delsol

Distributed generation system

• 2- solar 500 kw inverters
  480v output no neutral

Feed transformer wye/wye step up to 23 kv primary 700 ft underground to riser.

Primary is grounded and subcontractor connected grounding conductors to xo with ground strap in place as well.

System went off line and we found melted grounding conductors, overheated oil in transformer and B phase open on pole.

I am thinking of a few things that went wrong or occurred.

What do you guys think.

MDShunk

Didn't we just go over this the other day, or am I nuts?

__________________
-Marc, ABC, XYZ, PhD, 1-2-3

-Someday, I'll wear pajamas in the day time.

delsol

yes sir but...

I am trying to get my head around the grounding of the xo and what caused the melting of the conductors.

Would you normally terminate the grounding conductors on xo when there are no neutrals present fro DG system and the primary is also grounded?

Did the grounding conductors melt because the transformer went into ferroresonace when B phase opened on the pole?

InPhase277

I'm still curious why, if there is no neutral on the 480, the transformers are wired wye/wye? Also, the blown B phase fuse, if it was the fuse feeding the lines into the grid, then there had to be an overload or short that caused that fuse to blow. It had to be downstream of the fuse. So a line fault likely ocurred, blowing B fuse and melting your ground before the fuse opened.

In the system you describe, it seems like it would be best to have it set up delta/wye. Ground the neutral wye point. But a wye primary, with the neutral floating, seems like you would get strange secondary voltages depending on loading. I don't know this for a fact, but my gut says something strange would happen, at any rate.

j johnson

Do not ground H0 pont of tranformer.

bobelectric

[quote=delsol;86482]Distributed generation system

• 2- solar 500 kw inverters
  480v output no neutral

Feed transformer wye/wye step up to 23 kv primary 700 ft underground to riser.

Primary is grounded and subcontractor connected grounding conductors to xo with ground strap in place as well.

System went off line and we found melted grounding conductors, overheated oil in transformer and B phase open on pole.I think I wired it to the enginerred drawings

I am thinking of a few things that went wrong or occurred.

What do you guys think.[/quote I would say I wired it to the engineers drawinigs.

MDShunk

Along the lines of an RFI, I'd like to propose a new form to send to engineers. An AYS form, for "are you sure" ...that you really want it done this way.

__________________
-Marc, ABC, XYZ, PhD, 1-2-3

-Someday, I'll wear pajamas in the day time.

s.kelly

talked to a guy I'm working with this week about his engineer student brother. He was helping him move into an apartment, and furniture was laid out according to his drawings. The electrician says on the way to the new place he will bet dinner the drawing will not work, eng. in training says of course it will.... guess who bought dinner

seems he forgot molding around windows etc in his floor layout!

Toronto Sparky

I have never seen 3 phase power created by inverters.
How is that done?
I would have thought M/G set.

Guess I'm getting too old for new technology.

__________________
Don't fight .. Play nice!

Richard Rowe

Have you found out what happened to the B phase??? Thats the key I would think. How long did this set up run before the melt down?

mpoulton

Same way a VFD produces a 3 phase output to drive a motor. It uses three sets of switches (IGBT's, a type of semiconductor device). One switch goes from each of the phase outputs to the positive DC bus, the other goes from each phase output to the negative DC bus. The switches are turned on and off in the proper sequence. That's that. Mostly. It's a bit more complicated, since you actually have to turn them on and off repeatedly during each cycle to approximate a sine wave.

shieldcracker

Del sol are these inverters grounded elsewhere?