[RE-wrenches] Long transmission line inductance and LED light flicker

[Ray Walters]

I just had an idea on this situation from August's comment.  I'm sure 
you've checked already, but are you sure that ground and neutral aren't 
bonded in both locations, causing current to flow through the ground 
system? I've seen many multiple building properties inadvertently send 
both a ground wire and neutral to a separate structure with neutral 
bonded to ground in both locations.
If the separate structure has its own grounding system and bond, then 
disconnect the ground wire connection back to the other building, as it 
will still be bonded through the neutral.  The other option is to set a 
separate ground buss in the load center at the separate structure, and 
unbond neutral from ground, since it would bonded back at the other 
building.
Just an idea,  I've seen all sorts of weird things happen with current 
flow on the ground.  If you have uneven current flow on that long a run, 
it could definitely cause some issues.

R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760

On 2/12/2014 9:14 AM, Exeltech wrote:
> Troy,
>   
> Elsewhere in this thread, boB (Midnite) suggested connecting one of the problematic lights and dimmers directly at the inverter output.
>   
> This is a very sound recommendation, and would immediately rule in .. or rule out the conductors (and related circuits) as an issue.
>   
> Another Wrench suggested using an oscilloscope to check the waveform at the load end.  This too is excellent advice, and would be even more telling than connecting the lamps and dimmer directly at the inverter.  The ‘scope will reveal the AC voltage AND a visual indication of any waveform distortion, either aspect of which could potentially cause the flicker you describe.
>   
> If you don’t have access to a ‘scope, boB’s comment about connecting at the inverter won’t require any test equipment.
>   
> At a minimum, set your DVM to record the voltage minimum; connect it the lamp circuit, and turn on the 1 kW load you described.  If the voltage is dropping notably, this too would introduce visible flicker.  The DVM method is less accurate than an oscilloscope, but better than nothing, and depends greatly on the quality (or not) of your DVM.
>   
> The above aside, anything else would be strictly conjecture .. which we can do all day, and never be correct.
>   
>   
> Dan
>   
>   
>   
> --------------------------------------------
> On Wed, 2/12/14, August Goers <august at luminalt.com> wrote:
>
>   Subject: Re: [RE-wrenches] Long transmission line inductance and LED light flicker
>   To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
>   Date: Wednesday, February 12, 2014, 9:01 AM
>   
>   Hi Troy,
>
> Have you double checked that your grounding systems both in the house and at the inverters/array are all up to snuff?
>
> Sorry I can’t offer any help with the inductance issue.
>
> Best,
>
> August
>
>   
>
> From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Troy Harvey
> Sent: Tuesday, February 11, 2014 5:45 PM
> To: RE-wrenches
> Subject: Re: [RE-wrenches] Long transmission line inductance and LED light flicker
>
>
> Richard,
>
>
> The system configuration is:
> Approx 24.7kW of modules connected to:
>              2 x 9kW Sunnyboys
>              1 x 5kW Sunnyboys
>
> Plus
> 4 x 6kW sunnyislands, with 2 Parallel 48V Strings of (12 x 4V Surrettes ) using 350MCM cable
>
>
>
> Wire
>
> The wire is about 1000 feet long 350 MCM in a "twisted" bundle to this outbuilding
>
> Conditions
>
> The conditions were during the day with full sun, so during the test there is approx. 47kW of available inverter pointed at only >15 amps (120V) of load(!).
>
> The steady state conditions was a few LED lights, maybe 60 watts worth, plus a handful of vampire loads, maybe 100-200 watts total. When a pure resistance load, like a 1000W curling iron was turned on the lights would flicker.
>   
> Since the lights flickered from a resistive load, but didn't stay dim, I assumed it was from a reactive-phase issues due to the transient  turn-on - screwing with the LED dimmer circuits which are already doing a bit of magic to turn TRIAC waveforms into a DC constant current.
>
> thanks,
>
> Troy Harvey
> ---------------------
> Principal Engineer
> Heliocentric
> 801-453-9434
> taharvey at heliocentric.org
>
>
>
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