Questions

Multiple-choice questions you can practise one by one. Open a question, tap an answer and see at once whether it is right. For a random set, try Quick practice.

941 questions

• A gaseous insulator is subjected to increasing electric field intensity. Breakdown occurs when ionisation develops into a self-sustaining discharge. This phenomenon is primarily a…

  Electrical Engineering Materials › Unit 3: Insulating Materials · Hard

• Which statement about Class C insulation is the most appropriate?

  Electrical Engineering Materials › Unit 3: Insulating Materials · Hard

• Why does prolonged operation above the thermal rating of an insulation system generally reduce its service life?

  Electrical Engineering Materials › Unit 3: Insulating Materials · Hard

• Which sequence correctly represents the nominal maximum temperatures of Classes E, B, F and H, respectively?

  Electrical Engineering Materials › Unit 3: Insulating Materials · Hard

• An insulating material with a thermal class of 155°C is used in a machine operating continuously at 170°C. Which conclusion is correct if 155°C is its applicable maximum thermal l…

  Electrical Engineering Materials › Unit 3: Insulating Materials · Hard

• Why may dry wood be used as an insulating support in some electrical installations but not treated as a universal high-voltage insulator?

  Electrical Engineering Materials › Unit 3: Insulating Materials · Medium

• Why must the enamel coating on a winding wire be compatible with the operating temperature of the machine?

  Electrical Engineering Materials › Unit 3: Insulating Materials · Medium

• Why are winding wires coated with enamel rather than relying only on an external mechanical covering?

  Electrical Engineering Materials › Unit 3: Insulating Materials · Medium

• What is the principal benefit of applying insulating varnish to motor windings?

  Electrical Engineering Materials › Unit 3: Insulating Materials · Medium

• Why is silicone grease applied to some electrical insulating interfaces?

  Electrical Engineering Materials › Unit 3: Insulating Materials · Medium

• Which property makes PTFE useful in high-frequency electrical applications?

  Electrical Engineering Materials › Unit 3: Insulating Materials · Medium

• Why is PTFE, commonly known as Teflon, suitable for demanding electrical insulation applications?

  Electrical Engineering Materials › Unit 3: Insulating Materials · Medium

• Which characteristic explains the historical use of bitumen in some electrical insulating applications?

  Electrical Engineering Materials › Unit 3: Insulating Materials · Medium

• Which factor must be considered when selecting rubber insulation for an industrial cable?

  Electrical Engineering Materials › Unit 3: Insulating Materials · Medium

• Why is rubber widely used for flexible electrical cable insulation?

  Electrical Engineering Materials › Unit 3: Insulating Materials · Medium

• Why is dry insulating paper generally less suitable than properly impregnated paper for some high-voltage oil-filled equipment?

  Electrical Engineering Materials › Unit 3: Insulating Materials · Medium

• How does impregnation improve the performance of porous electrical insulating paper?

  Electrical Engineering Materials › Unit 3: Insulating Materials · Medium

• Which limitation is associated with untreated jute when used as electrical insulation?

  Electrical Engineering Materials › Unit 3: Insulating Materials · Medium

• What is an important reason for treating natural fibres such as silk and cotton before certain electrical insulation applications?

  Electrical Engineering Materials › Unit 3: Insulating Materials · Medium

• Why may cotton used as electrical insulation require impregnation or treatment?

  Electrical Engineering Materials › Unit 3: Insulating Materials · Medium