Alarms in DCS/PCS When Disconnect Closes 2

[StruggleEngr]

Hello All,

I am a field engineer helping with StartUp and Commissioning and have encountered a problem with the team that has us stumped. When we closed our 345kV switchyard disconnect onto our 500kV HVCB, we noticed false alarms on various instruments throughout the plant. These alarms include GSU high winding temp to fan motor vibration when neither equipment is in service right now. My first thought was improper shield connection of the instruments/devices.
Maybe related, we noticed that we had a capacitive coupling on our HVCB, but it dissipates when the generator braids are connected, completing the circuit, I guess. Is it possible that when the capacitive coupling dissipates through the generator, it causes severe noise in our instruments/devices, which gives false alarms in our DCS/PCS? I am sure some more information is needed, but I am checking to see if anyone has experienced this before. Thank you in advance for everyone's help.

 

[thermionic1]

We have numerous stations that when the circuit switcher feeding an unloaded transformer is opened dispatch sees everything as if all breakers are open. It takes a SCADA tech to run out to the station and reset the PLC to resolve. I haven't been involved personally in the troubleshooting, but they've suspected shielding, so one end, no ends, both ends grounding have been tried and the problem still exists.

One would think that the switching transient is being introduced into the system somewhere. Have you been able to verify shield continuity?

Can you clarify what the HVCB capacitive coupling is?

 

[itsmoked]

With those kinds of voltages involved these problems could be caused by numerous issues. Ground bounce, capacitive coupling, inductive coupling, power supply disturbances, or RF interception. In your arena I'd be using isolation techniques everywhere possible. That would be isolation blocks anywhere they can be inserted. RS485, CANbus, RS232, Ethernet, digital isolators, whatever signal system used. In some cases fiber optics can replace copper. The problem can be that one system's voltage rises rapidly and higher than another part of the interconnected systems. Shielding often can't help that or may fry due to imposed currents in the shield wires. Breaking the copper solves the issue.

If you have a specific piece of machinery that seems to be throwing error/faults start with installing an isolator between that machinery's sensors and the DCS/PCS inputs.

Web searches will provide a lot of isolator selections.

Keith Cress
kcress -

http://www.flaminsystems.com