Sizing start & run capacitors for 100hp 3 Phase motor - Page 3
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  1. #41
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    Quote Originally Posted by newbea View Post
    I did notice his errors and used it more for the practicalmachinist pdf that he linked as well as looking at the overall schematic. Can you expand on why a factor of 2 is more to deal with?
    Only about another 50 FLA.

    A 100Hp RPC is not a beginner's project. Here is some light reading material.

    https://lib.dr.iastate.edu/cgi/viewc...77&context=rtd

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    I think that you have become focused on the RPC instead of the best topology for the entire project. By spoon feeding us information you have been getting a lot of answers that have been evolving towards different solutions.

    Some have been concerned about price but now that I see a solar project with greater than $100K in materials not counting mounting hardware I question trying to save costs with an RPC.

    I would second (or is it third) the idea of designing the solar/inverter system for an output voltage of 480 VAC. This reduces the wire size and losses for your power distribution. Obviously your largest load is the hydraulic pump. Design for it. While there may be many more uses for 120 VAC, these are much lighter loads and are easily served with step down transformers.

    By using a VFD to power the hydraulic motor load, the startup surge would be almost eliminated by slowing accelerating the motor. In fact the hydraulic pump could probably be left connected to the motor at all times simplifying its design and reliability.

    Further that 93kW of solar will typically only supply about 80kW and that is only at noon. Without storage (batteries) the solar inverters will not have any surge capability. Assuming the RPC is successfully started using a pony motor there is now the issue of the start up current for the hydraulic motor. I question if it will be able to start the hydraulic pump even at noon.

    Now if the solar system is grid tie (again spoon feeding information) then power from the grid changes all that has been said.

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  5. #43
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    He really cannot get a 480 suitable DC voltage from typical panels, which are typically rated for use in up to 600V strings. If he uses utility type panels, that may change, I have not dealt with those, and can offer no input on them. UL only handles 600V and below, which is shy of the DC voltage required.

    The 240V is more do-able, and really is not bad for ~100kVA setups, current-wise.

    The project sounds as if it may need to be reviewed on an engineering level to see if the goals are meetable with the proposal as-presented. A power systems PE would be appropriate.

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    I am a little out of my pond on this one, but from a simplicity standpoint, it appears that the best is an inverter coupled to a step up transformer for the hydraulic motor.

    Tom

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    Quote Originally Posted by thermite View Post
    Transformers have "inrush" too. While of high nominal transfer efficiency, they also DO waste measurable and sometimes significant power even idle.

    PM has recent figures for the effect on a poster or two as to utility bills - transformer left ON 24 X 7 or switched OFF for all but one active shift's actual use.

    You may not have a "bill" here, but you still do have a budget of sorts in the power itself that is available and for what part of any given day.

    The higher the step-up ratio, the harder the hammer on that 120 VAC feed as well.

    Do the simplest of the maths. You are on the short end of a lever.

    Load Amps @ 220 or 440 translate to 4 or 2 times the Amps drawn at the low-voltage feed .... before you even think about single to 3-Phase as well.

    That will be hammering the PV system's inverters, and with "BFBI" at that?

    You can see where a soft-start/slow-rampable VFD with intelligent controls "talking" to the PV system as well as "Headquarters" can be gentler by far?

    Need to survive atmospheric air-mass electrical storms? Near-miss - and closer lightning strikes?

    Not new. Global telcos were at it even before Microwave and satellite arrived.

    There are ways.
    Thank you for this in depth write up of some of the pitfalls that I might face up ahead. These are the types of answers that I appreciate because they allow me to get a bigger picture idea and focus on solving each major problem that can arise.

    The soft-starter / vfd for this main motor would be a good solution to reduce the inrush current and maintain this 100hp motor.

    Having an inrush limiter between the PV inverter and the transformer could also help reduce the load on the PV system as well

    [edit - change the PV output current]
    Something like this
    Code:
    [solar pv] split ->  A) [110v for normal use]
                                    B) [current-limiter] -> [switch] -> [set-up transformer] -> [soft-starter/vfd] -> [100HP 3PH idler motor]
                                    or
                                    B) [3 Phase Inverter]
    After reading some more of the comments that reminded me, going from higher voltage to lower is more efficient.
    This increases the danger so the power needs to be better isolated.
    Code:
    [solar pv 440v] split ->  A) [switch] -> [step-down transformer] -> [110v for normal use]
                                    B) [current-limiter] -> [switch] -> [soft-starter/vfd] -> [100HP 3PH idler motor]
                                    or
                                    B) [3 Phase Inverter]
    Any feedback on this layout?
    Last edited by newbea; 11-30-2019 at 11:03 PM. Reason: changing some values

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    Quote Originally Posted by JST View Post
    Frankly, I think you have that backwards.

    You can run most any PV up to 600VDC per UL, as the panels should be set uop for it. Unfortunately, that is not super practical, because it is not convenient for any US voltages. (f you wanted 380V, it would be fine.)

    It sounds as if you ought to set up to produce the PV output a bit under 400VDC. From that you can produce 240VAC with an inverter directly, using the P V output directly into the DC bus of the inverter. Any solar inverter of the size you want will handle that fine, there are a number of makers of such units, although cheap they are not.

    From that, you can use transformers to get 120V, which is very likely the lowest power draw you will have.

    Starting from 120V, you would have the highest currents, and consequently the largest losses. Not a good plan, IMO

    Do you plan a battery system for "ride-through" and overnight?
    I should've read this before my previous reply but I didn't.
    First for the nights, nothing yet; batteries are super expensive and lithium still seem a bit dangerous; the fire hazard part at least.
    I agree with you that It does make sense to run higher voltages and step down to 110 for normal usage.

    Thanks for that reminder.

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    Quote Originally Posted by rpseguin View Post
    A pony is a good solution to solving the inrush startup current.
    I have questions about your 50HP load motor though.
    What are you driving?
    Are you actually going to use full rated power and current?
    Is it a hard start load? Ie, does it need to spin up fast/immediately, or can you slow/soft start it?
    Can you use a VFD to drive your 50HP load motor instead of using a RPC?
    The 50HP is started unloaded and most likely will not go to the full amp load, a soft starter can work. The main reason for avoiding a VFD is that I will eventually have more 3 Phase motors, nothing as large as 50HP but the complexity of adding a VFD for each new machine will become maintenance later.

    Having the 100HP idler can power the 50HP load and a few smaller machines.

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    Quote Originally Posted by rons View Post
    Only about another 50 FLA.

    A 100Hp RPC is not a beginner's project. Here is some light reading material.

    https://lib.dr.iastate.edu/cgi/viewc...77&context=rtd
    Thanks for the research paper, I am going to take some time and see what the research says.

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    Quote Originally Posted by TDegenhart View Post
    I am a little out of my pond on this one, but from a simplicity standpoint, it appears that the best is an inverter coupled to a step up transformer for the hydraulic motor.

    Tom
    The main concern with this setup is having to add additional 3 phase appliances; nothing as large as 50HP though. That would require redesigning parts of the system over time instead of just having the appliances plugged into the 3 phase line.

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    Quote Originally Posted by newbea View Post
    .....
    First for the nights, nothing yet; batteries are super expensive and lithium still seem a bit dangerous; the fire hazard part at least.
    ....
    The first advantage of a battery system is "brown-out" protection. There are clouds, and output drops like a stone when clouds cover the sun for short times on partly cloudy days. Even in Florida....

    The other advantage is "regulation".... batteries tend to keep a system regulated to their voltage, through the action of the charging system, which tracks the battery voltage. Otherwise you may have fauirly large changes in voltage..

    The batteries are a reference, a current sink, and a source for short times of no sun, even if they are not extremely large capacity. Of course the more capacity the better.

    This is a much more complex system than I believe is being understood... It needs careful evaluation for what is wanted, vs what is probably going to be provided by the system under the various choices of configuration you have available as choices.

    You might want to consider a grid tie system where the PV is the prime source, if you can get powerco approval for such a large system that may turn from a source to a sink in a few seconds (they hate that). In that way you have continuity through the powerco grid power when there is no sun, and generated revenue when there is solar input.

    I am still a bit unclear about what you expect from your proposed system. From the various statements made, I think it sounds as if it will not be able to do what may be expected, for a number of reasons, the largest of which is the variability of the power source (solar), which can drastically change in a few seconds. You need something to stabilize that.
    ".
    The powerco may be accepting inputs from many small solar systems (15kW max, typically), but they are usually scattered around, so that some may be shadowed, but others are not ("diversity"). The average tends to even out reasonably.

    You will have one large array, and no averaging over a large area. When you are shadowed, all your power is reuced, you have no "diversity". And, if I understand your statements, also no plan to stabilize output to cover your loads when you are shadowed.

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    Quote Originally Posted by newbea View Post
    The 50HP is started unloaded and most likely will not go to the full amp load, a soft starter can work. The main reason for avoiding a VFD is that I will eventually have more 3 Phase motors, nothing as large as 50HP but the complexity of adding a VFD for each new machine will become maintenance later.

    Having the 100HP idler can power the 50HP load and a few smaller machines.
    I'd STILL go VFD for the 50 HP. You really, really gain from ability to slow-ramp it as to essentially eliminating starting inrush TOTALLY as a hammer on the PV's inverters.

    AND THEN.. same again, VFD for the next LARGE unattended load, same reason.

    AND THEN.. much smaller RPC for smaller 3-P loads. Which might be used only when a two-legger is actual at the site.

    Given the KINDs of things as can go wrong?

    Maintenance helicopter or hovercraft should have an IC-engine driven welder/generator or gen set on the chopper or boat. Or truck. Or Mars lander. Wotever.

    Regardless.

    SOL if the PV array or inverters are what has gone pear-shaped, needs fixed.

    NO local power atall! Can't even re-charge cordless HAND tools!

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  16. #52
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    90 kW is a very large array for a single offgrid user.

    What JST and others have said, politely, I'll say bluntly, having installed and used these things for over 40 years. You don't understand your proposed PV system.

    You need to calculate your loads and usage realistically, then output (in kWh annually) from your panels, realistically. 93kW is just output at Standard Test Conditions. (See here for Standard Test Conditions for PV's.) They almost never exist in real life. There's also the local factor, too. Average ambient temperature, cloud cover, hours of sunlight, solar exposure, etc, etc. There'll be a local solar developer in your area that knows this, based on data from past installations. Installers, less likely. You will need to adjust that factor downward if it's for gridtied.

    Since this will be a remote system, not connected to the grid, you'll manage it in a much different way than if it were gridtied. In a gridtied installation every watt hr of generated energy is used onsite or goes into the grid. (Less inefficiencies, of course). In remote systems, the goal is to have power available at all times, with storage for overnight and cloudy days. The ideal is to have the battery bank at near full charge by noon on a sunny day, taper charge and feeding a dump load after that. More on this if you're interested.

    A battery bank with 3phase inverters is the best way to manage large loads. Lead acids are still the biggest bang for the buck. Li-ion is silly for a stationary application, in spite of all the PowerWall marketing. Get the biggest cells you can to avoid imbalances, in your case forklift size.

    Inverters from mfgers like Outback are stackable for 3 phase. Use a different inverter for your single phase loads, possibly even an inverter for each load. Inverters are very reliable these days - the industry standard warranty is now 10 years.

    Someone familiar with a remote system as large as you're proposing will be hard to find, but you need them and they'll be worth it. You're looking at a $100K PV system installed, minimum.

    And (if I haven't offended you already ) please, please give us an overview of your system and its intended purpose. Without it we won't be able to give you the best advice. Garbage in, garbage out.

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  18. #53
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    Quote Originally Posted by neilho View Post
    And (if I haven't offended you already ) please, please give us an overview of your system and its intended purpose. Without it we won't be able to give you the best advice. Garbage in, garbage out.
    Ahem... now that we are down to the proverbial "brass tacks"...?



    MY take (Dominant-Carrier Global Telco of the many-small-islands flavour)...

    is that our poster is one member of a team. Someone ELSE - or several - DOES have a klew. Or so one may hope.

    He's just fixated on "selling" a higher-up on RPC's being more durable than dirty-beach-sand.

    Could was. Or maybe not-so-much?

    But it isn't even remotely germane to this environment.

    That's the bedrock. The rest ain't my rice-bowl.

    Our supply boat only hit an island twice a year? It carried up to a year's worth of Diesel fuel. In case the bugger SANK before a replacement could be arranged, next go.

    BFBI, but the phone and telegraph worked and Carefree and Wifeless, Able & Tireless got paid.

    BTW.. More than one tribe of "middleman" in the world. Got medium-Voltage Dee Cee off a battery pile? Tap points? DC motors still exist. So do Hydraulic load-sharing goods.

    Ever heard the term "no single point of failure"?

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    Lots of good information coming to you.

    And JST is correct regarding my suggestion of 480V from a single phase inverter (and that is what I was thinking) is a no go. But he got me doing just a little more research.

    480 three phase is readily available with solar. With three phase 480 (or 240) and the system just got simpler as no RPC is required and those other 3 phase loads are easily handled. A vfd (or possibly some other soft start method) would still be needed to start 50 hp motor.

    As has been stated by others with far greater experience than I (I have only done 2 grid tie solar systems) without either grid tie or batteries the operation of this system will be tied to the whims of mother nature in addition to the schedule of the sun.

    I agree that a professional with experience in solar power generation and distribution should be consulted as there is a vast amount of information (not yet provided) to be digested to come up with the best solution.

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    Quote Originally Posted by newbea View Post
    Looking below a lot of people recommend the pony motor but I am currently testing at a factory that builds and tests motors. They have very high voltage and amp rated electricity; well above 600v and 300amp.

    I could use a pony motor since there are a few lying around.
    If you use a pony start motor there will be a pulley on both motors with a rubber belt connecting them together. How will you disconnect the belt once the
    target motor starts to run on it's own? Have you thought about spinning up the big motor with a wood faceplate attached to the motor instead of a pulley
    and using a very larger angle grinder/buffer to spin the wood wheel via friction When up to speed just remove the buffer pad from the wood wheel.

    BTW, in the video he uses a wood sheet to mount everything on. Forget about the fire hazard problem which is not as bad as a potential shock problem.

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    Quote Originally Posted by JST View Post
    With no balance capacitors, there will be minimal voltage/ current and no issue. If there are balance capacitors connected, they will provide exciting current assuming there is some residual magnetism in the iron to generate rotor currents during spin-up. That can load the pony, and also may have a sync issue.

    Answer, is "don't do that".
    Don't do what - balance capacitors, pony motor, or un-syncronized energizing of the idler?

    Honestly I cannot imagine how one *would* sync that up for a 100 hp idler. Nothing is variable as a rule, one would have to
    put a sync test device across the contactor and run the pony motor with a variable drive. But then I suppose that would be down
    in the noise in terms of cost for the test rig.

    I cannot imagine trying to start up a 100 hp idler without using a pony motor to spin it up.

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    Rons

    I have seen a lot of simple and clever designs for removing the belt from the pony motor. I would prefer to leave the belt engaged (whats the harm?) than have to hand hold some awkward pony while trying to press the start button.

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    Quote Originally Posted by jim rozen View Post
    Don't do what - balance capacitors, pony motor, or un-syncronized energizing of the idler?

    ......
    Don't try to spin it up with any capacitors connected. If you want 'em, connect them after it is running.

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    Quote Originally Posted by Bill Simmons View Post
    Rons

    I have seen a lot of simple and clever designs for removing the belt from the pony motor. I would prefer to leave the belt engaged (whats the harm?) than have to hand hold some awkward pony while trying to press the start button.
    One regular poster here had a very clever setup using a foot pedal to bring a friction roller in contact to connect the pony motor. My approach is to simply
    slack the belt that connects the two, and the belt flies right off. The weight of the pony motor tensions the belt during startup. Hinges, 2X4s, etc.

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    Remote and unattended, is this correct? If so, what good is a pony motor unless you plan on starting the RPC only and just let it run continuously.

    Tom


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