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JDZW-10R 11kV Cast-Resin Voltage Transformer for Substation Metering and Protection – IEC 61869-3 Certified
Introduction to the JDZW-10R Voltage Transformer
The JDZW-10R is a single-phase, indoor/outdoor rated, cast-resin insulated voltage transformer (VT) designed for accurate voltage transformation in medium-voltage power systems operating at nominal system voltages of 11kV (IEC standard) or 10kV (domestic Chinese grid equivalent). This device serves critical roles in both metering and protective relaying applications by providing galvanically isolated, scaled-down secondary voltages proportional to the primary system voltage. The transformer’s construction leverages vacuum pressure impregnation (VPI) epoxy resin technology, ensuring superior dielectric strength, mechanical robustness, and environmental resilience compared to traditional oil-immersed alternatives.
Operating Principle of Cast-Resin Insulation
Cast-resin insulation in the JDZW-10R employs a cycloaliphatic epoxy resin system cured under controlled temperature and vacuum conditions. This process eliminates air voids and moisture ingress pathways, resulting in a homogeneous solid dielectric with high partial discharge inception voltage (>20 kV at 1.2 Ur). The primary and secondary windings are fully encapsulated within this resin matrix, which bonds directly to the GOES (grain-oriented electrical steel) core laminations. This monolithic structure provides excellent thermal conductivity (0.2–0.3 W/m·K), enabling efficient heat dissipation during continuous operation at rated load. Unlike oil-filled units, there is no risk of leakage, fire hazard, or maintenance-intensive oil sampling, making the JDZW-10R suitable for urban substations, indoor switchgear, and environmentally sensitive zones.
Advantages Over Oil-Immersed Designs
The elimination of insulating oil confers multiple operational benefits. First, the fire point exceeds 500°C, satisfying IEC 61869-3 requirements for non-flammable equipment in confined spaces. Second, the absence of breathing mechanisms prevents moisture absorption, maintaining stable dielectric properties over decades. Third, the compact footprint—typically 30% smaller than equivalent oil units—reduces spatial requirements in ring main units (RMUs) and prefabricated substations. Additionally, cast-resin VTs exhibit lower lifecycle costs due to zero oil replacement, no need for conservator tanks, and immunity to oil degradation from oxidation or thermal aging. Field data from Chinese distribution networks indicate a mean time between failures (MTBF) exceeding 200,000 hours for properly installed JDZW-10R units.
Typical Applications Overview
The JDZW-10R is engineered for dual-purpose use: precision metering (accuracy class 0.2 or 0.5) and reliable protection (accuracy class 3P or 6P per IEC 61869-3). It is commonly deployed in 11kV/10kV primary distribution substations feeding commercial complexes, industrial parks, and municipal infrastructure. Its robust design supports operation in harsh environments, including coastal areas with salt fog (Class II pollution per IEC 60815) and high-altitude regions up to 2000 meters above sea level. The unit’s secondary outputs typically feed digital energy meters, multifunction relays (e.g., overvoltage, undervoltage, directional earth fault), and SCADA voltage monitoring channels.
Technical Specifications
The JDZW-10R adheres strictly to the performance envelopes defined in IEC 61869-3 and GB/T 20840.3. Below is a comprehensive specification table followed by service condition parameters.
| Parameter | Value |
|---|---|
| System Voltage (Ur) | 11 kV (IEC) / 10 kV (GB) |
| Rated Primary Voltage (Up) | 11 / √3 kV = 6.35 kV (phase-to-ground) |
| Rated Secondary Voltage (Us) | 100 / √3 V or 100 V (user-selectable) |
| Voltage Ratio | 6350 / 57.7 V or 6350 / 100 V |
| Accuracy Class (Metering) | 0.2, 0.5 |
| Accuracy Class (Protection) | 3P, 6P |
| Rated Output (per burden) | 10–100 VA (standard); up to 150 VA optional |
| Insulation Level (LI/AC) | 75 kV / 28 kV (1.2/50 µs lightning impulse & 1-min power frequency) |
| Short-Time Thermal Current | 100 A for 1 s (at rated frequency) |
| Core Material | GOES M4 grade, 0.3 mm thickness, step-lap joints |
| Resin System | Cycloaliphatic epoxy, VPI process, UL 94 V-0 rated |
| Weight | Approx. 35 kg |
| Dimensions (H×W×D) | 580 × 220 × 220 mm |
Standard Service Conditions
The JDZW-10R is rated for continuous operation under the following ambient conditions as per IEC 61869-1: ambient temperature range of –25°C to +40°C (with 24-hour average ≤35°C), relative humidity up to 95% at 25°C, and installation altitude ≤1000 m (derating required above 1000 m per IEC 60071-1). For altitudes between 1000–2000 m, the power frequency withstand voltage must be reduced by 1% per 100 m above 1000 m. The unit is designed for three-phase systems with effectively grounded neutrals (solidly grounded or low-resistance grounded), where phase-to-ground voltage is the reference for insulation coordination.
Accuracy and Burden Characteristics
Accuracy performance is validated at 80–120% of rated primary voltage and at specified burdens. For class 0.2, composite error must not exceed ±0.2% in ratio error and ±8 minutes in phase displacement at 100% Ur and rated burden. Protection class 3P requires ratio error ≤±3% and phase error ≤±120 minutes under fault conditions (up to 190% Ur for 30 seconds). The transformer maintains accuracy even with mixed burdens (e.g., one winding feeding a meter, another a relay), provided total VA does not exceed rated output. Burden impedance must be ≥ cos φ = 0.8 lagging for metering classes.
Typical Applications
The JDZW-10R’s dual-certification (IEC and GB) and robust construction enable deployment across diverse power infrastructure segments.
Substation Secondary Metering
In 11kV primary substations, the JDZW-10R supplies scaled voltages to revenue-class energy meters (e.g., IEC 62053-22 compliant). Its class 0.2 accuracy ensures billing precision within ±0.2%, critical for utility-grade metering. The transformer is typically installed on the busbar side of circuit breakers, with secondary wiring routed through shielded cables to metering cabinets. In China, this configuration complies with DL/T 448 technical management regulations for electric energy metering devices. The cast-resin body resists tracking from pollution, ensuring long-term stability in outdoor metering kiosks exposed to industrial contaminants.
Industrial Power Distribution
Within manufacturing facilities, the JDZW-10R monitors voltage quality for sensitive processes (e.g., semiconductor fabrication, data centers). It interfaces with power quality analyzers to detect sags, swells, and harmonics. The unit’s high short-circuit withstand capability (100 A for 1 s) protects against damage during downstream faults. In arc furnace plants or welding shops with high harmonic distortion, the GOES core minimizes additional losses from 3rd and 5th harmonics, preserving accuracy. Installation inside metal-enclosed switchgear (e.g., KYN28A-12) leverages the VT’s compact size and non-flammability.
Renewable Energy Integration
Solar PV and wind farms utilize the JDZW-10R for grid synchronization and anti-islanding protection. During grid faults, the VT must maintain output integrity to enable correct operation of distance relays and voltage-controlled inverters. The 6P protection class ensures reliable operation up to 190% Ur during transient overvoltages common in renewable-rich grids. In desert solar installations, the UV-stable resin housing withstands prolonged solar exposure without cracking, while the absence of oil prevents viscosity-related performance drift in extreme diurnal temperature swings (–10°C to +50°C).
Rural and Suburban Distribution Networks
In remote 10kV feeders, the JDZW-10R enables remote voltage monitoring via RTUs or smart meters. Its maintenance-free design reduces operational costs in hard-to-access locations. The unit often pairs with pole-mounted reclosers for sectionalizing and fault location. In humid tropical climates (e.g., Southeast Asia), the hydrophobic resin surface sheds water, preventing flashovers during monsoon seasons. Field trials in Guangxi province demonstrated 99.98% availability over five years with zero insulation-related failures.
Compliance with International Standards
The JDZW-10R is engineered to satisfy both global and domestic regulatory frameworks, ensuring interoperability and safety.
IEC 61869-3 Compliance Details
IEC 61869-3 specifies requirements for electromagnetic voltage transformers for measurement and protection. The JDZW-10R meets all clauses regarding insulation coordination (Section 5), accuracy limits (Table 3), temperature rise (≤60 K for resin, measured by resistance method), and short-circuit performance. Type tests include power frequency withstand (28 kV for 1 min), lightning impulse (75 kV positive/negative), partial discharge (<10 pC at 1.2 Ur/√3), and temperature rise (tested at 1.2× rated burden). Routine tests per Section 10 include turns ratio verification (±0.2% tolerance), polarity check, and insulation resistance (>1000 MΩ at 2500 V DC).
Alignment with GB/T 20840.3
GB/T 20840.3 is the Chinese national adoption of IEC 61869-3 with minor modifications. Key differences include: (1) mandatory requirement for 10kV system voltage labeling alongside 11kV; (2) stricter partial discharge limits (<5 pC at 1.2×10/√3 kV); and (3) additional seismic test requirement (0.2g horizontal acceleration) for units destined for earthquake-prone regions like Sichuan. The JDZW-10R undergoes full type testing at CNAS-accredited labs (e.g., China Electric Power Research Institute) to obtain the CQC certification mark, which is required for grid procurement in China.
Testing and Certification Requirements
Certification involves three test tiers: type tests (once per design), sample tests (per production batch), and routine tests (100% units). Type tests validate design integrity; sample tests verify material consistency; routine tests ensure individual unit quality. Critical acceptance criteria include: insulation resistance ≥1000 MΩ, ratio error within class limits, and no visible damage after mechanical vibration test (10 Hz–150 Hz sweep, 0.5g amplitude). All test reports must reference IEC 61869-1 general requirements and IEC 61869-3 specific VT clauses.
On-Site Testing Procedures
Post-installation commissioning tests verify integrity and performance before energization.
Insulation Resistance Test
Using a 2500 V DC megohmmeter, measure insulation resistance between primary winding and ground, secondary windings and ground, and primary-to-secondary. Acceptance criterion: ≥1000 MΩ at 20°C. Correct for temperature using RT2 = RT1 × 2(T1–T2)/10. Low readings indicate moisture ingress or resin cracking. Perform before and after dielectric tests to detect insulation degradation.
Turns Ratio Test
Apply 100–200 V AC to the primary and measure secondary voltage. Calculate actual ratio = Vp/Vs. Compare to nameplate ratio (e.g., 6350/57.7 = 110). Tolerance: ±0.2% for metering class, ±0.5% for protection class. Use a dedicated ratio tester (e.g., Omicron CT Analyzer) for automated comparison. Deviations >1% suggest inter-turn shorts or winding deformation.
Polarity Test
Verify reducing polarity per IEC 61869-3 Figure 4. Connect a 6–12 V battery momentarily between primary terminals (H1+, H2–). Observe secondary voltage polarity with a DC voltmeter: if X1 shows positive deflection when H1 is energized, polarity is correct. Incorrect polarity causes 180° phase shift, leading to metering errors or relay misoperation. Document results with oscillograms if possible.
Power Frequency Withstand Voltage Test
Apply 28 kV RMS at 50 Hz between primary and grounded secondary/core for 1 minute. Ramp up at ≤1 kV/s. No flashover or disruptive discharge permitted. Secondary windings must be short-circuited and grounded during test. This validates insulation integrity after transportation stresses. Reduce test voltage by 10% if performed on-site due to humidity effects.
Open-Circuit Characteristic Test
Gradually increase primary voltage from 0 to 190% Ur while measuring secondary voltage and excitation current. Plot Vs vs Iexc. Knee point should occur >150% Ur. Excessive excitation current (>10 mA at 100% Ur) indicates core saturation or shorted turns. This test is critical for protection-class VTs to ensure linear response during overvoltage faults.
Preventive Maintenance Guide
Although cast-resin VTs are largely maintenance-free, periodic checks extend service life and prevent unexpected outages.
Periodic Inspection Protocol
Conduct visual and thermographic inspections annually. Check for: (1) surface cracks or tracking marks on resin housing; (2) corrosion on terminal studs; (3) loose mounting bolts (torque: 25 N·m); (4) abnormal heating at connections (ΔT >10 K above ambient indicates high contact resistance). Clean housing with deionized water if salt or dust deposits exceed 0.1 mg/cm². Verify secondary wiring integrity—no frayed conductors or loose lugs.
Maintenance Intervals and Fault Diagnosis
Every 5 years, perform insulation resistance and turns ratio tests as baseline comparisons. Typical failure modes include: (1) moisture-induced partial discharge (evidenced by white powder residue near terminals); (2) core lamination delamination (audible humming at 100/120 Hz); (3) secondary winding open-circuit (zero output despite primary voltage). If ratio error exceeds 1%, replace the unit—field repair is not feasible due to monolithic resin encapsulation. Maintain a logbook recording all test results for trend analysis.
| Interval | Action |
|---|---|
| Annual | Visual inspection, IR thermography, terminal torque check |
| 5 Years | Insulation resistance, turns ratio, open-circuit test |
| After Major Fault | Full commissioning test suite |
| End of Life (25+ years) | Dielectric spectroscopy for aging assessment |
Conclusion
The JDZW-10R 11kV cast-resin voltage transformer represents a mature, field-proven solution for accurate voltage transformation in modern power systems. Its compliance with IEC 61869-3 and GB/T 20840.3 ensures global applicability while meeting stringent Chinese grid requirements. The use of GOES silicon steel cores minimizes core losses (<0.8 W/kg at 1.5 T, 50 Hz), contributing to high efficiency and thermal stability. The VPI epoxy resin encapsulation provides exceptional resistance to environmental stressors—including humidity, pollution, and UV radiation—eliminating the fire and environmental hazards associated with oil-filled units. With a design service life of 25–30 years under standard operating conditions, the JDZW-10R delivers exceptional lifecycle value through minimal maintenance needs and high reliability. Its dual accuracy classes (0.2/0.5 for metering; 3P/6P for protection) enable flexible deployment across utility substations, industrial facilities, and renewable energy sites. When installed and tested according to the procedures outlined in this document, the JDZW-10R consistently meets the demanding performance expectations of contemporary power system operators, supporting grid safety, revenue accuracy, and operational resilience. As distribution networks evolve toward smarter, more distributed architectures, the JDZW-10R’s robustness and precision will remain foundational to secondary system integrity.
Q1: Can the JDZW-10R operate on a 10kV system?
Yes. While rated for 11kV per IEC standards, the JDZW-10R is fully compatible with 10kV domestic systems (common in China). The primary insulation level (75/28 kV) exceeds requirements for 10kV systems (70/28 kV per GB 311.1), ensuring safe operation.
Q2: What is the maximum altitude rating?
Standard units are rated for ≤1000 m. For 1000–2000 m, apply altitude derating: reduce power frequency withstand voltage by 1% per 100 m above 1000 m. Custom designs are available for >2000 m.
Q3: Is the secondary winding grounded?
Per IEC 61869-3, the secondary winding must be grounded at one point (typically X2 terminal) to prevent capacitive voltage rise during open-circuit conditions. Never leave secondaries floating.
Q4: What burden is required for class 0.2 accuracy?
Class 0.2 is guaranteed only when connected to a burden within 25–100% of rated VA (e.g., 25–100 VA for a 100 VA unit) and power factor ≥0.8 lagging. Undersized burdens degrade accuracy.
Q5: Can multiple secondaries be loaded simultaneously?
Yes, provided the vector sum of all connected burdens does not exceed the rated output. Each secondary must meet its respective accuracy class burden requirements independently.