M. Huart

Paralleling of two large flywheel generators for the optimisation of the ASDEX Upgrade power supply

Abstract The power supply of the ASDEX Upgrade (AUG) tokamak consists of three pulsed distribution systems (110–85 Hz), each supplied by a dedicated flywheel generator: EZ2 (1.45 GJ/167 MVA) which solely feeds the toroidal field coils, EZ3 (500 MJ/144 MVA) and EZ4 (650 MJ/220 MVA). For quasi-stationary advanced tokamak experiments with extended flat-top phase, the power systems of EZ3 and EZ4 must be connected in parallel, so that full advantage of the installed generator power and flywheel energy can be realised. The variable frequency of the pulsed network, fast load changes (up to 1000 MW/s), together with the different parameters of the generators and saturation effects during pulsed operation, require detailed numerical models for an investigation of the stability limits of a parallel operation of the two machines on one common 10.5 kV busbar. The paper describes the dynamic load requirements of a feedback controlled plasma experiment, the controller development for paralleling two large flywheel generators, the results of system studies with optimised power supply and implications of these results on the technical realisation.

145 MVA modular thyristor converter system with neutral control for ASDEX upgrade

The power supply of the ASDEX Upgrade (AUG) tokamak consists of 11 thyristor converter modules which feed the poloidal field coils. All converters installed are powered by 10.5 kV flywheel generators starting at a frequency of 110 Hz, running down to 85 Hz during a pulse. For quasi-stationary advanced tokamak experiments with enlarged flat-top phase, the power supply system must be extended. The variable frequency of the pulsed network, fast load changes, together with the different parameters of the load coils require a very sophisticated converter design with reduced reactive power consumption. The paper describes the design and testing of the modular Thyristor Converter Group 6 with neutral control and four quadrant possibilities. It presents the various configurations available for operation on AUG magnetic coils, analyses the results of measurements obtained during commissioning, compares them to the calculated (design) values and reports on the performance achieved in fast four quadrant operation, improving the possibilities of the AUG feedback control of plasma shape and position.

Excitation of torsional oscillations in generator shaft lines by plasma feedback control

Abstract The ASDEX Upgrade (AUG) tokamak requires an electrical power up to a few hundred MVA for a time period of 10–20 s. The power and energy is provided by three separate networks based on flywheel generators. In 1999, during a routine check performed on generator EZ3, it was discovered that coupling bolts of the flywheel generator shaft were deformed. Given that the active load of the generator (∼100 MW) in service is well below the design value of the shaft (∼800 MW), the damages may only be explained by a torsional resonance of the shaft line, itself excited by active power transients from the converter loads. A value of 23.6 Hz was calculated for the first eigen-frequency of the shaft line. Frequencies between 10 and 30 Hz have been identified in the spectrum of the load curves. Since torsional shaft oscillations are characterised by very low damping, torsional resonance can become dangerous even for over-dimensioned generator shafts. Therefore, a novel ‘torque’ measurement system was installed. The paper presents results from calculations and measurements showing that devices capable to measure the stress in the shaft line are essential for generator protection in feedback controlled fusion experiments.

Operational experience with reactive power control methods optimized for tokamak power supplies

Abstract The power and energy of the ASDEX Upgrade (AUG) tokamak are provided by two separate 10.5 kV, 110–85 Hz networks based on the flywheel generators EZ3–EZ4 in addition to the generator EZ2 dedicated to the toroidal field coil. The 10.5 kV networks supply the thyristor converters allowing fast control of the DC currents in the AUG poloidal field coils. Two methods for improving the load power factor in the present experimental campaign of AUG have been investigated, namely the control of the phase-to-neutral voltage in thyristor converters fitted with neutral thyristors, such as the new 145 MVA modular thyristor converter system (Group 6), and reactive power control achieved by means of static VAr compensators (SVC). The paper shows that reliable compensation up to 90 MVAr was regularly achieved and that electrical transients in SVC modules can be kept at an acceptable level. The paper will discuss the results from the reactive power reduction by SVC and neutral thyristor control and draw a comparative conclusion.

The JET High DC Power Test Facility and the Life Testing of a High Current ITER Switch

JET has available one of the worlds most powerful AC/DC multi-convertor systems, with unique capabilities in terms of delivery of high DC voltages and currents. Whilst the primary purpose of the system is the supply of the loads required for the experimental sessions, there is scope for other uses, in particular for testing of high power electrical equipment. The first successful example of the utilization of these capabilities was achieved with the establishment of a new Test Cell powered by the Toroidal Flywheel Generator Convertor (TFGC). The new facility was used for the test of a prototype Bypass switch manufactured within the ITER programme. The aim was to prove the switch is able to fulfil the requirements concerning contact life and general reliability of the assembly.