Fatigue Fracture of the Copper Bridge in a Medium Voltage Make Switch

B. Fischer; A. Neidel; M. Giller

doi:10.1515/pm-2022-0035

Article

Fatigue Fracture of the Copper Bridge in a Medium Voltage Make Switch

B. Fischer

Boromir Fischer

completed a training as State Certified Technical Assistant for Metallography and Physical Material Analysis at Lette-Verein in Berlin. He has worked in the metallographic laboratory of the Siemens Gas Turbine Plant (Siemens-Gasturbinenwerk) Berlin for more than a decade. The key areas of his work are failure analysis and microstructural examinations using the field emission scanning electron microscope.
, A. Neidel and M. Giller

Madeleine Giller

Apprenticeship as a materials testing technician at the welding institute SLV Berlin-Brandenburg. After that, she studied materials science at the Berlin Institute of Technology. She graduated with a masters degree in materials science in 2012. Since November 2012 employment as engineer at the Metallography Laboratory of the Siemens Gas Turbine Works in Berlin. She has been appointed laboratory manager within the Berlin Testing Center of the Large Gas Turbine Engineering Group in 2014. Her main fields of expertise comprise failure analysis and microstructural investigations using the field emission scanning electron microscope.

Published/Copyright: June 30, 2022

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From the journal Practical Metallography Volume 59 Issue 6

Abstract

The case of damage presented here relates to the switching bridge of a medium voltage switch, a so-called make switch. Such assemblies are used for fast high current switching operations in medium voltage technology. The copper switching bridge failed due to low-cycle fatigue fractures symmetrically initiated where the transition radius between the copper bridge and the shaft was too sharp. The primary cause of the damage was the fact that the design principle of avoiding too sharp transition radii was needlessly violated where there were no apparent structural limitations. It is remarkable that, time and again, the violation of the same simple design rules causes component damages. The respective simple principles of good design practice thus violated are the same in virtually any mechanical engineering sector.

Kurzfassung

Der in diesem Beitrag vorgestellte Schadensfall betrifft die Schaltbrücke eines Mittelspannungsschalters, eines sog. Draufschalters. Diese Baugruppen werden in der Mittelspannungstechnik zum schnellen Schalten hoher Ströme eingesetzt. Die Schaltbrücke aus Kupfer versagte durch niederzyklische Schwingbrüche, die symmetrisch an zu scharfen Übergangsradien zwischen Kupferbrücke und Schaft eingeleitet wurden. Das ohne erkennbare konstruktive Einschränkungen, also “ohne Not” verletzte Konstruktionsprinzip der Vermeidung zu scharfer Übergangsradien war die Primärursache des Schadens. Bemerkenswert ist, dass es immer die gleichen einfachen Konstruktionsregeln sind, deren Verletzung zur Ursache von Bauteilschäden wird. Die dabei verletzten einfachen Prinzipien guter konstruktiver Praxis sind in fast allen Branchen des Maschinenbaus die gleichen.

Keywords: Medium voltage switch; make switch; copper bridge; fatigue fracture; low-cycle fatigue fracture; LCF; Cu-ETP; E-Cu; electrolytic copper

Schlagwörter: Mittelspannungsschalter; Draufschalter; Kupferbrücke; Schwingbruch; niederzyklischer Schwingbruch; LCF; Low Cycle Fatigue; Cu-ETP; E-Cu; Elektrolytkupfer

About the authors

B. Fischer

Boromir Fischer

completed a training as State Certified Technical Assistant for Metallography and Physical Material Analysis at Lette-Verein in Berlin. He has worked in the metallographic laboratory of the Siemens Gas Turbine Plant (Siemens-Gasturbinenwerk) Berlin for more than a decade. The key areas of his work are failure analysis and microstructural examinations using the field emission scanning electron microscope.

M. Giller

Madeleine Giller

Apprenticeship as a materials testing technician at the welding institute SLV Berlin-Brandenburg. After that, she studied materials science at the Berlin Institute of Technology. She graduated with a masters degree in materials science in 2012. Since November 2012 employment as engineer at the Metallography Laboratory of the Siemens Gas Turbine Works in Berlin. She has been appointed laboratory manager within the Berlin Testing Center of the Large Gas Turbine Engineering Group in 2014. Her main fields of expertise comprise failure analysis and microstructural investigations using the field emission scanning electron microscope.