PV system

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puckman

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ridgewood, n.j.
Maybe someone can explain how this works. I have a pv system where i work its output rating is 125amps at 480volts. The control box where all the cables enter is located outside and locked up so i could not look inside. It has a 150a 3 phase 480 volt line coming from our 600amp mcc that is feed from a switchgear room in another building. Also it has the dc lines coming from the roof to a trough that has two Sunny combine boxes nippled on it, the dc line go into the control box. also a 3/4 line going inside to a wireless box with an antenna attach to communicate with other panels else where in plant.
The control box out side has a panel meter reading unit output is 85 kw when air conditioner inside box is on and when it goes off meter reads 25kw. I hear about power going back into the grid, i just don't see how it happens here and why the 150amp line from the mcc. I don't see any other lines from the control box and there are no batteries. What am i missing and don't understand.
 
ohmhead

ohmhead

Senior Member
Location
ORLANDO FLA
Well heres how in simple words they make both types battery dc to ac inverters systems & a battery less dc to ac inverter type .

Basically a photovoltic cell bank which puts out 480 volts dc it also must have not only the series connection of 480 volts but the pv cells must have a paralleled connection meaning current wise for your load just like a battery series and paralled connection with out the use of a battery.

They take the dc power from the pv cells we send that to the inverter which pulse modulates the dc power coming in from the pv cells by electronic scr circuit it then goes into a isolation type transformer.



In some cases to change voltage up or down by pulse modulating the dc on the primary now produces a switching dc power source on that primary which the secondary sees as a ac pulse modulation source which is dc but changing direction at 60 cycles the primary is a center tapped type of connection and the switching is on one side part cycle to the other side part cycle a back and forth switching on primary so the output on that secondary is now ac power 480 v at what ever voltage or current is needed kw wise .


If you hook this up to your home service when it feeds or is connected to your incoming line it is like a paralleled source or kinda like putting two transformers in parallel it aids or feeds power into the line back feeding its power into the line which will slow that meter down if its a higher power source then whats coming in it will reverse that meter meaning no wattage used but your pv cells on your roof .

The power companys do this everyday
 
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ohmhead

ohmhead

Senior Member
Location
ORLANDO FLA
Well iam not a engineer by no means but just a little theory in electrical a 3 phase inverter is more complex but works by switching dc back to ac the same principal incoming dc power thur scr circuits timing and switching to make 3 phase just like single phase switching at different times to make ABC the phases and adjusting the pulses or cycles up or down for freq .

With 3 phase now thats how they can make a single phase input to a vfd and the end result produced a 3 phase output by alternation of dc pulses timing to give us our 3 phase output and use single phase to make 3 phase electronically .

By manipulating the pulses and switching them on or off at the correct timing to produce three outputs A B C using the same dc input

Find you a book on inverters lots of good reading .
 
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