Generator Digital Relay Alarms

[thermionic1]

I just finished a project upgrading 90's era protection and excitation with modern digital units. We had a very large number of red and green marks on our drawings at the end as the engineering was not exactly complete when handed to us. Part of this were the relay settings and various hardwired and soft (digital) alarms.

In reviewing the relay settings, it seems that accommodations were made for alarm level of Dev 24 (Volts/Hz) and 46 (Neg Sequence / Current Unbalance), but I see no mention of them in the DCS alarm logs. We do have alarms for the trip from these elements. The relay settings are poorly documented and didn't include any target logic.

During online AVR testing, I saw these alarm points at their respective relays, but no indication at DCS when we were testing various points on the capability curve. Both of our Scada and relay groups had their hands full just getting everything functioning properly and I'm wondering if the Alarm points for these elements were missed. We're preparing for another unit retrofit, so making and testing the changes shouldn't be a large effort.

No one on sight seems to have any insight as to whether these alarms should be active in DCS. This peaking plant is dispatched and monitored remotely.

Are these alarms commonly utilized in utility operations for 100MW machines?

 

[edison123]

"In reviewing the relay settings, it seems that accommodations were made for alarm level of Dev 24 (Volts/Hz) and 46 (Neg Sequence / Current Unbalance), but I see no mention of them in the DCS alarm logs."

May be these events never happened and hence were not rerecorded in the logs?

I do know that the overfluxing (V/Hz) and negative sequence protections (46) are must in utility generators to protect the stator winding and the rotor winding respectively.

Muthu

http://www.edison.co.in

 

[wcaseyharman]

In my experience older electromechanical relay systems would alarm on individual elements such as 46 and 24 - some plants would tie these output to a sequence of events recorder. However, because the new digital relays should have a detailed time stamped sequence of events list and high speed data capture, my engineering department does not design in specific element alarming to the DCS or turbine control system anymore. We usually have the relay annunciate the trip on the LCD screen and provide a “relay tripped” indication to the turbine control system, which generally is also a turbine shutdown command. In addition, we don’t provide specific alarms partly due to the requirement that our relay department is called out for any relay operation and will pull the events and send them to engineering for evaluation anyway.