technical of CORONA RINGS
1. Ultimate Tensile Strength (UTS)
1. Corona rings are not primary load-bearing parts but must still withstand mechanical forces from wind, vibration, and mounting.
2. Made from aluminum alloy (6061-T6 / 6101-T6) or sometimes stainless steel.
3. UTS typically ranges from 160–250 MPa (megapascals) depending on alloy and design.
4. Structural ring/frame UTS can translate to 5–15 kN for small rings and up to 25–30 kN for large UHV applications.
2. Working Load / Safe Working Load (SWL)
1. SWL is based on mechanical load the ring might endure from mounting, vibration, and wind pressure.
2. For a ring with UTS of 20 kN, SWL is generally kept at 6–10 kN, ensuring a safety factor of 2.5–3.0.
3. Designed for static suspension or attachment loads, not conductor tension.
3. Conductor Diameter Compatibility
1. Rings are sized and shaped to match insulator/conductor configurations.
2. Mounting clamps are designed for compatibility with:
a. Insulator necks of 50–100 mm
b. Conductor bundle spacing from 300 mm to 600 mm
3. Custom designs allow integration with both single and bundled conductors.
4. Slip Strength:
1. Critical for clamp-to-insulator neck or flange interface.
2. Slip strength depends on the torque of the bolts and gripping design — typically rated to withstand >3–5 kN axial load without slippage.
3. Uses set screws, U-clamps, or saddle clamps with serrated interfaces for strong grip.
5. Temperature Withstanding Capacity:
1. Designed to operate in ambient conditions of -40°C to +85°C continuously.
2. Can withstand short-term heating due to arcing or corona up to 200–250°C.
3. Aluminum alloys retain mechanical properties across wide temperature ranges.
6. Corrosion Resistance:
1. Made from high-purity aluminum alloy or stainless steel to withstand long-term outdoor exposure.
2. Surface treatments include:
I. Shot blasting
II. Anodizing / chromating (for aluminum)
III. Passivation (for stainless steel)
3. Designed for polluted, coastal, and desert zones.
7. Impact & Fatigue Strength:
1. Corona rings are tested for wind-induced vibrations and minor impact loads from tools, debris, or wildlife.
2. Aluminum alloy provides good energy absorption and ductility.
3. High-cycle fatigue tested via oscillation and vibration simulations.
8. Mechanical Endurance:
1. Service life of 30+ years under normal conditions.
2. Endurance tested by vibration fatigue, thermal cycling, and bolt-torque retention tests.
3. Rings remain effective unless physically damaged or oxidized beyond performance limits.
9. Design Safety Factors:
1. Mechanical safety factors: ≥2.5 for structural integrity, ≥3.0 for mounting components.
2. Electrical safety design includes optimized ring diameter and position to maintain uniform voltage gradient and reduce electric field stress at hardware terminals.
Top 5 Quality Assurance
1. Type & Routine Testing (Electrical + Mechanical)
a. Conducted as per IEC 60060-1, IEC 60660, or utility-specific HV test standards.
b. Includes:
I. Corona inception and extinction voltage tests
II. Voltage distribution (grading) tests
III. Mechanical torque, fatigue, and slip tests
2. Precision Dimensional & Surface Inspection
a. 100% inspection of:
I. Ring diameter tolerance (typically ±2 mm)
II. Weld seams (for circular or split rings)
III. Mounting hole positions and smoothness
b. Surface roughness and finish uniformity critical for corona suppression.
3. Corrosion & Environmental Testing
a. Salt spray test (500–1000 hours) as per ASTM B117
b. Humidity cycling, acid rain simulation, and UV weathering tests for outdoor life assurance
c. Visual inspection after tests to ensure no pitting or surface breakdown
4. Raw Material & Traceability Control
a. Use of certified aluminum billets or SS tubes only
b. Test certificates provided for each raw material batch
c. Each unit engraved/stamped with:
I. Manufacturer code
II. Batch number
III. Ring diameter
5. Documentation & Compliance
a. Supplied with:
I. Type Test Report (electrical + mechanical)
II. Routine Test Certificates
III. GTP (Guaranteed Technical Particulars)
IV. 3rd Party Inspection Certificates (if applicable)
b. Manufactured under ISO 9001 / ISO 14001 / IEC QA systems