AEP Material Selection & Properties 2 — Questions and Answers
Question 1: Which property describes a material's ability to return to its original shape after the applied load is removed?
- Plasticity
- Elasticity (Correct answer)
- Ductility
- Malleability
Correct answer: Elasticity
Elasticity is the property that allows a material to recover its original dimensions once the deforming stress is removed.
Question 2: In electrical applications, which material is most commonly used for overhead transmission line conductors due to its combination of conductivity and strength?
- Copper
- Steel
- ACSR (Aluminum Conductor Steel Reinforced) (Correct answer)
- Titanium
Correct answer: ACSR (Aluminum Conductor Steel Reinforced)
ACSR combines the high conductivity of aluminum with the tensile strength of a steel core, making it ideal for long-span overhead transmission lines.
Question 3: What does the term 'dielectric strength' refer to in electrical insulating materials?
- The material's ability to conduct heat
- The maximum electric field a material can withstand without breakdown (Correct answer)
- The material's resistance to mechanical stress
- The temperature at which a material loses its magnetic properties
Correct answer: The maximum electric field a material can withstand without breakdown
Dielectric strength is the maximum electric field intensity (V/m) that an insulating material can sustain without electrical breakdown.
Question 4: Which type of corrosion occurs when two dissimilar metals are in electrical contact in the presence of an electrolyte?
- Crevice corrosion
- Galvanic corrosion (Correct answer)
- Stress corrosion cracking
- Uniform corrosion
Correct answer: Galvanic corrosion
Galvanic corrosion occurs when two metals with different electrochemical potentials are coupled in a conductive electrolyte, causing the less noble metal to corrode faster.
Question 5: For transformer core laminations, which material property is most critical to minimize energy losses?
- High electrical conductivity
- Low magnetic permeability
- Low hysteresis and eddy current losses (Correct answer)
- High tensile strength
Correct answer: Low hysteresis and eddy current losses
Silicon steel with low hysteresis and eddy current losses is used for transformer cores to minimize the energy dissipated as heat during each magnetization cycle.
Question 6: What is the primary reason cross-linked polyethylene (XLPE) is preferred over paper-insulated lead cables (PILC) for modern underground power cables?
- Lower cost of raw materials
- Higher current-carrying capacity and no need for oil maintenance (Correct answer)
- Better performance at very low temperatures
- Easier to splice in the field
Correct answer: Higher current-carrying capacity and no need for oil maintenance
XLPE cables offer higher permissible operating temperatures, greater current-carrying capacity, and are dry-type insulation requiring no oil maintenance unlike PILC cables.
Question 7: Which hardness test uses a diamond pyramid indenter and is commonly used for very hard materials or thin sections?
- Brinell
- Rockwell B
- Vickers (Correct answer)
- Shore
Correct answer: Vickers
The Vickers hardness test uses a square pyramid diamond indenter and can be used for a wide range of materials including very hard metals and thin coatings.
AEP Material Selection & Properties 2
Which property describes a material's ability to return to its original shape after the applied load is removed?