3 PHASE 3 WIRE 250 VOLT TIE IN

[mdillonelectrician]

Hello I am looking into a 175 kw PV system tht will get line side tied back into a 3 phase 3 wire 250 volt system. Obviously this is a unique situation due to the grid voltage, anything that I should be aware of that could trip me up? Or is the application similar to any other line side tie situation? I was told voltage rise could be a concern but other than that I just want to be sure I give a fair overall analysys of the service to the potential customer. One more side note the main service is 3000 amp (FPE switchgear) any rules on tying into FPE gear for the the line side. Thanks in advance for any feedback.

 

[beanland]

Not too odd

Not too odd

Is the 250V 3-phase 3-wire ungrounded or center-side grounded? 240/120V 3-phase 4-wire is not uncommon with the stinger leg. That may be a problem to the inverter if it needs a ground reference of some kind. If that is an ungrounded 250V delta, those are subject to nasty voltage spikes coming through the inter-winding capacitance whenever there is a voltage spike on the POCO system.

175kW is 400A @ 250V 3-phase. That is small relative to the 3000A main. If the POCO transformer is sized for the 3000A main, the voltage rise will be minimal. e.g. simplistically a 5% 3000A-rated transformer will have 5% rise at 3000A. Even with no load, the rise from 400A is less than 1%.

 

[jaggedben]

If it is truly 250V (and not just a 240V service reading high?) then you may need to confirm with the inverter manufacturer that the voltage trip points can be adjusted upward. Almost always that is possible though, often it is on the spec sheet.

You will also need to make sure you choose an inverter(s) that is compatible with a 3-wire delta. Some require a ground reference (4th wire), some don't.

Good luck with the FPE switchgear.

 

[beanland]

BTW

BTW

BTW if the service is 240V ungrounded delta and the inverter is 208V wye, a few boost transformers configured the right way will get you both the voltage match and the needed neutral.

 

[mdillonelectrician]

Thanks

Thanks

It is definitely 3 phase 3 wire 250 delta i didnt see any type of ground going from the three transformers into the gear inside. the transformers are exposed behind a locked cage.You can literally see the wire going into the duct that leads to a 3000 amp main switch. We have confirmed with the inverter manufacturer that it is an acceptable voltage and we even discussed the voltage rise issue mentioned and we were told it could be adjusted but due to the short AC run and the size the service, it didnt seem like it would hurt us.

 

[Smart $]

It is definitely 3 phase 3 wire 250 delta i didnt see any type of ground going from the three transformers into the gear inside. the transformers are exposed behind a locked cage.You can literally see the wire going into the duct that leads to a 3000 amp main switch. We have confirmed with the inverter manufacturer that it is an acceptable voltage and we even discussed the voltage rise issue mentioned and we were told it could be adjusted but due to the short AC run and the size the service, it didnt seem like it would hurt us.

Check to see if it is corner ground or ungrounded. If ungrounded, there should be ground detectors on the system. Get with the manufacturer to see if the inverters are ground referenced, and to what system point. You will have to tie in ahead of any ground detector if an ungrounded POCO system. You also may need an isolation transformer between inverter outputs and service taps.