dry-type air-core reactor

Dry air-breathing reactor

I. Product Overview

Dry hollow series reactors are the primary specialized equipment for reactive power compensation and power quality management in power systems. They are primarily used in parallel capacitor bank circuits at 10 kV and 35 kV, forming a "capacitive reactance" compensation branch in series with the capacitors. Their primary function is to limit the capacitor bank's turn-on surge current, suppress the amplification of network harmonics, reduce overvoltage on circuit breakers, and protect capacitors and switching equipment.

This product overcomes the technical limitations of traditional iron-core reactors. It features a completely dry design, without iron cores or hollow windings, and is manufactured using vacuum casting with epoxy resin, using air as the insulating and cooling medium. This completely eliminates the risks of oil leakage and explosion typical of equipment immersed in oil, and also avoids problems of magnetic saturation, flux leakage heating, and excessive noise in iron-core reactors.

II. Basic structure and operating principle

(I) Basic structural composition

This product features a modular, integrated design, with its main components consisting of six main parts: a vacuum-cast winding, upper and lower star frames, a high-strength support insulator, a terminal block, a grounding system, and optional external protection components. The design is scientifically sound, optimizing both mechanical strength and electrical performance.

Vacuum-cast winding: the main functional component, wound from multiple strands of oxygen-free copper wire, has a conductor surface coated with high-temperature insulating paint, and is vacuum-cast using epoxy resin to form a solid insulating cylinder. The winding has a multi-layer, segmented structure with heat dissipation channels between the layers, which not only provides insulating properties but also ensures effective natural heat dissipation.

Star frame: Welded from high-strength aluminum alloy sections, the surface is treated with anodic oxidation and anti-corrosion protection, ensuring light weight, high strength, and corrosion resistance. The frame is used to secure the winding ends and dissipate the electrodynamic force of a short circuit, ensuring that the winding does not deform or shift under the influence of a short circuit.

Support insulator: Made of high-strength rod-shaped epoxy fiberglass insulators with insulation class ≥H and mechanical bending strength ≥12 kN. It is used to support the winding and frame, provide high- and low-voltage insulation, and support the winding weight and short-circuit electrodynamic force.

Terminal block: made of tinned red copper with a contact resistance of ≤50 μOhm, equipped with high-strength insulating shields. Flexible connection method (bolt/crimp connection), suitable for high-voltage cables and busbars of various cross-sections.

Grounding system: Including grounding bolts, grounding copper busbars and star-type grounding terminals, it ensures reliable grounding of all equipment, eliminates induced voltage and ensures the safety of operation and maintenance personnel.

Outdoor Protection Components (Optional): Outdoor products feature UV and rain-resistant covers, water-resistant bases, and an IP54-rated 304 stainless steel housing for use in harsh outdoor environments.

(II) Operating principle

In the high-voltage shunt capacitor bank circuit, a dry air-core series reactor is connected in series with the capacitor, and three main functions are realized by using the inductive reactive characteristics of the reactor:

Current limiting effect: When a capacitor bank is short-circuited, an inrush current is generated, which is several or tens of times greater than the rated current. The reactor limits the peak inrush current using its own inductive reactance (typically, the inrush current can be limited to 5 times the rated current), preventing damage to equipment such as circuit breakers and capacitors caused by the inrush current.

Filtering effect: By selecting the appropriate reactance value (such as 4.5%, 6%, 12%), the capacitor-reactance branch provides low impedance to certain harmonics (3rd, 5th, 7th), injects harmonic current into the branch to suppress harmonics, and prevents overheating and damage to capacitors caused by the amplification of harmonics in the network.

Voltage regulation effect: When a capacitor bank switches, a switching overvoltage is generated. The reactor's inductive reactance can smooth out the rate of overvoltage rise, reduce its amplitude, and protect the insulation of electrical equipment in the circuit.

III. Technical characteristics and parameters (full coverage and customization) 

Key Characteristics | Parameter Category | Detailed Description

Rated voltage: 10kV, 20kV, 35kV (can be changed to 66kV). Suitable for the main voltage levels of China's high-voltage power systems; customized models can meet the needs of specific power systems.

The rated current range is from 50 A to 1000 A (covering the entire range), precisely matched to the compensation capacity of the capacitor bank, allowing for individual customization and standardized series production.

Insulation class: F (155℃), H (180℃). Class H insulation standard is applicable to high-temperature environments; class F insulation meets standard application scenarios and provides the best value for money.

Construction: Dry hollow core radiator, fully vacuum molded with epoxy resin; coreless, oil-free, air-insulated for cooling; outdoor type, with special protective design.

Cooling method: natural air cooling (EVO), forced air cooling (FAC, optional). Natural air cooling is used in most cases; forced air cooling is applied under special conditions such as high load and high altitude.

Energy dissipation class: standard type, low dissipation type (adjustable). The energy dissipation of the low dissipation type is 15-25% lower than that of the standard type, resulting in greater energy savings in long-term use.

The noise level is ≤ 45 dB (under nominal conditions, at a distance of 1 meter), excluding magnetostrictive noise. This is significantly lower than that of an iron-core reactor (≤ 65 dB), and is suitable for quiet environments.

Short circuit withstand capacity: Withstands short circuit current 20 times the rated current for 2 seconds.

Protection level: IP30 for indoors, IP54 for outdoors (IP65 can be configured). IP30 prevents the ingress of foreign objects; IP54 protects against rain and dust; IP65 is suitable for extreme conditions such as coastal salt fog and heavy rain.

Working ambient temperature: -40℃ to +85℃; Humidity: ≤95% (non-condensing); Altitude: ≤4000 meters (parameters may change for higher altitudes). It can adapt to various harsh environments such as extreme cold, high temperature, high humidity, high altitude and salty fog.

Service life ≥ 30 years; epoxy resin insulation layer has anti-aging and anti-ultraviolet properties; oxygen-free copper windings are corrosion resistant.

Performance standard: GB/T 1094.6, GB/T 17004, IEC 60076-6, DL/T 840. Full compliance with national, industry and international standards, with controlled and traceable quality.

IV. Main advantages of the product

(1) Outstanding electrical performance, accurate and stable operation

- No magnetic saturation, high inductance linearity: the iron-core design eliminates the phenomenon of magnetic saturation; the inductance value remains stable in the range of rated current up to short-circuit current (linear error ≤ ±3%), which ensures the optimal operating state of the compensation system.

Low losses, high energy efficiency: windings made of multi-strand oxygen-free copper conductors reduce skin-effect losses; vacuum-cast epoxy resin provides a dense insulating layer with extremely low losses, below the established national standard.

(2) Excellent mechanical strength, high impact resistance

- Solid windings, short-circuit and electromagnetic shock protection: The windings formed by vacuum casting of epoxy resin have a robust structure and can withstand a short circuit of 20 times the rated current for 2 seconds without deformation or damage to the insulation.

- Earthquake and wind resistance: the lightweight structure, low center of gravity, and special earthquake-resistant foundation withstands earthquakes of magnitude 8 and typhoons of magnitude 12, making it suitable for challenging terrain.

(3) Environmental protection, safety and reliability, no operational risks

- Dry structure, fire resistance, explosion safety, eco-friendliness: air is used as thermal insulation and cooling medium, no oil or toxic gases are used, eliminating the risk of leaks and explosions; suitable for places sensitive to ignition sources.

- Low noise level: the main magnetostrictive element does not produce low-frequency noise; The noise level is ≤ 45 decibels under rated conditions, making it suitable for noise-sensitive locations.

- Excellent thermal insulation properties, resistance to aging and corrosion: the insulation material, made of epoxy resin obtained by vacuum casting, undergoes high-temperature curing; thermal insulation properties are stable in the temperature range from -40℃ to +85℃, making it suitable for harsh climatic conditions.

(4) Easy and efficient operation and maintenance, low life cycle cost.

Maintenance-free design: No oil tanks, tap changers, or vulnerable components are required; only an annual visual inspection and grounding check are required, reducing maintenance and labor costs.

V. Application Scenarios

Current limiting function in parallel-connected high-voltage capacitor banks: main application; used for reactive power compensation in 10kV/35kV substations, short-circuit current limiting, harmonic suppression and equipment protection.

Power quality management in renewable energy power plants: applied to wind power, photovoltaic power plants and power plants with integrated photovoltaic energy storage systems to suppress harmonics and stabilize voltage, ensuring uninterrupted connection to the grid.

- Harmonic control and reactive power compensation for industrial plants: specially designed for non-linear loads (such as frequency converters, electric arc furnaces, etc.) to compensate for reactive power and suppress harmonics.

- Modernization of urban distribution networks: applied to new or modernized reactive power compensation substations to solve short-circuit current and harmonic problems, thereby improving the quality of power supply.

- Special power supply systems for operation in high-altitude conditions, coastal zones, low temperatures and aggressive chemical environments, ensuring long-term stable operation.