In practical transmission engineering, what is the approximate loss angle (dielectric loss tangent angle) of a good-quality insulated cable?

Introduction / Context:
The loss angle (often discussed via tan delta) quantifies dielectric losses in insulated cables. A small loss angle indicates that the dielectric behaves almost ideally capacitive with minimal energy dissipation per cycle, which is desired in high-quality power and communication cables.

Given Data / Assumptions:

• Term: 'loss angle' refers to the angle between the current vector and the ideal quadrature (purely capacitive) current in a lossy dielectric.
• 'Good quality cable' implies low dielectric loss material (e.g., polyethylene, XLPE, PTFE).
• Typical power or RF usage where dielectric heating should be minimal.

Concept / Approach:

The dielectric loss tangent (tan δ) is the ratio of the resistive (loss) component to the reactive (capacitive) component of current. The loss angle δ is small for good dielectrics. Converting between tan δ and degrees, practical values for premium cable dielectrics correspond to loss angles well below a few degrees, commonly near 1° or less at the operating frequency.

Step-by-Step Solution:

Verification / Alternative check:

Manufacturers specify dissipation factor (tan δ) values; translating these to an angle confirms a very small δ, supporting the ~1° choice for a quick, standards-style question.

Why Other Options Are Wrong:

• 30°/70°/90°: Such large angles imply enormous dielectric loss, inconsistent with 'good quality' insulation.
• 15°: Still far too large for premium cable dielectric behavior.

Common Pitfalls:

Confusing loss angle with phase angle of current in an ideal capacitor; assuming higher operating temperature automatically implies large δ for good materials.

Final Answer:

1°