__________ exhibits low relative permeability and is used for field frames where cost is vital and weight is acceptable?
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Answer: D. Cast iron
Explanation
Cast iron possesses relatively low magnetic permeability and moderate mechanical strength compared to specialized electrical steels. Its low cost and ease of casting make it ideal for non-critical motor field frames where extra weight is acceptable. Engineers select cast iron when economic factors outweigh the need for high magnetic permeability in structural frames. Magnetic permeability measures a material ability to support the formation of a magnetic field within its volume. Field frames provide the mechanical housing and return path for magnetic flux in rotating electrical machines. Cast iron contains graphite flakes that interrupt the magnetic path, resulting in lower permeability and higher magnetic reluctance.
Cast steel offers higher magnetic permeability and better mechanical strength, making it more expensive than cast iron. Aluminium is a non-magnetic metal with permeability close to free space, unsuitable for conventional electromagnetic field frames. Soft steel provides superior magnetic properties and is typically reserved for active flux-carrying core parts rather than cheap frames.
- Subject
- Engineering
- Category
- Electrical Engineering
- Topic
- —
- Difficulty
- medium
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