Maximum utility backfeed current

German translation: Max. Netzrückstrom

GLOSSARY ENTRY (DERIVED FROM QUESTION BELOW)
English term or phrase:Maximum utility backfeed current
German translation:Max. Netzrückstrom
Entered by: Hewhotranslates

18:03 Aug 20, 2017
English to German translations [PRO]
Tech/Engineering - Energy / Power Generation / Photovoltaic system
English term or phrase: Maximum utility backfeed current
From an inverter spec sheet: "Max. Utility Backfeed Current: 400 A"

Is there a common German term for that?

Thanks in advance!
Hewhotranslates
Local time: 19:04
Max. Netzrückstrom
Explanation:
This technical bulletin provides information on the Xantrex GT3.0-NA-DS-240 PV Inverter. It confirms that the “Max Utility Backfeed” current is zero amps
Both UL1741 and NEC 690 have requirements addressing backfeed current that can flow from any source other than the solar array, onto the array wiring. In UL 1741, any current that can flow from the utility grid onto the array wiring through an inverter is called the "max utility backfeed current" and the standard requires labeling the inverter with that value. In addition, NEC article 690.9 requires that overcurrent protection for array wiring must take into account the current from all sources, including possible utility backfeed current through inverters.
To simplify the original evaluation of the GT3.0-NA-DS-240, the value of this backfeed current was assumed to be equal to the overcurrent protection provided in its AC output circuit. That reasoning lead to a marking of 20A for model GT3.0-NA-DS-240 based on its internal 20 amp AC output fuse rating.
A careful evaluation of the circuit by Xantrex and CSA has shown that there is no normal or single fault condition that can cause backfeed of any AC current through the GT3.0 onto the PV array wiring. Therefore, the correct value for the maximum utility backfeed current is determined to be 0 amps.
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd...

Maximum Utility Backfeed Current (AC) 0 A
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd...

Maximum utility backfeed current 0 A
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd...

Utility backfeed current 0.1 A
Utility backfeed current 0.1 A
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd...

Maximum utility backfeed current to utility ‒
Máxima corriente inversa desde la red hacia la empresa de suministro
Courant de rétro-alimentation maximal vers le réseau électrique public
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd...
(Dieser Wert wird in deutschsprachigen Technischen Daten von SMA nicht angegeben.)

Durch Kurzschlüsse könnenModulströme fehlgeleitet werden und ein PV-Modul mit einem so genannten Rückstrom belasten, der den normalen Maximalstrom (Kurzschluss) dieses PV-Moduls um ein Vielfaches überschreiten kann.
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd...
(bezieht sich auch hier nicht auf das Netz)

Netzrückstrom unterbunden (Schnelle Netztrennung)
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd...

Meines Wissens nach vertragen Inselwechselrichter keinen Rückstrom.
:
Ich denke auch, dass InselWR keinen Netzrückstrom vertragen, und wir werden das System dementsprechend aufbauen.
https://www.photovoltaikforum.com/pv-inselanlagen-f57/proble...


--------------------------------------------------
Note added at 1 day18 hrs (2017-08-22 12:15:10 GMT)
--------------------------------------------------

Da noch Unklarheiten zur Art des "utility back current" bestehen, insbesondere zur Frage, ob Gleichstrom aus der PV-Anlage oder Wechselstrom aus dem Netz und Anwendung auf PV-Module oder Wechselrichter gemeint ist, habe ich weiter gesucht und auch Wechselrichter gefunden, die mehr als 0 A Rückstrom zulassen:

Maximum Utility Backfeed Current (AC):30 A / 35 A / 30 A (277 V / 208 V Configuration Respectively)
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd...
(Anm.: In diesem Beispiel müssen die Paneele dafür geeignet sein. Bitte beachten, dass es sich um Wechselstrom aus dem Netz handelt, und nicht um Gleichstrom aus den PV-Modulen wie in folgendem Beispiel.)

Circuit protection design for photovoltaic power systems
:
Generally, the source of reverse current during a fault would be from back-feed current (IBACKFEED) from the other strings in the affected array. Figures 4a and 4b. IBACKFEED can be calculated to be approximately Isc x (n-1) where n equals the number of strings in the affected array. UL1703 and IEC60129 specifies PV panel testing to insure there is no dangerous overheating of the panel in the case of a back fed current equal to or less than Istring fuse x 135 percent for two hours. The UL PV fuse standard subsequently defined the PV fuse opening characteristic of not greater than Istring fuse x 135 percent for one hour. This guarantees proper coordination when using a UL or IEC panel with a UL fuse.
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd...

Back-feeding solar-generated power?
I'm curious how this is done safely. Engine-driven generators are required to be on a transfer switch specifically to prevent the back-feeding of power so that utility workers are not at risk of electrocution. So how is that risk addressed with the approved back-feeding of solar-generated power?

Answers:
The short explanation is that grid-tie inverter outputs are setup as a current source, rather than a voltage source. The utility system supplies the voltage. The inverter measures system voltage and cuts off its output when the voltage is not within its set nominal operating range.
:
Aside from voltage, a GT inverter also syncs to the grid frequency, so if it loses that it doesn't know what frequency to operate at and it shuts down.
:
When the grid goes down, your inverter can tell. Electronically how that happens is not really important unless you are an inverter designer, but it's not merely a function of increased load because it will shut down when you open the AC disconnect switch to the grid. Anyway, the UL1741 standard dictates that the inverter shut itself down within a very short time (a few milliseconds) when the grid voltage goes away. That protects any utility line workers who are making repairs as well as your inverter which would (as you pointed out) experience something very close to a dead short when the grid supply is cut off and the loads are still connected.
http://forums.mikeholt.com/showthread.php?t=138782
Selected response from:

Johannes Gleim
Local time: 04:04
Grading comment
Vielen Dank!
4 KudoZ points were awarded for this answer



Summary of answers provided
4 +1Max. Netzrückstrom
Johannes Gleim
3Maximaler Rückspeisestrom
Harald 4711


Discussion entries: 13





  

Answers


11 hrs   confidence: Answerer confidence 3/5Answerer confidence 3/5
maximum utility backfeed current
Maximaler Rückspeisestrom


Explanation:
k. T.

Harald 4711
Germany
Local time: 04:04
Native speaker of: Native in GermanGerman

Peer comments on this answer (and responses from the answerer)
agree  Kim Metzger: http://www.solarpanelstore.com/pdf/fronius_galvo_operation.p...
15 hrs

disagree  Johannes Gleim: Leider ohne Begündung. Auch der Fronius-Link enthält keine deutsche Bezeichnung. "Rückspeisestöme" sind bei PV gefährlich. Sie würden die Module aufheizen zund zerstören.
1 day 1 hr
Login to enter a peer comment (or grade)

22 hrs   confidence: Answerer confidence 4/5Answerer confidence 4/5 peer agreement (net): +1
maximum utility backfeed current
Max. Netzrückstrom


Explanation:
This technical bulletin provides information on the Xantrex GT3.0-NA-DS-240 PV Inverter. It confirms that the “Max Utility Backfeed” current is zero amps
Both UL1741 and NEC 690 have requirements addressing backfeed current that can flow from any source other than the solar array, onto the array wiring. In UL 1741, any current that can flow from the utility grid onto the array wiring through an inverter is called the "max utility backfeed current" and the standard requires labeling the inverter with that value. In addition, NEC article 690.9 requires that overcurrent protection for array wiring must take into account the current from all sources, including possible utility backfeed current through inverters.
To simplify the original evaluation of the GT3.0-NA-DS-240, the value of this backfeed current was assumed to be equal to the overcurrent protection provided in its AC output circuit. That reasoning lead to a marking of 20A for model GT3.0-NA-DS-240 based on its internal 20 amp AC output fuse rating.
A careful evaluation of the circuit by Xantrex and CSA has shown that there is no normal or single fault condition that can cause backfeed of any AC current through the GT3.0 onto the PV array wiring. Therefore, the correct value for the maximum utility backfeed current is determined to be 0 amps.
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd...

Maximum Utility Backfeed Current (AC) 0 A
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd...

Maximum utility backfeed current 0 A
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd...

Utility backfeed current 0.1 A
Utility backfeed current 0.1 A
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd...

Maximum utility backfeed current to utility ‒
Máxima corriente inversa desde la red hacia la empresa de suministro
Courant de rétro-alimentation maximal vers le réseau électrique public
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd...
(Dieser Wert wird in deutschsprachigen Technischen Daten von SMA nicht angegeben.)

Durch Kurzschlüsse könnenModulströme fehlgeleitet werden und ein PV-Modul mit einem so genannten Rückstrom belasten, der den normalen Maximalstrom (Kurzschluss) dieses PV-Moduls um ein Vielfaches überschreiten kann.
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd...
(bezieht sich auch hier nicht auf das Netz)

Netzrückstrom unterbunden (Schnelle Netztrennung)
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd...

Meines Wissens nach vertragen Inselwechselrichter keinen Rückstrom.
:
Ich denke auch, dass InselWR keinen Netzrückstrom vertragen, und wir werden das System dementsprechend aufbauen.
https://www.photovoltaikforum.com/pv-inselanlagen-f57/proble...


--------------------------------------------------
Note added at 1 day18 hrs (2017-08-22 12:15:10 GMT)
--------------------------------------------------

Da noch Unklarheiten zur Art des "utility back current" bestehen, insbesondere zur Frage, ob Gleichstrom aus der PV-Anlage oder Wechselstrom aus dem Netz und Anwendung auf PV-Module oder Wechselrichter gemeint ist, habe ich weiter gesucht und auch Wechselrichter gefunden, die mehr als 0 A Rückstrom zulassen:

Maximum Utility Backfeed Current (AC):30 A / 35 A / 30 A (277 V / 208 V Configuration Respectively)
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd...
(Anm.: In diesem Beispiel müssen die Paneele dafür geeignet sein. Bitte beachten, dass es sich um Wechselstrom aus dem Netz handelt, und nicht um Gleichstrom aus den PV-Modulen wie in folgendem Beispiel.)

Circuit protection design for photovoltaic power systems
:
Generally, the source of reverse current during a fault would be from back-feed current (IBACKFEED) from the other strings in the affected array. Figures 4a and 4b. IBACKFEED can be calculated to be approximately Isc x (n-1) where n equals the number of strings in the affected array. UL1703 and IEC60129 specifies PV panel testing to insure there is no dangerous overheating of the panel in the case of a back fed current equal to or less than Istring fuse x 135 percent for two hours. The UL PV fuse standard subsequently defined the PV fuse opening characteristic of not greater than Istring fuse x 135 percent for one hour. This guarantees proper coordination when using a UL or IEC panel with a UL fuse.
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd...

Back-feeding solar-generated power?
I'm curious how this is done safely. Engine-driven generators are required to be on a transfer switch specifically to prevent the back-feeding of power so that utility workers are not at risk of electrocution. So how is that risk addressed with the approved back-feeding of solar-generated power?

Answers:
The short explanation is that grid-tie inverter outputs are setup as a current source, rather than a voltage source. The utility system supplies the voltage. The inverter measures system voltage and cuts off its output when the voltage is not within its set nominal operating range.
:
Aside from voltage, a GT inverter also syncs to the grid frequency, so if it loses that it doesn't know what frequency to operate at and it shuts down.
:
When the grid goes down, your inverter can tell. Electronically how that happens is not really important unless you are an inverter designer, but it's not merely a function of increased load because it will shut down when you open the AC disconnect switch to the grid. Anyway, the UL1741 standard dictates that the inverter shut itself down within a very short time (a few milliseconds) when the grid voltage goes away. That protects any utility line workers who are making repairs as well as your inverter which would (as you pointed out) experience something very close to a dead short when the grid supply is cut off and the loads are still connected.
http://forums.mikeholt.com/showthread.php?t=138782

Johannes Gleim
Local time: 04:04
Specializes in field
Native speaker of: Native in GermanGerman
PRO pts in category: 116
Grading comment
Vielen Dank!

Peer comments on this answer (and responses from the answerer)
agree  Matthias Brombach: Ich denke mal, "Rückstrom" trifft den Sachverhalt korrekter als "Speisestrom", da eine "Speisung" für mich auch eine Nutzung impliziert (wie bei der Rückspeisung von elektrischer Bremsenergie bei Elektromotoren)
16 hrs
  -> Danke! In der Tat sollten die PV-Module nicht aus dem Netz gespeist werden.
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