half a megawatt solar interconnection

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Ggunn,
yes. 600V is the facility's system voltage. SMA inverters' availability was something to blame, i guess. 12 inverters were spread out on the flat roof, 3 different parts of buildings and many small arrays. bringing AC pipes to combine before leaving the roof.. hard labor, for sure.
 
Ken Forest said:
Ggunn,
yes. 600V is the facility's system voltage. SMA inverters' availability was something to blame, i guess. 12 inverters were spread out on the flat roof, 3 different parts of buildings and many small arrays. bringing AC pipes to combine before leaving the roof.. hard labor, for sure.
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So you are using a step up transformer to go from 480 to 600?
 
Excuse any stupidity on my part, I'm just trying to figure out the setup. You have 5 sets of cable, 400KCMIL, that totals 380A x 5 = 1900A worth of cable. It then drops to 4 sets of 400KCMIL , that totals 1520A worth of cable. It's going through a 600A fuse, so the most you can draw is 600A.

You can run approx. 1240ft with 4 x 400KCMIL, with 600A. This is assuming 480V 3ph circuit.

Is the tap that far away?
 
At system nominal voltage of 600V, the MAX could be 630V, allowed by IEEE. Are there transformer taps somewhere that are limiting this system to say 575V? Otherwise you are in jeopardy of overvoltage on the equipment rated for 600V MAX.
 
kingpb said:
Excuse any stupidity on my part, I'm just trying to figure out the setup. You have 5 sets of cable, 400KCMIL, that totals 380A x 5 = 1900A worth of cable. It then drops to 4 sets of 400KCMIL , that totals 1520A worth of cable. It's going through a 600A fuse, so the most you can draw is 600A.
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Yes, except that last sentence. The current service has a 1200A main, so the (4) sets 400 KCMIL are for that. Spliced to them is going to be (2) sets of conductors for the new 600A interconnection. The OP suggests making that nice splice at the same point the the upstream service conductors are currently spliced down from (5) sets to (4) sets.

Cheers, Wayne
 
electrofelon said:
I worked on a 2.7 MW 5 years ago that used the 33 KW tripowers. OMG it was so annoying, there must have been like 6,573 inverters there. I heard they "got a real good deal" on the inverters, but not sure the designers took into account that additional labor.
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I think string inverters are becoming the standard under 5MW. On the upside, they are like 275kW inverters. They are being used on systems up to 10MW. Back in the old days 275kW was a decent-sized central inverter.
Today's 2.5MW central inverters are so large that you have to have something over 10MW to make them work out.
 
Ken Forest said:
I am questioning about the whole deal with the limiter to my engineer now as this is costly and taking a lot of space. i am going to read the document you provided so i can understand better. i am not an engineer, but i would like to challenge one if he is wrong about this.
thanks for your input
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When used according to 705 with parallel conductors limiters are dangerous.
  • To isolate a fault in a parallel conductor circuit the limiters have to be installed on both ends. If it's only on one end then the fault will be back fed through the opposite end and the fault current may not be high enough to open the other limiters. NEC 705 does not require limiters on both ends.
  • In parallel conductors opening one limiter will result in the other parallel conductors being overloaded since the parallel circuit is typically sized to just carry the PV system current. Since limiters are only designed to open on short circuits they will not open on overload and the conductors may be smoking until they are eventually damaged enough to cause another short circuit.
  • A limiter opening is not indicated anywhere. These are installed in areas that have limited access so are hard to inspect and replace.
Cable limiter requirements were barely reasonable on single conductor circuits. I have no idea what the CMP was thinking when applying these to parallel circuits.
 
pv_n00b said:
I think string inverters are becoming the standard under 5MW. On the upside, they are like 275kW inverters. They are being used on systems up to 10MW. Back in the old days 275kW was a decent-sized central inverter.
Today's 2.5MW central inverters are so large that you have to have something over 10MW to make them work out.
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Yeah this was back in the mid teens, when I think about 60kw was the largest string inverter you could get - and thats what most of the systems I worked on used, so these 30's were annoyingly small.
 
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