Parallel operation of MEP-002A or MEP-003A, with video

[sewerzuk]

I have occasionally seen the question come up here, "Is it possible to wire my two -002a's together to double their output?" The answers range all over the board...mostly good information, sometimes the answer is a flat out "no." But I haven't seen anybody actually post a "how to."
I have a couple of decent -002A's in my shop right now, so I threw this short video together to demonstrate how to parallel them.
These are small machines so operating them in parallel can be a bit touchy. It is difficult to balance load between them and, even though I know what I am doing, I occasionally lose control of the real and reactive load balance and end up popping one of the breakers. BUT, with a bit of practice this can be done without much difficulty.
And, it has been my experience that a couple of -002A's operating in parallel are capable of quite a bit more load and larger starting surges than a single -003A is.
So, here's the video. Questions and comments are welcome!

http://www.youtube.com/watch?v=pdKAM2Xrtjc

 

[jbk]

great video, iam sure anyone whose had a couple of 002s have thought about it.
be cool to see a set of 003s.

 

[sewerzuk]

great video, iam sure anyone whose had a couple of 002s have thought about it.
be cool to see a set of 003s.

The next time I get a set of -003's in I'll do the same video. I can put more than enough load on them to really put them to work.

 

[m16ty]

Good vid.

I noticed at the end the text says to throttle one of the generators up if you wanted it to carry more load. First off, why would you want one set to carry more than the other and second, wouldn't throttling one up change the frequency?

 

[camp9]

How much fuel does a 002 use per hour under normal load?

 

[edgephoto]

How much fuel does a 002 use per hour under normal load?

According to the specification sheet .57 gal/hr at load.

 

[sewerzuk]

Good vid.

I noticed at the end the text says to throttle one of the generators up if you wanted it to carry more load. First off, why would you want one set to carry more than the other and second, wouldn't throttling one up change the frequency?

I knew this video would generate a lot of questions like this

Really, there is no good reason for one generator to carry more load than the other when the sets are this small. But, if the load was unbalanced when you first paralleled them, you may need to make slight adjustments with the throttle to balance the load. I have found that, with about 1kw on the running generator, if you set the "blink rate" of the incoming generator to about 1 per second, this will give you a perfectly balanced load. But, if the 2 generators don't have the same RPM droop characteristics, then the load may become unbalanced as the load changes.

When one generator's throttle is opened, that generator attempts to carry more REAL load (which does real work, causes the engine to work harder, etc.). When its voltage is raised, it attempts to carry more REACTIVE load (which does NO work; raises the current flow but does not place additional load on the engine).

Once the 2 generators are paralleled, their frequencies will ALWAYS remain EXACTLY the same. They physically cannot differ. It is the same thing as having them mechanically connected by their crankshafts.
In fact, it helps to think of the 2 generators being mechanically connected at the crankshaft. They will both always turn at the same RPM (since they are mechanically connected). Imagine the mechanical load placed on the generators is 100% of one engine. If the 2 engines are properly balanced, then they have equal 50% loads. If you open the throttle of one engine, then they still stay connected together but some of the load shifts to that engine (so now they are running at maybe 70% 30%). If you open the throttle more, one engine can pull the entire load while the other one does nothing (but they still stay turning at the same RPM). The same exact thing happens when 2 generators are ELECTRICALLY connected...

 

[3dAngus]

Fantastic job.

NOT for the novice. This kind of work can be very dangerous.

Intelligence required.

 

[sewerzuk]

Fantastic job.

NOT for the novice. This kind of work can be very dangerous.

Intelligence required.

Intelligence required, yep!
I'd say the dangerous part is mostly in the setup. If you aren't paying attention you could have live cables exposed to human touch.
But, once set up properly, I don't feel that there is too much risk. Even if you mess up the paralleling, the worst thing that should happen is a tripped breaker.
Of course, this does assume properly sized cables, a proper initial setup, and properly operating generators and breakers.

 

[glcaines]

That was a great piece of work. Thanks for putting that video together.

 

[Isaac-1]

I have to wonder what happens if fault conditions were to arise on either generator, say low oil pressure shut down or voltage regulator becoming unstable (high or low).

 

[m16ty]

It seems to me that if you have 2 sets running at 1800rpm each, if you open the throttle to one of them more you would increase the rpm of both of them.

I'm not doubting what you are doing or are trying to say. I'm just trying to understand. Not that I'd ever have the need to parallel two sets (my MEP 003 does all I need) but it is pretty neat to see it done.

 

[ETN550]

Intelligence required, yep!
I'd say the dangerous part is mostly in the setup. If you aren't paying attention you could have live cables exposed to human touch.
But, once set up properly, I don't feel that there is too much risk. Even if you mess up the paralleling, the worst thing that should happen is a tripped breaker.
Of course, this does assume properly sized cables, a proper initial setup, and properly operating generators and breakers.

Question: Are 2 lights for determining phase rotation only required for 3 phase? I noticed you used one light. If you had reverse rotation on single phase and PF less than 1.0 would this be an issue? Or is there such a thing?

Also, was this as close as you could get the 2 sets to run before closing the breaker? It seems like they were still very much out of scync when you threw the breaker. Marine engines and aircraft seem pretty easy to sync by ear.

I would think to be practcal one would need a master and slave voltage regulator. The governors could be set with some droop so that the throttles could easily split the load, but I would worry about trashing the voltage regulators. Also, are there any harmonics between the voltage regulators interacting with each other?

 

[patracy]

I never get tired of watching Sewerzuk's videos.

Well done sir.

 

[Triple Jim]

Once two synchronous generators are wired together, both engines are forced to run at exactly the same RPM. You could shut off one engine, and the running generator will force it to continue to turn at 1800 RPM unless a breaker trips. Increasing the throttle on one will put more torque into that generator, advancing it slightly in the cycle, and increasing its power output, but the RPM of the two engines will stay equal.

Sewerzuk explained that he found that having the generator he's bringing online running slightly faster, at the rate of about one pulse per second, works well because once it's connected to the other one and forced to slow down to match its speed, the extra throttle makes it share the load about right.

 

[sewerzuk]

It seems to me that if you have 2 sets running at 1800rpm each, if you open the throttle to one of them more you would increase the rpm of both of them.

I'm not doubting what you are doing or are trying to say. I'm just trying to understand. Not that I'd ever have the need to parallel two sets (my MEP 003 does all I need) but it is pretty neat to see it done.

Yes, the output frequency of the pair will increase slightly. However, the load shift is what is primarily accomplished when opening the throttle. It takes very little throttle adjustment to shift loads from one set to the other...

Question: Are 2 lights for determining phase rotation only required for 3 phase? I noticed you used one light. If you had reverse rotation on single phase and PF less than 1.0 would this be an issue? Or is there such a thing?

Also, was this as close as you could get the 2 sets to run before closing the breaker? It seems like they were still very much out of scync when you threw the breaker. Marine engines and aircraft seem pretty easy to sync by ear.

I would think to be practical one would need a master and slave voltage regulator. The governors could be set with some droop so that the throttles could easily split the load, but I would worry about trashing the voltage regulators. Also, are there any harmonics between the voltage regulators interacting with each other?

Yes, 2 lights are required for 3 phase paralleling. Much easier to demonstrate single phase paralleling, and much easier to show since my oscilloscope is only 2 channel!

It is possible to sync the sets exactly prior to paralleling. However, I've found that it is much easier to place a small load on one generator, and then set up the incoming generator with a slightly higher frequency. If I attempt to parallel them at exactly the same frequency, one tends to reverse power the other one.
Edit: You mentioned "by ear" in your post; you can certainly match frequency with this method, but not necessarily phase. Just because 2 machines are turning at the same speed, it doesn't mean that they are phase matched. If you watch my video, right at the point when I close the breaker on the incoming machine you will notice that the sounds of the 2 generators instantly "match."

You are correct; the big hanging up point with this setup is the 2 independent voltage regulators. I have never noticed any kind of "harmonics" but I have paralleled several different sets and I notice that it is necessary to adjust the voltage regulators as the load changes *sometimes*. This is necessary if you see the percent rated current meters reading abnormally high (or even pegged) without a corresponding frequency droop. If I know I only have a 4kw load on my twin -002A's, I only expect to see about 40% on the meters. If I see 100% or more, then I know I need to re-balance the reactive load by adjusting the voltage on one set. But...the method I posted in the video works. It does allow you to power much larger loads than a single MEP is capable of.
Edit: I know people are going to have a hard time grasping the concept of real and reactive loads (mostly because it was a difficult concept for me to grasp). It is a complete non-issue when you are running one generator. But when you are running 2 in parallel, it becomes VERY important. I didn't want to discuss it in the video, but I am more than willing to answer questions here. If I can find a good "reactive power for dummies" explanation somewhere, I'll be sure to share it here!

 

[sewerzuk]

Once two synchronous generators are wired together, both engines are forced to run at exactly the same RPM. You could shut off one engine, and the running generator will force it to continue to turn at 1800 RPM unless a breaker trips. Increasing the throttle on one will put more torque into that generator, advancing it slightly in the cycle, and increasing its power output, but the RPM of the two engines will stay equal.

Only one light is requred for either 3-phase or single phase synchronization. It's there only to show when the two units are in or out of phase with each other.

Sewerzuk explained that he found that having the generator he's bringing online running slightly faster, at the rate of about one pulse per second, works well because once it's connected to the other one and forced to slow down to match its speed, the extra throttle makes it share the load about right.

EXACTLY. Frequency does increase very slightly if you open the throttle of one generator (not visible on the analog meter, but measurable by a DVOM).
What Triple Jim says is correct; once the 2 generators are paralleled, it is nearly the same as if they were mechanically connected.

It really is easier to understand this if you try to ignore the electrical part of this project. Imagine the 2 engines are sharing some other kind of load...like a pump. It takes a constant amount of power to run this pump at a set speed. If you open the throttle of one engine slightly, it will take some of the load off of the other engine but overall RPM will increase very little amd the pump will be doing the same amount of work. The same exact thing is going on with the generators...

 

[Triple Jim]

I had previously edited my post a bit after you posted at 00:12, but I don't understand why two lights are needed for 3-phase synchronization. I would have thought that connecting one lead of the light to each generator at the same point would indicate the phase difference just like it does in single phase operation. I'm not disagreeing, just asking where I'm going astray.

Your video was really well done, by the way. Thanks very much for taking the time to make it.

Edit: Maybe two lights are used to verify that in 3-phase mode the two generators' outputs are rotating in the same direction? So if you knew the two units were wired the same, it wouldn't be necessary, but it should be done as a precaution if you didn't previously check?

 

[sewerzuk]

I had previously edited my post a bit after you posted at 00:12, but I don't understand why two lights are needed for 3-phase synchronization. I would have thought that connecting one lead of the light to each generator at the same point would indicate the phase difference just like it does in single phase operation. I'm not disagreeing, just asking where I'm going astray.

Your video was really well done, by the way. Thanks very much for taking the time to make it.

Edit: Maybe two lights are used to verify that in 3-phase mode the two generators' outputs are rotating in the same direction? So if you knew the two units were wired the same, it wouldn't be necessary, but it should be done as a precaution if you didn't previously check?

Your edit is correct; the 2 lights are kind of an assurance that both generators L1 L2 and L3 are wired the same internally and externally (i.e. rotating in the same direction). It is possible to have one output in phase with the other two out of phase if the 2 sets aren't wired the same. But, if 2 outputs are in phase then the 3rd is guaranteed to be in phase. Once you have verified this the first time the sets are paralleled, it really isn't necessary after that. The 2 lights should always blink the same.

Although I was an ET, I did qualify as an electrical operator when I was on the USS Buffalo. When we paralleled machines we used an analog phase meter (synchroscope). It is a meter with a full 360 degree sweep. The needle would rotate in a complete circle, indicating how closely the phases were matched. It only monitored a single phase of each machine. Since they were physically hardwired into the submarine's electrical system, it wasn't necessary to check the other phases each time the breaker was closed. Kind of like my light bulb method, only more accurate. AND, it was able to indicate which machine was running faster...clockwise rotation indicating the incoming machine was running faster than the running machine/bus, counter-clockwise indicated slower. My light bulb method can't do that...although it is possible to figure out. If you throttle up and the light blinks faster, then you know the machine is running at a higher frequency. If it blinks slower or stops, then it was running at a lower frequency.

 

[leedawg]

I had previously edited my post a bit after you posted at 00:12, but I don't understand why two lights are needed for 3-phase synchronization. I would have thought that connecting one lead of the light to each generator at the same point would indicate the phase difference just like it does in single phase operation. I'm not disagreeing, just asking where I'm going astray.

Your video was really well done, by the way. Thanks very much for taking the time to make it.

Edit: Maybe two lights are used to verify that in 3-phase mode the two generators' outputs are rotating in the same direction? So if you knew the two units were wired the same, it wouldn't be necessary, but it should be done as a precaution if you didn't previously check?

Im not sure it is necessary Jim. However If say your one light bulb did decide to burn out when it went dark and you then threw the breaker in you could end up with synchronization errors. However That is fairly unlikely and two light bulbs would be even more unlikley. All the set ups ive seen it done with usually have a synchroscope between all the hot leads between the two sets.

My logical next question is could you do this with your main service and reduce the load off your meter. Im pretty sure the power company would really frown on this but I dont see why it would not have the same effect except the lead generator is the power company and you are running the lag machine and taking up as much or as little of the load as you want.