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

[Troy Harvey]

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



On Feb 3, 2014, at 8:33 AM, Richard L Ratico <Richard.L.Ratico at VALLEY.NET> wrote:

> Hi Troy,
> 
> I'm assuming this is off grid. Could you please provide details for the system
> (inverters, batteries, etc.). 
> A single, sudden, 20 amp load is not necessarily small relative to the size of
> the system. Is the load 120V or 240 V?
> 
> Dick Ratico
> Solarwind Electric
> 
> 
> --- You wrote:
> On Sun, Feb 2, 2014 at 4:39 PM, Troy Harvey <taharvey at heliocentric.org>wrote:
> 
>> 
>> 
>> We've got a PV system that has long lines from the inverters to the house
>> (1000 ft or so). While the wires are properly sized (2x350MCMs), it
>> inherently has a lot of inductance due to the line-length. What We are
>> noticing is that dimmable LED lights flicker anytime a new load turned on,
>> even if that load is purely resistive and the overall current draw is small
>> (20 amps or so). What I "think" is happening is the LED dimmer circuits get
>> their cue from phase delays, and that the inductance of the line length
>> causes some phase jitter everytime a load is applied - thus causing flicker.
>> 
>> Has anyone dealt with this issue successfully (other than switching
>> to incandescent lights)? Would a static capacitor bank at the house do the
>> trick, or do we need some type of active PFC? And if static did you have
>> any issues with constant power draw from the capacitors?
>> 
>> 
>> 
>> Troy Harvey
>> ---------------------
>> Heliocentric
>> 
> --- end of quote ---
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