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

August Goers august at luminalt.com
Wed Feb 12 07:01:01 PST 2014


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



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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