A grid-tied inverter with storage is connected to a low voltage switchboard with stabilized mains supply and diesel generator power sources as shown below.

Which is the most appropriate location for installing CTs for an external Chint DTSU666 smart meter for zero export management?

(A) Between the change-over contactor and busbars

(B) Before the automatic servo voltage stabilizer

(C) Between the voltage stabilizer and utility meter

I'm inclined towards position (A) with the only drawback being that the DG set could run on < 30% load during grid loss events.

The most appropriate location for installing CTs for the Chint DTSU666 smart meter for zero-export management is (B) Before the automatic servo voltage stabilizer. This placement ensures the CTs measure only grid power, enabling accurate zero-export control without interference from the stabilizer or diesel generator. It avoids the drawback of option (A), where DG power could disrupt inverter operation, and is likely more practical than (C) due to typical wiring layouts.

Option (A) is less suitable because it measures both grid and DG power, which can mislead the inverter’s zero-export logic during grid outages. Your concern about the DG running at <30% load highlights this issue, as the inverter may attempt to supply power to the DG, reducing efficiency or causing instability.

Options (B) and (C) both focus on grid power, making them better for zero-export management. The choice between them depends on practical considerations (e.g., wiring access, space). Since the servo stabilizer primarily affects voltage, not current, placing CTs before the stabilizer (B) is typically more practical and standard, as it aligns with common inverter setups where CTs are installed close to the grid input.

4 hours ago, Powerforum Store said:

The most appropriate location for installing CTs for the Chint DTSU666 smart meter for zero-export management is (B) Before the automatic servo voltage stabilizer. This placement ensures the CTs measure only grid power, enabling accurate zero-export control without interference from the stabilizer or diesel generator. It avoids the drawback of option (A), where DG power could disrupt inverter operation, and is likely more practical than (C) due to typical wiring layouts.

Option (A) is less suitable because it measures both grid and DG power, which can mislead the inverter’s zero-export logic during grid outages. Your concern about the DG running at <30% load highlights this issue, as the inverter may attempt to supply power to the DG, reducing efficiency or causing instability.

Options (B) and (C) both focus on grid power, making them better for zero-export management. The choice between them depends on practical considerations (e.g., wiring access, space). Since the servo stabilizer primarily affects voltage, not current, placing CTs before the stabilizer (B) is typically more practical and standard, as it aligns with common inverter setups where CTs are installed close to the grid input.

During a power outage, the standby DG set will automatically start and supply power to the busbars after a couple seconds i.e. mains contactor open and generator contactor closed.

The external Chint DTSU666 smart meter will be powered through the busbars but CTs at position (B) will NOT read any current since the mains contactor open.

Is it right to assume that the inverter will not push power back to the grid loads and generator alternator since the CTs at (B) will read zero current draw?

Yes, your assumption is correct. With the CTs placed at position (B) before the automatic servo voltage stabilizer, they measure only the current flowing from the grid. During a power outage, when the mains contactor is open and the generator contactor is closed, the CTs at position (B) will read zero current because no grid power is being drawn.

As a result, the inverter, guided by the Chint DTSU666 smart meter’s zero-export logic, will not push power back to the grid or the generator alternator. The inverter will detect no grid demand (since CTs show zero current) and either reduce its output to match local load requirements or stop exporting entirely, depending on its configuration. This prevents the inverter from supplying power to the generator, avoiding potential inefficiencies or instability.