Development of a 3-Cycle High-Voltage Air-Blast Breaker with Interrupting Ratings up to 25,000 Mva [includes discussion]

This paper reports on the development of a multiple-break porcelainclad 3-cycle air-blast circuit breaker type DHF with 2,000-ampere continuous current capacity and with interrupting ratings up to 25,000 mva (megavolt-amperes), depending on voltage. The new design is based on long service experience and system tests carried out over the years with the smaller type DCF. Because of the exceedingly good record of the latter, its basic features could be conserved. Whatever changes were made, apart from size of components, were mainly in the form of refinements for improving the streamlining of the airflow, simplification of control, and protection of all moving parts from external influences. Direct verification of the full interrupting capability of breakers of such ratings is manifestly impossible. Therefore, all tests were made on a single interrupter. Because of the near-perfect mechanical and electrical symmetry of this design, the capability of a complete breaker can be deduced with a high degree of accuracy. This fact has been exhaustively investigated with the predecessor of the device reported on where it was still possible to verify the results of component testing by staged tests in very large systems. An outstanding feature of this type of circuit breaker is that, regardless of voltage identical interchangeable components are used throughout (except for the air tanks), not only for interrupters but also for blast valves, control mechanism, and tripping devices. This again is in line with previous practice. The advantages for both manufacturer and users are obvious.