802A Parallel operation ???

[bohunk]

Hi all... I am a newbie, so don't bite my head off if I've made a mistake and posted wrong... PLEZ!

I just purchased 2 MEP-802A gensets BECAUSE I was under the impression from reading the manuals that they could be paralleled using the proper cable. Well... the gensets worked PEREFECTLY once I found the proper filters and batteries; however, I found no parallel cable with either generator NOR did I find the "Unit-Parallel" switch that is required to operate them in parallel. I contacted the support department at Technology Research Corp (the company that made all the controls) and Doug couldn't tell me if the 802A has that ability. He suggested I contact this forum as you are the 'experts' when it comes to using these things... he just knows the controls. And BTW: because these units are 'current' military his company CANNOT supply any of the controls to us as end users. Luckily I don't require any parts as these started up and ran like they had eyeballs. And SO QUIET... totally amazing! Back to my issue... am I missing something here OR are the manuals incorrect? Can these be operated in parallel?? (without a PH D in generators)

Thanks in advance for your help.

 

[ClarkeF]

802A's and 803A's are not designed for parallel operation - there is no control or controls built in to sync externally. Some people have used the 002's and 003's in parallel mode by carefully timing the two units - but they aren't designed for it either. You can search youtube or here for a couple video's on how to parallel the gensets - but as I said, they aren't designed for it.

 

[Ratch]

Just curious, why would you want to do this rather than get a 10 kw genset?

 

[Keith_J]

Paralleling allows for scalable power which is more efficient. More units can be brought online during peak loads, when peaks are shed, the assistant gensets can be disconnected and shut down. Also, it can be used for uninterrupted power for when a unit needs to be serviced.

 

[Keith_J]

Yes, you CAN parallel a pair of 802a. But you need breakers and indicator lamps to show when the units are in phase. Say you have both sets in 120-240 volt 3 wire, single phase. This is L1 and L3 at 120 V over neutral (L0). The indicator lamps would be connected between the two L1s and L3s. When the lamps are flashing, there is voltage between the to L1s and L3s. You will then bring up the slower generator to 60 Hz which will slow the flashing. Once both lamps go out, the two are in sync and then the breaker connecting the two can be closed. Once this happens, the generators will work together to keep in sync.

 

[glassk]

2-8
PARALLEL OPERATION OF TACTICAL PRECISE GENERATOR SETS.
This paragraph provides load
connection and operating instructions for parallel operation of the 50/60 Hz and 400 Hz Tactical Precise Generator
Sets. Parallel operating procedures are given for Load Sharing and Load Transfer separately.

from



ARMY TM 9-6115-464-12






Precise generator sets equipped with the electric governor system cannot be

paralleled with sets that have the electrohydraulic governor system. Equipment

damage could result If caution is not observed.


thats 15KW's and up , guess that was the cut off point for UncleSam on the controls that it takes to Load share,..

 

[cuad4u]

The problem with paralleling 002A, 003A and similar generators that ARE NOT designed to be paralleled is this. In order to be successfully paralleled the sine wave current produced by one generator must be identical to and synchronized to the sine wave current produced by the other generator. Put another way when looking at the combined 60 Hz sine wave outputs of two generators, the output sine wave displayed on the oscilloscope should look like one sine wave. If you see two sine waves on the oscilloscope the outputs of the two generators are no longer in sync.

I have watched the youtube video paralleling two MEP generators. Sure you can use light bulbs or other means (oscilloscope) to synchronize the sine wave output of two MEP generators under no load, under partial load, under full load or any point in between. However when the load varies the governors in the two generators WILL NOT respond identically as the load changes. This will result in a slightly different Hz sine waves produced by each of the two generators, which are no longer in sync. This may cause serious problems on the generator end and probably will cause problems (smoke) from the devices connected.

cuad4u PE EE

 

[Ratch]

I understand the purpose of paralleling, just curious why you'd want to with units so small. My first thought was that it was an attempt at fuel saving, but running two gensets at half the consumption rating of one larger genset means zero fuel saving unless one spends more time turned off. However, you'd have pretty good fault tolerance and time with the lights on.

I was just wondering what kind of scenario you had that would have those requirements (IE powering a cabin for weeks at a time, keeping a supply warehouse open during major disasters, etc.). It's certainly your business and not mine, just seems like diminishing returns to me, so I was wondering.

I also have no idea what kind of governors are on these things, so for all I know, it may take almost no effort to sync them and be a very easy task.

If it is really easy after all, maybe I'll do it, too. I'm in the processing of acquiring a 20kw standby for my house, with the 802 for nighttime and low load periods. Two 802's paralleled for me would mean I can do something else with the 20kw.

 

[Keith_J]

When two generators are paralleled, the governors will then work in harmony because of back electromotive force. If set A's governor is sluggish compared to set B's, there will be more of the load borne by set B. Likewise with hunting or droop.

 

[CDR]

What if one generator drops out

 

[Ratch]

I always have trouble wrapping my head around that... Don't take me as being disagreeable, I'm just trying to understand it better.
Logic tells me that a slow or sloppy governor should then momentarily overload one set if there are already heavy loads on the pair. IE, there's a 9kw load across a pair of 5kw gens, and a 1kw motor load starts, causing a demand current spike for a moment. Since the load is now 10kw (momentarily), set A set can't carry that alone, so as it's overloaded, it will slow down until set B can carry the load or B's governor can catch it up. Obviously A can't carry the load and turn B up to speed, so there's some loss of capacity due to the slower governor of set B, and A is overloaded until B's governor can provide the fuel to provide positive force. For hypothetical sake, I'm ignoring the the windings and wiring current cap.
Won't set A be likely to stall or choke, then force B into the same load-bearing scenario A was just killed by, thereby creating oscillation or a complete stall of both units?

 

[Keith_J]

What if one generator drops out

Then circuit breakers will trip if there is a load. If no load, the generator that loses engine will turn into an electric motor, driving the engine.

 

[Keith_J]

Ratch, remember paralleled generators share the load because they are tied at the load terminals. And you have other electromotive force issues with power factor concerns, something that matters when talking about electric motors. Too complex to explain here..

 

[CDR]

Then circuit breakers will trip if there is a load. If no load, the generator that loses engine will turn into an electric motor, driving the engine.

Like a huge starter motor!

 

[cuad4u]

Go to:

www.cumminspower.com

Paralleling generators that were never designed with the additional circuitry to enable them to be safely and properly run in parallel, even identical generators such as two each MEP 002A's, can be risky. I am not saying it can't be done and I am not saying the MEP 002A and MEP 003A generators don't have enough over build to do it. You may have to navigate through the Cummins site, but there is a whole section of the do's and don'ts of paralleling AC generators, even identical generators. Personally I won't be trying it with mine.

 

[Ratch]

Ratch, remember paralleled generators share the load because they are tied at the load terminals. And you have other electromotive force issues with power factor concerns, something that matters when talking about electric motors. Too complex to explain here..

That's what has me stumped on this sometimes. The other genset becomes an electric motor itself that's bearing the load of the diesel engine. Then it would seem the proper speed unit has to carry the current demand load and the other genset.
No response needed, just why it bothers me...

 

[10Lugger]

Subscribed

 

[Keith_J]

In reality, the two governors work with each other. Watt et al have written scores of tomes covering the mathematics of governors, all of which are too complex to explain here. This happens every minute of every day, generators are connected to our respective grids. Frequency matching is the least of the worries, it happens automatically. The magic is how the utilities feed power into the grid. It is all about the timing of current to voltage.

 

[TurboJoe]

In reality, the two governors work with each other. Watt et al have written scores of tomes covering the mathematics of governors, all of which are too complex to explain here. This happens every minute of every day, generators are connected to our respective grids. Frequency matching is the least of the worries, it happens automatically. The magic is how the utilities feed power into the grid. It is all about the timing of current to voltage.

Grid sycn'd is a whole different ball game. The load of the grid is essentially infinite for the purposes of say a small 1 Megawatt diesel generator. If the generator is not making power it can be instead spun by the grid. This is called reverse power and there are usually reverse power relays that open up the grid ties in this case. However, running the generator at grid speed is actually not loading the generator at all, and most likely wreaking havoc on the power factor. What actually happens is the generator is always trying to accelerate past the grid frequency, and just how much faster is what dictates the amount of load on that generator.

The safe guards needed to be grid tied are pretty extensive, and way more then just sync check, reverse power, and phase sequence.

Now paralleling generators in an island (Not grid attached) situation as asked above is different. In general its best to have a generator with an electronic controlled governor and controller as a master, that brings online and load balances the sets. With just two Mep802's it would be a crap shoot. You wouldn't need to worry about phase sequence in single phase mode. You would still need to match up frequency and sycn check. With the electric output contactor I suppose it would be relatively easy to wire in a sync check relay that will close the contactor when the two are in sync. Kind of like the light bulb, except the proper way to do it. I still would like automatic shut down of the second generator depending on load. Of course I'd also want a load dump panel tied in to dump house loads until the second unit comes back online. All stuff we build every day at work, just not cost effective at all for a house. If I had two sets running I'd pull a sync check relay out of stock and try it. When I re-wire my set that caught fire I'm probably going to put in a controller that can control parallel sets, just not sure how well it would would with out governor control.

 

[bohunk]

WOW!... thanks (especially to Keith_J & TurboJoe) for the explanations. Before all the responses I had already determined that the information I acted upon was erroneous. The paralleling permissive relay started with the 804 & up models. However; I had seen the uTube videos using the 002's and the light bulb... so I was certain it COULD be done; but that doesn't mean it should. At the risk of boring everyone the question was asked why I wanted to parallel two 802's to begin with... here is my reasoning.

I had decided to build a solar array setup to provide power and cut my energy bill. Now I already have penciled this out and it doesn't make dollars and sense, but I am going to do it anyway. In the process I decided to expand my shop & add some equipment (I used to own an aero space machine shop for 27 years) and that led to me requesting a bid for 3 phase from the utility company. $65K bid later for a less than 300 yard run I decided on generators for 65K obvious reasons. Not needing 10K ALL the time and running diesel gensets at light loads is a no no AND reading in the Army manual that 802s & 803s could be paralleled I jumped on a couple of 802s. I later found out from Doug at Technology Research that the Permissive Paralleling relay started with the 804 and up model gensets. So now with two of these units I will include them in my solar shed and run 5 wires back to my shop so I have the 3 phase and when I fire up a couple of cnc machines, and the air compressor I will disconnect the gensets from the auto-transfer switch and parallel them back to my shop exclusively. AND THEN... in 'normal' or 'standby' mode two legs (L1 & L3 I believe) will go forward to the auto-transfer switch so that when the grid goes down the gensets will provide 120v & 240v to the house. As I live in the desert (Phx, AZ) Air conditioning is a requirement so when the power goes down I'll be ready... if I can get all the wire runs correct hopefully. I will only have the A/C, electric stove, dryer, and water heater grid tied... all other circuits will be moved into a sub-panel (including the two pool motors that run 4+ hours per day) and run from the 3 parallel inverters which are 220v capable and powered by the batteries that are charged by the solar array. As the 'prepers' say: Two is one and one is none... so in that regard I will be able to alternate which 802 comes on line and have a back-up... just in case. My philosophy is simple: some is good, more is better, and too much is just right AND to that end I even purchased an MEP-952A to charge the 24v batteries at night... just in case... as I didn't want to fire up an 802 just to charge the batteries.

I am finding that Military Gensets are not that easy to auto start from the inverter controllers, but I guess that will require separate controls.

AH... TurboJoe, what does that sync relay thingy cost?... and where can I get one?