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JDZW-35 33kV Cast-Resin Voltage Transformer for Substation Metering and Protection – IEC 61869-3 Certified
Introduction to the JDZW-35 Voltage Transformer
The JDZW-35 is a single-phase, indoor/outdoor-rated cast-resin voltage transformer (VT) engineered for high-accuracy voltage measurement and dependable protective relay coordination in 33kV (IEC standard) or 35kV (Chinese domestic system) medium-voltage networks. Designed in strict compliance with IEC 61869-3 and GB/T 20840.3, this instrument transformer leverages vacuum pressure impregnation (VPI) epoxy resin technology to fully encapsulate its magnetic core and windings, eliminating moisture ingress and enhancing dielectric integrity. Unlike traditional oil-immersed VTs, the JDZW-35 offers maintenance-free operation, superior fire resistance, and compact physical dimensions—critical advantages in space-constrained urban substations or environmentally sensitive installations.
Operating Principle of Cast-Resin Insulation
Cast-resin insulation in the JDZW-35 functions by embedding the primary and secondary windings—wound around grain-oriented electrical steel (GOES)—within a solid matrix of cycloaliphatic epoxy resin under vacuum and pressure. This VPI process ensures complete void elimination, preventing partial discharge inception even under transient overvoltages. The resin’s high tracking index (>600 V) and thermal class F (155°C) rating enable stable performance across ambient temperatures from –40°C to +40°C. Dielectric strength exceeds 20 kV/mm, supporting the required power frequency withstand voltage of 70 kV rms for 1 minute between primary and ground, as mandated by IEC 61869-3. The monolithic structure also provides mechanical rigidity, reducing vibration-induced winding fatigue during short-circuit events.
Advantages Over Oil-Immersed Designs
Compared to oil-filled VTs, the JDZW-35 eliminates fire hazards, environmental contamination risks, and periodic oil sampling requirements. Its dry-type construction achieves a lower total cost of ownership due to zero maintenance needs over its 25–30-year service life. The absence of conservators, breathers, or oil expansion tanks reduces footprint by up to 40%, facilitating retrofitting into legacy switchgear bays. Additionally, cast-resin VTs exhibit faster thermal response during overload conditions, with no risk of oil degradation or gas accumulation that could compromise insulation integrity. These attributes make the JDZW-35 ideal for indoor GIS compartments, offshore platforms, and data centers where safety and reliability are non-negotiable.
Typical Application Overview
The JDZW-35 serves dual roles: precision metering (accuracy classes 0.2 or 0.5) and protective relaying (3P or 6P). In utility substations, it supplies scaled-down secondary voltages (typically 100/√3 V or 100 V) to revenue meters, SCADA RTUs, and distance relays. Industrial facilities use it for motor protection schemes and power quality monitoring, while renewable energy plants integrate it into grid-synchronization controls for solar inverters or wind turbine step-up transformers. Its robust design supports continuous operation at 1.2× rated voltage (39.6 kV) for 8 hours and withstands 1.9× overvoltage (62.7 kV) for 30 seconds during ferroresonance events—key for networks with long cable runs or capacitor banks.
Technical Specifications
The JDZW-35 delivers precise voltage transformation under defined electrical and environmental parameters. All specifications adhere to IEC 61869-3:2011 and GB/T 20840.3-2013, ensuring interoperability across global and Chinese infrastructure projects.
Rated Electrical Parameters
Primary rated voltage: 33/√3 kV (line-to-neutral for grounded systems) or 33 kV (line-to-line for ungrounded). Secondary outputs include one or two windings: standard configurations offer 100/√3 V (for three-phase wye connections) or 100 V (delta-connected). Accuracy classes are selectable per application: Class 0.2 (±0.2% ratio error, ±10′ phase displacement) for revenue metering; Class 0.5 (±0.5%, ±20′) for commercial billing; Class 3P (±3%, ±120′) or 6P (±6%, ±240′) for protection. Rated burden ranges from 10 VA to 100 VA per winding, with thermal short-time current rating of 100 A for 1 second. Insulation levels meet IEC 60071-1: LI 170 kV (lightning impulse), AC 70 kV (power frequency, 1 min).
Environmental and Mechanical Ratings
Designed for both indoor and outdoor service, the JDZW-35 operates reliably at altitudes ≤1000 m (derating factor 1.1% per 100 m above). Ambient temperature range: –40°C to +40°C, with relative humidity ≤95% (non-condensing). Pollution degree: III per IEC 60664-1, validated by 24-hour salt fog testing per IEC 60068-2-11. Creepage distance ≥25 mm/kV (minimum 825 mm for 33 kV), achieved via ribbed shed design. Weight: approximately 85 kg; dimensions: 680 mm (H) × 320 mm (W) × 280 mm (D). Terminal studs comply with IEC 61290-1-2 for secure bolted connections (M12 standard).
Core and Winding Construction
The magnetic circuit employs CRGO (cold-rolled grain-oriented) silicon steel laminations, 0.3 mm thick, annealed to minimize hysteresis loss (<0.8 W/kg at 1.7 T, 50 Hz). Primary winding uses enamelled copper wire (Class H insulation), wound in concentric layers with electrostatic shielding between HV and LV sections to suppress capacitive coupling. Secondary windings feature bifilar winding techniques to reduce leakage inductance, critical for maintaining accuracy under low-burden conditions. Resin formulation includes UV stabilizers for outdoor longevity and alumina trihydrate filler for flame retardancy (UL 94 V-0 rated).
Typical Applications
The JDZW-35’s versatility stems from its dual-certification (IEC/GB), robust insulation, and flexible secondary configurations, enabling deployment across diverse power systems.
Substation Secondary Metering Systems
In 33kV transmission substations, the JDZW-35 feeds revenue-class kWh meters and demand recorders with Class 0.2 accuracy. For example, a typical 33/11 kV zone substation uses three JDZW-35 units in wye configuration to provide 100/√3 V secondaries to a multi-tariff metering cabinet. The VT’s low phase displacement error (<10 arcminutes) ensures accurate reactive energy measurement, critical for power factor penalty calculations. Its stability over temperature (ratio error drift <±0.05% from –25°C to +55°C) meets ENTSO-E metering code requirements for cross-border electricity trading.
Industrial Power Distribution Networks
Large manufacturing plants with 35kV primary distribution employ JDZW-35 VTs for motor protection relays (e.g., 50/51, 27/59 functions). In a steel mill, six JDZW-35 units monitor feeder voltages to detect undervoltage conditions that could stall induction motors. The 3P accuracy class ensures reliable operation of 27 relays set at 85% Vn, with burden compatibility verified at 30 VA (typical for electromechanical relays). The cast-resin housing resists chemical fumes from adjacent process areas, unlike oil-filled alternatives prone to gasket degradation.
Renewable Energy Integration
Solar farms connecting to 33kV grids use JDZW-35 VTs in collector substation switchgear for anti-islanding protection and voltage ride-through compliance. During grid faults, the VT must maintain output within ±10% for 150 ms to satisfy IEEE 1547-2018. The JDZW-35’s low remanence (<0.3 T) prevents core saturation during DC-offset fault currents, ensuring accurate voltage sensing for inverter trip logic. Dual secondary windings allow separate connections to protection relays (3P class) and SCADA (0.5 class), optimizing cost without compromising functionality.
Rural and Suburban Distribution Networks
In China’s rural electrification programs, JDZW-35 units (rated 35kV domestic) are mounted on pole-top switchgear for automatic voltage regulation (AVR) control. The VT supplies 100 V to capacitor bank controllers that maintain bus voltage within ±5% of nominal. Its outdoor rating withstands monsoon humidity (95% RH) and dust storms, with hydrophobic sheds preventing flashover. The 25-year service life aligns with government infrastructure depreciation schedules, reducing lifecycle replacement costs.
Compliance with International Standards
The JDZW-35’s design, testing, and certification strictly follow IEC 61869-3 and GB/T 20840.3, ensuring global acceptance while accommodating regional grid codes.
IEC 61869-3 Compliance Details
IEC 61869-3:2011 defines performance requirements for inductive voltage transformers. The JDZW-35 meets all clauses: ratio error and phase displacement limits per Table 2 (e.g., Class 0.2: ±0.2% ratio error at 25–100% Vn); temperature rise ≤55 K for windings (measured by resistance method); partial discharge <10 pC at 1.2 Um/√3. Type tests include temperature rise, short-circuit withstand (100 A, 1 s), and electromagnetic compatibility (EMC) per IEC 61000-4 series. Routine tests cover turns ratio (±0.25% tolerance), polarity, and power frequency withstand (70 kV, 1 min).
Alignment with GB/T 20840.3
GB/T 20840.3-2013 mirrors IEC 61869-3 but specifies 35kV as nominal system voltage (vs. 33kV IEC). The JDZW-35 accommodates both by designing insulation for Um = 40.5 kV (maximum system voltage), satisfying both standards’ dielectric requirements. Key GB-specific additions include mandatory seismic testing (horizontal acceleration 0.3g) for earthquake-prone regions and stricter creepage distance (≥31 mm/kV for heavy pollution). Accuracy verification uses Chinese national reference standards traceable to NIM (National Institute of Metrology).
Testing and Certification Protocols
Certification requires third-party validation by accredited labs (e.g., KEMA, CESI, or China National Electric Apparatus Quality Supervision Center). Type test reports document performance under extreme conditions: –40°C cold start, 95% RH humidity cycling, and 1.9 Un overvoltage endurance. Each production unit undergoes routine tests per IEC 61869-3 Clause 12: insulation resistance (>1000 MΩ at 2500 V DC), turns ratio (tolerance ±0.25%), and polarity (reducing polarity confirmed via DC kick test). Certificates include CE marking (EU), CCC (China Compulsory Certification), and CQC voluntary certification.
On-Site Testing Procedures
Post-installation verification ensures the JDZW-35 performs within specification before energization. All tests follow IEC 60060-1 and IEEE C57.13 guidelines.
Insulation Resistance Test
Measure insulation resistance between primary winding and ground, and between primary and secondary windings, using a 2500 V DC megohmmeter. Acceptance criterion: >1000 MΩ at 20°C. Correct for temperature using Rt = R20 × 2(20–t)/10. Low readings (<100 MΩ) indicate moisture ingress or resin cracking—requiring drying or replacement. Perform before and after power frequency withstand test to detect insulation degradation.
Turns Ratio Test
Apply 100–200 V AC to the primary and measure secondary voltage with a calibrated voltmeter (accuracy class 0.1). Calculate ratio as Vp/Vs; compare to nameplate value. Tolerance: ±0.25% for metering classes, ±0.5% for protection. Example: for 33,000/100 V VT, measured ratio must be 330 ±0.825. Use a dedicated ratio tester (e.g., Omicron CT Analyzer) for automated comparison and phase shift measurement.
Polarity Test
Verify reducing polarity (standard for IEC VTs) via DC method: connect battery (+) to primary H1, (–) to H2; connect galvanometer between secondary X1 (+) and X2 (–). Momentary switch closure should produce positive deflection. Incorrect polarity causes 180° phase reversal, leading to relay misoperation or meter reversal. Document polarity marks on terminal box per IEC 61869-3 Figure 3.
Power Frequency Withstand Voltage Test
Apply 70 kV rms, 50 Hz, for 1 minute between primary and grounded tank/secondary. Use a calibrated test transformer with overcurrent trip (≤1 A). Monitor for flashover, excessive leakage current (>1 mA), or audible discharge. Reduce test voltage to 80% if altitude >1000 m (per IEC 60071-2). Never perform this test if insulation resistance is <1000 MΩ.
Open-Circuit Characteristic Test
For VTs, apply variable voltage (0–120% Vn) to secondary while primary is open. Measure excitation current; plot V vs. I curve. Knee point should exceed 1.5× Vn (e.g., >150 V for 100 V secondary). Excessive magnetizing current at nominal voltage indicates core defects or shorted turns. Compare to factory baseline—deviation >10% warrants investigation.
Preventive Maintenance Guide
Although cast-resin VTs are maintenance-free, periodic inspections ensure long-term reliability in harsh environments.
Annual Visual and Electrical Inspection
Inspect for surface cracks, UV degradation (chalking), or tracking marks on sheds. Clean with mild detergent if salt/dust deposits exceed 1 mm thickness. Check terminal tightness (torque: 35 N·m for M12 studs) and corrosion on grounding lugs. Perform insulation resistance test annually; trend values should remain stable (±20% of baseline). Sudden drops indicate internal moisture—schedule dielectric frequency response (DFR) analysis.
Five-Year Comprehensive Assessment
Every 60 months, conduct partial discharge measurement per IEC 60270 at 1.2 Um/√3 (28 kV). Acceptance: <10 pC. Also verify ratio and polarity to detect winding deformation from seismic events. In coastal areas, inspect for chloride-induced corrosion on embedded hardware using ultrasonic thickness gauging. Replace if resin hardness (Shore D) drops below 80 (indicating polymer aging).
Maintenance Intervals and Fault Diagnosis
| Interval | Task | Acceptance Criteria |
|---|---|---|
| Annually | Visual inspection, IR test | IR >1000 MΩ; no surface damage |
| 5 Years | PD test, ratio verification | PD <10 pC; ratio error within spec |
| 10 Years | DFR analysis, core integrity | No significant capacitance change vs. baseline |
Common faults: secondary open-circuit (causes core saturation, overheating); external flashover (due to pollution); mechanical impact damage. Diagnose via thermal imaging (hot spots >10 K above ambient) or dissolved gas analysis (not applicable—dry type).
Conclusion
The JDZW-35 33kV cast-resin voltage transformer represents a benchmark in medium-voltage instrumentation, combining IEC 61869-3 and GB/T 20840.3 compliance with field-proven reliability. Its VPI epoxy resin encapsulation eliminates the operational hazards and maintenance burdens associated with oil-immersed designs, while the GOES core ensures metrological precision across metering (0.2/0.5) and protection (3P/6P) applications. Engineered for 25–30 years of service, the JDZW-35 withstands extreme environmental stresses—from –40°C arctic conditions to 95% humidity tropical climates—without performance degradation. Critical technical advantages include ferroresonance resilience (1.9× Un for 30 s), dual indoor/outdoor rating, and compact form factor enabling seamless integration into modern switchgear. With rigorous type testing, routine verification protocols, and a preventive maintenance strategy aligned with IEC 60270 and IEEE C57.13, this VT delivers unmatched accuracy, safety, and lifecycle value for utilities, industrial operators, and renewable energy developers worldwide.