35-220kV Voltage Transformer Technical Description A 35-220kV voltage transformer (VT), also known as a potential transformer (PT), is a critical component in high-voltage power systems, designed to accurately step down transmission or distribution voltages to standardized low-voltage levels (typically 100V or 110V) for metering, protection, and control purposes. These devices ensure safe and reliable operation by isolating secondary circuits from high-voltage hazards while providing precise voltage signals for instrumentation. Design and Construction 1. Insulation System: - Oil-Immersed Type: Commonly used for 35-220kV applications, these VTs employ mineral oil or synthetic ester for insulation and cooling. The oil-filled tank provides robust dielectric strength and thermal stability. - Gas-Insulated (SF6) Type: For higher voltages (e.g., 220kV), SF6 gas insulation offers compactness, reduced maintenance, and superior arc-quenching properties. - Dry-Type (Resin Cast): Less common at these voltages but used in specific environments where flammability risks must be minimized. 2. Core and Windings: - Precision-laminated silicon steel cores minimize losses and ensure linear voltage transformation. - Primary windings are rated for system voltages (35kV, 66kV, 110kV, 220kV), while secondary windings deliver standardized outputs (e.g., 100V/√3 for phase-to-ground measurements). 3. Bushings and Terminals: - Porcelain or composite polymer bushings provide external insulation and mechanical support. - Hermetic sealing prevents moisture ingress, critical for long-term reliability. Performance Characteristics - Accuracy Class: Typically complies with IEC 60044-2 or IEEE C57.13, with classes like 0.2 (metering) or 3P/6P (protection). - Burden Capacity: Supports secondary loads (e.g., relays, meters) without significant accuracy degradation. - Frequency Response: Maintains stability across nominal power frequencies (50/60Hz) and transient conditions. Applications - Revenue Metering: High-accuracy VTs (0.2 class) ensure fair billing. - Protection Relays: Provide voltage signals for over/under-voltage, distance, or differential protection schemes. - Synchronization and SCADA: Enable grid automation and real-time monitoring. Safety and Standards - Dielectric Tests: Withstand lightning impulse (e.g., 450kV for 220kV VT) and power-frequency withstand voltages per IEC 61869. - Short-Circuit Durability: Mechanically robust to withstand fault currents. - Environmental Compliance: Operates in temperatures from -40°C to +40°C, with anti-condensation measures for humid climates. Installation and Maintenance - Mounted on platforms or GIS compartments, with proper grounding to avoid floating potentials. - Routine checks include oil/gas quality analysis (for sealed types), insulation resistance tests, and accuracy verification. Conclusion 35-220kV voltage transformers are indispensable for grid safety and efficiency, combining advanced insulation, precision engineering, and compliance with international standards. Their role in enabling accurate measurement and fault detection ensures stable power system operation across utilities and industrial networks. (Word count: 500)