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SZ Series Three Phase OLTC Oil Immersed Power Transformer
Distribution Transformer

SZ Series Three Phase OLTC Oil Immersed Power Transformer

The SZ Series On-Load Tap-Changing (OLTC) oil-immersed power transformer is engineered for modern medium- and high-voltage distribution systems that require continuous voltage regulation under dynamic load conditions.

Designed for voltage levels up to 35kV and distribution networks up to 2500kVA and above, the SZ series enables real-time tap adjustment without interrupting power supply, ensuring stable operation in critical and load-sensitive environments.

Built with a fully sealed tank structure and advanced thermal management design, the transformer delivers long-term operational stability with reduced maintenance requirements. It is widely applied in renewable energy integration, urban substations, industrial facilities, and data-critical infrastructure.

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    Scope of Application

    Wind & Solar Power Plants

    The transformer effectively manages voltage fluctuations caused by intermittent renewable energy generation, ensuring smooth grid integration and improved power quality stability.

    Scope of Application (1)

    Urban Distribution Networks

    Designed for residential and commercial load variability, the SZ series supports stable voltage regulation during peak demand cycles and complex load transitions.

    Scope of Application (3)

    Data Centers & Precision Industry

    Provides high-reliability power supply for sensitive electronic systems, helping minimize operational risk a

    Scope of Application (2)

    Product Description

    • 1 - On-Load Voltage Regulation: Equipped with a vacuum-type OLTC system enabling continuous voltage adjustment under full load conditions without power interruption.
    • 2 - High-Efficiency Magnetic Design: Optimized core structure reduces no-load losses and improves long-term energy efficiency across the transformer lifecycle.
    • 3 - Advanced Thermal Performance: High-quality transformer oil and optimized tank design ensure efficient heat dissipation under varying load conditions.
    • 4 - Short-Circuit Strength Design: Reinforced winding and clamping structure improve mechanical stability under external fault conditions and electrical stress.
    • 5 - Intelligent Voltage Control: Compatible with automatic voltage regulation systems that continuously monitor and adjust output voltage within defined tolerance limits.
    • 6 - Fully Sealed Maintenance Design: Corrugated tank structure isolates internal components from environmental contamination, significantly reducing maintenance requirements.
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    Product Features

    On-Load Tap Changer (OLTC)

    On-Load Tap Changer (OLTC)

    Live tap switching under full-load conditions ensures continuous power delivery, eliminating production losses or data interruptions associated with de-energized adjustments.
    Energy-Efficient Magnetic Circuit

    Energy-Efficient Magnetic Circuit

    The core structure is optimized to minimize hysteresis and eddy-current losses, reducing no-load power consumption and delivering measurable electricity cost savings over the transformer's operational lifespan.
    Vacuum Arc-Quenching Technology

    Vacuum Arc-Quenching Technology

    Vacuum interrupters suppress arc erosion at the tap contacts during switching operations, extending mechanical endurance to 100,000 cycles and reducing maintenance frequency.
    High Short-Circuit Withstand Strength

    High Short-Circuit Withstand Strength

    Integral winding compression and rigid bracing securely anchor each coil assembly, enabling the transformer to withstand the instantaneous thrust forces imposed by external short-circuit faults.
    Intelligent Voltage Regulation

    Intelligent Voltage Regulation

    An external digital controller continuously samples the secondary-side voltage and issues tap-change commands automatically, ensuring output voltage remains within the preset tolerance band without manual intervention.
    Sealed Maintenance-Free Tank

    Sealed Maintenance-Free Tank

    Primarily utilizes off-circuit tap changing with streamlined protection systems, minimizing routine maintenance requirements.

    Main parameters

    Rated Voltage and Capacity: 10kV/0.4kV, 35kV/0.4kV; capacity 630kVA–31500kVA; non-standard customization available

    OLTC Voltage Regulation Range: Standard ±8×1.25% (16-step regulation); wide-range regulation of ±10% or ±16% available for special operating conditions

    Cooling Method: Standard ONAN (Oil Natural Air Natural); ONAF (Oil Natural Air Forced) cooling available for long-term heavy-load operation

    Winding Connection Group: Standard Dyn11 (three-phase balanced connection); other connection groups available upon request

    Execution standards

    VCG211294761765
    IEC 60076
    International general standard for oil immersed power transformers
    IEC 60214
    Technical standard for on-load tap changes (OLTC)
    GB/T 6451
    Chinese national technical specification for three-phase oil immersed transformers
    GB 20052
    National energy efficiency limit standard for power transformers

    Technical advantages

    VCG211335853348

    Our manufacturing facility is equipped with advanced production and testing systems, including core cutting lines, automatic winding machines, vacuum drying equipment, and full electrical testing laboratories.

    Each transformer is produced under strict quality control procedures covering material selection, winding accuracy, insulation treatment, and final performance testing.

    Our products have been successfully applied in national grid projects, railway electrification systems, and international export markets including Russia, Australia, and Southeast Asia.

    Continuous engineering development ensures improved performance in dielectric strength, thermal stability, and short-circuit resistance, supporting long service life under demanding operating conditions.