Summary
This project is intended to result in the replacement of the excitation systems (including the PPTs) for two (2) units at Powerhouse. Powerhouse contains two (2) main generating units, each with a nameplate rating of
20.579 MVA, 13.8 kV, at a rated power factor of 0.95. The OEM for these generators is Elliot Company. Both generators were rewound and uprated to the 115% continuous capability rating. Unit 1 was rewound by National Electric Coil (NEC) in 1983, and Unit 2 was rewound by Westinghouse in 1978. Both generators are connected to the electrical grid via three (3) single-single phase generator step-up transformers (GSU), each with a rating of 11.0/13.75 MVA (ONAN/ONAF) and an impedance of 12.04% @ 13.75 MVA, for a total rating of 33.0/41.25 MVA (ONAN/ONAF). The existing excitation systems are EX-1 analog static systems which were manufactured by Siemens and installed in 1995. The excitation system for each unit consists of medium-voltage cable which supplies power from the terminals of the generator to the power potential transformer (PPT), through current limiting fuses (CLFs) and disconnect switches installed in an enclosure adjacent to the PPT. The PPT low voltage winding is connected via cables to the excitation system cubicles, which are also adjacent to the PPT. The exciter contains redundant bridges which create the DC field voltage. Two parallel runs of DC cables run from the exciter to the collector rings inside a square enclosure that sits on top of the generator air housing. The PPT, the fused-disconnect switches, and exciter cabinets are at the same elevation as the Generator (Elevation 518.0 feet), close to each generator and the generator switchgear.