Retrofitting SCT-PPT excitation systems with digital control

Increases in power demand continue to burden power suppliers. Efficiency, reliability, improved control and uptime are key words to describe power production needs in today's power starved industry. Many operating power plants utilize excitation systems dating back to the 1960s and 1970s, using the original OEM-provided equipment. Such excitation systems are either obsolete or difficult to maintain in operating power plants today. These excitation systems are common on utility, industrial, and municipal steam and gas turbine generators. Each of these obsolete excitation systems represented a unique control design that today can be upgraded to a modern digital control excitation system. New "digitally" controlled systems will streamline the unit startup, improve the generator response, provide better monitoring and protection to the generating system, and make the Operator's job easier. This paper reviews a specific excitation system retrofit of the SCT-PPT (saturable current transformer/power potential transformer) static excitation system and the various factors involving a rehabilitation project that includes new equipment, design interface, installation, and commissioning. A successful retrofit project begins with proper planning to ensure that the new installation meets the schedule and on-time commitment for power production.