Parrallel Generators/Transformers/Earthing

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chaterpilar

chaterpilar

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Saudi Arabia
Hi members,

I have attached a layout for synchronising 3 LV generators with step up transformers.

Any thoughts on pros and cons of this layout in terms of earthing arrangements and choice of transformer or any other issue which you foresee are appreciated.



Cheers.
 
You need to tell this goofy American what is a YnD11?
I'm guessing it is a 380V Delta primary and a 13.8kv Y secondary.

carl
 
YND11 is a connection group code for setting the protection control. I only hear that when talking about utility sized transformers, normally. Going off memory, and I'm not 100% sure about the second character.

First character: Primary winding, Y for wye, D for delta, and Z for zig-zag
Second character: zero sequence filter Y=yes, N=no
Third character: Secondary winding, Y for wye, D for delta, and Z for zig-zag
Fourth & fifth characters: connection group vector, 10 for 2, 4, 6, 8, 10 and 11, for 1, 3, 5, 7, 9, 11
 
To add to what Marc already mentioned. Capitals mean High voltage and small letters means low voltage, and n = neutral

so in this case it is primary 380 volts delta and 13.8 kv secondary Star connected with neutral point and 11 is the vector group.

Well i can see, the image....any other members facing the problem in seeing layout in .doc file?
 
chaterpilar said:
To add to what Marc already mentioned. Capitals mean High voltage and small letters means low voltage, and n = neutral

so in this case it is primary 380 volts delta and 13.8 kv secondary Star connected with neutral point and 11 is the vector group.

Well i can see, the image....any other members facing the problem in seeing layout in .doc file?
Click to expand...
I can see the image just fine, but sorry - way over my head on the HV stuff.
 
Here's my translation (what I think you said)
1. Generators are solidly grounded 380V Y.
2. Transformer primaries are 380 D
3. Transformer secondaries are 13.8kv Y
4. Each xfm 13.8kv Y point is solidly grounded and bonded to the 480V earthing bar.

Question: Why is there a z-z earthing transformer? Your 13.8kv Y points are already grounded.

Comments:
If you don't have to have solidly grounded systems, consider:
1. impedance grounding the 13.8kv transformers. This will be a definite reliability (continuity of service) improvement.

2. Impedance grounding the 380V generators. Most all faults start phase to ground. Having each generator impedance grounded, limits the fault current to a low enough level there is no damage. One does have to quickly fix any L-G faults that show up.

edit: (fixed references to 480V to 380V)

also edited to add:
3. With the 380V generators solidly grounded, a L-G fault on anywhere in the 380V system, elevates the generator frames to 380V/(3^.5) above ground, until the CB's trip. Or if the fault occurs between the gen and the CB, then the frames stay hot until the protective relays shut down the gen driver (engine). You will need to add a disconnect in each generator neutral connection for maintenance.

I've seen this done two ways:
a. A separate single pole neutral disconnect mounted right next to each gen.
b. A four pole CB.

(mild disclaimer) I've never designed one of these (parallel generators, grounded systems) and I've never seen one with each generator having it's own xfm - so I could be all wet here.

I'm mostly curious about the need for a z-z grounding xfm.

carl
 
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You're welcome. Hope they helped.

Another thread brought up a good reference, IEEE std 142. If you haven't already looked at this, take a look at chapter 1.6.3 and see if this applies.

carl
 
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