Over voltage

[dansk]

Yellowvanman, I've read this thread ten times now, I'm with dp on this one, what you seem to saying is there is no volt drop from the head to the sub main, how does the inverter know the length and csa of the sub main cable? If at the sub main end there is nothing connected, and the volt drop over a 100m run is 6 volts, then the sub main is sitting at 6 less than the head, so how does the inverter know to add 6 then plus 2 to ensure it's higher than the head voltage?

 

[yellowvanman]

OK I'll try again and have made some assumptions on how inverters work! If my assumptions are incorrect then someone please let me know.

Inverter is turned on and analyses the voltage at the terminals. I don't know what the current the inverter consumes at this time but I would assume its very small. But if you have a 100m cable run there will be a small volt drop. So lets say there is 240V at the head and with the inverter in its start up mode there is 239V at its terminals. So the inverter decides on what voltage to start outputting, lets say its 239V + 2V = 241V.

When the inverter kicks in it starts to output some current, this current now needs to flow in the opposite direction to the initialisation current and the inverter voltage needs to be higher than the 240V at the service head. Without having any remote sensing then the inverter must work out what it has to do from its own terminals measurements. So my guess is that the inverter will increase the terminal voltage until the current it is generating flows in the right direction, so in effect will 'experiment' with its terminal voltage, and as the current is now flowing from inverter to service head, voltage at inverter will be at some voltage 240V + xV.

Depending on what power the array is generating then the added voltage value (xV) will fluctuate betwee cloudy and sunny times of the day and will be dynamically adjusted to ensure the current flows in the right direction (inverter to head), whilst compensating for the variable volt drop (due to varying current) from the cable to the sub main, and it'll also have to compensate for the variable voltage at the service head.

Hope that makes it clearer! As said previously i've made some assumptions of how an inverter works.

 

[dansk]

That makes total sense, and I guess why sticking to 1% vd is important. It was the dynamic part I couldn't not figure, and I think your right, it will keep upping the volts until it flows.

 

[SRE]

So, the DNO have done their tests and the voltage at the head ranges between 219v and 254v (which seems like a huge range to me) when the inverter kicks in it has been 5v more than the voltage at the head, tripping the inverter when the voltage at the head is over 251v - so I suppose that all makes sense except the inverter is set to 261v. The DNO are supposed to be turning down the power at the transformer this weekend but I won't know what has happened until our customers are back from holiday next weekend.

 

[JD6400]

OK I'll try again and have made some assumptions on how inverters work! If my assumptions are incorrect then someone please let me know.

Inverter is turned on and analyses the voltage at the terminals. I don't know what the current the inverter consumes at this time but I would assume its very small. But if you have a 100m cable run there will be a small volt drop. So lets say there is 240V at the head and with the inverter in its start up mode there is 239V at its terminals. So the inverter decides on what voltage to start outputting, lets say its 239V + 2V = 241V.

When the inverter kicks in it starts to output some current, this current now needs to flow in the opposite direction to the initialisation current and the inverter voltage needs to be higher than the 240V at the service head. Without having any remote sensing then the inverter must work out what it has to do from its own terminals measurements. So my guess is that the inverter will increase the terminal voltage until the current it is generating flows in the right direction, so in effect will 'experiment' with its terminal voltage, and as the current is now flowing from inverter to service head, voltage at inverter will be at some voltage 240V + xV.

Depending on what power the array is generating then the added voltage value (xV) will fluctuate betwee cloudy and sunny times of the day and will be dynamically adjusted to ensure the current flows in the right direction (inverter to head), whilst compensating for the variable volt drop (due to varying current) from the cable to the sub main, and it'll also have to compensate for the variable voltage at the service head.

Hope that makes it clearer! As said previously I've made some assumptions of how an inverter works.

Thank you this version makes perfect sense now .
I had not been making the assumption about the inverter , but if this is the case i can see the light now !

 

[cookiemonster]

hmmm great thread this one! so just to confuse matters further what happens with multiple PV inverters working in same street. E.g. when output voltage at substation transformer is say 240v and Mrs. Bloggs 's inverter is chucking out 240 plus 2 = 242v. is that not the effective voltage presented to all customers on her street. Well that is until Mrs Jones inverter kicks in and tries to chuck out 242 plus 2 = 244v. I guess what i'm really trying to ask is how do multiple inverters work that are trying to Export to DNO. They can't all be plus 2v up on each other? Any ideas?

 

[SRE]

That seems to be what our problem is - one job installed in Feb, one installed in April and one in July. All recommended us to the next neighbour. The trnasformer can only be reduced a certain amount of times after which there comes infrastructure costs - the poor custmer who has theirs installed when there's no more tweking to be done is going to be landed with a huge bill.

 

[SolarCity]

That seems to be what our problem is - one job installed in Feb, one installed in April and one in July. All recommended us to the next neighbour. The trnasformer can only be reduced a certain amount of times after which there comes infrastructure costs - the poor custmer who has theirs installed when there's no more tweking to be done is going to be landed with a huge bill.

As long as these installs are <4kWp then this is solely the responsibility of the DNO

 

[SRE]

Thats what I thought but our DNO who is usually quite good have indicated there may be some associated costs.

 

[SolarCity]

I don't think they have any right to charge additional costs. G83 connections don't even need prior notification so how could they try charging after the install was finished?

 

[Worcester]

@BiggsSolar Not quite, multiple installs in the same location even below 3.68kWp require a G83 Stage 2 Application.

G83 stage 2 is NOT Solely for >3.68kWp. http://www.electriciansforums.net/p...forum/34529-g83-1-1-updated-april-2011-a.html

 

[SolarCity]

Agreed, but assuming that the installs were not carried out concurrently then it doesn't come under stage 2.

 

[Cider]

When I did my PV training earlier this year at a large electrical company i heard rumours of the installer becoming responsible for any issues if they installed several systems in close proximity.?

 

[SRE]

I'm not sure how that can possibly happen. An area where we've been installing over the last few months has had several different installers doing single systems. How would you identify who would pay for what?

 

[MorganPVI]

I'd say the DNO would handle the issues outline above, on some recent installs we've seen 4 other systems from the roof were installing on. It would be silly to make the the installer of the next system pay for strengthening the local network to take the next installation. It's the role of the DNO to ensure the network capacity and supply the services needed for an area. If your installing months apart in a given street then i can't see any issues as they are all sperate installations - i.e not planned at the same time, therefore keep it under 16a and let the DNO worry about it.