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Forum Index : Other Stuff : Bore motor repair.......
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KarlJ Guru  Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
15HP 3 phase above ground bore pump motor here is the bill from the local electrical boys. replace overload relay replace contactor unit tripped on first attempt to start but ran OK on all other attempts Fault has to be with motor suspect broken rotor ring. Parts $791 labout $468 certificate of electrical safety $25 Total $1285 and not fixed. what is the rotor ring? is it repairable? Luck favours the well prepared |
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| Robb Senior Member  Joined: 01/08/2007 Location: AustraliaPosts: 221 |
Is the pump one of these. Mono for example. They were common 20+ years ago with above ground electric motors or diesels. These days everyone seems to use submersibles down the bottom of the hole. Some even powered by diesel gen sets. Sounds like the electrical guys are saying the load (pump or shaft assembly) may have a fault therefore stalling the motor. |
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Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
It had me stuffed what a rotor ring was so i had a search and found very little. See if this helps. * Squirrel-cage rotor The most common rotor is a squirrel-cage rotor. It is made up of bars of either solid copper (most common) or aluminum that span the length of the rotor, and those solid copper or aluminium strips can be shorted or connected by a ring or some times not, i.e the rotor can be closed or semiclosed type. The rotor bars in squirrel-cage induction motors are not straight, but have some skew to reduce noise and harmonics. ................ The current practice for manufacturing copper rotor cages for large AC traction motors uses brazing for assembling the longitudinal copper rotor bars to the end rings. The end rings and copper bars which position the interior laminated steel core are assembled and held in a fixture for the joining operation. The difficulty in welding heavy section copper components is due to the high thermal conductivity of copper which conducts the heat away from the surface to be joined. First, the entire assembly and fixtures are placed into an oven and preheated to 650° F. After soaking to a uniform temperature, the assembly is removed from the oven and the hand brazing operation is begun. After flux has been applied, each copper bar is brazed individually to the lower end ring. When all the bars have been brazed to one end ring, the assembly is inverted and the other ends of the bars are brazed to the other end ring using a hand torch. This brazing operation is costly and time consuming. In addition, the process is susceptible to producing defects and weak brazed joints since brazing the bars singularly produces uneven heating that generates thermal stresses. I would think the island dweller might know more on this. One question that comes to mind is what are the motor bearings like??? I have seen bad bearings cause starting problems. Pete. Sometimes it just works |
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oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
Glad I fix my own motors. Induction motors. ... The stator acts like a primary in a transformer. It effectively induces an EMF in the secondaries. These secondaries are in fact the rotor bars. They are explained as in the above from Pete.. Now once we have induced this EMF in the secondary (bars of copper in the rotor), we short it out. This means all the EMF is lost in this piece of "wire" shorted at both ends by the ring that joins them up. Because we have shorted this EMF, we get a current flowing proportional to the EMF and resistance in the wire/bar. (I=E^2/R) This flowing current does what all currents do, and makes a magnetic field around itself... which will be in opposition to the inducing field. So the resistance of the bars will have an effect on the stator current (not the induced EMF), and the slip and the start torque. A compressor duty motor will have very low R, so start currents are huge, but torque is large, and slip is smaller. If we use resistive bars, we can lower the start currents and torque, but the slip will be larger... centrifugal water pump duty... low torque start. Now if we have one or more of the bars break it's connection with the shorting ring, then we lose that magnet circuit, and less current should flow in the stator from the remaining bars to reflect this "loss of short circuit), and the slip will increase....and the current may rise again to try and keep up speed but if load is greater than the motor torque can supply, we stop and huge current can then flow in the remaining bars, Or if the start torque is not enough to get the rotor bars out of the way fast enough (stationary) then the current may trip the contactors instead from more current in the remaining bars. 
If the start torque is small, losing a bar or two should not stop the operation, as it will start on the others. There are lots of them in there. you can see the "lines" for each spiral down the rotor. If there has been significant movement for reasons I cant begin to guess, you may have broken a few or a lot of bars..... I have never seen this actually happen... so my predictions may be less then accurate, but I can't see why they would be. As I recall it... From start.....Once the rotor starts to move, the angle of the primary flux working on the secondary wires changes, and the induced EMF starts to drop as there is less magnetic lines cutting the rotor bar at the right time/angle... current drops to something sensible (E^2/R again)and we are running At synchronous speed, EMF would be nil.... so that won't happen, and so the slip angle will be a reflection of the resistance in the bars, and the angle required to cut them and develop a back MMF that keeps the rotor running at this equilibrium. At least thats how I remember it anyway. Edit: It seems a highly unlikely scenario. I have never seen evidence of or heard of an instance of rotor bars leaving the rings... although I recall in an old motor book there was a procedure for finding out using a growler I think. It smells..... ...........oztules Village idiot...or... just another hack out of his depth |
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GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
I doubt that an electrician would be able to determine if the squirrel cage rotor was damaged, broken bars in the squirrel cage, without dynamometer type testing, or other efficiency testing, or inspection and visible signs of patchy rotor overheating. If the pump, was a "mono" type, then these have much higher motor start current requirements, to a multi stage centfifugal type. Especially if the pump has not been used for a while. I think the "mono" ones I was involved with "submersible bore hole type", back in the 1980's, required 3-5x the start current of a centrifugal. Once the pump had been run for a while, subsequent starts are a litte easier on the current required. I had a successful experience, designing an inverter that allowed, starting and running 1.8kW 415V 3phase mono type pumps, from Solar panels. I don't recall any terminolgy of motor rings in any normal 3phase induction motors either. 15kW, is a decent size. I guess for irrigation. What was the SWL, or head required to be pumped? How many L/s? Gordon. become more energy aware |
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| KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
mmmm The sparkie is now somewhat annoyed with me for telling him that it was unacceptable to replace the overload relay with one that did not fit the original housing. (the reset button now cannot be pressed without removing the cover) I've told dad to stick up for himself and the sparkie to grow up and get over it, fix it properly, then we can get on and fix the pump! Luck favours the well prepared |
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| KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
BTW, the pump is at the bottom of the hole , connected by a shaft that runs in bearings down the 5"casing. Used for dual purpose, both irrigation, runs a dozen or so sprays on the flat (that go pretty hard) or pump to the tank ontop of the hill which is 70M head + the distance down the hole which is at least 20m. Pressure gauge reads 140psi when pumping to the top of the hill and about 30-40psi when irrigating. Pump runs every night in summer, with a few extra hours on the off peak over the weekends to "catch up" with pumping tot he tank on the hill or irrigate the "green band" which is a dozen sprays in front of the house used as a fire break. I've never seen 2" poly pipe like it (going up the hill) must be at least 8mm wall thickness, there was a time when the troughs on the flat were bursting pipes all the time as they did not realise everything at the bottom of the hill needed to deal with 140PSI. (which incidentally rips apart blueline pipe like a bannana!) To make matters worse I priced up an 11KW contactor from my local ideal electrical (not by any means the cheapest out there) and the contactor -retail for me off the street was $320.... a fair difference to $577 these rogues charged us. Luck favours the well prepared |
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| KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
WIN WIN WIN WIN Sparkie returned my call today and apoligised for the bill the excuse was that his new 18 year old girl doing the invoices was told the prices fr the parts and automatically added their "normal" margin. Unfortunately the prices quoted to her already included the margin. So he should be knocking off a few hundred bucks off that bill! Pump however is still causing grief so i'll get it apart next week for a look see with some luck. Luck favours the well prepared |
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| isaiah Guru Joined: 25/12/2009 Location: United StatesPosts: 303 |
KarlJ '  '
Im having some trouble here Why do you need a bore motor at all? You guys say you live downunder if so you should be able to just drill a hole up in the ground and the water should just run out. Like drilling a hole in the bottom of a water barrel. If you lived up here then you have to drill down and pump it up.' 'URL=http://www.motherearthnews.com/Renewable-Energy/1973-11- 01/The-Plowboy-Interview.aspx>The Plowboy Interview[/URL> |
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| neil0mac Senior Member Joined: 26/12/2009 Location: AustraliaPosts: 210 |
Riiiight, Isaiah. You'd get some belly laughs down 'ere if it wasn't for the gravity of the situation. |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
isaiah We use the pumps to keep the water in the ground not to get it out. 
If we didnt you side of the world would drain dry. Pete. Sometimes it just works |
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| isaiah Guru Joined: 25/12/2009 Location: United StatesPosts: 303 |
Hey is that where the term sh*t UP comes from. Do you guys use water or compressed air to flush your stools down there? Sounds like it would be a real pain keeping that stuff in the ground . Somebody said that you have to use a special stool also? Thats probably why we get all that stuff in the air and ground when it rains up here. URL=http://www.motherearthnews.com/Renewable-Energy/1973-11- 01/The-Plowboy-Interview.aspx>The Plowboy Interview[/URL> |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
As for stools, at least we dont turn our bar stools upside down and invite 3 mates around and call it a party. 
Pete. Sometimes it just works |
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MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Stools and bore pumps aside, is it feasible to use a windmill to pump your water? I always thought of using a 3-bladed, up-wind design driving a worm-and-down-gear wheel coupled to an off-center cam to run a pump rod up and down. The gear ratio could be easily managed by the worm and down-gear size selection. Just an idea, but it would require only a shot of grease every year or so and I don't think it would even have to be furled at all; just let it scream. Depending on the topography, the water may be shallower at the top of the hill. If that's the case (and it often is) you could put in a well up by the tank and use wind as your source and just forget about it. If your ground isn't like rock, sinking a well is no harder than driving a well point down past the water level and securing the pipe to a pump head up on top (little concrete pad). The down rod simply pulls a little slug with two check valves in it. Easy (kinda). In the "old days" the pump was leather and had to be primed, but these days, silicon check valves work like magic. Just an idea, but it may be just the ticket for the long haul. . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| isaiah Guru Joined: 25/12/2009 Location: United StatesPosts: 303 |
What are you really wanting to do here? My son has a very old one of those motors back by the woods. If you are serious I could get some pictures for you.??? might have to wait til snow goes off. I have a well with a picture pump on it and I pump water with it every day and have done so since 1999.I did change the leathers once . If you pump once a day you dont need to prime. I have it set up with a weep hole and a small drain tube so it dosent freeze in the winter. I also have a couple of old Airmotors the one is a 1931 but they are gear driven. The one jr has is the one with the up and down rackafrackaus. That would be a good project for you to make a 1/2 or 14 scale model. ' 'URL=http://www.motherearthnews.com/Renewable-Energy/1973-11- 01/The-Plowboy-Interview.aspx>The Plowboy Interview[/URL> |
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| KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
Unfortunately the bore is dual purpose irrigation and stock watering / water for the rental we have on the property too, (she's just there to tell us there is no water otherwise shed be long gone -hopeless at paying the rent even at $80/per week!) Delivery req is thus ML / year, windmill would need to be 20KW plus and on a massive tower as the bore is on the flat, drilling new bores is VERY expensive think at least $50K to set up. Luck favours the well prepared |
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| KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
last but certainly not least, got the revised bill today they knocked off $450. Not bad for asking the question and catching them out! Luck favours the well prepared |
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