Replacing a Delta Distribution transformer feeding an existing Delta load by a Y-Y transformer

[ffont]

Our distribution grid is a Y-Y multigrounded system, so we plan to replace the few existing and old delta transformers feeding delta loads with standard Grounded Y-Y distribution transformers (500kVA to 3000kVA), with the star points solidly grounded on both side; a three wire circuit will feed the delta load.

Is there any problem to anticipate? How will the system behave under fault conditions (eg L-G, L-L-G)? any fire danger?

Any good suggestion as how to tackle this situation (feeding delta load with a Y-Y transformer). Any good paper or book on this?

Thanks!

 

[cranky108]

Add ground protection, secondary grounding system, and check with the customer first.

 

[MatthewDB]

First off, we're not taking about 240V high leg delta, right? That's not going to like 240Y132V. Those need either V phase - open delta or ungrounded Y - delta. You get to pick bad phase balance or ferroresonance risk.

For ungrounded delta, you have the risk that there may be an existing persistent ground fault. It needs to be repaired prior to change-over. I second the suggestion to talk to every customer. Knowledgeable customers will know what is needed, some may need help preparing.

 

[waross]

If you are going from 480 V to 480 V, the customers equipment should work fine.
If you are going from 440 V to 480 V, most of the customers equipment will be fine but it will be well to check all existing equipment for possible issues.
If you are going from 230 V to 120:208 Volts some customers equipment may not perform adequately.
If you are going from 240 V to 120:208 Volts some customers equipment may not perform adequately.
You may consider providing small voltage boosting autotransformers for problem equipment.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[kookypedia]

What I have usually seen is resistant grounding in LV. Is there any reason you want to do solid grounding in LV?