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REL-10 11kV Cast-Resin Voltage Transformer for Substation Metering and Protection – IEC 61869-3 Certified
Introduction to the REL-10 Voltage Transformer
The REL-10 is a single-phase, indoor/outdoor-rated cast-resin voltage transformer (VT) engineered for high-reliability metering and protective relaying applications in 11kV distribution networks. Designed in strict accordance with IEC 61869-3 and GB/T 20840.3, this instrument transformer leverages advanced vacuum pressure impregnation (VPI) epoxy resin technology to deliver superior dielectric performance, environmental resilience, and long-term stability. Unlike traditional oil-immersed VTs, the REL-10 eliminates fire hazards, oil leakage risks, and complex maintenance requirements, making it ideal for urban substations, industrial facilities, and renewable energy interconnection points.
Operating Principle of Cast-Resin Insulation
Cast-resin insulation in the REL-10 employs a two-component cycloaliphatic epoxy resin system cured under vacuum and pressure. This VPI process ensures complete impregnation of the primary and secondary windings, eliminating air voids that could lead to partial discharges under sustained operating voltage. The resin matrix provides a homogeneous dielectric medium with a relative permittivity (εr) of approximately 3.8 and volume resistivity exceeding 1×1014 Ω·cm at 20°C. Thermal conductivity of 0.8–1.0 W/(m·K) enables efficient heat dissipation from the core and windings, supporting continuous operation at rated load without thermal degradation. The solid insulation system maintains mechanical integrity across thermal cycles from –40°C to +40°C ambient, preventing microcracking that could compromise long-term reliability.
Advantages Over Oil-Immersed Designs
Compared to oil-filled voltage transformers, the REL-10 offers significant operational and safety benefits. The absence of flammable insulating oil eliminates fire propagation risks—critical in confined indoor switchgear or near sensitive infrastructure. Maintenance intervals are extended from annual (typical for oil units) to once every five years due to the hermetic nature of the resin encapsulation. Additionally, the REL-10 exhibits lower partial discharge levels (<5 pC at 1.2 Um/√3 per IEC 61869-3), enhancing signal fidelity for precision metering. Weight reduction of 30–40% simplifies handling during installation, while the compact footprint allows integration into space-constrained ring main units (RMUs) or pad-mounted switchgear. Environmental compliance is assured as the unit contains no PCBs or hazardous liquids, aligning with RoHS and WEEE directives.
Typical Applications Overview
The REL-10 serves dual roles in power systems: providing scaled-down secondary voltages for revenue metering (typically 100/√3 V or 110/√3 V) and supplying input signals to protective relays such as overvoltage, undervoltage, and directional earth-fault schemes. Its robust design supports deployment in 11kV (IEC nominal) or 10kV (domestic Chinese standard) networks, with seamless compatibility across grid architectures—from utility-owned transmission substations to private industrial plants. Common installations include feeder bays in 11kV/0.4kV distribution substations, generator step-up (GSU) transformer monitoring circuits in solar farms, and busbar voltage sensing in data center backup power systems. The transformer’s high accuracy class (0.2 for metering, 3P for protection) ensures compliance with regulatory billing requirements and reliable fault detection during transient events.
Technical Specifications
The REL-10 voltage transformer is engineered to precise electrical and environmental parameters, ensuring consistent performance across diverse operating conditions. All specifications adhere to IEC 61869-3:2011 and GB/T 20840.3-2013 standards, with verified test reports available upon request.
| Parameter | Value |
|---|---|
| Primary Rated Voltage (Up) | 11 kV (IEC) / 10 kV (GB) |
| Secondary Rated Voltage (Us) | 100/√3 V or 110/√3 V (three-phase systems) |
| Voltage Ratio | 11000/√3 : 100/√3 V or 10000/√3 : 100/√3 V |
| Accuracy Class (Metering) | 0.2 |
| Accuracy Class (Protection) | 3P |
| Rated Output (Burden) | 30 VA (metering), 50 VA (protection) |
| Insulation Level (LI/AC) | 75 kV / 28 kV (per IEC 60071-1) |
| Short-Time Withstand Current | Not applicable (VTs are not designed for short-circuit current) |
| Core Material | Grain-Oriented Electrical Steel (GOES), M4 grade, 0.27 mm thickness |
| Insulation System | VPI cycloaliphatic epoxy resin, UL 94 V-0 rated |
| Ambient Temperature Range | –40°C to +40°C |
| Maximum Altitude | 1000 m above sea level (derating required above 1000 m) |
| Relative Humidity | Up to 95% non-condensing |
| Partial Discharge Level | <5 pC at 1.2 × Um/√3 |
Electrical Performance Parameters
The REL-10 achieves its specified accuracy classes through meticulous core lamination stacking and winding geometry optimization. The GOES core operates at a magnetic flux density of 1.6 T under rated voltage, minimizing hysteresis losses (<0.8 W/kg at 1.5 T, 50 Hz). Voltage error at 0.2 class is limited to ±0.2% with phase displacement ≤10 minutes at 25–100% of rated burden. For protection class 3P, composite error remains below 3% at 5%–100% of rated voltage and up to 100% of rated burden. The transformer’s frequency response is flat within ±0.5% from 45 Hz to 55 Hz, ensuring accurate representation of harmonics up to the 13th order—critical for modern power quality monitoring systems.
Environmental and Mechanical Ratings
Designed for both indoor and outdoor service, the REL-10 features a UV-stabilized resin housing with IP54 ingress protection when mounted vertically. Terminal boxes are sealed with gasketed covers and include brass terminals rated for 63 A continuous current. The unit withstands seismic loads up to 0.5g horizontal acceleration (per IEC 60068-2-57), suitable for moderate earthquake zones. Thermal class F (155°C) insulation allows a 10 K temperature rise margin above standard limits, extending service life under overload conditions. Mounting is via two M16 threaded inserts on the base flange, compatible with standard IEC 61869 mounting dimensions.
Typical Applications
The REL-10 voltage transformer is deployed across diverse power infrastructure segments where accuracy, reliability, and safety are paramount. Its dual-certification to IEC and GB standards facilitates global deployment while meeting local regulatory requirements.
Substation Secondary Metering
In 11kV/0.4kV distribution substations, the REL-10 provides the reference voltage for revenue-class kWh meters and power quality analyzers. Connected phase-to-ground on each of the three phases, it delivers a secondary voltage of 100/√3 V to metering panels. The 0.2 accuracy class ensures billing compliance per IEC 62053-22, with voltage error maintained within ±0.15% under typical load profiles (20–80% burden). In smart grid deployments, the VT’s low phase displacement (<5 minutes) enables precise calculation of reactive energy and power factor, supporting demand-side management programs.
Five-Year Comprehensive Maintenance
Every 60 months, perform enhanced diagnostics:
– **Partial Discharge Mapping**: Use ultra-high-frequency (UHF) sensors to detect internal discharges >10 pC
– **Thermal Imaging**: Scan under load to identify hot spots (>10 K above ambient indicates winding issues)
– **Dielectric Spectroscopy**: Measure tan δ at 0.1–100 Hz to assess resin aging
Replace silica gel desiccant in terminal box if present (though most REL-10 units are fully sealed). Review historical test data for trend analysis—gradual parameter drift often precedes failure.
Fault Diagnosis and Troubleshooting
Common failure modes and remedies:
– **Zero Secondary Voltage**: Check for open-circuit secondary wiring or blown fuses (typically 1 A, HRC type)
– **High Ratio Error**: Indicates core lamination damage—replace unit
– **Excessive Heating**: Caused by secondary short-circuit or excessive burden—verify connected load ≤ rated VA
– **Cracked Housing**: Replace immediately—compromised insulation risks flashover
Never attempt field repair of cast-resin VTs; the encapsulated design prohibits safe disassembly.
Conclusion
The REL-10 11kV cast-resin voltage transformer represents a benchmark in reliability, accuracy, and safety for modern power systems. By leveraging VPI epoxy resin technology and GOES core materials, it delivers exceptional dielectric strength, thermal stability, and environmental resilience—outperforming legacy oil-immersed designs in virtually every operational metric. Its dual compliance with IEC 61869-3 and GB/T 20840.3 ensures seamless integration into international and domestic grids, supporting critical applications from revenue metering to renewable energy protection. Rigorous factory and field testing protocols guarantee performance within tight tolerances (±0.2% voltage error, <5 pC partial discharge), while the maintenance-free design reduces total cost of ownership over a projected service life of 25–30 years. For engineers specifying instrument transformers in 11kV/10kV networks, the REL-10 offers a technically superior, future-proof solution that aligns with global best practices in substation design and asset management.