Type tests of the ITER switching network unit components and protective make switches

Highlights: • The results of the type tests of the main power switching unit prototypes for ITER coil power supply system are presented. • Short description of technical specifications of switching units is given. • Test procedures for SNU switching units and PMS are considered in detail. • Positive test results proved proper functionability and reliability of switches and allowed start of series manufacturing. • Switches are designed for commutation of direct current up to 55 kA, with insulation level 12 kV. -- Abstract: In ITER, each circuit of the central solenoid as well as poloidal field coils PF1 and PF6 is provided with a system for plasma initiation, called the Switching Network Unit (SNU), able to supply voltage up to 8.5 kV for the coils. This will be obtained by inserting resistors in series with the pre-energized coils by means of a DC current commutation unit (CCU) composed of connected-in-parallel mechanical bypass switch and a thyristor circuit breaker. After a short description of the design, the paper focuses on the procedures and results of the type tests performed on the full-scale prototypes of CCU switching units, namely, the Bypass Open Switch (BPOS) and Bypass Make Switch (BPMS), which are able to perform commutation of direct current up to 55 kA at a voltage of 10 kV within 2–4 ms. In addition, Protective Make Switch (PMS) is considered, which is similar to BPMS in design. This device is intended to shunt the AC/DC converter supplying power to the coil in case of its failure or in case of a quench, when the energy stored in the magnet system is rerouted into fast discharge resistors (FDR) by a special fast discharge unit (FDU). Various types of electrical, hydraulic, pneumatic tests, performed in 2017–2018 are described as well as EMC tests and functional tests with control system. The successful results of the type tests confirmed the suitability of the design and compliance with the ITER requirements making it possible to start manufacturing of the switches for delivery to the ITER Site.