array insulation resistance

[The Dav]

does anyone understand that dti guide. itsays to do test [ir] on array cables. how can this be acheived during daylight. also if not earthing array frame if using isolating transformer inverter with tncs do you probe earth on ac isolator switch for pos-earth neg-earth on test.comments welcome.

 

[VMan]

Not to sure about ir on array frames, but using with an isolating transformer you just earth with your normal CPC on the AC side with the twin & earth, no need for spike.
The spike is for earthing the array but as you are using an isolating transformer (Assuming using class 2 panels, connections & not in equipotential zone ect) you do not need spike or bond the arrays.

 

[VMan]

Confirmed with a lecturer today, you cannot to a IR test on DC side as it is always live, you should do the Voc and Isc tests.

 

[BruceB]

Yes you can do IR tests. Look at Appendix C page 53 of the DTI Guide.
Regards
Bruce

 

[VMan]

hmm, interesting it seems you test between pos / neg and earth, but if the array is a class 2 rated how is this possible? i will pass this by a lecturer tomorrow, unless anyone can explain their procedure??

 

[BruceB]

How is it possible? Just, select the test voltage as per the Guide, connect your meter leads and press the button. The point is of course your meter should not detect any leakage current.
Regards
Bruce

 

[VMan]

Quick search brought up this previous post no.12
http://www.electriciansforums.net/photovoltaic-solar-panels-green-energy-forum/24036-p-v-array-testing-2.html

It appears you should test + to array frame, then - to Array frame. i will try to get more info for tomorrow.

 

[BruceB]

Or you can short circuit them and just do the one test according to the Guide
Regards
Bruce

 

[The Dav]

how can you do this during the daytime when circuit is live!!

 

[BruceB]

I appreciate EAWR, but there is no particular problem doing it live unless I am missing something? A good argument for doing it during the day is that it would be more dangerous doing it at night when you cannot see as well. If you want to reduce the voltages present then cover the panels.
Regards
Bruce

 

[VMan]

Sorry Bruce you mean using a DC clamp and irradiance meter to calculate the any current lost when modules are in sort circuit?

 

[BruceB]

NO. Perhaps we are talking at cross purposes. I was talking about doing an insulation resistance check between the dc cables and local earth or array framework. There is simply no problem doing it in daylight while the array is live, but before it is connected to the input of the inverter. The 2 cables from the panels are connected a dc isolator. Then either test each individually or using the dc isolator short circuit the array and then test both together. The process and safety precautions are described in detail in the DTI guide. In order that voltage being generated by panels + voltage you are testing at does not exceed the maximum voltage of the cable and switchgear you need to choose the test voltage carefully. But it is all laid out in the DTI guide as I said.

Regards
Bruce

 

[VMan]

Got Ya, simples when explained now, i was thinking you were looping the mc3/mc4 connectors and was wondering how you would test conductor to earth.

Got there in the end tho and wasn't even my Q.

Cheers Bruce.