Submersible Well Pump Chews Contactors

I have a wee technical problem that I would appreciate some wisdom on :

A customer of my employer installed a submersible well pump on a farm. The pump is a Davey brand 1.12HP submersible The installation is a fairly typical rural irrigation-pump with a centrifugal pump about 70m down the well. The pump draws a balanced 2.6A per phase in normal running. Starting is DOL, using one of our 4KW DOL starters and an appropriately-rated Thermal Overload relay. Being a centrifugal pump, I am told that the starting load is quite light.

The problem is that the line contactor keeps getting its contacts chewed. Given that it is good for about 4x as much motor power as it is switching, this should not be happening. When the first contactor fried, it could be dismissed as one rogue contactor, but when a second fried too, there is clearly something wrong, but what?

The float switches are sufficiently far apart that frequent on/off cycling can be ruled out. The thermal overload is set to manual reset, so it is not cycling on/off due to the TOR tripping. There is no PFC installed, and there are no co-connected loads. Like most NZ electrical contractors, this one has a Megger and knows how to use it, and all seems well as far as insulation resistance goes.

Thoughts, anyone?

Electric Car Project

I would appreciate comments on a personal project that I am scoping out.

My project is inspired by the rising cost of motor fuel. It seems to me that the economics of a battery-electric car are looking better with every petrol price increase. I plan to build a battery-electric car by fitting out a small passenger car with a 3-phase induction motor, speed drive, and a battery pack.

MOTOR :

A 2-pole 15KW 3-phase induction motor. This will spin out to just short of 3000rpm at 50HZ, I am hoping for a little higher when driven by the VSD. This motor will drive through the original car gearbox, via a primary drive with a drive ratio that gives a speed of 110 Kph at 3000rpm. My mechanical gurus are still debating whether chain or gear drive is likely to be best, but I am assured that either is able to be done.

BATTERY :

The battery pack will consist of about 36 x 12V deep-cycle lead-acid batteries of 35-40 Ah each.
(It would be nice to use lithium batteries but while they are available they are still quite expensive.) The fitting of the batteries will be one of the biggest challenges in this project, I think. A tray across the top part of the engine compartment will hold over half of them, and the rest will go to the rear in the space vacated by the fuel tank.
The batteries will be series-connected for a DC bus of about 400V.

VSD :

The VSD will be supplied from the 400V DC bus, and will drive the motor. I am told that there are already turbine-electric busses on the road that use relatively standard VSDs to drive from a DC supply. As well as providing drive to the motor, it would be good to have regenerative braking too.

Also on board this car will be a switchmode battery charger that I expect I will have to design and build, this will accept a 230V 10A supply as input and will series-charge the batteries while monitoring each battery in the pack and equalising the charging.

If it all comes together, the result should be a car that will do a little more than 100Kph, and will travel 100km on a full charge. Recharging should take about 8 hours from a 230V 10A outlet. It should have a similar level of acceleration to a car with a 1000cc petrol engine.

This is, in brief, what I want to do. Question is, is this a reasonable proposition, or am I overlooking one or more obvious flaws/problems? I would appreciate any wisdom that anyone may care to contribute.

Thanks, and best regards

Mark Monson

Mccb Selection For Use With Vsd

To introduce myself, and this thread, let me say that I am an EE who is employed by a company which manufactures/builds switchboards, and which sells the components including circuit breakers.

I was asked the other day to recommend a MCCB for use with an irrigation pump motor which was being run via a VSD.

Since the installation was connected to a rural supply with a fairly lengthy supply feeder, the choice between a 36KA and a 50KA MCCB pointed towards the 36KA.

Then the question arose as to the type of trip unit that was required. It turned out that the least-cost option was a thermal-magnetic trip, and so this was what was settled on. I have since trolled through our supplier's technical data, but I can find little about the best type of trip unit to use with a VSD, and it is this that I wish to ask about.

Our supplier recommends two options for DOL (or, presumably, star-delta) starting : either 1) a magnetic-only MCCB followed by a line contactor/thermal overload combination, or 2) electronic thermal/magnetic (adjustable) trip and line contactor only.

My thoughts are that for use with a VSD, a magnetic-only breaker is probably quite OK, but that the thermal-magnetic with the thermal trip wound up higher than the level at which the VSD is set to 'trip' at would provide a comforting measure of redundancy.

Comments anyone?

X-power Energy Saver

I have just had an email from an irritated seller of the X-Power Energy Saver after I tried to post a comment on his video on youtube.

I Quote : "Hi,
I am not sure you understand how you determine kWh.
Here is the Formula: KWH = Amps X volts / 1,000 X estimated hours.

Amps is a definite part of the kWh equation.

Do your reseach please before making such claims in apublic forum. And please look at the electric bills at http://www.xpowertechnology.com/testimonies.html

Notice that the kWh is reduced on the bills.

Sincerely
Bill Wynne
646-290-9339".

I have responded with a correction to his formula.

I urge other forum members, particularly US-based members, to get onto youtube and comment in these videos :
http://www.youtube.com/watch?v=1JCj4rVoAPM
http://www.youtube.com/watch?v=XX84iJ-xAgE
http://www.youtube.com/watch?v=AHsfZmzhmG0
http://www.youtube.com/watch?v=1AhEzmpiLUI
http://www.youtube.com/watch?v=Mv7hayXSKRc
http://www.youtube.com/watch?v=LwBayX1Dibc

With any sort of effort, these scam artists will shut up shop and stop preying on the ignorance of innocent people.