The ITER Pulsed Power Electrical Network (PPEN)

ITER's ac power is derived from the 400 kV, 6.5 . 12 GVA, Double Circuit Grid and transformed to an intermediate voltage level (66 kV) via three step down transformers of 300 MVA (continuous duty), 400/66/22 kV, YNynd11 each. Each transformer feeds one interconnected 66 kV distribution bus. Most of the large and dynamic loads are directly fed from the 66 kV bus. Loads with relatively lower power (normally less than 20 MVA/unit) and more or less steady duty are fed from the 22 kV bus, are powered from the 66 kV bus via three step down transformers of 50 MVA (continuous duty), 66/22 kV each (Scheme I) OR through 22 kV Delta connected tertiary windings on the 400kV transformers (Scheme II). The loads are primarily thyristor rectifier AC/DC converter power supplies that supply DC power to the ITER superconducting magnet coils to produce magnetic field to confine and shape the plasma and heating and current drive power supplies to supply DC power to neutral beam and radio frequency plasma heating systems to heat the core of the plasma. The ITER pulsed power electrical network (PPEN) is capable of supplying 500 MW of pulse power and consumes around 1 Gvar of reactive power. In addition, the conversion plant is always operated in dynamic conditions in terms of the plasma control requirements. Abundant harmonics generated by the pulsed power supply, large installed power compared with the short circuit capacity and complicated interaction with the grid means that stability of the power system becomes a significant issue. This paper focuses on the merits and demerits of the above two possible schemes to be adopted for the ITER PPEN. The Scheme I is defined in the ITER 2001 Baseline design whereas Scheme II is derived from system and value engineering. The analysis results: load flow, short circuit, harmonics, reliability, under/over voltage and cable sizing, are compared for both schemes and consider the initial and extended phase of ITER operation