How much signals or data can we transfer from Protection relays to RTU or vice versa on Modbus protocol? Also how reliable is Modbus as compared to IEC protocols?
If you ensure that you use good quality cables, keep away from RFI, don't try to communicate over large distance and choose a suitable baud rate, Modbus to protection relays can be quite reliable.
In my experience the suppliers of motor protection relays do not bundle their 'commonly' used registers in nice contiguous blocks so you end up with a few extra reads & writes to get all of the data you want. In the past I've been able to get 80-100 registers passed over a Modbus link with around 2-3 seconds delay quite reliably. Please note that this may vary depending on the DCS/PLC you are communicating with.
Thanks for the reply. The information you send me is quite informative. If I communicate Modbus on Ethernet, then what distance can we go? 20km max? Also what baud rate will be suitable for the same?
