DC circuit breakers and transformerless Inverters

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Re: DC circuit breakers and transformerless Inverters

Postby jono2b » Sat Feb 05, 2011 1:30 am

westy wrote:Why would you use a breaker anyway. Use isolators and if you need protection PV fuses.

Most people use breakers since they are generally just as cheap as an equivalent isolator anyway, and there seems to be a bigger range. Are there any isolators in particular you would recommend? Especially high voltage ones?

westy wrote:This is a serious issue as a lot of TL inverters have high voltage windows. I just looked at one with 850V max

Yeah I agree. ABB make a 4 pole circuit breaker which is rated for 1600V (400 per pole) when used in this manner. The specs say 1200V, but 800V on each set of two poles is ok as long as there is never more than 1200V across it which there won't be.
It is expensive and physically quite big but can do the job for strings up to 666 Voc (800/1.2). Above that I don't know what to use.

westy wrote:Speaking direct with manufacturers, the rest of the world are not even considering this an issue. Why are we so special?

I'd like to know more about this too. In the US their standards limit PV arrays to 600V and all their inverters have to have the isolators built-in so its probably not that big an issue. In Germany I think they may not require external isolators (like Australia does) since for SMA inverters the built-in ESS seems to be ok. This only disconnects the positive leg so perhaps they only require an isolator on one pole. I'm not too sure why that is ok though...
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Re: DC circuit breakers and transformerless Inverters

Postby SolarInstalla » Sat Feb 05, 2011 10:07 am

So the practicalities are what i am concerned with, what would be a suitable isolator to use for the PV array to satisfy the VOC x 1.2 rule?

Also, I guess I should be using 10A string fuses as string protection on the roof instead of 10A double pole dc breakers when there are 2 or more strings?
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Re: DC circuit breakers and transformerless Inverters

Postby rg767 » Sat Feb 05, 2011 12:45 pm

you definitely shouldn't be using [EDIT: polarised] breakers as a string fuse - in a fault condition they get reverse current flow through them.
Last edited by rg767 on Sat Feb 05, 2011 12:54 pm, edited 1 time in total.
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Re: DC circuit breakers and transformerless Inverters

Postby rg767 » Sat Feb 05, 2011 12:48 pm

DKSH do a good 700V isolator for about $120.
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Re: DC circuit breakers and transformerless Inverters

Postby jono2b » Sat Feb 05, 2011 1:44 pm

rg767 wrote:DKSH do a good 700V isolator for about $120


Which one is that? I've seen a 600V which they sell, which is made by Multi-Contact. And is a fair bit cheaper than that.

In any case I don't think it solves SolaInstallers problem.

SolarInstalla wrote:So the practicalities are what i am concerned with, what would be a suitable isolator to use for the PV array to satisfy the VOC x 1.2 rule?

If you are looking for something that complies with the CEC's rules of 1.2x Voc per pole, then I would recommend a 4 pole 1000V breaker. Eltech make one.
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Re: DC circuit breakers and transformerless Inverters

Postby rg767 » Sat Feb 05, 2011 1:51 pm

Yes on the price i am not quoting wholesale.

K&N do a heap of different combos one of which could help.
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Re: DC circuit breakers and transformerless Inverters

Postby franks » Sat Feb 05, 2011 7:48 pm

I Can see the CEC will mandate HRC fuses, Diodes and Switched Isolators, Between PVs and Inverter just to be safe to cover all possible fault cases.
3.04kW Grid Tie system 16 of 190W PVs, Samil 3.3kW
3.8kW PV Stand Alone Off Grid.. 5-8kWHr Per day
24 of 190W PVs
Midnite Classic 150 & Lite MPPT
8 of 6V 600 AH flooded cells (24 volt 1200 AH)
Outback VFX3024E Inverter Charger
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Re: DC circuit breakers and transformerless Inverters

Postby rg767 » Sun Feb 06, 2011 11:24 am

Fuses won't really help at all for isolation. It is really up to the standards committee to make a decision about polarised circuit breakers, not the CEC.

For a long time there though there was no funding for standards development, and so here we are.
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Re: DC circuit breakers and transformerless Inverters

Postby franks » Sun Feb 06, 2011 12:12 pm

Makes you wounder what does the $880 CEC Acretiation fees are used for , your builder, sparky, plumber, cabler, licencing fees are fraction of the CEC.
The CEC should be checked by the ACCC for price gouging!
3.04kW Grid Tie system 16 of 190W PVs, Samil 3.3kW
3.8kW PV Stand Alone Off Grid.. 5-8kWHr Per day
24 of 190W PVs
Midnite Classic 150 & Lite MPPT
8 of 6V 600 AH flooded cells (24 volt 1200 AH)
Outback VFX3024E Inverter Charger
franks
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Re: DC circuit breakers and transformerless Inverters

Postby franks » Sun Feb 06, 2011 12:21 pm

The mistake with DC breakers is assuming you need the full Voc covered on both -ve and +ve. It's just not the case, something I believe the CEC has admitted.
[/quote]

What, a 1st year apprentce knows the 2 poles with respect of the voltage source are in Series, so the rating is doubled if used as a single pole :?
How Can the CEC get it so wrong?
3.04kW Grid Tie system 16 of 190W PVs, Samil 3.3kW
3.8kW PV Stand Alone Off Grid.. 5-8kWHr Per day
24 of 190W PVs
Midnite Classic 150 & Lite MPPT
8 of 6V 600 AH flooded cells (24 volt 1200 AH)
Outback VFX3024E Inverter Charger
franks
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