Tucson Area Reliability Mike Flores Control Area Operations Tucson Electric Power May 2000

Continuity of Service to Tucson Customers n Continuity of service is TEP’s responsibility as a T&D company n Reliability Criteria  Primary WSCC Standard: Continuity of service is maintained after loss of any single system element (transmission or generation facility) at peak loads  TEP Practice: System is planned to maintain service to all customers after the loss of any single system element

Tortolita South Vail Greenlee Westwing TEP Service Area 500 kV 345 kV North Loop Irvington Voltage Remote Generation + Firm Purchases + Economy Power Limit of 1,350 MW TEP Import Paths

System Reliability n Four EHV lines supply remote power to Tucson n TEP’s ability to transfer bulk power into Tucson over these lines is voltage stability constrained n Because of the possibility of the loss of EHV ties or local generators, a minimum level of generation must be on-line in Tucson to guard against voltage collapse -- the amount depends on load level n This translates into a maximum safe level of power imports

2000 Loads & Resources

Experience n During 1999 TEP experienced annual system peak load of 1767 MWS on July 1, To-date the 2000 annual system peak is 1516 MWS on May 15, n A remedial action scheme is available in the event of significant transmission contingencies. n TEP’s transmission system has been adequate with respect to energy transfers in the past and no problems are anticipated in n Voltage stability studies are conducted annually by transmission planning. The results are used for planning each spring. In 1998 TEP added 150 Mvars of capacitors to its 138kV system. An additional 50 Mvars were installed this Spring.

System Improvements n Capacitor Bank at Tucson Station (50MVA, 138kV) n New Controls for Combustion Turbines n New Voltage Regulator for Irvington #2 n New 138kV Transmission Line Between Snyder & Northeast n Emergency Operating Procedures Updated & Practiced n Summer Operating Studies Completed n Morning Conference Calls to Security Coordinator n Major Maintenance on Springerville #1 Completed

New Market Issues n New Control Area Interface - Scheduling Coordinators n 888/889 Separation n New Generation - Transmission

Curtailment Process n Terminate Economy Sales n Activate Reserves  Start Gas Turbines  Activate Spinning Reserves  Curtail Interruptible Loads n Request Operating Reserves from SRSG n Activate WSCC Procedure for Securing Emergency Service n Drop Load