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karlheinzhaller avatar image
karlheinzhaller asked

Earth Fault Alarm Monitor in parallel to the MPPT250/100

Hi, in Australia we must install an Earth Fault Monitor in parallel to the MPPT250/100 resp. 250/85 if the Array voltage is above LV (120VDC).
We have installed an EFM Model DDEA from Thiim in Denmark. As soon as we turn on the Array DC circuit breaker the DDEA indicates an Earth Fault from MINUS to Earth. As soon as we disconnect the MPPT from the circuit the Earth Fault disappears. When we megger the resistance at the array from MINUS to Earth resp. PLUS to Earth the resistance is well above the minimum value of 30kOhm.
I contacted Thiim and there response was that there is an earth leakage in the MPPT from MINUS to Earth. That proves it as the Earth Fault disappears as soon as we disconnect the MPPT.
As we are going to have two more Off Grid system to install and have already purchased the Thiim ELM's i would appreciate your assistance solving this problem. Thank you.

MPPT Controllers
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2 Answers
Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

Hello Karl,

I will consider your issue more shortly, as I would like to have a recommended solution that allows for legal use of the 250V MPPT's in Australia, which necessitates an earth fault alarm.

Here are a few notes about the grounding/isolation of MPPT solar chargers that I have at hand:

  • No isolation between PV input and DC output

  • Basic isolation between input/output and chassis.

  • Do not ground the positive or negative of the PV array: the PV negative input of the MPPT is not isolated from the negative output. Grounding the PV will therefore result in ground currents.

  • The PV frames however may be grounded, either close to the PV array or (preferably) to the central ground. This will provide some protection against lightning.

  • Ground close to the battery. The battery poles are supposed to be safe to touch. The battery ground should therefore be the most reliable and visible ground connection.

  • Required cross-section: DC ground cabling should be able to carry a fault current at least equal to the DC fuse rating.

  • The chassis of the inverter or Multi/Quattro must be grounded (basic insulation between AC and chassis).

  • The chassis of the MPPT solar charger must be grounded (basic insulation between DC and chassis).



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luka avatar image luka commented ·

Hallo Guy Stewart,


could you please inform me if it is possible to do a positive grounding on the system, which is common for Telco systems.

for your information the used equipment is:
  • Smartsolar MPPT 250/70
  • Quattro inverter
  • and a battery protect.

Would appreciate an answer soon.


Thanks.


Luka


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Craig Myatt avatar image
Craig Myatt answered ·

I have just come up against the same issue: noting that the actual wording of the standard, AS5033 PV installations, cl 3.4.1 states that

PCE charge controllers used on LV PV arrays shall also provide fault detection and alarm functions. An exception to this is only if no product is available on the market.

While it would be good to use products like the Morningstar earth fault interrupter, by a strict reading of that standard, that product is not an earth fault alarm, but an earth fault interrupter, which means there are not any (by my google searches), available products on the market, meaning it could be legitimately omitted, in this country. While that may be disputed, it also reflects a reasonable response to what appears to be an over-reaction to the possible earth faults, often arising from roof mounted DC isolators, something which Australian authorities chose to implement, and which have been, ironically, the main cause of fires in solar installs. Put more simply, it would be a reasonable response to omit the earth fault alarm, for DC coupled solar, providing the other earthing/safety directions in AS5033 relating to LV PV arrays are met, for safety. Or if desired, add a Morningstar EFI.

Victron also may consider that the main function of the earth fault alarm is to alert a user to a fault arising from leakage of current, from one or both legs of the PV array pos/neg poles, eg to the metal roof, or other conductors, possibly water damaged. That means there may be a simple way of doing that, by a firmware update (ie by software), in 150/XX and 250/XX MPPT units. Basically put, it would involve ensuring that the current/voltage for each pole of the PV input is in a reasonable tolerance range, by measuring it inside the MPPT unit, which I presume is possible now. And then if there is a current leakage, apparent by the comparison of the two poles, it could be alerted to a GX device for an email/alarm alert, or close the relay on smart versions, to trigger an audible alarm.

That would be if possible, low cost for Victron to implement, and then require not much more than a piezo type audible alarm to be setup on a Smartsolar MPPT relay connected to a battery voltage, where it had the new firmware installed. That is, the earth fault causes the MPPT relay to close, the relay sounds the audible alarm. (and the user/installer supplies the alarm/circuit.)

While I have not extensively analysed all the fault conditions mentioned in Appendix B to AS5033...I think that covers the main ones, and also meets the requirement, for a basic earth fault alarm in AS5033, and does so simply/inexpensively for an installer and a user. Would be good if victron could look at that as a future firmware update, for Australia/elsewhere.

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