Micro hydro

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Biner
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Micro hydro

Post by Biner »

Hi everyone

I am wondering whether anyone has inspected a grid tied micro hydro system before? Specifically a powerspout. I have visited a site that contains 3 × PLT 200 (200V dc) 1kw Paralled up, located in a shed.. They are connected to a grid tied inverter located 100m away. The cable for the DC is 25mm2 N/S, Negative being the screen. This is an unusual design for my likening, the only reason the electrician designed this this way is that the inverter has wifi limitations that wouldnt reach the shed. If the turbines freewheel for whatever reason (assume grid failure?) Voltage could reach up to 600v. The neutral screen is rated 600/1000v, but would the electrician need to get the specs from the manufacturer to state that it is suitable for 600vdc? I know for Pv systems a cable needs to be marked with pvf-1 (5033) but there is nothing specific for hydro. I assumed that the dc cable would need to be flex however reading of 4777:1 2016 which is a little more in depth that 2005, it states that this requirement is only required for wind or vibrations.

The electrician has also driven an earth electrode at the shed for the earthing of the turbines, however stated in ASNZS3000 section 7?, earthing needs to run to the earth bar of the main switchboard.
Thoughts?Opinions?

The installation is quite agricultural, including using 32amp hrc fuse holders to disconnect the DC. But before i proceed any further I would like to know others opinions on the design.

Thanks for your time
AlecK
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Re: Micro hydro

Post by AlecK »

I believe the intent of ESR 6A is that installation of the part of the system that's actually connected to the grid is what is considered high risk PEW.

For comparison; consider a PV array supplying the inverter: inly the inverter part is treated as 'mains parallel'.
The array gets considered separately; ELV arrays being "not PEW" (though still having to comply with '5033'), while LV arrays are high risk in their own right.
Following the same logic would have your inverter as the "mains parallel" component;
as it really makes no difference to the risks relating to "mains parallel" what sort of d.c. source feeds the inverter.

"3000" takes the same approach in Clause 7.3 , treating the inverter as a form of [LV a.c.] generation.
Which is technically incorrect, as an inverter doesn't generate anything; it converts one waveform of electrical energy to another.
And Clause 4.12 (correctly) calls inverters "electricity converters".

All of which is interpretation, and therefore open to argument.
The definition of "mains parallel generation" is quite wide, and can easily be read as covering both the inverter and the source that supplies it.

Supporting argument to include the d.c. source in this case is two-fold
Firstly because generation means to produce electrical energy from another form of energy.
PV modules convert light energy to electrical energy; batteries produce electrical energy from chemical, and hydro produces it from mechanical (as does wind, or an engine-driven genset)
Secondly because its an LV d.c. source; and if an LV photovoltaic array is classed as high risk when it inherently current & voltage limited; then logic suggests LV d.c. hydro should be as well.
However ESR 6A does not currently make that classification; and officially it's "general" PEW.

So up to you whether you include it in your inspection.

----------------------
To your specific points:
I believe the voltage rating of the cable is fine.
The "PVF-1" required for array LV string cables by "5033" is not relevant for non-array purposes.
Same for being flexible, simply not required in this case.
It's OK to use the additional guidance of a later edition of 4777.1; as long as that doesn't create a conflict with the cited edition (2005)

Yes, 7.3.6 if "3000" requires exposed conductive parts of the "electricity generation system" to be connected to installation MEC.
But firstly (as mentioned above") 7.3 treats the inverter as the generating system [refer 7.3.1(c)] so that's what this requirement relates to.
Secondly note the Exception that allows systems up to 25 kVA to be arranged as isolated supplies.

I would be guided by the inverter manufacturer's instructions as to whether & how the d.c. input should be earthed .
But I don't believe simply connecting to a local earth electrode will be either effective or compliant.

HRC fuses will provide the necessary overload protection; but need to check whether they can provide short circuit protection (can the hydro units provide enough current ?)
They'll also be OK as a means of isolation[2.3.2.1.2]
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