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Another Rotary Phase Converter

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Keith Foor

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#61
OK, So I am looking at the wiring and design on this. And while I hate to pick apart things, I really hate things getting smoked and giving people issues. So, I see how you are wiring up your run capacitors with independent switches. Might be a good idea, but Im not seeing individual wires running back to a high current buss connection. What wire are you shipping the high current back from? Each cap seems to have 12 gauge wire on it, but do they go to a number 6 or something that runs to the motor lugs or is it run on 12 gauge? The running current in each cap with 12 gauge wire will be fine. But the caps as a whole will have alot of current flow. Something to think about. Might also look at the switches. for the smaller caps, a 5 amp switch would be ok, but bigger caps bigger currents. Switches may be rated in HP and not amps. Once your switches are set, make sure that you are not going to exceed the current rating of the switches. Only reason I bring this up is I have seen home built and factory built RPC's that had all the caps jumpered together with 12 gauge wire, and then a single 12 gauge wire running over to the motor. On a 1 or 2 HP converter, it's fine. On a 10 or bigger HP RPC, 12 gauge ain't gonna cut it and what typically happens is all the current, remember that EVERY amp of current in the created leg WILL flow across the run capacitors, overheats the 1/4 blade connector, and it gets weak, starts arcing, gets hotter and finally burns off the wire. If you have already thought of this, then disregard all this.... if not, it might be something to consider.
 

JimDawson

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#62
OK, So I am looking at the wiring and design on this. And while I hate to pick apart things, I really hate things getting smoked and giving people issues. So, I see how you are wiring up your run capacitors with independent switches. Might be a good idea, but Im not seeing individual wires running back to a high current buss connection. What wire are you shipping the high current back from? Each cap seems to have 12 gauge wire on it, but do they go to a number 6 or something that runs to the motor lugs or is it run on 12 gauge? The running current in each cap with 12 gauge wire will be fine. But the caps as a whole will have alot of current flow. Something to think about. Might also look at the switches. for the smaller caps, a 5 amp switch would be ok, but bigger caps bigger currents. Switches may be rated in HP and not amps. Once your switches are set, make sure that you are not going to exceed the current rating of the switches. Only reason I bring this up is I have seen home built and factory built RPC's that had all the caps jumpered together with 12 gauge wire, and then a single 12 gauge wire running over to the motor. On a 1 or 2 HP converter, it's fine. On a 10 or bigger HP RPC, 12 gauge ain't gonna cut it and what typically happens is all the current, remember that EVERY amp of current in the created leg WILL flow across the run capacitors, overheats the 1/4 blade connector, and it gets weak, starts arcing, gets hotter and finally burns off the wire. If you have already thought of this, then disregard all this.... if not, it might be something to consider.
Keith, I appreciate your comments. Please read the description below and see if there is a flaw in my thinking.

It's a little hard to see in the pictures in the posts above. The switches are fed from 60 amp terminal blocks (red and black) on the door which in turn are fed with dual #10 wires from the power distribution block. My biggest concern is really the jumper strips on the terminal blocks, I've had problems with those in the past and will be re-tightening them down the road a bit. The switches are rated at 20 amps. The manufactured leg bus (yellow) is a row of 60 amp terminal blocks fed with four #12 wires (I couldn't find any #10 yellow THHN). You are correct, the caps are connected together with #12 wire, with the exception of the the 60uF caps which are connected to the buss with dual #12's. From the switches to the caps it is all #12 with the exception of the 60uF caps which are fed with #10. The total value of each row of caps adds up to 30uF or less, with the largest cap in the row nearest the buss on the right. The connectors I used are high quality and have a high spring rate for a good grip, hopefully they will be OK. Like you I have seen many push on connectors fail, and if these give me any problems, I'll do something different. I couldn't figure out how to calculate or even guestimate the expected current in each row of caps so I gave it my best shot and also kind of went by a professionally built 20HP RPC that I installed for a customer a while back.

The main power wiring between the power distribution blocks and the main contactors is all dual #10. The motor will be connected with short run # 8 wire from the 3 terminal power block. The lathe will be connected to the 3 terminal power block with a run of #6 THHN.
 
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JimDawson

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#63
1510611795231.png

I'm learning a lot about 3 phase motors. I just got back from the motor shop with some interesting results. The motor shop had never seen one like it. After some head scratching, they hooked up the motor to a 150V, 60 Hz, 3 phase supply and it ran, but was drawing 22 amps which is way high for that motor unloaded operating at reduced voltage, and is consistent with the results I experienced when I tried to fire it up on 240 volts. The conclusion is that either the windings are internally shorted, or........ possibly the motor is so special and designed to run at a minimum of 84 Hz that there are fewer turns on the windings and using bigger wire to run at the nameplate rating of 84 to 114 Hz and that it just won't run at 60 Hz.

Unfortunately the shop didn't have a 15 Hp motor in stock, so I'm on the hunt for one. There was a Baldor on the local Craigslist a few days ago for $200, but the ad is no longer up. I have a couple local guys I'm going to check with before I widen my search area.

Stay tuned for the continuing saga :)
 
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Karl_T

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#64
Man, i must be lucky. there's a place called Borchart Industrial , http://www.borchartsteel.com/index.html about 40 miles from me. They must have a 1000 three phase motors in an old warehouse. Their initial asking price is $100 plus $5 a horse. But they will deal if your money is green, if you want several, you'll take an ungly one, yada yada.

I'm sure a new motor will solve your converter issues.
 

mksj

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#65
Interesting, I am always learning new things by following these posts. Hard to know if it the design of the motor or a fault, as it runs.
May want to go for a new motor, but shipping is going to be killer if you need to go that route and can't find anything local. Dealer's Electric often has reasonable NOS and lists one recommended for use as a phase converter.
http://dealerselectric.com/S2532.asp

eCrap special maybe if you can reasonable shipping and are looking for something new. Like the industrial duty Leeson, Marathon and Baldor motors.
https://www.ebay.com/itm/New-Leeson-AC-electric-motor-15HP-1765-RPM/332231194245

Super build quality, nicely done on the cabinet.
 

Ulma Doctor

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#67
well that's a first for me!
i have not seen a motor with a 84 to 114 Hz ratings :chagrin:

was the motor from a screw compressor??? that would explain some things if it were
 

JimDawson

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#70
A little update, nothing is happening on the RPC :grin: I'll have a new motor here in a week or so.

But..... A small problem. We brought in a 25 KW, 3 phase generator to test the lathe. That didn't go well...Tripped the main breaker in the control panel instantly. Based on some very quick troubleshooting, it looks like there is a short somewhere in the main servo drive power circuit. I need to isolate the individual devices to track down the problem. I guess the 1700 mile trip home didn't agree with it. :(
 

Karl_T

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#71
There's something about moving old CNCs... Seems to just kill them.

I bought a really nice Vectrax mill (Brand sold by MSC) with a Fanuc 0M and it ran fine till I moved it into my shop. Now a gremlin lives in there :( I am about to give up and refit the machine to a control I can maintain. The trouble is probably easy to solve by an experienced Fanuc technician. But that guy just don't live in this rural area.

Hope your issues are easier than what I've experienced.

Karl
 

JimDawson

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#72
There's something about moving old CNCs... Seems to just kill them.

I bought a really nice Vectrax mill (Brand sold by MSC) with a Fanuc 0M and it ran fine till I moved it into my shop. Now a gremlin lives in there :( I am about to give up and refit the machine to a control I can maintain. The trouble is probably easy to solve by an experienced Fanuc technician. But that guy just don't live in this rural area.

Hope your issues are easier than what I've experienced.

Karl
I hope so too. It wouldn't bother me at all to rip out the entire control system and install my own, including my software. I'll bet I can get enough money out of the Fanuc hardware to more than pay for a complete retrofit.

I've had a chance to do a bit more troubleshooting and it looks like the main power transformer may have a shorted winding. Phase to phase resistance is 0.8, 0.4, 0.8 ohms. That is not a good sign. Next I'll check the inductance on the windings to see what that looks like. Then maybe head to the local transformer shop to see what they have to say.
 

Blackjackjacques

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#74
Running an AC motor at frequencies less than designed for should cause a pretty quick and substantive increase in magnetizing current and ultimately saturation. With respect to cooling, speed as well as magnetizing current, typical AC motors are designed for a narrow window of both voltage and frequency (V/Hz). You can run a 50 Hz motor at 60 Hz power line frequency and not have a problem with cooling, mag current, but speed will increase 6/5 and pf will also denigrate. If you go the other way, cooling is denigrated as well as mag current, and rpm will, of course, decrease to 5/6 -- generally meaning you have to derate the motor at the very least. VFD rated motors are specifically designed to consider the wider frequency window, and provide adequate cooling means, increased current, etc for worst-case (e.g., lowest speed, etc) circumstances. It sounds like the subject 84 - 114 Hz motor to be an application specific type motor permitting a 1.4 speed range window -- or maybe perhaps subject to some frequency control, etc. Good luck
 
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JimDawson

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#75
UPDATE: IT'S ALIVE !!!!!!!!!

Finally have a working RPC. We found a Baldor 15HP motor on ebay for $300, with FREE shipping. Not a bad deal. Had to put bearings in it but that was cheap.

1512606063246.png

Fired right up, was drawing about 24.5 amps on L1-L2 unloaded with no capacitors switched in. So I started switching caps in and got the legs kinda close before I ran out of caps to switch in. Need to do some swapping around on the caps. As I switched in caps, the current draw went down to about 16 amps unloaded. Once I complete the balance I suspect that will drop more, then I'll start switching in power factor correction and get it down more. Ideally, I can get the idle apparent power down to zero, we'll see how that affects the new smart meters, kinda curious about that.

Then we load tested it. This is the 6500 watt, 3 phase, Flux Resistor. :grin: ~8 HP worth. Interestingly enough, when loaded, the current was only about 25 amps, which means the incoming power didn't even see the RPC motor, because the load was about 25 amps. Note the ground clamp on the left o_O

1512606785711.png


With the caps switched in the T1 T3 leg is a bit high (255V) unloaded and is low when loaded (223V), but the T2 T3 balanced out to within 1 volt of T1 T2 (239V vs. 238V) I have a bit of voltage drop on the line to my shop, the picture is in the unloaded condition.
1512607117132.png

1512608419053.png

1512608460073.png

1512608487526.png
Anyway, it has been a long arduous journey to get to this point. In hindsight we should have just bought a motor to start with, would have saved a week's worth of work. But we didn't expect the motor problems we had.

But the good news is that it works now, and we'll get it wired into the lathe this weekend.

:dancing banana: 1512608419053.png 1512608460073.png 1512608487526.png
 
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JimDawson

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#76
Final update We finally got the RPC wired into the lathe.

It doesn't seem to matter which way you spin the idler motor up to start. I tried it in both directions, and the only thing I noticed was the minor vibration changed a bit between CW and CCW, but nothing bad happened in either direction. Took some experimenting to get the low leg on the correct set of caps, but swapping leads at the motor end fixed that.

I made a slight tactical error when I chose the enclosure, I grabbed a 6 inch deep box off of the shelf and I should have used an 8 inch deep box, I have 2 of them on the shelf. The door won't shut all the way :mad: The caps hit the wireways on the door, poor planning on my part. I'm going to build a 1 1/4 inch extension for the box, not a huge deal, but irritating.

I'm pleased with the voltage balance. 239 (incoming), 237, 239, 236. Incoming power is running 1.4KW with the lathe powered up and the spindle running unloaded. Max system load seems to be about 9.5KW with the spindle at 150% power on accel. What I find a bit odd is the incoming power is 11.8 amps, but the 3 legs of the 3 phase are right around 20 amps. I guess the PF correction is doing its job, glad I added that. Hopefully the power company will only see the 11.8 amps. :grin: But I suspect the new smart meters read KVA rather than KW like the old ones did, I'm going to see if I can figure that out. The incoming power reads about 25 amps with the PF correction out of the circuit. These numbers verified by my Fluke clamp on. Everything seems to run OK.

1514389537086.png

1514391237828.png
 

Blackjackjacques

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#80
Nice - when redoing your door, remember to leave about at least an inch of clearance between the panel door and any current carrying part. I cannot for certain figure out what is going on with your pf and the meter readings. The pf corrected circuit should normally read substantially less current than uncorrected. From your photos, the L1 L2 meter shows 11.8 A before pf correction and about 21A when corrected -- if I am reading your meters correctly and assuming that L1L2 is your single phase input and T1 T2 T3 is your derived 3 phase output. It would be helpful if you can provide a simple one-line schematic showing the connection of the motors, including the load motors and how everything is wired.
 

JimDawson

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#81
Nice - when redoing your door, remember to leave about at least an inch of clearance between the panel door and any current carrying part. I cannot for certain figure out what is going on with your pf and the meter readings. The pf corrected circuit should normally read substantially less current than uncorrected. From your photos, the L1 L2 meter shows 11.8 A before pf correction and about 21A when corrected -- if I am reading your meters correctly and assuming that L1L2 is your single phase input and T1 T2 T3 is your derived 3 phase output. It would be helpful if you can provide a simple one-line schematic showing the connection of the motors, including the load motors and how everything is wired.
It is a bit confusing. The L1-L2 meter at the top is showing PF corrected incoming power and the CT is on the input leg. From the panel T1, T2, T3, go to the motor, the lathe is paralleled off of the motor leads at a J-box on the wall. There is a CT on each leg in the panel. Once the two power contactors pull in, the PF correction caps are across T1(L1)-T2(L2), and the balance correction caps are across T1-T3, and T2-T3.

RPC As Built.png

Actually I have just figured out how to build an over unity machine, puts out more power than it is supplied with :cautious::grin:
 
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Blackjackjacques

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#82
It is a bit confusing. The L1-L2 meter at the top is showing PF corrected incoming power and the CT is on the input leg. From the panel T1, T2, T3, go to the motor, the lathe is paralleled off of the motor leads at a J-box on the wall. There is a CT on each leg in the panel. Once the two power contactors pull in, the PF correction caps are across T1(L1)-T2(L2), and the balance correction caps are across T1-T3, and T2-T3.

View attachment 251419

Actually I have just figured out how to build an over unity machine, puts out more power than it is supplied with :cautious::grin:
For over unity it is called a synchronous condenser, or just a synchronous motor to provide leading power factor. If you are making more power than put in, then Elon Musk and the Nobel committee would like to talk with you. :)

In the old days, engineers used to mix, where they could, synchronous motors with induction motors to balance pf where the motors are on at the same time, etc. However, having too much leading VARs can be as bad as having too much lagging VARs. I'm confused as to what the meters are showing. I assume that the Idler and Lathe motors are both wired Delta. If you can provide the particulars for these two motors, I can run a quick analysis for you to model and predict the actual parameter values, VA, VAR, I, etc. Motor nameplate data will do, but if you have actual resistance/inductance for the windings, I give you a precise picture.
 
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Blackjackjacques

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#84
The idler is a standard 9 lead, Y connected. http://www.baldor.com/catalog/CEM2333T#tab="specs"

The lathe 1 hp hydraulic pump is also a 9 lead, Y connected, but the other motors are all AC servos.

The following analysis may help your efforts to validate the design and if you are getting the targeted performance of your system. Double check my math, but it seems viable.

On the 15 hp Baldor - since you are running 2 Y (low voltage)or two identical Y windings in parallel, the impedance of the windings would be half than if you ran it in the 1 Y configuration. The 0.83 power factor rating for the motor does not indicate if that is for the motor running 1Y or 2Y, but my expectation is that the winding configuration would impact power factor. This is where having the actual measured impedance of the motor windings would have been more valuable – and especially when we are configuring this 15hp motor to be placed in parallel with yet another (load) motor winding system. But let's go with the manufacturer’s .83 rating for now:

Looking at the 15 hp motor alone and to take the pf from 0.83 to 0.95

AT.83 PF
Watt(P) (input) to motor = HP x 746 / eff. = 12.11 kW (bottom of the pftriangle)
VA(S) =P/pf = 14.6 kVA
VAR(Q) = VA Sin Θ= 14.6 kVA Sin 33.9 degrees = 8.14 kVAR
I= VA/V = (14.6 kVA/(230 x 1.73)) = ~36.7 A

AT.95 PF
Watt(P) (input) to motor = HP x 746 / eff. = 12.11 kW (bottom of the pftriangle)
VA(S) =P/pf = 12.7 kVA
VAR(Q) = VA Sin Θ= 12.7kVA Sin 18.2degrees = 3.97 kVAR
I= VA/V = (12.7 kVA/(230 x 1.73)) = ~32A

So 8.14 - 3.97 kVAR = 4.17 kVAR leading are needed or C=kVAR/ώV2=4.17 kVAR/2*Π*f*V2=209mfd. Connecting the capacitors in DELTA across the 2Y connections =209 mfd/3 = 70 mfd across each line.

So this approach improves the power factor for the 15 horse motor from0.83 to 0.95 and reduces the current from 36.7 A to 32 A.

Looking at the 1 hp motor alone and using typical NEMA values for eff. = 82.5% and pf = 0.8:

AT.80 PF
Watt(P) (input) to motor = HP x 746 / eff. = 0.9 kW (bottom of the pftriangle)
VA(S) =P/pf = 1.13 kVA
VAR(Q) = VA Sin Θ= 1.13kVA Sin 36.9degrees = 0.678 kVAR
I= VA/V = (1.13 kVA/(230 x 1.73)) = ~2.8 A

AT.95 PF
Watt(P) (input) to motor = HP x 746 / eff. = 0.9 kW (bottom of the pftriangle)
VA(S) =P/pf = 0.95 kVA
VAR(Q) = VA Sin Θ= 0.95kVA Sin 18.2degrees = 0.297 kVAR
I= VA/V = (0.95 kVA/(230 x 1.73)) = ~2.4 A

So 0.678 – 0.297 kVAR = 0.381kVAR leading are needed or C=kVAR/ώV2=0.381 kVAR/2*Π*f*V2=19mfd. Connecting the capacitors in DELTA across the Y connection = 19mfd/3 = 6.3mfd across each line.

So this approach improves the power factor for the 1 horse motor from0.82to 0.95 and reduces the current from 2.8A to 2.4A

Therefore, with the 15 hp generator motor in parallel with the 1 hp load motor, the total capacitance across-the-lines would, in theory, be 70 + 6.3mfd = ~75 mfd to bring the system pf to 0.95 and the total corrected rms current you should see on your Fluke should be about 34.5 A.

What is missing in the analysis is the fact that the 15 hp drive motor is being driven with one broken leg, so its shaft hp would be reduced at least one third and the inrush power requirements will increase correspondingly, and its anybody's guess how the power factor will present until the motor comes to steady-state speed.

However, the analysis is valid if the drive motor was operated in a true motor-generator configuration.
 
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