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IEC 61869-3 Certified 33kV Voltage Transformer JDZW-35K for Metering & Protection Applications
Introduction to the JDZW-35K Voltage Transformer
The JDZW-35K is a single-phase, indoor/outdoor rated, cast-resin insulated voltage transformer (VT) designed for accurate voltage measurement and reliable protective relay operation in 33kV (IEC) / 35kV (domestic) power systems. It operates on the fundamental principle of electromagnetic induction, where the primary winding—connected across the high-voltage line—induces a proportional secondary voltage suitable for instrumentation and protection circuits. The transformer’s core is constructed from grain-oriented electrical steel (GOES), which minimizes hysteresis and eddy current losses, ensuring high efficiency and thermal stability under continuous load.
Cast-Resin Insulation Technology
The JDZW-35K employs vacuum pressure impregnation (VPI) epoxy resin casting technology, wherein the entire magnetic assembly—including windings and core—is fully encapsulated in a solid, void-free epoxy matrix. This process eliminates air pockets that could lead to partial discharges, significantly enhancing dielectric strength and long-term reliability. Unlike oil-immersed VTs, the cast-resin design is non-flammable, requires no oil containment or monitoring, and exhibits superior resistance to environmental contaminants such as moisture, dust, and salt fog. The resin formulation includes UV stabilizers and hydrophobic additives, enabling safe outdoor deployment without degradation over decades of service. Partial discharge levels are maintained below 10 pC at 1.2 × Um/√3 (22.9 kV), well within IEC 61869-3 limits.
Advantages Over Oil-Immersed Designs
Compared to traditional oil-filled voltage transformers, the JDZW-35K offers multiple engineering advantages. First, it eliminates fire hazards associated with mineral oil, making it ideal for urban substations, industrial plants, and indoor switchgear rooms where safety codes restrict flammable materials. Second, its maintenance-free nature reduces lifecycle costs—no oil sampling, degassing, or leakage inspections are required. Third, the compact mechanical footprint allows for higher equipment density in space-constrained installations. Finally, the solid insulation provides consistent performance across wide temperature ranges (–40°C to +40°C ambient), with negligible aging effects due to oxidation or moisture ingress. These attributes make the cast-resin VT the preferred choice for modern distribution networks prioritizing safety, reliability, and minimal operational overhead.
Typical Application Overview
The JDZW-35K is engineered for dual-purpose use: precision metering (Class 0.2 or 0.5) and protective relaying (Class 3P or 6P). It is commonly deployed in 33kV transmission substations, industrial power distribution centers, renewable energy interconnection points (e.g., solar farms and wind parks), and rural electrification schemes. Its robust design supports both phase-to-ground and phase-to-phase configurations, with standard secondary outputs of 100/√3 V or 100 V. The transformer integrates seamlessly with digital relays, revenue meters, and SCADA systems, providing stable, low-distortion voltage signals even during transient fault conditions. With a typical service life exceeding 25 years, the JDZW-35K represents a long-term investment in grid accuracy and protection integrity.
Technical Specifications
The JDZW-35K adheres to stringent electrical and mechanical parameters defined by IEC 61869-3 and GB/T 20840.3. Below is a comprehensive specification table followed by detailed subsections on service conditions and performance envelopes.
| Parameter | Value |
|---|---|
| System Voltage (IEC) | 33 kV |
| System Voltage (Domestic) | 35 kV |
| Rated Primary Voltage | 33/√3 kV (phase-to-ground) |
| Rated Secondary Voltage | 100/√3 V or 100 V |
| Voltage Ratio | 33,000/√3 : 100/√3 V (standard) |
| Accuracy Class (Metering) | 0.2, 0.5 |
| Accuracy Class (Protection) | 3P, 6P |
| Rated Output (per burden) | 10–100 VA (configurable) |
| Insulation Level (Um/LI/AC) | 36 kV / 170 kV / 70 kV |
| Short-Time Thermal Current | 1 sec @ 100 A (secondary short-circuit) |
| Ambient Temperature Range | –40°C to +40°C |
| Altitude Limit | ≤ 1000 m (derating above 1000 m) |
| Relative Humidity | ≤ 95% (non-condensing) |
| Core Material | Grain-Oriented Electrical Steel (GOES) |
| Insulation System | VPI Epoxy Resin (Class F, 155°C) |
Electrical Performance Envelope
The JDZW-35K maintains voltage error and phase displacement within IEC 61869-3 tolerances across its rated burden range. For Class 0.2 metering, voltage error must not exceed ±0.2% and phase error ≤ ±10 minutes at 25–100% of rated voltage and 25–100% of rated burden. Protection classes (3P/6P) permit larger errors—±3% or ±6% voltage error—but guarantee linear response up to 5× rated voltage during fault transients. The transformer’s magnetizing current is kept below 0.5% of rated primary current to minimize core saturation effects. Frequency response is flat between 48–52 Hz, critical for synchronism checks and harmonic-rich environments like variable-speed drives or inverter-based resources.
Environmental and Mechanical Ratings
Designed for both indoor switchgear and outdoor pole-mounted applications, the JDZW-35K features a UV-resistant, tracking-resistant epoxy housing with creepage distance ≥ 25 mm/kV (medium pollution class). Terminal blocks comply with IEC 61439, using tinned copper connectors rated for 125 A continuous. The unit withstands seismic loads per IEC 60068-2-57 (0.5g horizontal, 0.3g vertical) and meets IP2X ingress protection for live parts. At altitudes above 1000 m, the power frequency withstand voltage must be reduced by 1% per 100 m increment; e.g., at 2000 m, AC test voltage = 70 kV × 0.9 = 63 kV.
Typical Applications
The JDZW-35K serves as a foundational component in diverse power system architectures, delivering precise voltage scaling for measurement and dependable signal fidelity for protection logic.
Substation Secondary Metering
In 33kV transmission and distribution substations, the JDZW-35K supplies scaled-down voltages to revenue-class kWh meters, demand recorders, and power quality analyzers. Its Class 0.2 accuracy ensures billing compliance per regulatory standards (e.g., EN 50163). The low phase displacement (<5 minutes at 100% burden) prevents reactive energy measurement errors. Multiple secondary windings can be specified—one for metering (0.2 class) and another for auxiliary functions (e.g., synchrocheck relays)—isolated via separate cores to avoid cross-interference. This configuration is standard in utility-owned substations requiring audit-ready data integrity.
Industrial Power Distribution
Large manufacturing facilities operating at 33kV utilize the JDZW-35K for motor protection, bus undervoltage tripping, and arc-flash mitigation systems. Here, the 3P or 6P protection class ensures relays receive accurate voltage signals during deep sags or asymmetrical faults. For example, in a steel mill with cyclical load swings, the VT’s low remanence core prevents false tripping due to residual flux. The cast-resin body resists chemical vapors and particulate contamination common in heavy industry, eliminating the need for sealed enclosures required by oil-filled units.
Renewable Energy Integration
Solar photovoltaic (PV) farms and onshore wind turbines frequently connect to 33kV collector grids. The JDZW-35K provides voltage feedback to anti-islanding relays, low-voltage ride-through (LVRT) controllers, and SCADA telemetry. Its fast transient response (<1 ms rise time) captures rapid voltage fluctuations caused by cloud cover or gust fronts. Additionally, the absence of oil simplifies permitting in environmentally sensitive zones. In hybrid microgrids, dual-secondary models support both local control (protection class) and remote monitoring (metering class) simultaneously.
Rural and Suburban Distribution Networks
In remote areas with limited maintenance access, the JDZW-35K’s maintenance-free design reduces outage risks. Mounted on poles or pad-mounted switchgear, it enables automated feeder reconfiguration via voltage-sensing reclosers. The 35kV domestic rating aligns with legacy Chinese and Southeast Asian distribution systems, while the 33kV IEC rating facilitates export compatibility. Its lightweight (≈85 kg) simplifies helicopter or drone-assisted installation in mountainous terrain. Utilities report >99.5% field reliability over 15 years in such deployments.
Compliance with International Standards
The JDZW-35K is certified to IEC 61869-3:2011 (“Instrument transformers – Part 3: Additional requirements for inductive voltage transformers”) and harmonized with China’s GB/T 20840.3-2013 standard.
IEC 61869-3 Certification Details
Compliance encompasses type tests, routine tests, and special tests per Clause 7 of IEC 61869-3. Key verified parameters include: temperature rise (≤60 K for windings), short-circuit withstand (thermal and dynamic), partial discharge (≤10 pC at 1.2 × Um/√3), and accuracy verification across burden and voltage ranges. The certification is issued by an ISO/IEC 17025-accredited laboratory, with test reports traceable to national metrology institutes. Notably, IEC 61869-3 mandates composite error testing for protection classes—a requirement absent in older standards like IEC 60044-2.
Alignment with GB/T 20840.3
GB/T 20840.3 mirrors IEC 61869-3 but includes supplementary clauses for Chinese grid conditions, such as enhanced lightning impulse withstand (185 kV vs. IEC’s 170 kV for 36 kV Um) and stricter humidity resistance. The JDZW-35K exceeds both, featuring 190 kV LI capability and 95% RH operational tolerance. Domestic certification (e.g., CMA/CNAS) validates these enhancements, facilitating procurement by State Grid and China Southern Power Grid.
Key Differences Between IEC and Domestic Standards
While IEC emphasizes global interoperability, GB standards prioritize regional resilience. For instance, GB/T 20840.3 requires 10,000-hour thermal endurance testing at 155°C (Class F), whereas IEC references generic insulation class tables. Similarly, GB mandates salt-fog testing per IEC 60507 for coastal deployments—a de facto requirement in Guangdong and Fujian provinces. The JDZW-35K’s design incorporates both, using halogen-free flame-retardant resin and reinforced creepage paths to satisfy all criteria without model variants.
On-Site Testing Procedures
Post-installation verification ensures the JDZW-35K performs within specifications. All tests follow IEC 61869-3 Annex B and IEEE C57.13 guidelines.
Insulation Resistance Test
Using a 2500 V DC megohmmeter, measure insulation resistance between primary winding and ground, and between primary and secondary windings. Acceptance criterion: ≥1000 MΩ at 20°C. Correct for temperature using Rt = R20 × 2(20–t)/10. Values below 500 MΩ indicate moisture ingress or resin cracking and require drying or replacement. Perform before and after power frequency withstand tests to detect insulation degradation.
Turns Ratio Test
Apply 1–5 kV AC to the primary and measure secondary voltage with a calibrated voltmeter (accuracy ±0.1%). Calculate actual ratio: Vp/Vs. Tolerance: ±0.2% for metering class, ±1% for protection class. Use a dedicated turns ratio tester (e.g., Omicron CT Analyzer) for automated comparison against nameplate values. Deviations beyond tolerance suggest winding shorts or incorrect tap connections.
Polarity Test
Verify reducing polarity per IEC 61869-3 Figure B.3. Momentarily apply 12 V DC to primary (H1+ to H2–); observe secondary voltage spike direction with an oscilloscope. Positive spike at X1 confirms correct polarity. Incorrect polarity causes 180° phase reversal, leading to metering errors or directional relay misoperation. This test is mandatory for differential or vector-group protection schemes.
Power Frequency Withstand Voltage Test
Apply 70 kV RMS (50 Hz) for 1 minute between primary and grounded tank/secondary. Monitor for flashover, excessive leakage current (>1 mA), or audible discharge. The test validates basic insulation level (BIL) integrity after transport stresses. Reduce voltage by 1% per 100 m above 1000 m altitude. Never perform if ambient humidity exceeds 80% to avoid surface tracking.
Open-Circuit Characteristic Test
With secondary open, gradually increase primary voltage from 0 to 190% of rated (62.7 kV). Record excitation current and secondary voltage. The knee point should occur above 150% rated voltage; premature saturation indicates core damage. Plot Vs vs. Iexc—nonlinearity beyond 120% suggests degraded GOES laminations. This test is critical after fault exposure to rule out hidden core faults.
Preventive Maintenance Guide
Although cast-resin VTs are largely maintenance-free, periodic checks extend service life and prevent unexpected failures.
Annual Visual and Functional Inspection
Inspect for surface cracks, tracking marks, or discoloration on the resin housing. Clean terminals with isopropyl alcohol to remove oxidation. Verify torque on bolted connections (15 N·m for M8 studs). Perform insulation resistance and ratio tests annually in critical applications (e.g., hospital or data center feeders). Check secondary wiring for loose strands or corrosion—common failure points in humid climates. Document all readings for trend analysis; a 20% drop in insulation resistance over two years warrants further investigation.
Five-Year Comprehensive Assessment
Every five years, conduct partial discharge (PD) mapping using an IEC 60270-compliant detector. Acceptable PD magnitude: ≤15 pC at 1.2 × Um/√3. Also repeat the open-circuit test to confirm core health. If installed outdoors, inspect mounting hardware for galvanic corrosion—replace stainless steel bolts if pitting exceeds 0.5 mm depth. Review historical fault records; VTs exposed to repeated close-in faults may require early retirement despite passing electrical tests due to cumulative mechanical stress.
Maintenance Intervals and Fault Diagnosis
| Interval | Action | Fault Indicator |
|---|---|---|
| Annually | IR test, visual check, terminal cleaning | IR < 500 MΩ → moisture ingress |
| Every 5 Years | PD test, ratio verification, core test | PD > 20 pC → internal voids |
| After Major Fault | Full suite of on-site tests | Ratio shift >1% → winding damage |
| As Needed | Thermal imaging during peak load | Hotspot >10°C above ambient → connection fault |
Common failure modes include secondary winding burnout (due to open-circuit operation) and resin delamination (from thermal cycling). Never operate the JDZW-35K with secondary open during primary energization—this induces dangerous overvoltages (>10 kV) that puncture insulation.
Conclusion
The JDZW-35K 33kV cast-resin voltage transformer exemplifies modern instrument transformer engineering, combining IEC 61869-3 compliance with ruggedized design for global deployment. Its epoxy-encapsulated GOES core delivers exceptional accuracy for revenue metering (Class 0.2) while maintaining linear response during fault transients for protection applications (Class 3P/6P). The elimination of flammable oil enhances safety in confined or populated areas, and the solid insulation system ensures decades of maintenance-free operation—even in harsh coastal or industrial environments. With a proven service life of 25–30 years, the JDZW-35K reduces total cost of ownership through reliability, precision, and resilience. Its dual compliance with IEC and GB standards facilitates seamless integration into both international projects and domestic Chinese infrastructure. For engineers designing next-generation substations, the JDZW-35K provides a technically sound, future-proof solution for voltage sensing that aligns with evolving grid digitization and decarbonization goals. As renewable penetration increases and grid dynamics grow more complex, the demand for high-fidelity, robust voltage transformers like the JDZW-35K will only intensify, cementing its role as a cornerstone of modern power system instrumentation.