01 Basic Understanding of Voltage Levels

1.Voltage levels (voltage classes) refer to standardized nominal voltages used in power systems and electrical equipment. The rated voltage defines the operational voltage range for devices and systems, ensuring compatibility and safety. For instance, household appliances (e.g., refrigerators, TVs) typically use 220V; deviations may cause malfunctions.

02 Importance of Voltage Classification

1.Standardization: Enables interoperability of equipment from different manufacturers.

2.Efficiency: Higher voltages reduce energy loss during transmission (e.g., 500kV lines lose <0.8‰/km).

3.Safety: Insulation requirements and protection mechanisms vary by voltage (e.g., ≤36V for medical devices).

4.Scalability: Supports renewable energy integration and smart grid development.

03 Common Voltage Classifications

1.Safety Voltage (≤36V): Used in hazardous environments (e.g., 12V pool lighting, 6V toys). Complies with GB/T 3805-2008.

2.Low Voltage (220V/380V): Three-phase four-wire systems with ±7% tolerance (GB/T 12325). Requires 30mA residual current protection.

3.Medium Voltage (10kV-35kV): Dominates urban grids (10kV cable capacity: 300A/km).

4.High Voltage (110kV-220kV): Transmits 50-500MW over 50-300km.

5.EHV/UHV (≥330kV): ±800kV HVDC transmits 8000MW over 1,500km.

04 Classification Criteria

1.National Standards: GB/T 156-2017 aligns with IEC 60038 for 50Hz AC systems.

2.Transmission Distance: 0.4kV for <0.6km; 1000kV AC for 800-1,500km.

3.Power Capacity: 220kV carries 4x more power than 110kV.

4.Technical Challenges: Insulation materials (e.g., for 1100kV) and cooling systems.

05 Voltage vs. Transmission Parameters

06 Equipment Voltage Specifications

1.Generators: Rated voltage 5% higher than grid voltage to offset line losses.

2.Transformers:

· Primary winding: Matches grid voltage (or generator voltage if connected directly).

· Secondary winding: 5-10% higher than grid voltage based on line losses (e.g., 5% for short lines).