35-220kV Current Transformers: Technical Overview and Applications Current transformers (CTs) are critical components in electrical power systems, designed to step down high currents to standardized, measurable levels for protection, metering, and control purposes. In the 35-220kV voltage range, CTs play a vital role in ensuring safe and efficient grid operation. Below is a detailed technical description of their design, functionality, and applications. 1. Design and Construction 35-220kV CTs are typically oil-immersed, gas-insulated (SF6), or resin-cast types, depending on the application and environmental conditions. Key design features include: - Core Material: High-permeability silicon steel or nanocrystalline alloys for accurate linearity and low losses. - Windings: Primary windings handle the system’s full current, while secondary windings deliver reduced currents (e.g., 1A or 5A) to instruments. - Insulation: Oil-paper or epoxy resin ensures dielectric strength, while SF6 gas-insulated CTs offer compactness for GIS (Gas-Insulated Switchgear) installations. - Burden Capacity: Designed to operate reliably under specified burdens (e.g., 15-30 VA) without saturation. 2. Accuracy and Performance - Accuracy Classes: Metering CTs (Class 0.2, 0.5) ensure precision for billing, while protection CTs (Class 5P, 10P) prioritize stability during faults. - Saturation Limits: Protection CTs must avoid saturation at high fault currents (e.g., 20× rated current) to ensure relay coordination. - Frequency Response: Optimized for 50/60Hz systems with minimal phase displacement. 3. Key Applications - Metering: Revenue-grade CTs measure energy consumption for billing. - Protection: Relay-grade CTs detect faults (overcurrent, differential) and trigger circuit breakers. - Grid Monitoring: Integrates with SCADA systems for real-time current data. 4. Installation and Safety - Mounting: Installed on bushings, switchgear, or standalone platforms. - Grounding: Secondary windings must be grounded to prevent open-circuit risks. - Standards Compliance: Adheres to IEC 60044, IEEE C57.13, and regional grid codes. 5. Challenges and Innovations - Transient Response: Advanced cores mitigate DC offset effects during faults. - Digital Integration: Hybrid CTs with Rogowski coils or optical sensors support smart grids. Conclusion 35-220kV CTs are indispensable for power system reliability, balancing accuracy, durability, and safety. Their evolving designs align with trends like digital substations and renewable energy integration, ensuring continued relevance in modern grids. (Word count: 500)