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XGW-12 11kV Cast-Resin Voltage Transformer for Substation Metering and Protection – IEC 61869-3 Certified
Introduction to the XGW-12 Voltage Transformer
The XGW-12 is a single-phase, indoor/outdoor rated, cast-resin insulated voltage transformer (VT) designed for accurate voltage measurement and reliable protective relay operation in medium-voltage power systems operating at 11kV (IEC standard) or 10kV (domestic Chinese system). As a critical component of secondary instrumentation circuits, the XGW-12 provides galvanic isolation between high-voltage primary conductors and low-voltage metering, monitoring, and protection devices. Its design adheres strictly to IEC 61869-3 and GB/T 20840.3, ensuring global interoperability and performance consistency.
Operating Principle of Cast-Resin Insulation
Cast-resin insulation in the XGW-12 employs vacuum pressure impregnation (VPI) technology using cycloaliphatic epoxy resin. This process fully encapsulates the high-voltage winding, low-voltage winding, and magnetic core assembly under controlled vacuum and pressure conditions, eliminating voids and moisture ingress pathways. The resulting monolithic structure exhibits superior dielectric strength (≥30 kV/mm), excellent tracking resistance (CTI ≥600), and minimal partial discharge (<5 pC at 1.2 × Um/√3). Unlike oil-filled alternatives, the solid epoxy matrix provides inherent fire resistance (IEC 60695-2-1), zero risk of leakage, and immunity to environmental contaminants such as dust, salt fog, and industrial pollutants. Thermal conductivity of the resin (~0.8 W/m·K) ensures efficient heat dissipation during continuous operation, supporting stable accuracy over the full temperature range.
Advantages Over Oil-Immersed Designs
Compared to traditional oil-immersed VTs, the XGW-12’s cast-resin construction offers significant operational and safety benefits. It eliminates the need for oil containment systems, reducing civil works costs and environmental liability. The absence of flammable oil makes it suitable for confined spaces such as indoor substations, underground vaults, and urban switchgear rooms where fire codes restrict hydrocarbon-based equipment. Maintenance requirements are drastically reduced—no oil sampling, degassing, or level checks are necessary. Additionally, the compact footprint (typically 30–40% smaller than equivalent oil units) enables higher equipment density in space-constrained installations. The mechanical rigidity of the epoxy housing also enhances seismic resilience (tested per IEC 60068-2-57), making it ideal for earthquake-prone regions.
Typical Applications Overview
The XGW-12 is engineered for dual-purpose use: precision metering (accuracy classes 0.2, 0.5) and dependable protection (accuracy class 3P or 6P). It is commonly deployed in 11kV distribution substations, industrial plant switchyards, wind/solar farm collector systems, and railway traction networks. Its robust design supports both grounded-wye and open-delta configurations, enabling phase-to-ground and phase-to-phase voltage sensing. In smart grid applications, the XGW-12 interfaces seamlessly with digital relays, revenue meters, and SCADA systems, providing stable secondary output (typically 100 V or 100/√3 V) under varying load and fault conditions.
Technical Specifications
The XGW-12 is rated for a system voltage of 11kV (Um = 12kV) per IEC 61869-3, with a domestic equivalent rating of 10kV (Um = 11.5kV) per GB/T 20840.3. Its core is constructed from grain-oriented electrical steel (GOES) with a maximum flux density of 1.6 T, minimizing core losses (<0.8 W/kg at 1.7 T, 50 Hz) and ensuring low no-load current (<0.5% of rated primary current).
| Parameter | Value |
|---|---|
| Primary Voltage (Unp) | 11,000 V (IEC) / 10,000 V (GB) |
| Secondary Voltage (Uns) | 100 V or 100/√3 V |
| Voltage Ratio | 11,000/100, 11,000/100/√3, 10,000/100, etc. |
| Accuracy Class (Metering) | 0.2, 0.5 |
| Accuracy Class (Protection) | 3P, 6P |
| Rated Output (per burden) | 10–100 VA (e.g., 30 VA @ 0.2 class) |
| Insulation Level (LI/AC) | 75 kV / 28 kV (1 min, 50 Hz) |
| Creepage Distance | ≥25 mm/kV (heavy pollution: ≥31 mm/kV) |
| Frequency | 50 Hz or 60 Hz |
| Ambient Temperature Range | –25°C to +40°C |
| Altitude | ≤1,000 m (derating required above) |
| Relative Humidity | ≤95% (non-condensing) |
Rated Voltage and Ratio Configuration
The XGW-12 supports multiple ratio configurations to accommodate diverse system topologies. For 11kV systems with solidly grounded neutrals, common ratios include 11,000/100 V (phase-to-phase) and 11,000/100/√3 V (phase-to-ground). In ungrounded or resonant-grounded networks, two or three units may be connected in open-delta to detect earth faults. The secondary terminals are clearly marked (a, n for metering; da, dn for residual voltage) and housed in an IP2X-protected terminal box. Ratio tolerance is ±0.1% for metering classes and ±1% for protection classes under rated burden conditions. Custom ratios (e.g., for 60 Hz systems) are available upon request with adjusted core dimensions to maintain flux density within safe limits.
Standard Service Conditions
The XGW-12 is designed for operation under normal service conditions as defined in IEC 61869-3: ambient temperature from –25°C to +40°C, daily average ≤35°C, relative humidity up to 95% (non-condensing), and installation altitude not exceeding 1,000 meters above sea level. For altitudes between 1,000 m and 3,000 m, the power frequency withstand voltage must be derated by 1% per 100 m increment. In coastal or industrial environments with high pollution severity (IV per IEC 60815), extended creepage distance variants (≥31 mm/kV) are recommended to prevent surface flashover. The unit is suitable for both indoor switchgear compartments and outdoor pole-mounted or pad-mounted installations when equipped with UV-stabilized resin and appropriate sealing.
Typical Applications
The versatility of the XGW-12 enables deployment across a broad spectrum of power infrastructure scenarios, each demanding precise voltage transformation with long-term reliability.
Substation Secondary Metering
In 11kV primary substations, the XGW-12 provides the reference voltage signal for revenue-grade energy meters, power quality analyzers, and demand monitors. Connected in wye configuration with a grounded neutral, it delivers phase-to-ground voltages (100/√3 V) to multi-function meters compliant with IEC 62053-22. The 0.2 accuracy class ensures billing accuracy within ±0.2% over 20–100% of rated voltage and 25–100% of rated burden. Its low phase error (<10 minutes) minimizes reactive energy measurement drift. In digital substations, the analog output may feed merging units for IEC 61850-9-2 LE sampled value transmission.