Well pump starting help

[Doug]

Actualy Jim it does work:

Way back when 3 phase power was only commonly used in large industrial plants many small shops used a 3 phase pony motor in this fasion to generate a third phase. The more motors running in the shop the more stable the third pahse became and the better the starting torque for all. But this isn't exactly what we are talking about here were looking at a single phase system. When you add a large motor like this in an off grid system thats running no load all that inertia is storing energy. When a second load is added and the system is disturbed the induction motor will drive a certain % of power back in and can contribute a small amount of extra current and stability to the system. The cost is wasted watts spinning a machine that does nothing.

Just to give an example of how much power induction machines can suply. In the plant where I work we have verry large Ac machines driving fans, compressors and crushing machines. Under these conditions a short circut in the plant can and often does have higher fault currents tearing up cables and machinery then if the same fault were to happen on a non production day when little is running. The power they contribute has to be calculated to insure that fuses and CBs don't explode under the stress and buss bars don't teare free of their insulators under the high magnetic fields produced by a 50,000 amp short circut. The actual time that induction machines can contribute power varies based in size and other factors and is usualy only as short as 5 to 10 Ac cycles. In the case of the Listeroid grunting to pull a heavy load up its also decelerating and providing reactive power to the pony motor so it will contribute some power from its stored inertia for longer, maybe as much as a second.

Doug

[Andre Blanchard]

Won’t work.  Here’s two reasons:

1.  Operating an auxilary motor in this fashion is a basic induction generator.  The problem with induction generators is that they can deliver power only to loads that operate at a leading power factor.  A motor starting up, such as the well pump, presents a lagging power factor to the source.  Thus, the induction generator doesn’t have the ability to deliver power to the intended load.

The engine powered generator is still running just bogged down, it will keep the field current going in the induction generator just fine.

2. Induction generators only deliver power into a network if they are driven at super-synchronous speed.  But, as we all know, induction motors normally operate with some slip, and thus  turn at sub-synchronous speed.  So, let’s say your aux motor is humming along at 3450 rpm (about 4% below synchronous speed in a  60 Hz system), it can’t begin to deliver it’s full rated power until the network (in this case your 3 kW generator) slows down to 8% under the nominal 60 Hz.  I’m pretty sure the flywheel and governor on the Changfa is gonna keep the generator speed fairly constant duting the starting event. 

As I mentioned earlier power factor correction capacitors are the only hope, short of getting a bigger generator or 3-wire pump.

Hence the reason for an easy, free spinning motor to start with.  We want that motor to get as close to sync speed as possible to get it into action as soon as possible.  Any flywheel added should be smooth and aerodynamic, no spokes.  If you want to take it to an extreme take the motor apart and break off any fan blades on the rotor and smooth it up.  That will put a big limit on the duty cycle of the flywheel motor but if all it is used for is to get the pump running a few times a day it does not mater.  As soon as the pump is running the flywheel motor can be turned off.
I am thinking that Changfa is slowing down more then you think or the drive belt to the generator is slipping.
A quick test would be to plug in a bench grinder or three before starting the well pump.
__________
Andre' B.

[Jim Mc]

Doug,

I agree with everything in your post, except your conclusion.  Your real world examples are spot on, but this system is different, even though it does involve induction motors.

I’ve designed and built a pair of 50 HP rotary phase converters for a friend's machine shop, where 3-phase mains power wasn’t available.  So, I have a pretty good understanding of rotary phase converters.  I also don’t doubt for a second that the induction motors in a large plant can deliver a huge amount of current from their stored energy during a fault condition.   

But the system being described is different than a rotary phase converter.  And just because a spinning induction motor can deliver electrical energy, doesn’t mean it will help start another motor.  The energy being delivered has to be at the correct frequency and phase in order to be useful.

We can ASSUME anything you want about the engine slowing down under the starting load of the well pump, but the OP didn’t mention it, so since the Changfa is rated 9 HP, I assumed the speed wasn’t drooping.  I could be wrong, and if the speed is drooping by 8% or more, than my reason #2 is moot, and under that condition, the induction generator can deliver power into the system.

But, as mentioned in my reason  #1, induction generators can’t deliver power to a load operating at a lagging power factor, such as another motor.  I’d refer to you to any one of a number of engineering texts on this.  Search eBay for AC machines texts or something similar, and you could find a decent book to add to your library.  The old ones are just fine, as this technology hasn’t changed much in that last 70 years. 

And yes, Andre, plugging in a 240V bench grinder would be a great way to check this out. 

[GuyFawkes]

disclaimer, I'm not a sparky.

a 3ph sparky I once knew used to say that you could tell who under stood the math and theory by asking them to do the calculations to predict current and voltage in a tesla primary and secondary, cos everything in the secondary is induced and dependent upon tuning.

[europachris]

Wow, this is certainly turning out to be an interesting topic!

To my original posting, I could definitely hear the Changfa bogging down under the full load.  How much exactly, I don't know, as I couldn't be in the basement flipping breakers and put the tach on the generator shaft at the same time.  But, I was pegging two 2500 watt meters on the transfer switch, so I was pulling a solid 5 to 6kW from my 3.2kW generator, which is rated for 200% surge capacity.  Since it's an R185, and rated 8.8hp MAX at 2200 rpm, and I'm running it at about 1870 rpm with my pulley ratio, I'm good for about 7 hp.  So, I was pretty much loading it up to full smoke.  I'm using a Browning industrial 6 rib "L" section Poly-V belt setup, and my drive setup is rated at about 30 horsepower, so I'm definitely not slipping.

An email to Franklin Electric came back with the reply that my well pump needs a 4800 watt generator to start.  That would be a 20A at 120V unit nominal, and give 40 Amps peak.  My pump pulls just over 40A at locked rotor (starting) conditions, so that works out.  The big flywheel on the Changfa would have enough inertia to pull the peak load on the generator to get the pump started, but under continuous load, it would bog.  Therefore, a 5kW head would provide enough peak power to start the pump, but really wouldn't give me a lot more useable KW due to horse power limitations - same issue for a 6/1 Listeroid.  They are good for 3700 watts or so max continuous, but will deliver a LOT more peak power from a ST5 head due to inertia.

I've got a call into the local Markon sales rep to see if there is a two bearing 5kW head available for a decent price.  I got a screaming deal on my current head from them several years ago, and a 5kW head would be plug-and-play compatible.  That would give me the peak juice to start the pump, and also give me more flexibility to run 120V loads when connected 240V (peak power per winding).

I'll have to get ambitious and see if I can rig up the motor on my table saw for 240V and use it for a 'booster'.  It might just supply the extra 10 or 12 amps for that split second to get the well pump going.

I just don't want to end up blowing up my setup or frying the well pump trying to screw with this.  The easy solution is to just get the bigger head.

Chris

[Jim Mc]

...you could tell who under stood the math and theory by asking them to do the calculations to predict current and voltage in a tesla primary and secondary...

Some truth to that.  A guy could make a lifelong career out of accurately modeling and analyzing a Tesla coil.  BTW, guess who came up with the induction motor?  Tesla.  It's a similarly complex nightmare to analyze...

[Tom]

I still think you should change your pump to a Grundfos SQFlex. I am running mine on a 6/1 with a 5kw head and you can't even tell when it is plugged in. I did a lot of research on pumps before I bought mine and this pump is ideal for what you are trying to do. This pump is design includes generator operation. I have no interest in the company, just a satisfied user. When not running of generator you will be saving $ every day of the year. What is different about this pump is that it uses a positive displacement screw instead of turbines to pump and runs about 1/3 the speed. Since Grundfos "upgraded" their web site I can't even show pumping specs, but they had a program that would allow you to calc kw used per 1k gal of water pumped which was neat. Anyway good luck with it.

[europachris]

I've been looking at the Grundfos line.  VERY nice stuff.  It appears that even something like the basic SQ or SQE line would work nicely with much less current draw.  The SQE is a constant pressure system that varies the pump speed to match flow rate and pressure setting. It only needs a little 2 gallon pressure tank!  Very cool.  I'd jump all over that in a second if our pump failed. 

Chris

[Tom]

In my case I have 2 3000 gal tanks up the hill I need to fill and then it is gravity feed back to the home site. I also don't like the idea of a constantly running pump and much rather have a large pressure tank so you will still have pressure for a while when the gennie is not running.

[Doug]

Ok Jim:

Your right an induction motor won't needs to be run at Unity or leading PF.
But I stand by my statement that an induction motor with a high inertia load on it can provide additional starting current for other motors on a system or in this case a generator trying to start a pump. I'm not pulling this out of text books or remebering this from classes way back when this is a fact. I wish I could prove it too you but unless you want to come to the nickel city and watch me fire up a few thousand hp of fans compressors and crushers in different sequences. Frequency and phase have nothing to do with it if your running one the buss with a heavy constant load you contribute stability.  If your frequency and phase are different your not on the same system.

I am currious about the add-a-phase you built. could you briefly discribe them?

Doug

[Jim Mc]

... I stand by my statement that an induction motor with a high inertia load on it can provide additional starting current for other motors on a system or in this case a generator trying to start a pump. ...

I'll continue to think on it, but for now I guess we'll just have to respectfully disagree on that point, Doug.

As for the phase converters I built, They're nothing more than 3-phase 4-pole motors with a capacitor-start system, and a bank of 'tuned' running capacitors to help balance the current.  Lots of info on the web - try a Google search, if you want to build one.

[Doug]

Its more than ok to disagree. Don't take too serious if I seem abrasive at times.

Here let me give you some more food for thought. As loads change and decreas in a system voltage tends to rise a bit. In an induction more this leads to more stator flux and a reduction of slip, and the same is true in reverse. Even an inductive load like a motor will convert some of its stored energy (reactive power in this case) and support the bus voltage for a very short period of time of under a sudden load does that make sence?

As for the add-a-phase when you told me how large they were it sounded like something special. I wound some in the past. As a rule of thumb the induced phase would have 10% more turns, ballance capcitors as you mentioned and my boss was fond of using the starting relays from large AC compressors for the start Caps.  ( Clever I thought ). But I never made one that big (  or for that matter many maybe 3 or 4 in the years before I left that trade ) Uusaly in the 5 to 7 HP range at the very max.

Doug

[diesel guy]

This is why all our 6/1’s we build run at 670 RPM @61 cycles with a ST 7.5 KW generator head. It might burn a touch more fuel but can supply 50% higher surge capability than a 5 KW, which could increase the operational life of the pump motor.

Diesel Guy

[dkwflight]

Hi One thing you could try is to raise the voltage your gen produces. I have my meter in commercial power all the time. I see 120-128 volts ant 248 sometimes on a so-called 220 volt circut. These voltages result in lower running amps on the motors and the starting amperes are lower as well.
Good luck
Dennis

[europachris]

Hi One thing you could try is to raise the voltage your gen produces. I have my meter in commercial power all the time. I see 120-128 volts ant 248 sometimes on a so-called 220 volt circut. These voltages result in lower running amps on the motors and the starting amperes are lower as well.
Good luck
Dennis

Thanks, Dennis.  Tried that, too.  I just simply don't have enough surge power to start the pump.  The generator just collapses under the strain, although the Changfa keeps happily chugging along un-fazed.

I'm about to purchase a 5kW Markon head to replace the 3.2kW head, and that will provide the surge power needed.  The R185 won't pull 5kW, but it's got enough inertia to keep it going long enough to start the pump.

Chris