Phase imbalance means the three AC phase voltages or currents at the grid connection are not equal. Power quality meters report it as negative-sequence and zero-sequence imbalance in percent for both voltage and current, and can log it as a one-minute average. Monitoring platforms can raise a default alert when the meter phase voltages are not within 5% of each other. Inverters may trip on a grid voltage imbalance fault and normally reconnect once the grid returns to normal. If the fault keeps coming back, measure the actual grid phase voltages first. A large difference points to the utility side, so contact the power company. If the measured difference is within what the local utility allows, the inverter imbalance threshold can be adjusted. Contact the manufacturer if the fault persists after that. On the transformer side, check for low or variable load, check the primary voltage, and make sure the ground connections and tank grounding are correct.
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observed_asc1 drafted · lead Negative-sequence voltage imbalance
Revenue/PQ meter quantity V_IMB in percent, updated every 10/12 cycles; reported as zero when positive-sequence voltage is below 13 V.
tbl=367 h=dc6dc586373asec=h559 h=bf4e428b2cdatbl=75.r7 h=a3fbcec75cb8c2 drafted · lead Negative-sequence current imbalance
Meter quantity I_IMB in percent; reported as zero when positive-sequence current is below 10 mA.
tbl=367 h=dc6dc586373asec=h559 h=bf4e428b2cdatbl=75.r7 h=a3fbcec75cb8c3 verified · fact Zero-sequence imbalance
V0_IMB and I0_IMB; zero-sequence voltage imbalance reads zero on delta-connected (Form 5) meters.
tbl=367 h=dc6dc586373asec=h559 h=bf4e428b2cdaverified by: review-workflowverified on: 2026-10-20
c4 verified · fact Phase voltage spread alert
Default monitoring alert checks that meter phase voltages are within 5% of each other.
tbl=12.r10 h=cec53a327f7bverified by: review-workflowverified on: 2026-10-20
c5 drafted · lead Grid voltage imbalance fault
Inverter fault (e.g. Sungrow fault code 17) raised when grid phase voltages differ beyond a settable imbalance threshold; inverter reconnects when grid returns to normal.
tbl=40.r1 h=3d7464a5ab51tbl=9 h=7abcbbacf5betbl=33 h=7abcbbacf5bereview note: support check: partial - The fault, reconnection on grid recovery, and the adjustable imbalance parameter are stated. The passages don't say the fault is raised when phase voltages exceed that threshold. They also don't say the inverter's fault code 17 is a Sungrow-specific example beyond what is shown.
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