Bostjan, Even though PV array can be subject to lightning strikes, to my knowledge there is no specific requirement for OV transients occurring on the DC side of your inverter. This leaves you in a bit of a quandary fro spacings determination on the DC side, especially if you have no transformer isolation.
Although your power production is from DC to AC, your system is still subjected to OV transients originating from the AC side mains connections. These connections will indeed be category IV if you are connected to the LV side of an MV transformer. For the DC side, I would use the Controlled Overvoltage requirements in of UL 840 for the DC side (see Clause 8.7). Depending on the design of your product and the likelihood of AC side transients propagating through to the DC side, you may be able to reduce the OV Cat by one full step or more on the DC side. This can be achieved in a few ways, transformer isolation being the most obvious. However, the standard does allow attenuation by impedance networks. In this case the impedance network is comprised of your AC EMI filter, AC line reactors, and DC bus cap. Approved transient suppression devices can also be useful. If you believe your system is able to absorb or suppress these transients to a level below Cat IV by virtue of the impedance network, you can prove this is true through test by applying OV Cat IV impulses the mains and monitoring the circuit in question using an oscope (UL 840 section 12.1). In this case use the 1.25/50 uS impulse test. Be certain your application of the impulses and the connection of you oscope is in all orientations of line to line and line to earth, in order to see the maximum impulses available on the DC side. Your results should not exceed OV Cat III, for example. Good luck, –doug Douglas E Powell http://www.linkedin.com/in/dougp01 On Wed, Aug 6, 2014 at 12:25 PM, Boštjan Glavič <bostjan.gla...@siq.si> wrote: > Dear Rich, > > Thank you. DC input comes from solar cells therefore from outside. UL 1741 > states that OVC IV needs to be used and for 120/240V it means 4000V. So > what transient should I use from DC side? > > Why table 8.1 in UL840 also mentions dc input? > > Best regards, > Bostjan > > Boštjan Glavič > Vodja laboratorija, Laboratorij za elektroniko > Head of Laboratory, Laboratory of Electronic Engineering > > [SIQlogo60px] > www.siq.si<http://www.siq.si/> > > SIQ Ljubljana, Trzaska c. 2, SI-1000 Ljubljana, Slovenia, VAT ID: > SI23509678 > t +386 (0)1 4778 265<tel:+386%20(0)1%204778%20265>, m +386 (0)41 391 > 283<tel:+386%20(0)41%20391%20283>, > f +386 (0)1 4778 444<tel:+386%20(0)1%204778%20444> > > > > > On 6. avg. 2014, at 20:17, "Richard Nute" <ri...@ieee.org<mailto: > ri...@ieee.org>> wrote: > > > > Dear Boštjan: > > > Despite UL1741 and UL 840, OVC does not apply to DC. There is > no research that I know of that supports use of AC OVC to DC. > > If the 450 V DC is not outside the building or is otherwise not > subject to lightning-caused overvoltages, OVC does not apply. > > Likewise, if the 450 V DC only supplies a limited number of other > loads (which are assumed to generate transients when switched > on or off), OVC does not apply. > > Since there is no isolation from input to output, whatever insulation > between input and output is "functional" insulation. The transients > that appear on the AC output side (generated by load switching and > lightning) will also appear on the DC side. > > 120\240 V overvoltages are OVC II and are 3 kV according to > IEC 60664, not 4 kV. > > > Best regards, > Rich > > > On 8/6/2014 10:39 AM, Boštjan Glavič wrote: > Dear experts, > > I am trying to figure out how to determine correct spacings for > non-isolated inverter. According UL1741 OVC IV needs to be considered for > inverter. From table 8.1 from UL840 I get a transients of 8,0kV for 450VDC > input. Is that correct? > > Output of inverter is connected to AC grid 120/240V. This results in 4kV > transients. > > We have no insulation input/output. Which transient level should I then > use? 8kV transient on AC output side is almost impossible for the design. > > Any idea? > > Best regards, > Bostjan Glavic > SIQ > - > ---------------------------------------------------------------- > > This message is from the IEEE Product Safety Engineering Society emc-pstc > discussion list. To post a message to the list, send your e-mail to < > emc-p...@ieee.org<mailto:emc-p...@ieee.org>> > > All emc-pstc postings are archived and searchable on the web at: > http://www.ieee-pses.org/emc-pstc.html > > Attachments are not permitted but the IEEE PSES Online Communities site at > http://product-compliance.oc.ieee.org/ can be used for graphics (in > well-used formats), large files, etc. > > Website: http://www.ieee-pses.org/ > Instructions: http://www.ieee-pses.org/list.html (including how to > unsubscribe)<http://www.ieee-pses.org/list.html> > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > Scott Douglas <emcp...@radiusnorth.net<mailto:emcp...@radiusnorth.net>> > Mike Cantwell <mcantw...@ieee.org<mailto:mcantw...@ieee.org>> > > For policy questions, send mail to: > Jim Bacher <j.bac...@ieee.org<mailto:j.bac...@ieee.org>> > David Heald <dhe...@gmail.com<mailto:dhe...@gmail.com>> > > - > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society emc-pstc > discussion list. To post a message to the list, send your e-mail to < > emc-p...@ieee.org> > > All emc-pstc postings are archived and searchable on the web at: > http://www.ieee-pses.org/emc-pstc.html > > Attachments are not permitted but the IEEE PSES Online Communities site at > http://product-compliance.oc.ieee.org/ can be used for graphics (in > well-used formats), large files, etc. > > Website: http://www.ieee-pses.org/ > Instructions: http://www.ieee-pses.org/list.html (including how to > unsubscribe) > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > Scott Douglas <emcp...@radiusnorth.net> > Mike Cantwell <mcantw...@ieee.org> > > For policy questions, send mail to: > Jim Bacher: <j.bac...@ieee.org> > David Heald: <dhe...@gmail.com> > -- Douglas E Powell doug...@gmail.com Skype: doug.powell52 http://www.linkedin.com/in/dougp01 - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@radiusnorth.net> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
