Insulation design targets For a good insulating material intended for AC applications, the desired combination of dielectric strength and dielectric loss is:

Introduction / Context:
Insulators in cables, transformers, capacitors, and high-voltage equipment must withstand electric fields without breakdown while minimizing energy dissipation as heat. Two key specifications are dielectric strength and dielectric loss (often expressed via loss tangent, tan δ).

Given Data / Assumptions:

• Dielectric strength: maximum field before breakdown (kV/mm).
• Dielectric loss: power dissipated per unit volume under AC field, related to ε′′ and tan δ.
• Operation under rated temperature and frequency.

Concept / Approach:

High dielectric strength allows thinner insulation or higher operating voltages with safety margin. Low dielectric loss reduces heating, improving efficiency and prolonging life by mitigating thermal aging. Hence, the optimal pair is “high dielectric strength” and “low dielectric loss.”

Step-by-Step Solution:

Verification / Alternative check:

Material datasheets (e.g., PTFE, XLPE, mica) emphasize high breakdown fields and low tan δ at operating frequencies as key selling points.

Why Other Options Are Wrong:

A wastes energy and risks overheating; B is contradictory (weak insulation); D implies poor voltage endurance; E is non-optimal compared to achievable materials.

Common Pitfalls:

Equating low loss with low permittivity; conflating dielectric strength with mechanical strength.

Final Answer:

high and low