In China’s State Grid—the world’s largest power grid—voltage transformers (VTs, or potential transformers, PTs) play a pivotal role in ensuring the safe, reliable, and efficient operation of power systems. As critical instrument transformers, they:
Reduce High Voltages: Convert grid voltages (e.g., 10kV, 35kV, 110kV, or higher) to low, measurable levels (e.g., 100V or 100/√3 V) for metering, protection, and control.
Enable Grid Monitoring: Provide real-time voltage data to SCADA systems, substations, and relay protection devices.
Support Grid Stability: Detect voltage abnormalities (e.g., overvoltage, undervoltage, phase imbalance) to trigger protective actions and maintain grid reliability.
Voltage Measurement: VTs are installed in substations to monitor busbar voltages, feeder voltages, and transformer terminal voltages. For example, in a 110kV substation, VTs convert high voltages to 100V for connection to voltage meters and energy 计量表 (energy meters).
Relay Protection: VTs supply voltage signals to protective relays, which detect faults (e.g., short circuits, ground faults) and trip circuit breakers to isolate faulty sections.
Precision Metering: State Grid requires high-accuracy VTs (e.g., Class 0.2 or 0.5) for revenue metering in transmission and distribution grids.
Smart Grid Integration: VTs in smart substations interface with digital meters and IoT devices to support real-time energy management and demand response.
Voltage Regulation: VTs provide feedback to automatic voltage regulators (AVRs) in power plants or substations, adjusting generator excitation or tap changers to maintain voltage within ±5% of nominal levels.
Fault Detection: In high-voltage transmission lines (e.g., 500kV), VTs work with current transformers (CTs) to identify symmetrical or asymmetrical faults, enabling rapid isolation and minimizing downtime.
State Grid imposes strict standards on VT design and performance, aligned with GB/T 1207 (Chinese national standard) and IEC 60044-2:
Accuracy Classes:
Metering: Class 0.2S or 0.5S for energy metering (e.g., in distribution transformers).
Protection: Class 3P or 6P for relaying applications (e.g., in transmission line protection).
Burden Management: VTs must operate within rated burden (e.g., 30VA, 50VA) to avoid core saturation. For example, a 10kV VT with a secondary burden of 50VA can drive up to five protective relays or meters.
Voltage Levels: VTs are designed for voltage classes ranging from 0.4kV (low voltage) to 1000kV (ultra-high voltage, UHV).
Environmental Resistance:
Outdoor VTs: Epoxy-cast or oil-immersed designs with IP54/IP65 protection against dust, water, and corrosion (e.g., in coastal substations).
Indoor VTs: Dry-type, epoxy-encapsulated designs for switchgear rooms (e.g., in urban distribution substations).
Short-Circuit Strength: VTs must withstand transient fault currents (e.g., 31.5kA for 10kV systems) without mechanical damage.
Surge Protection: Integrated surge arresters or fuses protect VTs from lightning strikes or switching overvoltages in overhead lines.
As a State Grid partner (e.g., suppliers like Xiamen First Transformer Co.), manufacturers must meet rigorous bidding and certification processes:
Bid Compliance: Suppliers must demonstrate compliance with State Grid’s technical specifications (e.g., for 10kV indoor VTs with double windings: 10/√3 kV primary, 100/√3 V and 100V secondary).
Type Testing:
Partial Discharge (PD) Testing: Ensures insulation integrity (e.g., PD ≤ 10pC for 10kV VTs).
Temperature Rise Testing: Verifies safe operation under full load (e.g., ≤60K temperature rise for epoxy-cast VTs).
Quality Management:
ISO 9001, ISO 14001, and ISO 45001 certifications are mandatory for manufacturers.
State Grid’s annual quality inspections ensure long-term reliability (e.g., 25-year design lifespan for oil-immersed VTs).
Grid Complexity: Rising renewable energy integration (e.g., solar, wind) introduces voltage fluctuations and harmonics, requiring VTs with extended frequency response (e.g., up to 2kHz).
UHV Grid Demands: UHV VTs must address corona discharge, electromagnetic compatibility (EMC), and long-term aging under extreme voltages.
Smart Grid Upgrades: Legacy VTs in rural grids need retrofitting for digital interfaces (e.g., IEC 61850 protocol) to support substation automation.
Digital VTs (EVTs): Electronic voltage transformers using capacitive dividers or optical sensors (e.g., FOCTs—Fiber Optic Current Transformers) eliminate magnetic cores, reduce size, and support digital substation standards (IEC 61850).
IoT-Enabled VTs: Built-in sensors monitor temperature, humidity, and insulation resistance, enabling predictive maintenance via State Grid’s IoT platform.
Eco-Friendly Materials: Biodegradable insulating oils (e.g., natural esters) and amorphous alloy cores reduce energy loss and environmental impact.
Grid Modernization:
Renewable Energy Integration:
UHV and HVDC Expansion:
Standardization and Globalization:
State Grid’s international projects (e.g., in Southeast Asia, Europe) will adopt IEC standards for VTs, facilitating cross-border grid interconnections.
Voltage transformers are the "eyes and ears" of State Grid’s power systems, ensuring accurate measurement, reliable protection, and efficient grid management. As China advances its "Double Carbon" strategy and smart grid initiatives, VTs will evolve toward higher precision, digital integration, and sustainability, solidifying their role as critical enablers of a resilient and low-carbon energy future. Manufacturers partnering with State Grid must prioritize innovation, compliance, and lifecycle management to meet the evolving demands of one of the world’s most complex power networks.
