Ungrounded PV System & Utility Isolation

[shortcircuit2]

I'm interested in what various utility companies require for connection of Ungrounded PV Systems less than 100KW to the local grid. For instance I recall reading about a 1/1 ratio transformer requirement for ungrounded systems in California by PG&E? Is this requirement to prevent DC Injection onto the local network? Are there other reasons for isolation through a transformer such as harmonics or power factor?

 

[jaggedben]

...For instance I recall reading about a 1/1 ratio transformer requirement for ungrounded systems in California by PG&E? Is this requirement to prevent DC Injection onto the local network?

If PG&E ever had this requirement, they no longer do, and haven't for the last 3 years at least.

I remember reading something about LADWP requiring a transformer. I don't know if they still do. I would imagine that transformerless inverters are now common enough and well understood enough that they probably have dropped this.

Are there other reasons for isolation through a transformer such as harmonics or power factor?

I can't imagine that a transformer would help a whole lot with power factor. Harmonics, maybe, but I'm doubtful it matters there either.

 

[ggunn]

I'm interested in what various utility companies require for connection of Ungrounded PV Systems less than 100KW to the local grid. For instance I recall reading about a 1/1 ratio transformer requirement for ungrounded systems in California by PG&E? Is this requirement to prevent DC Injection onto the local network? Are there other reasons for isolation through a transformer such as harmonics or power factor?

I know of no distinction from the utilities' POV between DC grounded and ungrounded PV inverters.

 

[shortcircuit2]

Here is some info I found at PG&E...

Regulation Requirements for units connected to Distribution

Inverters connected at the distribution level shall meet the requirements of Section G2.9.5 for power factor control. The total harmonic distortion in the output current of the inverters must meet ANSI/IEEE 519 requirements. Inverter-type generators connected to the PG&E Power System must be pre-approved by PG&E. For units over 10 kW, a dedicated transformer will be required to minimize the harmonics entering into the PG&E Power System.

 

[GoldDigger]

Which is very interesting, given that AFAIK a grid interactive inverter is likely to either produce a cleaner sine wave than POCO or else faithfully replicate the harmonic content of the POCO voltage source.
Can anyone confirm or refute that?

Tapatalk!

 

[ggunn]

Here is some info I found at PG&E...

Regulation Requirements for units connected to Distribution

Inverters connected at the distribution level shall meet the requirements of Section G2.9.5 for power factor control. The total harmonic distortion in the output current of the inverters must meet ANSI/IEEE 519 requirements. Inverter-type generators connected to the PG&E Power System must be pre-approved by PG&E. For units over 10 kW, a dedicated transformer will be required to minimize the harmonics entering into the PG&E Power System.

Inverter-type generators and solar inverters are two different animals.

 

[gadfly56]

Inverter-type generators and solar inverters are two different animals.

I'm guessing they use the term to cover any type of generator, e.g. wind turbine, solar, or mini-hydro.

 

[jaggedben]

Here is some info I found at PG&E...

Regulation Requirements for units connected to Distribution

Inverters connected at the distribution level shall meet the requirements of Section G2.9.5 for power factor control. The total harmonic distortion in the output current of the inverters must meet ANSI/IEEE 519 requirements. Inverter-type generators connected to the PG&E Power System must be pre-approved by PG&E. For units over 10 kW, a dedicated transformer will be required to minimize the harmonics entering into the PG&E Power System.

This language doesn't make clear to me whether a transformer installed in or with an inverter counts, or whether they mean that it must be connected to a dedicated transformer owned by them. Or if it can be either, or who must pay for it.

I think I've yet to work on a +10kW system with transformerless inverters.

 

[ggunn]

I'm guessing they use the term to cover any type of generator, e.g. wind turbine, solar, or mini-hydro.

That's not how I read it. An inverter-type generator means something specific to me, i.e., a spinning generator that makes DC which is converted to AC by an inverter.