SG(B)11-RL Series Three-dimensional Wound Core Class C Insulated Dry-type Transformer

Product Introduction
The Class C wound core SGB11 series non-encapsulated dry-type power transformers are manufactured using the UL-listed NOMEX® insulation system from the United States. They feature a more reasonable structure, high safety and reliability, environmental friendliness and energy efficiency, fire and explosion protection, antifouling, dustproof and moisture-proof properties, strong overload capacity, compact size and easy maintenance. With advanced design, rational structure and attractive appearance, all key performance indicators of the products exceed domestic standards. They are ideally suited for environments with high fire protection requirements, large load fluctuations and frequent overload operation, and are applicable to high-rise residential buildings, airports, stations, ports, subways, hospitals, power plants, metallurgical industries, shopping malls, densely populated residential areas, as well as petrochemical plants, nuclear power plants, nuclear submarines and other facilities.
Product Advantages
Safety
The transformers adopt a Class C insulation system based on NOMEX® paper from DuPont, USA, with a thermal class of 220℃, featuring flame resistance, self-extinguishing properties, non-toxicity and fireproofing.
Utilizing advanced VPI equipment and vacuum pressure impregnation technology, the UL-certified high-quality impregnating varnish forms a hybrid insulation system with NOMEX® solid paper, delivering outstanding moisture resistance. This enables the non-encapsulated open-type dry-type transformers to resist moisture ingress and provides:
High tensile strength and tear resistance.
Excellent abrasion resistance and cut-through resistance.
High compressive strength, ensuring the stability and robustness of the insulation structure under short-circuit or other mechanical stresses.
Outstanding moisture resistance, antifouling, dustproof, mildew-proof and salt-fog resistance of the products.
Compact Size and Light Weight
With DuPont NOMEX® paper as the main insulation material and part of the hybrid insulation system at the transformer’s hottest spot, the products feature a high thermal class. The non-encapsulated open-type coil structure delivers superior heat dissipation, resulting in a smaller size and lighter weight for the transformer.
NOMEX® paper, the main insulation material of the transformer, has a very low dielectric constant (1.5–2.5), close to that of ambient air (≈1). Under the same electric field strength, NOMEX® paper can withstand higher electric stress compared with other insulation materials, allowing air to bear lower electric stress. This reduces the required air insulation clearance, enabling smaller dimensions for relevant components and further minimizing the overall outline size of the transformer.
Product Structure
Three-Dimensional Triangular Wound Core
Adopting a three-dimensional triangular structure, the core arrangement is combined in a more rational manner, with three identical single frames assembled to form a three-dimensional equilateral triangle. This achieves fully symmetrical and equal-length three-phase magnetic circuits, ensuring balanced three-phase power supply, while greatly reducing magnetic reluctance and significantly lowering excitation current and no-load loss.
Each single frame is continuously wound from several trapezoidal strips with continuously varying widths. During winding, a special winding machine automatically displaces the strips synchronously to one side for asymmetric winding, forming a cross-section with a 30° inclination angle, thus ensuring a good mating surface when the three single frames are assembled.
All assembly fixtures are specially designed to prevent deformation of the wound core during annealing, shaping and other processes.
The advantages of this structure are:
Remarkable energy-saving effect: The three-dimensional triangular wound core is seamless, meaning there are no high-energy-consumption zones. It fully exploits the high magnetic permeability of high-quality core materials, greatly reducing losses caused by air gaps formed at joints.
Miniaturization: Featuring a high space utilization factor, the transformer adopts a triangular structure, resulting in a smaller volume than conventional transformers, with a compact structure, attractive appearance and small footprint.
Low noise: As the three-dimensional triangular wound core is wound sequentially from several types of trapezoidal strips, the silicon steel strips are tightly wound, and their magnetic conduction direction is fully consistent with the magnetic circuit direction of the core. This leads to minimal vibration during operation, eliminating noise caused by discontinuous magnetic circuits in laminated cores and minimizing noise to the greatest extent.
Windings
The high-voltage coils use low-oxygen, high-conductivity oxygen-free copper wires insulated with NOMEX® paper, while the low-voltage coils adopt a foil-type (copper foil) structure, produced by a special three-dimensional triangular foil winding machine.
The high-voltage coils are of pie-type structure with comb-shaped spacers to enhance heat dissipation and short-circuit withstand capability.
Foil-type coils eliminate the helix angle of wire-wound coils, improving short-circuit withstand and lightning impulse resistance. Copper foil and terminal bars are welded on a welding platform using a hydrogen arc welder, producing firm and reliable welds. The terminal bars are locked with special fixtures to prevent displacement during coil winding. The winding machine is equipped with a tension device, and the number of turns is controlled by a computer, ensuring high coil precision and compliance with dimensional process requirements. One or more air ducts can be configured for rapid heat dissipation to meet temperature rise requirements.
The above design improves heat dissipation capacity and achieves the goals of enhancing mechanical strength and electrical strength.
Core Insulation
Both interlayer insulation and end insulation adopt NOMEX® paper. After multiple baking processes, vacuum pressure impregnation and curing, the coil forms an integral unit.
The core assembly adopts a cushion block compression structure, equipped with tension screws and pressure nails to ensure sufficient axial compression force for the coil.
High-performance engineering insulation materials are used as supporting plates between the low-voltage coil and the iron core, which not only fix the coil but also tighten the iron core. Silicone gaskets placed between the coil and pressure blocks securely compress the coil while creating an elastic buffer zone between the iron core clamps and the coil, reducing transformer noise.
Vacuum Pressure Impregnation
Advanced VPI equipment and vacuum pressure impregnation technology are adopted. The UL-listed high-quality German Altana impregnating agent and American NOMEX® paper form a hybrid insulation system, aiming to improve the product’s moisture resistance and structural integrity, as well as further reduce product noise.
■ Technical Parameters
Performance Parameters of SG(B)11－RL