Thytronic SPR10

Name: Thytronic SPR10
Brand: Thytronic
SKU: f1e1437a-f3b3-4258-b366-f2a73e1ca55b

Self-powered overcurrent relay for feeders and transformers, fed by its own current transformers.

The Thytronic SPR10 is a self-powered protection relay that guards medium voltage feeders and power transformers against phase and earth faults, taking its energy from the current transformers. This Modbus RTU template reads the phase, residual and negative sequence currents, breaker position, start states and trip counters, and lets you change protection settings and send breaker, store and reset commands from ModbusCloud.

Protocol: Modbus RTU
Connection: RS485, 9600 baud
Registers: 433, read and write

Brand: Thytronic
Key readings: Phase currents · Residual current · Negative sequence current · Breaker position · Protection start states · Trip counters
Available commands: Overcurrent thresholds · Operate and reset times · Setting profile A or B · Breaker open and close · Store and reset commands
Compatible models: SPR10
Last updated: 12 October 2026

Registers (433)

428 read, 354 write

Name	Unit	Access
Phase Current L1 (x In)		Read
Phase Current L2 (x In)		Read
Phase Current L3 (x In)		Read
Residual Current (x IEn)		Read
Calculated Residual Current		Read
Maximum Phase Current (x In)		Read
Minimum Phase Current (x In)		Read
Average Phase Current (x In)		Read
Negative Sequence Current (x In)		Read
2nd Harmonic Current L1 (x In)		Read
2nd Harmonic Current L2 (x In)		Read
2nd Harmonic Current L3 (x In)		Read
2nd Harmonic Ratio	%	Read
Frequency	Hz	Read
24 V Supply Voltage	V	Read
Trip Output Voltage	V	Read
Power Control Current (x In)		Read
Breaker Position		Read
Breaker Position Source		Read
Start I>		Read
Start I>>		Read
Start I>>>		Read
Start IE>		Read
Start IE>>		Read
Start IE>>>		Read
Start IEC>		Read
Start IEC>>		Read
Start IEC>>>		Read
Start I2>		Read
Start I2ndh>		Read
Input IN1		Read
Input IN2		Read
Input IN3		Read
Output Relay K1		Read
Output Relay K2		Read
Output Relay K3		Read
Output Relay K4		Read
Protection Health		Read
Self-Test Level		Read
Power Supply Mode		Read
Active Setting Profile		Read
Active Session		Read
Settings Command		Write
Reset and Recorder Command		Write
Log Reset Command		Write
Breaker Command		Write
Rated Frequency Setting	Hz	Read and write
Phase CT Primary Current	A	Read and write
Residual CT Primary Current	A	Read and write
Measurement Reading Mode		Read and write
Counters Enable		Read and write
External Flag Pulse Width	ms	Read and write
Trip Command Pulse Width	ms	Read and write
Input IN1 Logic		Read and write
Input IN1 Function		Read and write
Input IN2 Logic		Read and write
Input IN2 Function		Read and write
Input IN3 Logic		Read and write
Input IN3 Function		Read and write
Relay K1 Mode		Read and write
Relay K1 Logic		Read and write
Relay K1 Minimum Pulse	ms	Read and write
Relay K2 Mode		Read and write
Relay K2 Logic		Read and write
Relay K2 Minimum Pulse	ms	Read and write
Relay K3 Mode		Read and write
Relay K3 Logic		Read and write
Relay K3 Minimum Pulse	ms	Read and write
Relay K4 Mode		Read and write
Relay K4 Logic		Read and write
Relay K4 Minimum Pulse	ms	Read and write
LED Start Latching		Read and write
LED Trip Latching		Read and write
LED 1 Latching		Read and write
LED 2 Latching		Read and write
LED 3 Latching		Read and write
LED 4 Latching		Read and write
LED 5 Latching		Read and write
Self-Test Relay Level		Read and write
Self-Test Relay Output		Read and write
Setting Profile Select		Read and write
Profile A I> Enable		Read and write
Profile A I> Curve		Read and write
Profile A I> Definite Pickup (x In)		Read and write
Profile A I> Definite Operate Time	s	Read and write
Profile A I> Reset Time	s	Read and write
Profile A I> Inverse Pickup (x In)		Read and write
Profile A I> Inverse Time Factor	s	Read and write
Profile A I> 2nd Harmonic Block		Read and write
Profile A I> Start Relay		Read and write
Profile A I> Trip Relay		Read and write
Profile A I> Start LED		Read and write
Profile A I> Trip LED		Read and write
Profile A I> Front Flag		Read and write
Profile A I> External Flag Output		Read and write
Profile A I> Breaker Trip Output		Read and write
Profile A I>> Enable		Read and write
Profile A I>> Curve		Read and write
Profile A I>> Definite Pickup (x In)		Read and write
Profile A I>> Definite Operate Time	s	Read and write
Profile A I>> Reset Time	s	Read and write
Profile A I>> Inverse Pickup (x In)		Read and write
Profile A I>> Inverse Time Factor	s	Read and write
Profile A I>> 2nd Harmonic Block		Read and write
Profile A I>> Start Relay		Read and write
Profile A I>> Trip Relay		Read and write
Profile A I>> Start LED		Read and write
Profile A I>> Trip LED		Read and write
Profile A I>> Front Flag		Read and write
Profile A I>> External Flag Output		Read and write
Profile A I>> Breaker Trip Output		Read and write
Profile A I>>> Enable		Read and write
Profile A I>>> Definite Pickup (x In)		Read and write
Profile A I>>> Definite Operate Time	s	Read and write
Profile A I>>> Reset Time	s	Read and write
Profile A I>>> 2nd Harmonic Block		Read and write
Profile A I>>> Start Relay		Read and write
Profile A I>>> Trip Relay		Read and write
Profile A I>>> Start LED		Read and write
Profile A I>>> Trip LED		Read and write
Profile A I>>> Front Flag		Read and write
Profile A I>>> External Flag Output		Read and write
Profile A I>>> Breaker Trip Output		Read and write
Profile A IE> Enable		Read and write
Profile A IE> Curve		Read and write
Profile A IE> Definite Pickup (x IEn)		Read and write
Profile A IE> Definite Operate Time	s	Read and write
Profile A IE> Reset Time	s	Read and write
Profile A IE> Inverse Pickup (x IEn)		Read and write
Profile A IE> Inverse Time Factor	s	Read and write
Profile A IE> 2nd Harmonic Block		Read and write
Profile A IE> Start Relay		Read and write
Profile A IE> Trip Relay		Read and write
Profile A IE> Start LED		Read and write
Profile A IE> Trip LED		Read and write
Profile A IE> Front Flag		Read and write
Profile A IE> External Flag Output		Read and write
Profile A IE> Breaker Trip Output		Read and write
Profile A IE>> Enable		Read and write
Profile A IE>> Curve		Read and write
Profile A IE>> Definite Pickup (x IEn)		Read and write
Profile A IE>> Definite Operate Time	s	Read and write
Profile A IE>> Reset Time	s	Read and write
Profile A IE>> Inverse Pickup (x IEn)		Read and write
Profile A IE>> Inverse Time Factor	s	Read and write
Profile A IE>> 2nd Harmonic Block		Read and write
Profile A IE>> Start Relay		Read and write
Profile A IE>> Trip Relay		Read and write
Profile A IE>> Start LED		Read and write
Profile A IE>> Trip LED		Read and write
Profile A IE>> Front Flag		Read and write
Profile A IE>> External Flag Output		Read and write
Profile A IE>> Breaker Trip Output		Read and write
Profile A IE>>> Enable		Read and write
Profile A IE>>> Definite Pickup (x IEn)		Read and write
Profile A IE>>> Definite Operate Time	s	Read and write
Profile A IE>>> Reset Time	s	Read and write
Profile A IE>>> 2nd Harmonic Block		Read and write
Profile A IE>>> Start Relay		Read and write
Profile A IE>>> Trip Relay		Read and write
Profile A IE>>> Start LED		Read and write
Profile A IE>>> Trip LED		Read and write
Profile A IE>>> Front Flag		Read and write
Profile A IE>>> External Flag Output		Read and write
Profile A IE>>> Breaker Trip Output		Read and write
Profile A IEC> Enable		Read and write
Profile A IEC> Curve		Read and write
Profile A IEC> Definite Pickup (x In)		Read and write
Profile A IEC> Definite Operate Time	s	Read and write
Profile A IEC> Reset Time	s	Read and write
Profile A IEC> Inverse Pickup (x In)		Read and write
Profile A IEC> Inverse Time Factor	s	Read and write
Profile A IEC> 2nd Harmonic Block		Read and write
Profile A IEC> Start Relay		Read and write
Profile A IEC> Trip Relay		Read and write
Profile A IEC> Start LED		Read and write
Profile A IEC> Trip LED		Read and write
Profile A IEC> Front Flag		Read and write
Profile A IEC> External Flag Output		Read and write
Profile A IEC> Breaker Trip Output		Read and write
Profile A IEC>> Enable		Read and write
Profile A IEC>> Curve		Read and write
Profile A IEC>> Definite Pickup (x In)		Read and write
Profile A IEC>> Definite Operate Time	s	Read and write
Profile A IEC>> Reset Time	s	Read and write
Profile A IEC>> Inverse Pickup (x In)		Read and write
Profile A IEC>> Inverse Time Factor	s	Read and write
Profile A IEC>> 2nd Harmonic Block		Read and write
Profile A IEC>> Start Relay		Read and write
Profile A IEC>> Trip Relay		Read and write
Profile A IEC>> Start LED		Read and write
Profile A IEC>> Trip LED		Read and write
Profile A IEC>> Front Flag		Read and write
Profile A IEC>> External Flag Output		Read and write
Profile A IEC>> Breaker Trip Output		Read and write
Profile A IEC>>> Enable		Read and write
Profile A IEC>>> Definite Pickup (x In)		Read and write
Profile A IEC>>> Definite Operate Time	s	Read and write
Profile A IEC>>> Reset Time	s	Read and write
Profile A IEC>>> 2nd Harmonic Block		Read and write
Profile A IEC>>> Start Relay		Read and write
Profile A IEC>>> Trip Relay		Read and write
Profile A IEC>>> Start LED		Read and write
Profile A IEC>>> Trip LED		Read and write
Profile A IEC>>> Front Flag		Read and write
Profile A IEC>>> External Flag Output		Read and write
Profile A IEC>>> Breaker Trip Output		Read and write
Profile A I2> Enable		Read and write
Profile A I2> Definite Pickup (x In)		Read and write
Profile A I2> Definite Operate Time	s	Read and write
Profile A I2> Reset Time	s	Read and write
Profile A I2> 2nd Harmonic Block		Read and write
Profile A I2> Start Relay		Read and write
Profile A I2> Trip Relay		Read and write
Profile A I2> Start LED		Read and write
Profile A I2> Trip LED		Read and write
Profile A I2> Front Flag		Read and write
Profile A I2> External Flag Output		Read and write
Profile A I2> Breaker Trip Output		Read and write
Profile A I2ndh> Enable		Read and write
Profile A I2ndh> Threshold	%	Read and write
Profile A I2ndh> Reset Time	s	Read and write
Profile A I2ndh> Start Relay		Read and write
Profile A I2ndh> Trip Relay		Read and write
Profile A I2ndh> Start LED		Read and write
Profile A I2ndh> Trip LED		Read and write
Profile B I> Enable		Read and write
Profile B I> Curve		Read and write
Profile B I> Definite Pickup (x In)		Read and write
Profile B I> Definite Operate Time	s	Read and write
Profile B I> Reset Time	s	Read and write
Profile B I> Inverse Pickup (x In)		Read and write
Profile B I> Inverse Time Factor	s	Read and write
Profile B I> 2nd Harmonic Block		Read and write
Profile B I> Start Relay		Read and write
Profile B I> Trip Relay		Read and write
Profile B I> Start LED		Read and write
Profile B I> Trip LED		Read and write
Profile B I> Front Flag		Read and write
Profile B I> External Flag Output		Read and write
Profile B I> Breaker Trip Output		Read and write
Profile B I>> Enable		Read and write
Profile B I>> Curve		Read and write
Profile B I>> Definite Pickup (x In)		Read and write
Profile B I>> Definite Operate Time	s	Read and write
Profile B I>> Reset Time	s	Read and write
Profile B I>> Inverse Pickup (x In)		Read and write
Profile B I>> Inverse Time Factor	s	Read and write
Profile B I>> 2nd Harmonic Block		Read and write
Profile B I>> Start Relay		Read and write
Profile B I>> Trip Relay		Read and write
Profile B I>> Start LED		Read and write
Profile B I>> Trip LED		Read and write
Profile B I>> Front Flag		Read and write
Profile B I>> External Flag Output		Read and write
Profile B I>> Breaker Trip Output		Read and write
Profile B I>>> Enable		Read and write
Profile B I>>> Definite Pickup (x In)		Read and write
Profile B I>>> Definite Operate Time	s	Read and write
Profile B I>>> Reset Time	s	Read and write
Profile B I>>> 2nd Harmonic Block		Read and write
Profile B I>>> Start Relay		Read and write
Profile B I>>> Trip Relay		Read and write
Profile B I>>> Start LED		Read and write
Profile B I>>> Trip LED		Read and write
Profile B I>>> Front Flag		Read and write
Profile B I>>> External Flag Output		Read and write
Profile B I>>> Breaker Trip Output		Read and write
Profile B IE> Enable		Read and write
Profile B IE> Curve		Read and write
Profile B IE> Definite Pickup (x IEn)		Read and write
Profile B IE> Definite Operate Time	s	Read and write
Profile B IE> Reset Time	s	Read and write
Profile B IE> Inverse Pickup (x IEn)		Read and write
Profile B IE> Inverse Time Factor	s	Read and write
Profile B IE> 2nd Harmonic Block		Read and write
Profile B IE> Start Relay		Read and write
Profile B IE> Trip Relay		Read and write
Profile B IE> Start LED		Read and write
Profile B IE> Trip LED		Read and write
Profile B IE> Front Flag		Read and write
Profile B IE> External Flag Output		Read and write
Profile B IE> Breaker Trip Output		Read and write
Profile B IE>> Enable		Read and write
Profile B IE>> Curve		Read and write
Profile B IE>> Definite Pickup (x IEn)		Read and write
Profile B IE>> Definite Operate Time	s	Read and write
Profile B IE>> Reset Time	s	Read and write
Profile B IE>> Inverse Pickup (x IEn)		Read and write
Profile B IE>> Inverse Time Factor	s	Read and write
Profile B IE>> 2nd Harmonic Block		Read and write
Profile B IE>> Start Relay		Read and write
Profile B IE>> Trip Relay		Read and write
Profile B IE>> Start LED		Read and write
Profile B IE>> Trip LED		Read and write
Profile B IE>> Front Flag		Read and write
Profile B IE>> External Flag Output		Read and write
Profile B IE>> Breaker Trip Output		Read and write
Profile B IE>>> Enable		Read and write
Profile B IE>>> Definite Pickup (x IEn)		Read and write
Profile B IE>>> Definite Operate Time	s	Read and write
Profile B IE>>> Reset Time	s	Read and write
Profile B IE>>> 2nd Harmonic Block		Read and write
Profile B IE>>> Start Relay		Read and write
Profile B IE>>> Trip Relay		Read and write
Profile B IE>>> Start LED		Read and write
Profile B IE>>> Trip LED		Read and write
Profile B IE>>> Front Flag		Read and write
Profile B IE>>> External Flag Output		Read and write
Profile B IE>>> Breaker Trip Output		Read and write
Profile B IEC> Enable		Read and write
Profile B IEC> Curve		Read and write
Profile B IEC> Definite Pickup (x In)		Read and write
Profile B IEC> Definite Operate Time	s	Read and write
Profile B IEC> Reset Time	s	Read and write
Profile B IEC> Inverse Pickup (x In)		Read and write
Profile B IEC> Inverse Time Factor	s	Read and write
Profile B IEC> 2nd Harmonic Block		Read and write
Profile B IEC> Start Relay		Read and write
Profile B IEC> Trip Relay		Read and write
Profile B IEC> Start LED		Read and write
Profile B IEC> Trip LED		Read and write
Profile B IEC> Front Flag		Read and write
Profile B IEC> External Flag Output		Read and write
Profile B IEC> Breaker Trip Output		Read and write
Profile B IEC>> Enable		Read and write
Profile B IEC>> Curve		Read and write
Profile B IEC>> Definite Pickup (x In)		Read and write
Profile B IEC>> Definite Operate Time	s	Read and write
Profile B IEC>> Reset Time	s	Read and write
Profile B IEC>> Inverse Pickup (x In)		Read and write
Profile B IEC>> Inverse Time Factor	s	Read and write
Profile B IEC>> 2nd Harmonic Block		Read and write
Profile B IEC>> Start Relay		Read and write
Profile B IEC>> Trip Relay		Read and write
Profile B IEC>> Start LED		Read and write
Profile B IEC>> Trip LED		Read and write
Profile B IEC>> Front Flag		Read and write
Profile B IEC>> External Flag Output		Read and write
Profile B IEC>> Breaker Trip Output		Read and write
Profile B IEC>>> Enable		Read and write
Profile B IEC>>> Definite Pickup (x In)		Read and write
Profile B IEC>>> Definite Operate Time	s	Read and write
Profile B IEC>>> Reset Time	s	Read and write
Profile B IEC>>> 2nd Harmonic Block		Read and write
Profile B IEC>>> Start Relay		Read and write
Profile B IEC>>> Trip Relay		Read and write
Profile B IEC>>> Start LED		Read and write
Profile B IEC>>> Trip LED		Read and write
Profile B IEC>>> Front Flag		Read and write
Profile B IEC>>> External Flag Output		Read and write
Profile B IEC>>> Breaker Trip Output		Read and write
Profile B I2> Enable		Read and write
Profile B I2> Definite Pickup (x In)		Read and write
Profile B I2> Definite Operate Time	s	Read and write
Profile B I2> Reset Time	s	Read and write
Profile B I2> 2nd Harmonic Block		Read and write
Profile B I2> Start Relay		Read and write
Profile B I2> Trip Relay		Read and write
Profile B I2> Start LED		Read and write
Profile B I2> Trip LED		Read and write
Profile B I2> Front Flag		Read and write
Profile B I2> External Flag Output		Read and write
Profile B I2> Breaker Trip Output		Read and write
Profile B I2ndh> Enable		Read and write
Profile B I2ndh> Threshold	%	Read and write
Profile B I2ndh> Reset Time	s	Read and write
Profile B I2ndh> Start Relay		Read and write
Profile B I2ndh> Trip Relay		Read and write
Profile B I2ndh> Start LED		Read and write
Profile B I2ndh> Trip LED		Read and write
External Trip Relay		Read and write
External Trip LED		Read and write
External Trip Front Flag		Read and write
External Trip External Flag Output		Read and write
External Trip Breaker Output		Read and write
Breaker Command Sources		Read and write
Breaker Open Relay		Read and write
Breaker Close Relay		Read and write
Oscillography Enable		Read and write
Oscillography Max Record Time	s	Read and write
Oscillography Pre-Trigger Time	s	Read and write
Oscillography Post-Trigger Time	s	Read and write
Oscillography Channel IL1		Read and write
Oscillography Channel IL2		Read and write
Oscillography Channel IL3		Read and write
Oscillography Channel IE		Read and write
Oscillography Digital Channels		Read and write
Modbus Address		Read and write
RS485 Baud Rate		Read and write
RS485 Parity		Read and write
RS485 Stop Bits		Read and write
RS485 TX Enable Delay	ms	Read
Set Clock Year		Read
Fault Record Select		Read and write
Event Record Select		Read and write
Trip Count I> (Partial)		Read
Trip Count I>> (Partial)		Read
Trip Count I>>> (Partial)		Read
Trip Count IE> (Partial)		Read
Trip Count IE>> (Partial)		Read
Trip Count IE>>> (Partial)		Read
Trip Count IEC> (Partial)		Read
Trip Count IEC>> (Partial)		Read
Trip Count IEC>>> (Partial)		Read
Trip Count I2> (Partial)		Read
Trip Count I2ndh> (Partial)		Read
Clock Year		Read
Faults Stored		Read
Selected Fault Number		Read
Events Stored		Read
Selected Event Number		Read
Oscillography Max Records		Read
Oscillography Record ID		Read
Calibration Command		Write
Dip Switch Flags		Read and write
Factory Serial Number		Read
Power Basic Threshold (x In)		Read
Trip Output Minimum Voltage	V	Read
Device Identification		Read
Product Code		Read
Display Language		Read
Rated Frequency	Hz	Read
Calibration Reading IL1 (x In)		Read
Debug Data Block 1		Read
Debug Data Block 2		Read
Debug Data Block 3		Read
Debug Data Block 4		Read
Debug Data Block 5		Read
Debug Data Block 6		Read
Debug Data Block 7		Read
Debug Data Block 8		Read
Debug Data Block 9		Read

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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

Show the phase and residual currents of each feeder on a dashboard and keep a year of history per value.
Send an e-mail or webhook alert when the breaker position changes or a start state switches on.
Follow the trip counters per element to see how often a feeder or transformer sees faults.
Watch the supply mode and the protection health to see when the relay runs short of current.
Check thresholds and operate times in both setting profiles remotely and adjust them during commissioning.

Installation

Wire the rear RS485 terminals A+ and B- of the SPR10 to the RS485 port of the ModbusCloud Gateway, and terminate the bus at both ends with 120 Ω.
On the relay, open the Communication menu and note the address, baud rate and parity (default 1, 9600 baud, no parity, 1 stop bit).
In ModbusCloud, add a Modbus device on the RS485 port of the Gateway with the same address, 9600 baud, 8 data bits, no parity and 1 stop bit.
Import the Thytronic SPR10 template and check that the phase currents and the breaker position come in while the feeder carries load.
Compare the currents with the relay display; with the default Reading Relative they are multiples of the rated current In.

Things to watch for

The Gateway gets no answer from the SPR10. What should I check?

The SPR10 is powered by its current transformers, so it answers only when the feeder carries enough current, or when the Dual Power version has its auxiliary supply. Then check that address, baud rate and parity match the device in ModbusCloud, that A+ and B- are not swapped and that the bus is terminated with 120 Ω.

The currents show small numbers like 0.850. Why?

With the default Reading Relative the relay reports currents as multiples of the rated current, so 0.850 means 85 % of In. Multiply by the phase CT primary current to get primary amps, and compare with the relay display in the same reading mode.

I wrote a new threshold, but it is gone after a restart. Why?

The SPR10 keeps changed settings in temporary memory until it receives the store command. After writing, write Store to the Settings Command register, or Clear to discard the changes. Each threshold belongs to profile A or B, so check which profile is active, and read a setting before you write it.

Some values stay empty while the currents come in. Is that normal?

The clock, the identification, the start states, the counters and the fault and event records are part of larger messages that the relay may only send as a whole. When one of those stays empty, the currents, inputs, output relays and breaker position are still read as normal.

Can a command from ModbusCloud open the circuit breaker?

Yes. The Breaker Command register opens or closes the breaker once Modbus is allowed as a command source on the relay and a relay output is assigned. Only use it when switching the feeder is safe. Leave the Calibration Command alone, it is meant for factory calibration with a test current.

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