Technical Guide P92x/EN CT/E11
Modbus Protocol
MiCOM P921-P922-P923 Page 1/118
CONTENTS
1. MODBUS PROTOCOL 5
1.1 MODBUS communication characteristics 5
1.1.1 MODBUS network characteristics 5
1.1.2 Parameters of the MODBUS connection 6
1.1.3 Synchronisation of exchanged messages 6
1.1.4 Message validity check 6
1.1.5 Address of the MiCOM relays 7
1.2 MODBUS functions of the MiCOM relays 7
1.3 Presentation of the MODBUS protocol 7
1.3.1 Frame size received by the MiCOM P92x relay 7
1.3.2 Format of frames sent by the MiCOM P92x relay 8
1.3.3 Messages validity check 8
1.4 Modbus request definition used to retrieve the disturbance records 9
1.4.1 Request to know the number of available disturbance records in the Saved RAM. 9
1.4.2 Service request 10
1.4.3 Request to retrieve the data of a disturbance record channel 10
1.4.4 Request to retrieve an index frame 10
1.5 Modbus request definition used to retrieve the event records 10
1.5.1 Request to retrieve the oldest non-acknowledge event 11
1.5.2 Request to retrieve a dedicated event 11
1.6 Modbus request definition used to retrieve the fault records 11
1.6.1 Request to retrieve the oldest non-acknowledge fault record 12
1.6.2 Request to retrieve a dedicated fault record 12
1.7 MiCOM P921-P922-P923 database organisation 13
1.7.1 Description of the MODBUS application mapping 13
1.7.2 Page 0 : Product information, remote signalling and remote measurements 14
1.7.3 Page 1 : Remote settings 17
1.7.4 Page 2 : Protective functions - Remote settings for group 1.25
1.7.4.1 Undervoltage protection (P921- P922 and P923) 25
1.7.4.2 Overvoltage protection (P921 -P922 and P923) 26
1.7.4.3 Zero sequence overvoltage protection (P921- P922 and P923) 27
1.7.4.4 Negative sequence overvoltage protection (P922- P923) 28
1.7.4.5 Positive sequence undervoltage protection (P922 – P923) 28
1.7.4.6 Under/overfrequency (P922 – P923) 29
1.7.4.7 Rate of change of frequency ( Only MiCOM P923) 29
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