pump out water, the water level falls at rate depending up on many factors.  The important factors are your average discharge rate of the pump out put, the formation transmissivity and the storage coefficient of your bore well locality.

Normally during and immediately after rainy season the static water level move up and this in line with the aquifer characteristic of your site, changes the hydrostatic pressure head, which try to achieve equilibrium condition spontaneously, while you pump out water from the bore well at the rate depending up on the formation characteristics. 

Invariably the transmissivity changes with depth due to hetrogeneous behaviours of the ground water body and the water level in the bore well will start falling irrespective of the season.  Only the rate of fall may be high during summer and the rate of fall will be low during rainy season and immediate months that follow due to increase storage in the ground water medium nearby.

When the water level falls, the motor has to exert or spend to push out water from deeper and deeper depths and hence more energy will be spend.  During rainy season your tank will get filled faster and during summer the tank filling will take more time for the same pump fixed at the same depth under same conditions.

Hence your bill will be higher during summer when compared to that during rainy season.  Are in your way you will be using more unit of electricity during summer than the rainy season.  

One more clarification is at what depth you fix your submersible pump is not mattered but where the dynamic water level ( at what depth level) at the end of the pumping period.  

Say your bore well is 250 feet and static water level is 30 feet and after one hour pumping the water level falls down to 90 feet at the maximum. Then if you ix your submersible pump at 100 feet or 180 feet of 200 feet is not going to alter your electricity spend only the dynamic head matters which changes or falls down instantaneously while pumping. 

I trust the concept is clear to you.

A. Raja mohamed

Geophysicist

Coastal Energy Pvt Ltd

Chennai.

A. RAJAMOHAMED AMBALAM GEOPHYSICIST COASTAL ENERGY Pvt Ltd, CHENNAI +919443619352

4. Query about motor life when it runs without water

What about the life of motor when the water level goes beyond minimum pumping level  and the pump runs without water?

Regards
R Viswanathan

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