Hi, I an electrician and I'm currently installing grid connect pv systems, have so for over a year, so I'm still learning. The company I work for uses HRC fuses for string protection. Some are starting to blow, I'm wondering if anyone here could suggest possible reasons for this. The panels we use have an ISC of 5.23amp, and the size of the fuses are 10amps. At first I thought maybe it was just a dodgy fuse, but its happening more often now. Any help would be greatly appreciated.
HRC fuses
(15 posts) (7 voices)-
PV2010
MemberThe voltage is the other one, if your string is getting above the rated voltage of the fuse it will cause issues. The fuse will have a code on it, you will be able to get the specification sheet from there. It might reveal something
I have seen (MCB) fuses blown after lighting strikes, but usually there's a bit more collateral. Other causes of failure have been down to poor connections, either at the junction box or the marshaling box.
You can test the array by short circuiting, make sure every thing else is isolated. A current clamp will show you the actual ISC. You can compare this to the rated ISC, don't try the test unless your confident you know what your doing.
Also I'd ask your boss why your using HRC,seems old school or cost cutting to me. I cannot recall seeing HRC's used in marshaling boxes this millenia .Posted Thursday 23 Sep 2010 @ 10:52:50 am from IP # -
solardude
MemberThe fuses are 600v. Will be looking at a system with blown fuses tomorrow if i get time. I doubt it would be lighting, I'm in SA and don't get too much lighting here.
I've done a few short circuit tests, but I doubt a string ISC would be up to 10amps if the panels are rated at 5.23 amps.When I did the accreditation training at TAFE, their systems had HRC fuses in them, they also recommended using HRC fuses, for reasons I can't remember. I've also looked at a couple of other systems by other companies and they to use HRC fuses.
Posted Thursday 23 Sep 2010 @ 11:25:48 am from IP # -
PV2010
Memberyeh lighting leaves typically leaves a nice mess.
At 5.23 amps, with correct voltage and voltage range a 10A HRC fuse should not be blowing from ISC, as you say.
What about a dodgy inverter, you mentioned this has happened alot so I can't imagine multiple inverter failures.
Anyway good luck it'll be interesting to see what conclusion you reach.Posted Thursday 23 Sep 2010 @ 1:03:15 pm from IP # -
olfella
MemberHello Solardude.
One uses HRC fuses because they are faster to blow & protect any system than the switching time of circuit breakers.You don't mention which panels you are installing, but you might need to investigate their potential voltage or current peaks/spikes produced by rapidly changing shade conditions which might be effecting the array.
I have a system using the 300W Sunpower panels & have not had a problem, but my fuse protection allows a 150% margin on nominal current.
Posted Friday 24 Sep 2010 @ 4:16:06 am from IP # -
PV2010
MemberOlfella
Interesting comment on the HRC, I'd be interested to see why the experienced engineers at companies I have worked with moved to MCB's from HRC. I'd require more data before I insist all my projects have them installed. That said, essentially I am just interested that the industry maintains quality installs and that includes my own!Anyway... Interesting you mention Sunpower, recently I was advised that the new E19s were not compatible with the "TL" range of inverters, I will have to confirm this with both manufacturers, I might be getting the run around.
Posted Friday 24 Sep 2010 @ 11:57:48 am from IP # -
guy
Memberif you are using the same batch of the same brand of hrc fuses chances are you have installed bad fuses if thats possible. you get bad batches of circuit breakers and rcds where under testing or fault current they explode. remember by rights when circuit breakers and the like are given clearance to be sold over here its true they might be tested beforehand but in that case you are only testing the design not the ongoing manufacturing integrity. it might be they've spolit the fuse wire so that its more likely to blow for no reason.
if i were you i would start recording what hrc fuses are blowing and then see if you can see a pattern same brand, high current for example.
Posted Saturday 25 Sep 2010 @ 3:42:03 am from IP # -
olfella
MemberG'day PV2010
Yes MCB more practical for sure. Only mentioned the theory bit about HRC v MCB bit in response to solardude wondering why his course taught them. An old lecturer I knew was deadset anti MCBs; never trust new fangled gadgets syndrome.The other thing about HRCs is as Guy says, variations, bad batches or just been up to the edge one too many times. Sometimes these high speed fuses just go too easily & just subbing an MCB ends the regular (and depending on rating, costly), trek to the fuse box.
Thats interesting about the E19s. I noticed a lot of comment in the US about Sunpower not supplying E19s to buyers unless they also buy the Sunpower branded inverters, which from memory I think are made for them by SMA. It appears this might be an attempt by Sunpower to make it a proprietory market for system components. Sunpower panels are fairly unique in requiring positive grounding, but most of the main inverter supplier accomodate that. It seems to me the one unique thing about Sunpower inverters is they're only suitable for +ve grounding.
I notice several posts of late in US based PV forums suggesting systems are being installed with transformerless or 'micro' inverters & some Sunpower distributors are offering E19s with Enphase inverters which I know are TL from their specs. One can't assume what one sees in forums is correct, so I'd want more info before putting money down, but it appears Sunpower might have been just using the E19s selling points to boost their own inverter sales.
Have a look at: http://www.wind-sun.com/ForumVB/showthread.php?p=64248
Sunpower certainly don't carry any qualification of inverter/E19 specs on their website.Posted Saturday 25 Sep 2010 @ 6:44:12 am from IP # -
rsigmund
MemberI also studied solar at TAFE
HRC for solar should be DC rated fuses!
Using AC circuit breakers for DC current is a bad idea according my teacher! Something to do with the gap in the AC breaker being smaller because of the zero voltage every 20mS ?
By MCB do you miniature circuit breaker or Magnetic circuit breaker because most miniature circuit breakers are AC breakers
Posted Wednesday 29 Sep 2010 @ 6:28:41 am from IP # -
PV2010
MemberMCB is a generic term for Mini Circuit Breaker (at least it was last time I looked!). As you say MCB can be rated AC or DC, its just historically there has been minimum demand for DC equipment in the standard house. In the "old days" pre PV, 99% of grid connect domestic wiring was AC (exceptions ? irrigation switching and ummmmmm.....). And yes AC breakers can fail under DC load fault conditions and be difficult to isolate due to DC arcing. I don't think any of the posts were recommending AC breakers instead of DC.
BTW....If you've ever short circuited a DC string it gives great arcs, you can pull the cables apart some way before the electrical field collapses, all those electrons flying through the air always amazes me...still (not that I'd recommend it!).Posted Wednesday 29 Sep 2010 @ 9:34:40 am from IP # -
olfella
MemberPV,
You should have seen what happenned one day in the late 1970s, when a young overly helpful cadet engineer decided to help while we were trying to put an additional laminated spreader between 6"x 1/2" vertical busbars, carrying +/-50Vdc away from the battery banks.The helpful little fellow ran up & stuck a crowbar in between, while two stunned mullets screammed ... NO! It is amazing how long a couple of coats of red & blue dulux work as insulation, before all hell broke loose!
Given we were in the main battery room for an international comms terminal, it is a miracle none of us were killed. As for the young ginger beer; he decided things that go bang & spray molten metal weren't for him; went off to become a programmer.
Posted Friday 1 Oct 2010 @ 3:21:28 pm from IP # -
swanning_it
MemberMost common brand MCBs do have a dc rating (usually only to 65Vdc or so). From memory, it's both the contact gap and the arc shutes which are undersized preventing full dc voltage rating. I tend to agree with olfella, in that MCBs are really only better than fuses for convenience sake. The trip curves of some MCBs can be woeful really, but not usually too big an issue with tolerances.
For the problem at hand, can I suggest you upsize the fuse cartridge? If it's not a faulty batch (as has been suggested already) it is an overcurrent, spike or surge from some source because of some parameter (is a back emf spike possible from the inverters?). As it's dc, I'd be assuming the cabling is already upsized to account for voltage drop and as the overcurrent protection is there for cable protection only, that should be a suitable solution. What cable size are you protecting with the 10A fuse?
PS - MCB is a generic term which may be applied to thermal and magnetic hydraulic breakers of a minature case size, but is most commonly used to describe the standard din rail mounted units seen commonly in residental installations in Australia.
Posted Friday 1 Oct 2010 @ 9:57:13 pm from IP # -
Lazy
MemberHi Interesting fault.
The HRC fuse is usually used where there is a possibility of exceptionally large fault currents, where other means of circuit protection may not be able break the arc. The HRC fuse has an inverse trip time, what that means is the closer it is operating to rated current the shorter the trip time. HRC fuses are often used in applications such as motor start where the motor draws about 6 times run current, the fuse allows it to start but as the motor draws current the trip time reduces. I have a HRC fuse in front of me that will carry over a 1000 Amps for a part of a second, see charts on pre acr time. The HRC fuse is not normally used because of its speed of operation but because its capacity isolate high fault currents. EG on the battery of a standalone system. The circuit protection on a PV system, whatever method used should only operate when a fault has occurred. There is a chance that you may have a bad batch of fuses check where they are manufactured. If your are continually blowing fuses I would be concerned about feedback from the inverter, particularly if you have by pass diodes in place Does the inverter have some form of galvanic isolation? My next concern would be ground faults. What is the window voltage of the inverter?
Cheers
LazyPosted Tuesday 30 Nov 2010 @ 10:16:34 am from IP #