ggunn-
the transformer apps engineers have a much better shot at getting it right
Sure, I hear you, not trying to argue- but the xfmr guys aren't going to do the math/run same simulations that the grid people do.
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Originally Posted by
jim dungar
Then you haven't done a very good design job.
Actually I think PVfarmer has a valid point (for once). Some utilities have rules about DG that just don't really make any engineering sense. In some cases it's an overly broad principle that does not need to be applied to every system.
:blink:
Um...thanks, jb!
Could you give an overly broad example of something like that? Just out of curiosity.
I'd like to add to that- as well as rules that might not make sense, the POCO documents have parts that are sort of "left open", like the below.
There's another part of another doc that says over 50kW of PV "may have to be 3 phase...please consult the Company...".
So I'll change this:
"no, you can't do that" from the POCO.
to: the POCO might say "there's a a better way to do that in that particular area due to interface/balance issues".
As in, the farther out in the sticks a project is, the more important the single vs. 3 phase thing becomes. (also perhaps why they try not to offer delta service anymore?)
At the same time, you (or customers) don't really want to rewire a customer's entire system.
If the system in place is 120/240V, you'd probably just go with the same voltage inverters, unless of course you're going 50kW or more and "have to" (by POCO) go 3 phase.
My point being: standard services are 120/240, 208/120, and 480/277.
These "rules" (or guidelines) below could all be explained more clearly. Pretty sure it's saying you can connect PV to any service you want, but...what does "expand" mean here? I read it as "increase xfmr capacity".
So if you already have any of the bolded, you can add a PV system as long as the output doesn't exceed the xfmr capacity you have- if you want to go bigger, you get a new service.
But it's just plain confusing- they don't mention WHY 2400, 4160 and 4800V are still available.
Then the last line below kinda reads as if ONLY standard services are available, when it mentioned 2400V etc two lines before!
Further examples:
Someone has an old non-standard 240V delta service which is 30kVA (3 x 10kVA bank) and wants to install PV.
You might be able to use somewhere around 20
-25kVA of inverters with that. It could be three 7000w single phase 240V inverters or a single 20kW three phase inverter stepped down thru xfmr.
But you sure couldn't install 40kVA of inverters- you'd need at least 50kVA of xfmrs for that, or you'd need at least 75kVA of xfmrs for 60kW of inverters.
Now..if there was 75kVA of 240 delta service, getting 60kW of 480/277V inverters and stepping every watt down to 240V might not make sense.
But with 75kVA of 480V delta service, the same 60kW-480/277V to 480 delta might just be enough of an improvement (over losses from stepping down to 240V, other costs, etc) to work....or you'd want a 480V delta inverter instead.
Or....you could get new standard service of 480/277- but standard is 200A @ 480/277V- that's kinda way to much for the same 60kW of 480/277V inverters (which are 72.4A max output).
I hope this helps prove my point that...it isn't always "simple"!
To rephrase that- the best standard service for any customer usage (which is also what the premises are wired at) might not be the same as the best service for same customer's PV ouput/grid connection, so if the PV output is 2x or 3x the usage...you'd match the inverter(s) to the service and use step-down xfmr(s) for the usage. PV is fairly new and all systems are different sizes and/or equipment- there aren't really "standards".
shall consult with the
Company to
obtain a standard single or three phase 60 Hertz service at an appropriate delivery voltage.
shall not expand the use of such service, except in
very limited circumstances
3.8 SERVICES NO LONGER STANDARD
Non-standard services include, but are not limited to: 25 Hertz, 2 phase systems, 2 wire 120 volts,
240 volts delta, 460 volts wye, 480 volts delta, 600 volts delta,
2400 volts, 4160 volts or 4800 volts
services.
While 2400 volts, 4160 volts, or 4800 volts are no longer standard, they may still be available
at certain locations; consult the Company.
Customers now receiving non-standard service shall not expand the use of such service, except in
very limited circumstances at the sole discretion of the Company.
Customers with an existing non-standard service requesting a service change shall consult with the
Company to
obtain a standard single or three phase 60 Hertz service at an appropriate delivery voltage.