Solid-State Transformer(SST)

Also known as power electronic transformers, solid-state transformers (SSTs) are advanced smart power equipment that replace traditional line-frequency electromagnetic transformers by leveraging power electronics conversion technology and high-frequency isolation technology. Discarding bulky iron-core structures, SSTs integrate multiple functions such as voltage transformation, electrical isolation, and AC/DC power conversion, making them one of the core equipment types in modern power systems.

Their working principle typically adopts a three-stage topology: First, the primary-side rectification stage converts line-frequency AC power into DC power. Then, electrical isolation and voltage amplitude regulation are achieved through a high-frequency transformer, which significantly increases the operating frequency and reduces the equipment size. Finally, the secondary-side inversion stage converts the DC power into AC power of the required specifications, enabling flexible power conversion and stable output.

SSTs have a wide range of application scenarios, primarily used for renewable energy grid integration—such as photovoltaics and wind power—to accommodate the intermittent generation characteristics of renewables. They are also suitable for hybrid AC/DC microgrids, energy storage power stations, electric vehicle fast-charging stations, and railway transit power supply systems. Additionally, they can be utilized in smart distribution networks to achieve precise voltage and power regulation as well as grid fault isolation.

Their advantages are prominent: their size and weight are far smaller than traditional transformers, resulting in high power density; they possess strong controllability, enabling the active optimization of power quality and harmonic suppression; and they support bidirectional AC/DC conversion, adapting to diversified power supply scenarios. Their disadvantages include complex structures, higher device costs, greater switching losses and thermal management pressures under high-frequency operation, as well as weaker high-voltage tolerance and overload capacity compared to traditional equipment, leading to higher maintenance requirements.

Overall, with the rapid iteration of wide-bandgap semiconductor devices such as silicon carbide (SiC) and gallium nitride (GaN), the challenges of losses and thermal dissipation in solid-state transformers are being gradually overcome. In the future, relying on their core advantages of intelligence, lightweight design, and multifunctionality, SSTs will gradually replace traditional line-frequency transformers and find widespread application in renewable energy grid integration, smart grids, transportation electrification, and other fields, boasting broad development prospects.

Data Center Solid-State Transformer

Also known as a power electronic transformer, a solid-state transformer (SST) is constructed from novel power semiconductor devices. The entire equipment adopts a high-frequency conversion architecture, with the core transformation function implemented via the integration of IGBTs and silicon carbide (SiC) power modules. Its core concept is the Power Electronic Building Block (PEBB). They typically adopt a modular series-parallel topology to achieve the flexible integration of different voltage levels, capacity levels, and power forms, facilitating flexible configuration across various application scenarios.

Charging-Type Solid-State Transformer

Also known as power electronic transformers, solid-state transformers are based on the core concept of Power Electronic Building Blocks (PEBBs). They typically adopt a modular series-parallel topology to achieve the flexible integration of different voltage levels, capacity levels, and power forms, facilitating flexible configuration across various application scenarios.

In charging scenarios, solid-state transformers (SSTs) can replace traditional line-frequency transformers and the internal AC-DC stages of charging modules, enabling direct medium-voltage connection. EV charging stations can then be established simply by pairing them with DC-DC modules on the back end. Compared to traditional solutions, the comprehensive charging efficiency of the station is improved by approximately 3 percentage points, which extends the equipment's full life-cycle return and provides higher operational reliability.

The optical-storage-charging DC-coupled solution discards the traditional 380V AC-coupled architecture and can replace conventional power conversion systems (PCS) and PV inverters, thereby improving the comprehensive utilization rate of photovoltaics and energy storage. The DC-coupled control logic is simple, requiring only voltage regulation. It completes all-DC integration in coordination with DC energy storage cabinets and photovoltaic maximum power point tracking (MPPT), further enhancing overall system efficiency.

High-Speed Service Area Integrated Solution: During holidays, the loads on both sides of a service area are often unbalanced. By utilizing SSTs to build flexible interconnection cubicles and connecting the power service areas on both sides via a medium-voltage DC bus, power supply capacity can be shared between them, effectively doubling the overall power supply capability.

After flexible interconnection, the associated charging piles can expand their charging capacity to 1.5 times the original. For example, a traditional 1.25 MW transformer can only support 20 charging parking spaces, but with an SST, this can be expanded to 30–40 spaces, stabilizing load operation through capacity mutual assistance. At the same time, the DC bus can be integrated with distributed photovoltaic and energy storage equipment in the service area, enabling the mutual flow and circulation of regional green energy.

Quality Assurance & Core Process：

1. High-Permeability Grain-Oriented Electrical Steel

We utilize Hi-B high-permeability grain-oriented (HPGO) electrical steel—the same grade specified by TBEA and CHINT—as the transformer core material, with standard nominal thicknesses of 0.23 mm and 0.27 mm. Core laminations are manufactured using high-precision cutting equipment to guarantee a burr height of ≤0.02 mm. The assembly incorporates a precision step-lap lamination structure, maintaining optimal clamping pressure without imparting excessive mechanical stress to the electrical steel, combining high-B steel characteristics with an optimized magnetic flux density.

2. High-Conductivity Winding Conductors & Core-Coil Assembly

High-conductivity electrolytic copper or aluminum conductors are selected based on transformer capacity, voltage class, and loss requirements. Incoming materials undergo stringent quality inspections for dimensions, electrical resistance, surface quality, and traceability. During the winding process, conductor tension, winding height, layer insulation, and conductor positioning are precisely controlled to ensure resistance consistency and mechanical stability, thereby minimizing load losses and temperature rise during operation.

During core-coil active part assembly, coil height, axial clamping force, radial support, and spacer block positioning are precisely controlled. Proper mechanical clamping prevents coil displacement during transport, normal operation, and short-circuit conditions. Meanwhile, clamping forces are strictly regulated to avoid excessive stress on conductors and insulation materials. Our mechanical design accounts for both radial and axial electromagnetic forces, safeguarding short-circuit withstand capability and long-term dimensional stability.

3. Advanced Insulation System (Oil-Immersed & Dry-Type)

For oil-immersed transformers, we utilize high-grade insulation materials, including Kraft paper, thermally upgraded paper, pressboard, and transformer-grade laminated board. For dry-type transformers, we employ DMD, NMN, Nomex, fiberglass, and epoxy resin systems. Insulation thickness, overlap width, oil duct dimensions, electrical clearances, and mechanical positioning are strictly regulated. All insulation materials are stored under climate-controlled conditions to minimize moisture absorption and contamination, ensuring stable dielectric strength and long-term insulation reliability.

4. Controlled Vacuum Drying

We apply a controlled drying curve regulated by temperature, vacuum level, and duration parameters, rather than relying on fixed cycle times. The process comprises controlled pre-heating, evacuation, primary drying, and final soak phases, with continuous temperature and vacuum monitoring and logging. End-point determination is based on validated process criteria and moisture limits. This process minimizes residual moisture in cellulose insulation, maximizing dielectric strength, retarding insulation aging, and extending overall service life.

5. Vacuum Epoxy Resin Casting

For cast-resin dry-type transformers, we utilize controlled vacuum casting technology. Resin-to-hardener ratio, material temperature, vacuum level, mixing time, pouring conditions, and curing temperatures are strictly regulated. Vacuum degassing minimizes micro-voids prior to pouring, while controlled curing ensures stable mechanical and thermal properties. Finished coils undergo thorough visual and electrical inspections, including routine partial discharge (PD) testing. This process eliminates internal voids, ensuring reliable insulation performance throughout the transformer's service life.

6. Clean Assembly & Torque Control

Final assembly takes place in a controlled environment to minimize contamination from dust, metallic particles, and foreign objects. Critical components are inspected for cleanliness, dimensional accuracy, and insulation condition. Electrical clearances, lead routing, grounding connections, and mechanical supports are rigorously controlled throughout assembly. Critical bolted joints are tightened to specified torque values using calibrated equipment and fully logged. Prior to sealing the tank or enclosure, a thorough internal inspection ensures no tools, loose parts, or foreign material remain.

7. 100% Factory Routine Testing

Every transformer undergoes 100% routine testing prior to dispatch, complying with applicable IEC standards, approved technical specifications, and customer requirements. Standard test routines include winding DC resistance, voltage ratio, vector group verification, no-load loss and current, load loss and short-circuit impedance, applied voltage withstand, and induced overvoltage withstand tests. Special tests—such as partial discharge (PD), dissipation factor (tan δ), or sweep frequency response analysis (SFRA)—are conducted upon request. Each unit is assigned a unique serial number linked to its material records, manufacturing data, and final test reports, ensuring end-to-end traceability.

FAQs about Dry-type Transformer:

1. What are the specific application environments where international standards strictly mandate the use of dry-type transformers instead of oil-immersed ones?

• Answer: According to international safety codes (such as IEC and IEEE standards), indoor locations with strict fire safety, explosion protection, and environmental requirements—such as high-rise buildings, underground commercial complexes, hospitals, data centers, and subway stations—prohibit oil-filled equipment. Dry-type transformers, being fire-resistant and pollution-free, serve as the mandatory compliant solution for these zones.

2. How do high-grade vacuum cast resin dry-type transformers maintain reliable insulation performance in high-humidity or tropical coastal environments?

• Answer: High-end cast resin transformers utilize fully automated vacuum overall casting processes where the high- and low-voltage windings are hermetically encapsulated in dense epoxy resin. This completely blocks moisture and airborne salinity, allowing the equipment to operate stably in high-humidity ambient conditions and enabling immediate re-energization after a shutdown without requiring complex pre-drying.

3. How do dry-type transformers withstand severe short-circuit electromagnetic forces in demanding utility or industrial grids?

• Answer: Because short-circuit events generate massive electrodynamic forces, structural integrity is critical. Top-tier dry-type units utilize precision-wound structures combined with high-strength epoxy glass cloth spacer bars and an elastic compression system, cured through a multi-stage thermal process to achieve exceptional mechanical strength against radial and axial short-circuit stresses.

4. Why is maintaining an extremely low partial discharge (PD) level critical for the long-term operational reliability of export-grade dry-type transformers?

• Answer: Partial discharge is a primary indicator of localized insulation degradation under high electric field stress. Advanced manufacturing techniques thoroughly expel microscopic inter-turn voids during vacuum casting, keeping partial discharge levels strictly controlled (typically (le 10 ext{ pC})). This minimizes long-term thermal-electrical aging and extends the operational life of the asset.

5. Can dry-type transformers operate safely under overload conditions, and what are the limitations of forced air cooling (AF)?

• Answer: Under standard natural air cooling (AN), dry-type transformers handle rated capacity continuously. When equipped with a forced air cooling (AF) system, short-term capacity can typically be boosted by up to 50%. However, sustaining heavy overloads beyond thermal design limits accelerates insulation degradation, requiring active management via embedded temperature monitoring systems.

6. How is transformer audible noise managed to meet strict international municipal noise-emission regulations for indoor commercial and residential areas?

• Answer: Transformer noise primarily stems from core magnetostriction under alternating magnetic flux. Premium units mitigate this by utilizing high-permeability grain-oriented silicon steel or optimized core-clamping structures to lower baseline vibration. For noise-sensitive environments (e.g., corporate offices, luxury residential towers), acoustic enclosures or external vibration isolators are deployed.

7. What is the standard configuration and functional logic of the temperature control and protection system embedded in industrial dry-type transformers?

• Answer: Standard configurations include PT100 temperature sensors embedded directly into the three-phase windings to provide real-time thermal tracking. The intelligent controller automatically initiates cooling fans when winding temperature reaches preset warning thresholds, and triggers visual/audible alarms or trips the circuit breaker if critical temperature limits are breached.

8. How do maintenance requirements and total lifecycle costs for dry-type transformers compare against oil-immersed alternatives in international facilities?

• Answer: Because dry-type transformers eliminate insulating oil entirely, they completely remove the need for periodic oil sampling, dissolved gas analysis (DGA), fluid filtration, and leak mitigation checks. This drastically cuts routine upkeep, delivering near-maintenance-free operation and a lower total cost of ownership (TCO) over the asset lifecycle.

9. What specialized logistics, handling, and on-site storage protocols must be followed to prevent mechanical damage before commissioning?

• Answer: Due to the rigid nature of cast resin coils, long-distance transport and rigging require strict monitoring of shock acceleration limits to prevent micro-fissures or core shift. On-site storage must be in clean, dry indoor spaces protected from condensation and extreme thermal shock, and vertical lifting must strictly utilize engineered lifting lugs.

10. How do heavy non-linear industrial loads (such as variable frequency drives and rectifiers) impact the thermal performance and sizing of dry-type transformers?

• Answer: Non-linear loads introduce high-order harmonics that escalate stray eddy current losses in structural components and drive up winding hot-spot temperatures. When deploying dry-type units in harmonic-rich environments, engineers must evaluate the harmonic profile, specify K-factor compliance, or apply capacity derating to prevent premature thermal failure.

Quality Assurance & Core Process：

1. High-Permeability Grain-Oriented Electrical Steel

We utilize Hi-B high-permeability grain-oriented (HPGO) electrical steel—the same grade specified by TBEA and CHINT—as the transformer core material, with standard nominal thicknesses of 0.23 mm and 0.27 mm. Core laminations are manufactured using high-precision cutting equipment to guarantee a burr height of ≤0.02 mm. The assembly incorporates a precision step-lap lamination structure, maintaining optimal clamping pressure without imparting excessive mechanical stress to the electrical steel, combining high-B steel characteristics with an optimized magnetic flux density.

2. High-Conductivity Winding Conductors & Core-Coil Assembly

High-conductivity electrolytic copper or aluminum conductors are selected based on transformer capacity, voltage class, and loss requirements. Incoming materials undergo stringent quality inspections for dimensions, electrical resistance, surface quality, and traceability. During the winding process, conductor tension, winding height, layer insulation, and conductor positioning are precisely controlled to ensure resistance consistency and mechanical stability, thereby minimizing load losses and temperature rise during operation.

During core-coil active part assembly, coil height, axial clamping force, radial support, and spacer block positioning are precisely controlled. Proper mechanical clamping prevents coil displacement during transport, normal operation, and short-circuit conditions. Meanwhile, clamping forces are strictly regulated to avoid excessive stress on conductors and insulation materials. Our mechanical design accounts for both radial and axial electromagnetic forces, safeguarding short-circuit withstand capability and long-term dimensional stability.

3. Advanced Insulation System (Oil-Immersed & Dry-Type)

For oil-immersed transformers, we utilize high-grade insulation materials, including Kraft paper, thermally upgraded paper, pressboard, and transformer-grade laminated board. For dry-type transformers, we employ DMD, NMN, Nomex, fiberglass, and epoxy resin systems. Insulation thickness, overlap width, oil duct dimensions, electrical clearances, and mechanical positioning are strictly regulated. All insulation materials are stored under climate-controlled conditions to minimize moisture absorption and contamination, ensuring stable dielectric strength and long-term insulation reliability.

4. Controlled Vacuum Drying

We apply a controlled drying curve regulated by temperature, vacuum level, and duration parameters, rather than relying on fixed cycle times. The process comprises controlled pre-heating, evacuation, primary drying, and final soak phases, with continuous temperature and vacuum monitoring and logging. End-point determination is based on validated process criteria and moisture limits. This process minimizes residual moisture in cellulose insulation, maximizing dielectric strength, retarding insulation aging, and extending overall service life.

5. Vacuum Epoxy Resin Casting

For cast-resin dry-type transformers, we utilize controlled vacuum casting technology. Resin-to-hardener ratio, material temperature, vacuum level, mixing time, pouring conditions, and curing temperatures are strictly regulated. Vacuum degassing minimizes micro-voids prior to pouring, while controlled curing ensures stable mechanical and thermal properties. Finished coils undergo thorough visual and electrical inspections, including routine partial discharge (PD) testing. This process eliminates internal voids, ensuring reliable insulation performance throughout the transformer's service life.

6. Clean Assembly & Torque Control

Final assembly takes place in a controlled environment to minimize contamination from dust, metallic particles, and foreign objects. Critical components are inspected for cleanliness, dimensional accuracy, and insulation condition. Electrical clearances, lead routing, grounding connections, and mechanical supports are rigorously controlled throughout assembly. Critical bolted joints are tightened to specified torque values using calibrated equipment and fully logged. Prior to sealing the tank or enclosure, a thorough internal inspection ensures no tools, loose parts, or foreign material remain.

7. 100% Factory Routine Testing

Every transformer undergoes 100% routine testing prior to dispatch, complying with applicable IEC standards, approved technical specifications, and customer requirements. Standard test routines include winding DC resistance, voltage ratio, vector group verification, no-load loss and current, load loss and short-circuit impedance, applied voltage withstand, and induced overvoltage withstand tests. Special tests—such as partial discharge (PD), dissipation factor (tan δ), or sweep frequency response analysis (SFRA)—are conducted upon request. Each unit is assigned a unique serial number linked to its material records, manufacturing data, and final test reports, ensuring end-to-end traceability.

Youth Transformer Co.,Ltd.