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Thread: MEP-002A and -003A main breaker

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    The Fluke 337 is a nice meter, I have been looking for a deal on one on ebay for a while now

    I bought a problematic Fluke 1507 insulation tester off ebay a couple of months ago for a really good price, the only problem turned out to be a oddly bad fuse (it had high enough resistance that the meter would not zero out over 2 ohms I think), the self test would say the fuse had failed, but it would still measure resistance when the test button was pressed.

    Ike

    p.s. if you have a 1507 and need a new fuse buy an Amprobe packaged one, same exact fuse, same OEM markings, but a 4 pack is cheaper than 1 from Fluke

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    This site is awesome! I'm trying to absorb as much knowledge as possible to prep me for the task in April of starting my new units. Speddmnn, you are an encyclopedia. Thanks and happy new year to all!
    Jerry
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    Quote Originally Posted by sewerzuk View Post
    I decided to wait until I could get my hands on a good clamp ammeter; I wanted as much info as I could get before I started playing with R3.

    I just picked up a used Fluke 337 off of Ebay; got it in the mail a few days ago. It has the ability mt record min, max, and peak inrush currents. I'm going to hit my 003's and 002's with some starting surges and find out exactly what current is causing them to trip, then I'll begin toying with the R3 setting...

    I'll be sure to post my findings here.
    Have you had a chance to play around with the readings and settings yet?

    I completely understand if you've been waiting out the winter months. We've been having a long cold winter here ourselves. I'm getting anxious to see what your findings are.
    Quote Originally Posted by Recovry4x4 View Post
    That's why I knew the answer and you didn't. I read the kindling.
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    Quote Originally Posted by Speddmon View Post
    Have you had a chance to play around with the readings and settings yet?

    I completely understand if you've been waiting out the winter months. We've been having a long cold winter here ourselves. I'm getting anxious to see what your findings are.
    I did get a few minutes last week to play with it; I only got the chance to work with one of my -003's, so not sure yet on the -002's or my other -003. But, here is what I did:

    Checked the setting on R3, it was perfect

    Hooked up a large load (10HP 3 phase motor) and started it a few times on the generator. I used my clamp meter on each line to measure starting current. The breaker tripped nearly instantly on each start. My reading varied a bit, but was pretty consistently in the 28-32 amp range on all 3 phases.

    I adjusted R3 to its lowest and highest settings and repeated my tests; there was no measurable difference in the peak current; all of the readings were in the same range. What this tells me is that R3 has little effect on the surge rating of the breaker/CT system...

    I chose the 10HP motor thinking that it would be the largest load that the generator could handle with a large starting current; unfortunately, I never did get the motor up to speed without the breaker tripping. I do have a 7.5HP 3 phase motor in my lathe; the next time I get some free time I will perform the same tests with that motor.
    I am also planning on loading my generator to 100% with a resistive load, and then slowly adding 500w loads until the breaker trips to find out how R3 affects the breaker's trip setpoint without a surge. I need to come up with a way to do this...right now my load bank consists of an instant-hot water heater and some other heater elements...need to add something that I can use to switch in smaller 500W loads with.

    It will likely be another several weeks before I get this done; projects on my deuce have been taking up my free time, and I'm in the process of building a trailer for portable polyurethane and polyurea spray equipment (powered by one of my -003's, of course )

    I'll stay on it though...and I may have some more results as I build the trailer, as I will be running a couple of smaller electric motors, lights, and some heater elements with the -003. This setup may give me the opportunity to test R-3 and the breaker under some varied conditions.
    Sold most of my military toys and bought an airplane
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    Blind squirrel rehabiltator Speddmon's Avatar
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    Those are some pretty odd readings you're getting. I'll gaurantee the starting current of a 10 HP 3 phase motor is mugh higher then 28-32 amps. Typical rule of thumb is 6 times the FLA for the starting current. It sounds like your meter isn't capturing the peak reading.

    Either way, it's interesting that the R3 adjustment had no affect on the set being able to start the load. Keep up the good work and keep us posted, I am very interested in the information you are gathering.
    Quote Originally Posted by Recovry4x4 View Post
    That's why I knew the answer and you didn't. I read the kindling.
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    1970 M35A2 "The Stone Wagon" SOLD
    1985 M1028/M1031 w/700R4 "Road Oiler"
    MEP-003a 3000 hrs
    MEP-003a 1500 hrs
    1964 Case 530CK "Construction King" Backhoe/loader "Yard Oiler"

    MEP-002a & MEP-003a Spin-on oil filter kits are still 4 sale in the classified section

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    Quote Originally Posted by Speddmon View Post
    Those are some pretty odd readings you're getting. I'll gaurantee the starting current of a 10 HP 3 phase motor is mugh higher then 28-32 amps.
    I agree with you on this; these reading were lower than I expected. Here were my thoughts on this:

    1. The generator's breaker is tripping before the VR has the chance to recover from the initial surge, causing the voltage to drop rapidly and limiting the peak current sent to the motor

    2. My fluke meter has a 100mS response time for measuring peak inrush current; although I don't have a way to accurately time how long the breaker is shut after the load, it is certainly under 1 second. It may be opening too quickly for the meter to get an accurate reading. However, I did consistently get reading in that range for around 30-40 trips, so I'm guessing that it is close

    3. I want to try this again with my MEP-006A and take some more readings...then I can get an accurate measurement for the starting surge for that exact motor.


    I chose that motor thinking that I should be able to get the -003 to start and run it...obviously I was wrong. If I can get it to run my lathe, then I should be able to get good peak current numbers. If they are higher than the numbers I got for the 10HP motor, then I will know my meter isn't fast enough to get an accurate measurement.
    Sold most of my military toys and bought an airplane
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  7. #27
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    I was doing a little research on the internet this morning into your issue with the starting currents. I found some interesting information for you. I don’t think there is anything wrong with your main breakers, it’s just that you are trying to start a motor that is just way too large for the type of overload (OL) protection on the generator.

    Follow me on this little adventure…

    I found this cool website on the internet for sizing generators for larger applications such as larger induction motors and industrial facilities (Gillette Generators). On the website it had a bunch of charts and some useful formulas that helped me determine why I think you are trying to start a motor way too large.

    To start off, the starting capacity of the generators we are using has never really been stated or documented as far as I know, but we generally assume it is about 300%. The LRA (Locked Rotor Amps) rating of the motor is also the starting current drawn because if the rotor of a motor is not turning, it is said to be locked. Keep in mind that this current is only present for a split second. If the rotor were actually locked due to an overload or bad/frozen bearing, the current would be there for a much longer time, and eventually trip out whatever means of OL protection you may have.

    One of the formulas on the website was to calculate the LRA rating for a motor of a specific HP. Generally speaking there are two styles (so to speak) of common motors when dealing with LRA, many more are made but not as common. Code “G” (typically 3 phase) and Code “L” motors (typically single phase), Code “G” motor typically require 3 times the running watts to start, and Code “L” motor need 5 to 6 times. The first chart on the website lists the Locked Rotor KVA per HP for each different motor code. We’ll use Code “G” numbers for our example since it is the smaller of the two and will produce lower values. It states that the KVA/HP of a Code “G” motor is 5.6 to 6.29 KVA/HP.

    The formula for determining LRA is Motor HP x KVA/HP x (1000 / (Volts x 1.73)). Lets plug in some values…

    Motor HP…10
    KVA/HP…5.6 to 6.29
    Volts…208

    The website recommends using the larger of the range of KVA/HP, so this gives us

    10 x 6.29 x (1000 / (208 x 1.73))
    10 x 6.29 x (1000 / (359.84))
    10 x 6.29 x 2.78
    Or
    174.86 Amps LRA. If we use the smaller KVA/HP of 5.6 we get 155.68 Amps.

    The next formula that is very useful is the formula to determine how many Kilowatts (KW) that is. That formula would be 1.73 x Volts x Amps x PF / 1000

    This gives us

    1.73 x 208 x 174.86 (or 155.68 ) x 0.8 /1000
    Or
    50.3 (or 44.8 ) KW

    Being that we say the starting capacity of our sets is about 300% that would be 30 KW, even using the smaller of the numbers you are still over by almost 15 KW trying to start that 10 HP motor with an MEP-003a. While I think the actual generator and engine would start the motor with no problems, the type of OL protection that is built into them will not allow it due to the nature of the trip settings. The reason they put that kind of OL protection on the MEP-002a and MEP-003a is due to the different voltages it can produce. That’s the only way they can protect the generator no matter what voltage you are using.

    The only way around that would be to bypass the main breaker of the generator and come right off of the generator side of the breaker lugs and run that to some other type of OL protection specifically for the motor you are starting. That would effectively bypass the main breaker so even if it tripped you would still have power to your motor and dedicated OL protection. If that secondary OL device would trip, it would disconnect from the generator thereby protecting the generator as well.

    This digging also tells me your amp meter is not catching anywhere near the peak starting current of your motor. I would be curious however to know if the generator would start that motor for sure if you were to be brave enough to bypass the main breaker and do as I suggested above and install some type of dedicated OL protection for the motor...don't do it on my account though...I am just curious.
    Last edited by Speddmon; 02-19-2011 at 12:22.
    Quote Originally Posted by Recovry4x4 View Post
    That's why I knew the answer and you didn't. I read the kindling.
    He is "anti-doghead".

    Even a blind squirrel finds an acorn every now and then!



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    1985 M1028/M1031 w/700R4 "Road Oiler"
    MEP-003a 3000 hrs
    MEP-003a 1500 hrs
    1964 Case 530CK "Construction King" Backhoe/loader "Yard Oiler"

    MEP-002a & MEP-003a Spin-on oil filter kits are still 4 sale in the classified section

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  9. #28
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    Quote Originally Posted by Speddmon View Post
    While I think the actual generator and engine would start the motor with no problems, the type of OL protection that is built into them will not allow it due to the nature of the trip settings. The reason they put that kind of OL protection on the MEP-002a and MEP-003a is due to the different voltages it can produce. Thatís the only way they can protect the generator no matter what voltage you are using.

    This digging also tells me your amp meter is not catching anywhere near the peak starting current of your motor. I would be curious however to know if the generator would start that motor for sure if you were to be brave enough to bypass the main breaker and do as I suggested above and install some type of dedicated OL protection for the motor...don't do it on my account though...I am just curious.
    This was kind of my point in starting this thread; I, too think that the engine and generator should be capable of starting a 10HP motor, especially a 3 phase one. The OL system that is built into a generator should be restrictive enough to prevent damaging the generator, engine, and the loads, yet not so restrictive that it prevents you from running loads that have temporary starting surges within the capacity of the genset. Some concessions must have been made in designing the main breaker system into the -002's and -003's.
    I am in the process of installing one of my -003's in a polyurethane spray trailer; I haven't designed the wiring setup yet, but I am thinking about bypassing the genset's breaker altogether and simply running a conventional 3 phase breaker panel. This will give me answers to some of the questions raised here...specifically whether or not the 10HP motor is within the capacity of the -003.
    As for my meter catching the peak starting current of the motor, I am thinking that the surge is tripping the breaker so fast that the meter doesn't have time to catch an accurate measurement. If the breaker is tripping less than 100ms after the motor is turned on, then the meter won't read an accurate current.
    When I get a chance, I'll run that motor with my -006 and get some better numbers...
    Sold most of my military toys and bought an airplane
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    Trying to protect a generator with a thermal magnetic output breaker is next to impossible the thermal side will have to sized too small, and the magnetic will trip too fast for momentary starting loads assuming the generator can even sustain the magnetic trip current. A better approach seems to be to use the output breakers for wiring protection and include a load transducer that feeds a shunt trip breaker to collapse the field of the voltage regulator, this is the way many of the better industrial generators handle the problem and depending on the load transducer system multiple trip points can be set with both delayed and instant trip.

    Ike

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    Quote Originally Posted by sewerzuk
    This was kind of my point in starting this thread; I, too think that the engine and generator should be capable of starting a 10HP motor, especially a 3 phase one. The OL system that is built into a generator should be restrictive enough to prevent damaging the generator, engine, and the loads, yet not so restrictive that it prevents you from running loads that have temporary starting surges within the capacity of the genset.
    That last sentence is the key point of my post. Like I said, I Believe the MEP engine is strong enough to start the motor, and the generator is probably heavy enough to handle the inrush of that large of a motor. But even at the 300% surge rating we assume they are capable of, the 10 HP is still over that, closer to 500%. While the running and full load amperage ratings are within the Spec of the MEP-003, that much starting current is not within the design limits. I know they are overbuilt for the military, but NOBODY will EVER size any OL protection on a generator to handle a 500% starting surge (not OEM anyway...too many liability issues). For what you are planning to do with it, if you feed a 3 phase breaker panel with it, and have a breaker sized properly for the motor, as long as that's all you are doing with it, you should still be safe. I would still use the OEM main breaker if you plan on using it in any other voltage mode.
    Quote Originally Posted by Recovry4x4 View Post
    That's why I knew the answer and you didn't. I read the kindling.
    He is "anti-doghead".

    Even a blind squirrel finds an acorn every now and then!



    1970 M35A2 "The Stone Wagon" SOLD
    1985 M1028/M1031 w/700R4 "Road Oiler"
    MEP-003a 3000 hrs
    MEP-003a 1500 hrs
    1964 Case 530CK "Construction King" Backhoe/loader "Yard Oiler"

    MEP-002a & MEP-003a Spin-on oil filter kits are still 4 sale in the classified section

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