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JDZW-35K 33kV Cast-Resin Voltage Transformer for Substation Metering and Protection – IEC 61869-3 Certified

Introduction to the JDZW-35K Voltage Transformer

The JDZW-35K is a single-phase, outdoor-rated, cast-resin insulated voltage transformer (VT) engineered for high-reliability applications in 33kV (IEC) / 35kV (domestic) electrical systems. Designed in strict compliance with IEC 61869-3 and GB/T 20840.3, this instrument transformer delivers precise secondary voltage signals for metering, protective relaying, control, and monitoring functions within utility substations and industrial power networks. Unlike power transformers that transfer bulk energy, VTs like the JDZW-35K operate under near no-load conditions, requiring exceptional accuracy, phase-angle stability, and long-term insulation integrity.

Operating Principle of Cast-Resin Insulation

The JDZW-35K employs vacuum pressure impregnation (VPI) epoxy resin technology to fully encapsulate its primary and secondary windings along with the GOES (grain-oriented electrical steel) magnetic core. During manufacturing, the wound core assembly is placed in a mold, evacuated to remove air pockets, and then flooded with a two-component epoxy resin under controlled pressure. The resin cures into a monolithic, void-free solid that provides superior dielectric strength, mechanical rigidity, and environmental resistance. This process eliminates partial discharge inception below 10 pC at rated voltage—well within IEC 61869-3 limits—and ensures stable performance across thermal cycles from –40°C to +40°C ambient. The absence of liquid insulation eliminates fire hazards, oil leaks, and maintenance associated with traditional oil-filled VTs, making it ideal for urban substations, indoor switchgear, and environmentally sensitive sites.

Advantages Over Oil-Immersed Designs

Compared to conventional oil-immersed VTs, the JDZW-35K offers significant operational and safety benefits. Its dry-type construction removes flammability risks, satisfying stringent fire codes in commercial complexes and underground installations. The epoxy matrix resists tracking, UV degradation, and pollution accumulation, enabling reliable service in coastal (salt fog), industrial (chemical), and desert (sand/dust) environments without periodic cleaning or oil testing. Additionally, the compact footprint—typically 30–40% smaller than equivalent oil units—reduces civil works costs and facilitates retrofitting in space-constrained substations. Crucially, the cast-resin design exhibits negligible aging under continuous overvoltage conditions up to 1.2 × U_n, ensuring decades of stable ratio and phase error performance without recalibration.

Typical Application Overview

The JDZW-35K is predominantly deployed in 33kV transmission and distribution networks where accurate voltage sensing is critical. Primary use cases include feeding revenue-class kWh meters in utility billing stations, supplying inputs to distance relays (e.g., impedance-based line protection), synchronizing generators during grid interconnection, and providing voltage references for power quality analyzers. Its robust construction supports both indoor GIS (gas-insulated switchgear) and outdoor AIS (air-insulated switchgear) configurations, with standard mounting options for pedestal, bracket, or direct busbar attachment. In renewable integration projects, such as solar farms or wind parks connected at 35kV, the JDZW-35K enables precise reactive power control and fault ride-through compliance per grid codes like IEEE 1547 or IEC 61400-21.

Technical Specifications

The JDZW-35K adheres to a rigorously defined set of electrical and mechanical parameters aligned with international and domestic standards. Below is a comprehensive specification table followed by environmental and operational constraints.

Standard Service Conditions

The JDZW-35K is rated for operation under IEC 60060-1 standard atmospheric conditions: ambient temperature range of –40°C to +40°C, relative humidity up to 100% (condensing permitted), and installation altitude ≤ 1000 m above sea level. For altitudes exceeding 1000 m, dielectric withstand voltages must be derated by 1% per 100 m increment above 1000 m, as per IEC 60071-2. The unit is designed for continuous operation at system voltages up to 1.05 × U_n and can tolerate transient overvoltages up to 1.2 × U_n for 30 seconds without degradation. Pollution degree is classified as III (medium conductivity dust or dry non-conductive pollution), suitable for most industrial and rural environments; for severe coastal or chemical zones, optional hydrophobic silicone coating is recommended.

Accuracy and Burden Performance

Accuracy classes define permissible errors under specified burdens and load conditions. For class 0.2, the voltage error must not exceed ±0.2% and phase displacement ≤ ±10 minutes at 25–100% of rated burden and 80–120% of rated voltage. Protection class 3P allows ±3% voltage error and ±120 minutes phase error under fault conditions (up to 1.9 × U_n). The rated output (e.g., 50 VA) represents the maximum apparent power the VT can deliver while maintaining accuracy; exceeding this burden increases ratio and phase errors nonlinearly. Designers must ensure total connected burden—including meter coils, relay inputs, and wiring resistance—does not surpass the VT’s rated output. For example, a 0.5-class JDZW-35K with 30 VA rating should not feed more than three 10 VA digital meters simultaneously.

Typical Applications

The JDZW-35K serves diverse roles across modern power infrastructure, leveraging its precision, reliability, and environmental resilience.

Substation Secondary Metering

In utility-owned 33kV/11kV distribution substations, the JDZW-35K provides the reference voltage for revenue metering at the high-voltage side. Paired with class 0.2S current transformers, it enables accurate billing for large industrial consumers or feeders. The VT’s low phase error (<5 minutes at 0.2 class) ensures minimal distortion in power factor calculations, critical for tariff structures involving reactive energy penalties. Installation typically involves mounting on the 33kV busbar with secondary leads routed through shielded cables to a secure metering cabinet, minimizing electromagnetic interference.

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