SunSpec Model 709 — DER Trip LF
SunSpec Model 709 (DER Trip LF) is the IEEE 1547-2018 low-frequency trip information model for distributed energy resources such as inverters and battery storage systems. Via Modbus TCP, this template reads and manages the fixed-block header registers covering model identity, length, enable state, curve-adoption request and result, curve geometry metadata, and the Hz and Tms scale factors that govern how frequency-time trip curves are interpreted. Knowing whether the trip function is active and which curve set is armed lets commissioning engineers verify grid-protection compliance without opening the device web interface.
- Protocol
- Modbus TCP
- Connection
- Ethernet, Modbus TCP
- Registers
- 9, read and write
- Brand
- SunSpec
- Compatible models
- SunSpec Model 710 — DER Trip HF
- Last updated
Registers (9)
9 read, 2 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| id | Read | ||||
| l | Read | ||||
| ena | Read and write | ||||
| adptcrvreq | Read and write | ||||
| adptcrvrslt | Read | ||||
| npt | Read | ||||
| ncrvset | Read | ||||
| hz_sf | Read | ||||
| tms_sf | Read |
Loading registers…
Send your device list
If a device is not in the library yet, we build the template for free as soon as we have the register data.
Use cases
- Verify the low-frequency trip function is enabled on all site inverters after initial commissioning.
- Monitor the adopt-curve result register to confirm a new trip curve was accepted without errors.
- Track the active curve-set index to detect unauthorised changes to low-frequency protection settings.
- Alert on unexpected disable of the trip function, which may indicate a misconfiguration or firmware issue.
- Compare Hz and Tms scale factors across devices to identify register-interpretation mismatches between sites.
Installation
Enable Modbus TCP on the DER device under the communication or Modbus section of its web interface, and note the assigned TCP port (commonly 502).
Connect the DER device to the same LAN segment as the ModbusCloud Gateway, or verify IP reachability if the device is on a separate VLAN.
In the ModbusCloud portal, add the Gateway, import the SunSpec Model 709 DER Trip LF template, and set the device unit ID to match the value configured on the inverter (commonly 1 or 126 for SunSpec-compliant devices).
Spot-check the id register at offset 0: it must read 709; if it returns 0xFFFF the model is not present at that base address and you need to run SunSpec model discovery to find the correct offset.
Things to watch for
The id register returns 0xFFFF instead of 709. Why?
SunSpec models are placed dynamically after the Common Model at base address 40001. The offset of Model 709 depends on which models precede it. Run a SunSpec model discovery scan from the portal or use a tool like pysunspec2 to enumerate all model IDs and their base addresses, then update the template base address to match.
Hz and Tms values look wrong or are orders of magnitude off. What now?
All frequency and time point values in Model 709 are raw integers scaled by hz_sf and tms_sf respectively. For example, if hz_sf reads -2 and the Hz register reads 5950, the actual frequency is 59.50 Hz. Confirm the scale factor registers are being applied before interpreting curve point data.
Writing to adptcrvreq has no visible effect. What is wrong?
The adopt-curve operation requires that the target curve index be greater than 1 (index 1 is the read-only active curve). Write the desired curve index to adptcrvreq, then read adptcrvrslt: a COMPLETED result confirms the new curve was promoted; IN_PROGRESS means the device is still processing; FAILED indicates the index was out of range or the curve data was invalid.
Is it safe to write to the ena or adptcrvreq registers on a live grid-connected system?
Proceed with caution. Disabling the low-frequency trip function (ena = 0) removes IEEE 1547-2018 grid-protection behaviour and may violate interconnection agreements or utility requirements. Similarly, adopting an untested curve set can change the trip threshold immediately. Always coordinate with the site engineer and utility before writing to these registers on an energised installation.
Knowledge base articles for this device
SunSpec Modbus: one register map for many inverters
SunSpec Modbus is the open register map SMA, Fronius, SolarEdge and Kostal share. The layout, int+SF vs float, the TCP port per brand and reading a mixed fleet.
Fronius Modbus: read a Symo GEN24 over Modbus TCP
Fronius Modbus explained: enable Modbus TCP on the Symo GEN24 on port 502, choose between int+SF and float, read the right SunSpec registers and scale them correctly. Practical guide for solar installers.
SMA Modbus: reading a Sunny Boy over Modbus TCP (installers)
SMA Modbus explained: enable the Modbus TCP server on port 502, choose between the SMA profile (unit ID 3) and SunSpec (unit ID 126), read the right registers, and handle the NaN values at night. Practical guide for installers.
Want to see how it works?
