Thytronic SME3
Directional earth fault and short-circuit detector with event log for MV secondary substations.
The Thytronic SME3 is a directional earth fault and short-circuit detector for MV secondary substations that measures the phase voltages, phase currents and residual current of an MV line and logs faults with date and time. This Modbus RTU template reads the voltages, currents, residual voltage, fault angle, self-test and event count, and lets you set fault thresholds and operate times and send store, reset and test commands from ModbusCloud.
- Protocol
- Modbus RTU
- Connection
- RS485, 9600 baud
- Registers
- 59, read and write
- Brand
- Thytronic
- Key readings
- Phase voltages · Phase currents · Residual current · Residual voltage · Fault angle · Self-test status · Stored events
- Available commands
- Earth fault thresholds · Overcurrent thresholds · Operate times · Event selection · Store and test commands · Calibration start
- Compatible models
- SME3
- Last updated
Registers (59)
53 read, 25 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| Phase Voltage V4 (x Vn) | Read | ||||
| Phase Voltage V8 (x Vn) | Read | ||||
| Phase Voltage V12 (x Vn) | Read | ||||
| Phase Current I4 | A | Read | |||
| Phase Current I12 | A | Read | |||
| Residual Current IO | A | Read | |||
| Residual Voltage VO | % | Read | |||
| Residual Angle Theta | ° | Read | |||
| Residual Current IO True RMS | A | Read | |||
| Residual Voltage VO Average | % | Read | |||
| Residual Voltage Component VX | % | Read | |||
| Residual Voltage Component VY | % | Read | |||
| Voltage Angle Alfa RS | ° | Read | |||
| Voltage Angle Alfa RT | ° | Read | |||
| Voltage Dissymmetry | ° | Read | |||
| Residual Current Distortion | % | Read | |||
| Phase Voltage V4 Uncalibrated (x Vn) | Read | ||||
| Phase Voltage V8 Uncalibrated (x Vn) | Read | ||||
| Phase Voltage V12 Uncalibrated (x Vn) | Read | ||||
| Direction Reversal Input (INV) | Read | ||||
| Self-Test Level | Read | ||||
| Calibration Result | Read | ||||
| Oscillography State | Read | ||||
| Events Stored | Read | ||||
| Selected Event Number | Read | ||||
| U0> Threshold | % | Read and write | |||
| IED> Threshold | A | Read and write | |||
| 67 Sector Start Angle | ° | Read and write | |||
| 67 Sector End Angle | ° | Read and write | |||
| 67 Operate Time | ms | Read and write | |||
| I> Threshold Multi-Phase Fault | A | Read and write | |||
| I> Threshold Earth Fault (51N) | A | Read and write | |||
| 51 Operate Time | ms | Read and write | |||
| Voltage Presence Time (27/59) | ms | Read and write | |||
| Fault Masking Time | ms | Read and write | |||
| Intermittent Fault Threshold | % | Read and write | |||
| Intermittent Fault Pickup Delay | ms | Read and write | |||
| Intermittent Fault Dropout Delay | ms | Read and write | |||
| Current Output Rated Current | A | Read and write | |||
| Theta Correction | ° | Read and write | |||
| Event Record Select | Read and write | ||||
| Settings Command | Write | ||||
| Recorded Data Command | Write | ||||
| Reset Command | Write | ||||
| Board Reset Command | Write | ||||
| Test Command | Write | ||||
| Calibration Start Command | Write | ||||
| Oscillography Trigger Count | Read | ||||
| Oscillography Trace A -40 ms | Read | ||||
| Oscillography Trigger | Read | ||||
| Calibration Report EPOT VR | Read | ||||
| Clock Year | Read | ||||
| Device Identification | Read | ||||
| System Release | Read | ||||
| Mean Processing Cycle Time | Read | ||||
| Serial Number Setting | Read and write | ||||
| EPOT Test Value | Read and write | ||||
| Configuration Switches | Read and write | ||||
| Set Clock Year | Read |
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Use cases
- Show the phase voltages, phase currents and residual current of each secondary substation on a dashboard, with a year of history per value.
- Send an alert as soon as the number of stored events changes, so every new trip or loss of voltage is reported.
- Send an e-mail or webhook alert when the residual current or residual voltage rises above a level you choose.
- Get an alert when the self-test level is no longer None, so a faulty detector is replaced before the next fault.
- Check the earth fault and overcurrent thresholds remotely and adjust them during commissioning.
Installation
Connect the front RJ45 port of the SME3 with the Thytronic SOC003 adapter to an RS232 to RS485 converter, and wire the converter to the RS485 port of the ModbusCloud Gateway (A to A, B to B).
The SME3 talks at 9600 baud, 8 data bits, no parity and 1 stop bit. Use one converter per detector and terminate the RS485 side with 120 Ω.
In ModbusCloud, add a Modbus device on the RS485 port of the Gateway with address 1, 9600 baud, 8 data bits, no parity and 1 stop bit.
Import the Thytronic SME3 template and check that the phase voltages and the residual current come in.
Compare the values with ThySetter on a PC, and start a calibration only with the line energised and no fault on the network.
Things to watch for
The Gateway gets no answer from the SME3. What should I check?
The SME3 speaks Modbus on its front RJ45 port at RS232 level, so it needs the SOC003 adapter and an RS232 to RS485 converter. Check the converter wiring to A and B on the Gateway, 9600 baud without parity, and address 1. If address 1 does not answer, look up the address with ThySetter.
Why do the phase voltages show values around 1 instead of kV?
The SME3 reports the phase voltages as a multiple of the rated voltage Vn and the residual voltage as a percentage of Vn. A value of 1.00 means rated voltage. If the three phases differ a lot with the line in service, run the calibration again with no fault on the network.
I wrote a new threshold, but it is gone after a restart. Why?
The SME3 keeps changed settings in temporary memory until it receives the store command. After writing new values, write Store to the Settings Command register, or Clear to discard them. Read a setting first before you write it, so you know the current value.
Some values stay empty while the voltages come in. Is that normal?
The clock, the selected event, the event count, identification, self-test, calibration report and oscillography data are part of larger messages that the detector may only send as a whole. When one of those stays empty, the voltages, currents and angle are still read as normal. Set the clock with ThySetter.
Can a test command signal a fault to the remote control unit?
Yes. The relay tests close the 51, 67 or voltage presence contact to the remote control unit, which handles it as a real signal. Only use them during commissioning or maintenance with the control room informed, and write Test off afterwards.
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