O&M – Balance of Plant: Arlington Valley Energy Facility

Time sync of plant clocks ensures data collection accuracy

Arlington Valley Energy Facility
Owned by LS Power Group, Operated by NAES Corp
570-MW, gas-fired, 2 × 1 combined cycle located in Arlington, Ariz
Plant manager: Greg Nugent
Key project participants: Robert Gilmore, I&E tech Les Matsumoto; I&E techRon Sager; production manager Alan Tolman, maintenance manager; Arlington Valley O&M staff


Time settings of plant computers oftentimes are not synchronized. This can cause many issues, such as difficulty troubleshooting sequences of events from divergent data sources. At our plant the problem was manifested in two events that caused us to seek a better approach.

The first was a power grid event causing a protective relay to activate. When collecting historical data from the protective relay and the DCS, it was noticed that the time stamps between the two systems were different. The second was an event with the steam plant causing a steam-turbine trip. When collecting historical data from the Mark VI turbine controls, the generator protection relays, and the DCS, personnel noticed the time stamps among the three systems also were different.


We approached the problem with a multi-pronged approach. The first solution employed was to install Schweitzer GPS IRIG-B synchronized real-time clocks at all of the generator and main transformer protection relays. This involved three different devices sharing their outputs to the relays at each location.

The second solution was to install another set of GPS time clocks at the main power feeder relays and the main transmission line relays. We also installed a GPS time clock with multiple outputs to send real-time signals to the turbine controls, BOP DCS, CEMs, water plant controls, and inlet chiller controls.


All of the computers used in the operation of the plant and all of the critical relays used for main power feeders, transmission lines, and generator protection are all synchronized using GPS real-time clocks.

After the installation was complete, an event occurred at another powerplant both causing us to lose power and the protective relays to operate. After collecting historical data from the different relays and computers that recorded the event, it was noticed that all of the devices had the same time down to one hundredth of a second.

When troubleshooting a steam-plant event after the project was complete, there was an assurance that the data events were chronologically correct. The result of the improved time- stamp integrity was simplified troubleshooting and assured quality inferences from the recorded data.