jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
I believe it's become less common to use single phase inverters as three-phase have become more available, but yes, you can do it.
Breakers warming quickly
- Thread starter matt123
- Start date
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I believe it's become less common to use single phase inverters as three-phase have become more available, but yes, you can do it.
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Electrical Engineer - Photovoltaic Systems
Yes, you can. You would connect the single phase inverters (ideally a number of them divisible by three for balancing) phase to phase (A-B, B-C, and C-A) or phase to neutral (A-N, B-N, and C-N). As jben says, it's not as common as it used to be when there were a lot fewer 3 phase inverters. My first commercial system was 72 SMA 7000's phase to neutral on a 480V service.
ptonsparky
Tom
- Occupation
- EC - retired
My help just replaced a panel interior where the breakers were getting to the 180 degree range. Bad connection to the buss. They used a small handheld thermal scanner to read the temps.
kwired
Electron manager
- Location
- NE Nebraska
Do they have ability to know if they are supplying 208 vs 240 volts? Either automatic or with manual settings? Same unit that supplies 240 volts line to line being used on 208 three phase would need to adjust I would think.
Something that is single voltage and connects line to neutral would put out 120 volts either way.
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Electrical Engineer - Photovoltaic Systems
In my case it was 277V (phase to neutral on 480V). I do not remember if we had to tell the inverters to run at 277V or if they just did it in response to the voltage they saw; it was nearly 10 years ago.
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
Judging from the products out there, it's not that hard to engineer a product that can handle both 240 and 208, and even 277. It just needs components rated high enough for the highest voltage and highest current it would be used at. The rest is just software. The datasheet will usually specify a different max current output for the different voltages. If there is a neutral then detection is usually automatic, if there is not then manual, there are exceptions to that.
I checked up the other day. Not so hot but some vibration through the breakers. , slight humming. Thoughts?
ptonsparky
Tom
- Occupation
- EC - retired
Normal.
DL-PE
Member
- Location
- Dallas/Fort Worth
Single-phase Inverters Connected to Three-phase Grid
Single-phase Inverters Connected to Three-phase Grid
This isn't entirely correct. If single-phase inverters are connected to a three-phase grid topology, the system must comply with Articles 705.42 and 705.100. Conditions exist (e.g. 240 volt delta) where one phase could open, creating an "open delta". Single-phase inverters connected in such a configuration won't sense the lose of one phase, and will continue to export power.
To remedy this condition requires the use of external sensing and control hardware to open all three phases should one phase open. For those not familiar with an open delta, the voltage across the "open" phase will still measure essentially the same as for the other two phases. Inverters connected to the "open" phase will not sense the loss of that phase, and will continue to export power. Depending on the wattage of the solar array connected across an open phase, it's entirely possible to overload the transformer, since an open delta is rated for 57.7% of a full delta transformer.
There is also a risk of phase imbalance if part of an array should cease to export power. This could occur if a breaker in that array should trip, and the other two arrays continue in full operation.
Single-phase inverters *can* be used in a three-phase topology if all requirements in Article 705 are met. This requires multiple points of sensing, multiple types of sensing, and three-pole relays or contactors of appropriate ratings to open all three phases with the loss of any one phase in the system. Grid-interactive inverters will cease exporting power with loss of the grid as required in UL 1741, UL 1741SA, and UL 62109. IEEE 1547 contains the details of the required shutdown conditions, and is a subset of the UL Standards just mentioned.
Since inverters are a source, not a load, traditional methods of sensing an open phase may not be effective in such cases. Moreover, solar inverters are a current-limited current-source, making over-current in the event of the loss of a phase an impossibility, as would be the case such as for a large three-phase motor.
Lacking the protections just referenced, a Code violation exists when single-phase inverters are connected to a three-phase grid because inverters on the unaffected phases won't cease to export power in the event of the loss of a phase.
Single-phase Inverters Connected to Three-phase Grid
This isn't entirely correct. If single-phase inverters are connected to a three-phase grid topology, the system must comply with Articles 705.42 and 705.100. Conditions exist (e.g. 240 volt delta) where one phase could open, creating an "open delta". Single-phase inverters connected in such a configuration won't sense the lose of one phase, and will continue to export power.
To remedy this condition requires the use of external sensing and control hardware to open all three phases should one phase open. For those not familiar with an open delta, the voltage across the "open" phase will still measure essentially the same as for the other two phases. Inverters connected to the "open" phase will not sense the loss of that phase, and will continue to export power. Depending on the wattage of the solar array connected across an open phase, it's entirely possible to overload the transformer, since an open delta is rated for 57.7% of a full delta transformer.
There is also a risk of phase imbalance if part of an array should cease to export power. This could occur if a breaker in that array should trip, and the other two arrays continue in full operation.
Single-phase inverters *can* be used in a three-phase topology if all requirements in Article 705 are met. This requires multiple points of sensing, multiple types of sensing, and three-pole relays or contactors of appropriate ratings to open all three phases with the loss of any one phase in the system. Grid-interactive inverters will cease exporting power with loss of the grid as required in UL 1741, UL 1741SA, and UL 62109. IEEE 1547 contains the details of the required shutdown conditions, and is a subset of the UL Standards just mentioned.
Since inverters are a source, not a load, traditional methods of sensing an open phase may not be effective in such cases. Moreover, solar inverters are a current-limited current-source, making over-current in the event of the loss of a phase an impossibility, as would be the case such as for a large three-phase motor.
Lacking the protections just referenced, a Code violation exists when single-phase inverters are connected to a three-phase grid because inverters on the unaffected phases won't cease to export power in the event of the loss of a phase.
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