GTI non linear load

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We have an installation where due to the wiring method, it is important that the neutral of the 3 phase inverter output circuit(s) is a non current carrying conductor per 310.15(B)(5). This hasnt been inspected yet, but I am a little paranoid. Any advice on what I can tell the inspector if he says something like "its electronic so its non linear" or "prove to me that it is a linear load". The manufacturer states: "Harmonics <3%" Does that do it?
 

Besoeker

Senior Member
Location
UK
We have an installation where due to the wiring method, it is important that the neutral of the 3 phase inverter output circuit(s) is a non current carrying conductor per 310.15(B)(5). This hasnt been inspected yet, but I am a little paranoid. Any advice on what I can tell the inspector if he says something like "its electronic so its non linear" or "prove to me that it is a linear load". The manufacturer states: "Harmonics <3%" Does that do it?
GTI in this context?
 

Besoeker

Senior Member
Location
UK
it's likely coupled to the grid with a xfmr which will lower it further
Possibly there is for isolation and voltage matching but wouldn't such a transformer be considered part of the GTI system and thus already included in the calculations?

Some we did (not PV) had to feed the grid at 3.3kV. This was achieved by taking the inverter output through a step up transformer. Calcs for losses and harmonics took that tranny into account.

Maybe it's different for PV.
 
it's likely coupled to the grid with a xfmr which will lower it further

Possibly there is for isolation and voltage matching but wouldn't such a transformer be considered part of the GTI system and thus already included in the calculations?

Some we did (not PV) had to feed the grid at 3.3kV. This was achieved by taking the inverter output through a step up transformer. Calcs for losses and harmonics took that tranny into account.

Maybe it's different for PV.

Practically all String inverters are transformerless now. I Cant really speak about central inverters since I dont come across those much (unfortunately). Typically what Isee for systems up to several MW is 480 string inverters. Facility takes service at 480. Utility provides transformer from their system, usually 7.2/12.47 or 7.62/13.2. I am not sure how it is typically done in those really large systems.

Edit to add: Sometimes the customer will transform the inverter output. Most commonly this happens if they have a 120/208 service since there is much less choice in 208V inverters.
 
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Besoeker

Senior Member
Location
UK
Practically all String inverters are transformerless now. I Cant really speak about central inverters since I dont come across those much (unfortunately). Typically what Isee for systems up to several MW is 480 string inverters. Facility takes service at 480. Utility provides transformer from their system, usually 7.2/12.47 or 7.62/13.2. I am not sure how it is typically done in those really large systems.

Edit to add: Sometimes the customer will transform the inverter output. Most commonly this happens if they have a 120/208 service since there is much less choice in 208V inverters.

Not my field so thank you kindly for the education and edification.
 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
Electronics normally cause harmonics on the input side.

On the output side, the load will mostly determine if there are any harmonics present.
 

Besoeker

Senior Member
Location
UK
Electronics normally cause harmonics on the input side.

On the output side, the load will mostly determine if there are any harmonics present.
The input is DC and the output is the grid in this case.
If the grid is fairly stiff, as it usually is, one might assume that the concern is over current harmonics being injected into the grid.
 

Sahib

Senior Member
Location
India
If the grid is fairly stiff, as it usually is, one might assume that the concern is over current harmonics being injected into the grid.
If OP does not have equipment like harmonics analyser at hand to prove that, one easy to prove it, IMO, is to measure with a simple voltmeter to see whether 1.732 times phase voltage= line voltage, which would not be the case if voltage harmonics is present.
 

Besoeker

Senior Member
Location
UK
If OP does not have equipment like harmonics analyser at hand to prove that, one easy to prove it, IMO, is to measure with a simple voltmeter to see whether 1.732 times phase voltage= line voltage, which would not be the case if voltage harmonics is present.
As I posted, I think the concern would be current harmonics.
 
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