BN 3500 Rack is installed for Steam Turbine protection. Different signals become Bad for 10 sec and then become ok. The HP differential expansion signal connected with Module 3500/45, became bad and then became ok. This repeated many times. Now Radial Vibration 5Y connected with Module 3500/42, became bad and then became ok. This repeated many times.
Please help why different signals of different modules become bad and become ok.
How is the 3500 rack connected to the ST? Are you losing the signals from the field device to the rack or from the rack to the ST? Is there a network connection (ethernet) and the signals are Modbus? If so, there may be a network issue. A faulting switch or router or ethernet cable (or any fiber optic and transceiver, if used) could be going bad. If this is a network issue it would be nice if you could interrogate, or watch, the traffic going through the switches to help identify an issue. If you have no way to watch the network traffic then you may get lucky by replacing network elements one at a time to see if it clears, but that is not the ideal way to find the problem.