SMA TL series arc fault on inverter display.

Dave Angelini · April 2015

I was asked to look at a previously working SMA Grid tie system for an electrician.

I disconnected the (2) parallel 250V strings at the arrays and the arc fault went away. I connected each string and got the arc fault with either 250 volt string.

There is not any power being produced and I am wondering if the wiring (underground) from the arrays is breaking down under voltage but looking OK to the inverter when there is not any DC.

I am also wondering if the inverter has been damaged. Any great ideas are appreciated! I will start reading the SMA manual.... Thanx

inetdog · April 2015

Dave Angelini wrote: »

I was asked to look at a previously working SMA Grid tie system for an electrician.

I disconnected the (2) parallel 250V strings at the arrays and the arc fault went away. I connected each string and got the arc fault with either 250 volt string.

There is not any power being produced and I am wondering if the wiring (underground) from the arrays is breaking down under voltage but looking OK to the inverter when there is not any DC.

I am also wondering if the inverter has been damaged. Any great ideas are appreciated! I will start reading the SMA manual.... Thanx

Well, the Arc Fault detection is by its nature a passive thing, so with no DC present I would certainly not expect an AF trip to happen.
Ground Fault or Ground detection, on the other hand, can be done actively by putting a signal onto the wiring even when no power is coming from the panels. Active GF detection is still not required though, so that also may only trip when panels are active.

Dave Angelini · April 2015

Good point ! The arc fault Det. is internal on The TL series. Since this happens with either array I will need to bypass the underground wiring or substitute 200vdc into the inverter to go any farther.
Maybe a beer and a nap. Thanx!

solarix · April 2015

Arc fault circuits operate by sensing noise on the array conductors which is characteristic of the high-frequency noise that arcs entail. Any loose connection, extraneous noise, or shorting taking place can cause faults. I t can be a real hunt to find the cause. Process of elimination is your best strategy. SMA inverters are not known to be prone to false faults whereas other brands are (PowerOne's Aurora).

westbranch · April 2015

A loose connection? Strange that it is on both arrays, so does that narrow it down to after a/the combiner?

Dave Angelini · April 2015

westbranch wrote: »

A loose connection? Strange that it is on both arrays, so does that narrow it down to after a/the combiner?

Yes this was part of my halfs-plitting of the failure. All I can think of besides a spare inverter which I do keep for my offgrid clients is running a couple above ground # 12's from an array to the inverter.

Very unlikely that 2 arrays would have an arc fault when each has a midnite SPD that glows bright in the sunshine. The manuals circa 2013 were fairly useless BTW.

Dave Angelini · April 2015

This system is pretty remote and the owner is rarely at the home. He told me that the arc fault message has been on for a few weeks but only a day or so ago has the output/harvest gone to zero.
So it seems it has degraded from a warning to a failure. Anyone know if the TL series logs anything? There are not any external devices.

BB. · April 2015

The TL series is transformerless... And, from what little I could find about (probably a different brand TL inverter), one method for "arc fault" detection is to do a continuity test of the solar array every dawn (basically measure the resistance between array and safety ground) every morning before "starting up" power transfer.

I would try disconnecting the Midnite Surge Suppressors. It is possible that the leakage current of the MOVs and/or LEDs is enough to cause the array self test to fail (I don't know at what level the TL "faults").

However, the SMA unit sounds like it has a "true" radio frequency energy detector (user manual PDF)--Is is possible that the Arc Fault was detected when somebody was using a brush/universal motor (vacuum cleaner, electric mixer, etc.)? These have been known to trip Arc Fault breakers used in main panels of homes. I don't know if the SMA could be tripped by load side "arcs" or not.

In the manual, it says that the controller gives 10 seconds to allow the person to "tap" the inverter panel to cancel an Arc Fault detection, otherwise the inverter shuts down "permanently" until a service person comes out to reset the inverter with an installer's too/password. That sound like a pain for the installer.

At least,those are my first guesses why there could be a "false" Arc Fault detection. Otherwise, a phone call to SMA is probably needed to find out more about how the "arc fault" system works.

-Bill

Dave Angelini · April 2015

BB. wrote: »

The TL series is transformerless... And, from what little I could find about (probably a different brand TL inverter), one method for "arc fault" detection is to do a continuity test of the solar array every dawn (basically measure the resistance between array and safety ground) every morning before "starting up" power transfer.

I would try disconnecting the Midnite Surge Suppressors. It is possible that the leakage current of the MOVs and/or LEDs is enough to cause the array self test to fail (I don't know at what level the TL "faults").

However, the SMA unit sounds like it has a "true" radio frequency energy detector (user manual PDF)--Is is possible that the Arc Fault was detected when somebody was using a brush/universal motor (vacuum cleaner, electric mixer, etc.)? These have been known to trip Arc Fault breakers used in main panels of homes. I don't know if the SMA could be tripped by load side "arcs" or not.

In the manual, it says that the controller gives 10 seconds to allow the person to "tap" the inverter panel to cancel an Arc Fault detection, otherwise the inverter shuts down "permanently" until a service person comes out to reset the inverter with an installer's too/password. That sound like a pain for the installer.

At least,those are my first guesses why there could be a "false" Arc Fault detection. Otherwise, a phone call to SMA is probably needed to find out more about how the "arc fault" system works.

-Bill

Thanks Bill, Yep the midnite SPD's came out right away, they were still glowing before I removed them. There was not any protection on the AC side and so I agree the utility could be the source here. It is on my list to call SMA later today. I did get the tap warning but every power-up of line and load has the Arc warning.

Dave Angelini · April 2015

The source of the failure was water in the underground conduit. There probably was damaged insulation but I never looked for it and had my dirt man re-wire it. The code for resetting an SMA TL inverter deep into Arc-fault shut down is to repower and 2 knocks on the display before 10 seconds is up. Not too bad Bill but I agree a pain. SMA said they have to make it hard because 690 codes......

SMA TL series arc fault on inverter display.

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