inverter fault current

Take a look at this inverter spec:
http://pvpowered.com/inverter_pvp5200.php
Look particularly at the "Maximum Output Fault Current" rating.
That's only 25 amps. Sure, this is a smaller inverter. But this fault current is a mere 15.4 % more than the rated continuous VA level.
So what happens if you do short circuit this thing on a 15 amp branch circuit. Well, you won't have all that much of a fault arc. But depending on where and how the fault happens, this could actually be quite dangerous because it's not going to trip a 15 amp breaker all that quick.
Is this common for inverters in the "natural energy market"?
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It will shut down pretty quick once the current exceeds its max electronic overload setting. These things are pretty cleaver.
If you short the output it will probably just stop, sharpish.
sQuick..
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sQuick wrote:

Are you sure about that? Where is that stated in the spec? If it feeds a continuous 25A into a fault, that's a big problem (particularly since that web page advertises a 30A overcurrent setting).
A good design could easily incorporate a shutdown or foldback regulation. But I didn't see that anywhere on the page.
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wrote: | sQuick wrote: |>
|> |> > Take a look at this inverter spec: |> > |> > http://pvpowered.com/inverter_pvp5200.php |> > |> > Look particularly at the "Maximum Output Fault Current" rating. |> > That's only 25 amps. Sure, this is a smaller inverter. But this |> > fault current is a mere 15.4 % more than the rated continuous VA |> > level. |> > |> > So what happens if you do short circuit this thing on a 15 amp |> > branch circuit. Well, you won't have all that much of a fault |> > arc. But depending on where and how the fault happens, this |> > could actually be quite dangerous because it's not going to trip |> > a 15 amp breaker all that quick. |> > |> > Is this common for inverters in the "natural energy market"? |> > |> |> It will shut down pretty quick once the current exceeds its max |> electronic overload setting. These things are pretty cleaver. |> |> If you short the output it will probably just stop, sharpish. | | Are you sure about that? Where is that stated in the spec? If it feeds a | continuous 25A into a fault, that's a big problem (particularly since | that web page advertises a 30A overcurrent setting). | | A good design could easily incorporate a shutdown or foldback | regulation. But I didn't see that anywhere on the page.
If I put a transformer on a high available fault current AC system, such as a utility service drop, that is rated for my expected peak load, as calculated and planned, I can easily expect that under a secondary side short circuit fault condition that transformer can deliver a substantial amount of current, typically 20 to 30 times the maximum rating, for the typical 5% to 3% impedances I see. Even though the transformer could deliver such current, if there was no overcurrent protection and that fault persisted, you can expect the transformer to burn out soon (if not the wiring). I'm not expecting a transformer to be _rated_ for continuous duty at the same current level it could deliver very briefly in a fault. So if I connect an inverter to a set of batteries that can deliver a very high fault current, I would like to see the inverter be able to BRIEFLY deliver a very high current peak, even though if it were called upon to deliver that current continuously, and such a high current were not interrupted, I could expect the inverter to burn up.
I would want that high current briefly just to start motors. This is a common power system design aspect. I do know generators tend to have some problem with this as that requires substantial brief mechanical mover energy to provide.
One possible solution might be to supplement the inverter with large flywheel type system (motor/generator in the same windings) that can provide that "quick kick" when needed. But is this economical?
Another possibility is a separate inverter for each circuit. But I do suspect this is quite non-economical (for that cost you could have a big huge 100 kVA inverter that could deliver fault current to smaller branch circuit OCP).
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|
| |> Take a look at this inverter spec: |> |> http://pvpowered.com/inverter_pvp5200.php |> |> Look particularly at the "Maximum Output Fault Current" rating. |> That's only 25 amps. Sure, this is a smaller inverter. But this |> fault current is a mere 15.4 % more than the rated continuous VA |> level. |> |> So what happens if you do short circuit this thing on a 15 amp |> branch circuit. Well, you won't have all that much of a fault |> arc. But depending on where and how the fault happens, this |> could actually be quite dangerous because it's not going to trip |> a 15 amp breaker all that quick. |> |> Is this common for inverters in the "natural energy market"? |> | | It will shut down pretty quick once the current exceeds its max | electronic overload setting. These things are pretty cleaver. | | If you short the output it will probably just stop, sharpish.
So, then, why have branch circuit breakers if "the main" is always going to be the one to trip?
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Inverters are not that clever when it comes to a fault on the motor side. We had a 160kW pump (690 Volts) develop a fault, and it took out the inverter with a bang. The IGBT's blew with a lot of other things. This was a twelve pulse unit, also took out 5 of 6 semiconductor fuses. Cheaper to replace inverter than repair. Cost, approx 11,000. It seems that fault current damages inverters (depending on the type of fault, and fault level) quicker than any protection systems that are installed.


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| Inverters are not that clever when it comes to a fault on the motor side. We | had a 160kW pump (690 Volts) develop a fault, and it took out the inverter | with a bang. The IGBT's blew with a lot of other things. This was a twelve | pulse unit, also took out 5 of 6 semiconductor fuses. Cheaper to replace | inverter than repair. Cost, approx ?11,000. | It seems that fault current damages inverters (depending on the type of | fault, and fault level) quicker than any protection systems that are | installed.
What is "motor side"? The load? Sounds like this is more of a motor controller you are talking about that works from DC input.
Apparently what some might need in inverters is a design level that can handle the high currents for a brief period of time.
If I could find real schematics of real modern inverters, then maybe I could better understand how they work. I can envision quite a variety of ways to design them, some efficient and some not. An inverter could be made basically like an audio amplifier, but that would be quite inefficient. My thoughts right now are along the lines of pulse switching in the VHF/UHF range driving an LC tank circuit resonant at the power frequency (60 Hz in my case) or simply through a low-pass filter circuit.
Of course if you are doing a variable speed motor, your inverter is going to be varying the operating frequency. Do you even need sine wave for a motor like a 12 pulse type?
Maybe semiconductors would make great (but expensive) fuses :-)
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Should have been motor size 160 kW, 690 VAC


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