Petrochemical plants are classified as high-risk environments due to the presence of flammable gases, volatile liquids, and combustible dust, where even the smallest electrical spark or excessive heat can trigger catastrophic explosions or fires. As critical power supply equipment in petrochemical facilities, explosion-proof dry-type transformers play an irreplaceable role in ensuring the safe and stable operation of production lines, control systems, and auxiliary equipment. Unlike conventional dry-type transformers, those designed for petrochemical plants must meet stringent explosion-proof requirements, adapt to harsh operating conditions, and comply with global industry standards. This article details the key considerations in the design of explosion-proof dry-type transformers for petrochemical plants, covering explosion-proof structure, material selection, insulation design, thermal management, environmental adaptability, standard compliance, and intelligent monitoring, to provide a comprehensive design guide for ensuring operational safety and reliability.
The primary core of explosion-proof dry-type transformer design for petrochemical plants is the explosion-proof structure, which directly determines the equipment’s ability to prevent internal electrical sparks, arcs, or high temperatures from igniting external flammable media. The selection of explosion-proof types must be strictly based on the hazard level of the petrochemical plant’s operating area. According to international standards such as IEC 60079 and domestic standards such as GB/T 3836.1—2021, petrochemical plant areas are divided into different explosion hazard zones (Zone 0, Zone 1, Zone 2 for gas environments; Zone 20, Zone 21, Zone 22 for dust environments) and gas groups (Group IIA, IIB, IIC), with corresponding temperature classes (T1-T6). For most petrochemical production areas (such as oil refineries, chemical synthesis workshops), flameproof type (Ex d) is the most widely used explosion-proof structure, which confines internal explosions within the shell and prevents the transmission of flames and pressure to the external environment, thus avoiding ignition of flammable gases in the surrounding area.
In the design of the flameproof shell, several key parameters must be strictly controlled to ensure explosion-proof performance. First, the shell material must have sufficient mechanical strength and impact resistance to withstand the pressure generated by internal explosions (usually 1.5 times the maximum test pressure as required by IEC 60079-1:2014) without deformation or damage. Common materials include high-strength cast iron, aluminum alloy, and stainless steel, among which stainless steel is preferred for coastal petrochemical plants or areas with high corrosive gas concentrations due to its excellent corrosion resistance. Second, the joint surface of the shell (such as the cover and the body, cable entry) must be designed with a reasonable flameproof gap and length. The gap size is determined by the gas group: for IIC group gases (such as acetylene, which have high explosion hazard), the gap must be ≤0.15 mm, while for IIB group gases (such as propane), the gap can be slightly larger, but must not exceed 0.25 mm. The length of the joint surface should be at least 25 mm to ensure effective flame quenching and prevent flame leakage. Additionally, cable entry devices must use explosion-proof cable glands that match the cable diameter, and the gap between the cable and the gland must be sealed with flame-retardant and explosion-proof materials to avoid gas leakage into the shell.
Material selection is another critical consideration in the design of explosion-proof dry-type transformers for petrochemical plants, as the equipment must withstand harsh conditions such as high temperature, humidity, corrosive gases, and mechanical vibration. The core and winding materials directly affect the transformer’s performance and service life. For the core, cold-rolled silicon steel sheets with high magnetic permeability and low loss should be selected to reduce iron loss and heat generation, which is crucial for preventing excessive temperature rise in explosion-proof structures. For windings, two main insulation types are commonly used in dry-type transformers: epoxy resin cast windings and Nomex paper insulation windings. Epoxy resin cast windings (such as SCB series) have high mechanical strength, good insulation performance, and excellent dust and moisture resistance, making them suitable for high-dust and high-humidity petrochemical environments; Nomex paper insulation windings (such as SGB series) have high temperature resistance (long-term operating temperature up to 180℃) and good thermal stability, which is suitable for areas with high ambient temperatures, such as near high-temperature reaction furnaces.
All materials used in the transformer must meet flame-retardant and explosion-proof requirements. For example, the insulation materials should be flame-retardant grade F or higher, and should not produce toxic or flammable gases when heated or burned. The paint used on the shell surface should be anti-corrosive, flame-retardant, and suitable for petrochemical environments, with good adhesion and resistance to sulfide (H₂S), nitrogen oxide (NOₓ), and other corrosive gases. Additionally, fasteners (such as bolts, nuts) should be made of stainless steel or galvanized steel to prevent rust and corrosion, ensuring the tightness of the shell joint surface and avoiding gap enlargement due to corrosion, which would compromise explosion-proof performance. It is also important to note that the selection of materials should comply with the trend of localization, as domestic high-quality materials have achieved significant progress in performance and cost-effectiveness, with a market share of over 65% in the petrochemical field.
Insulation design is closely related to the safety and reliability of explosion-proof dry-type transformers, especially in petrochemical environments where insulation aging is accelerated by high temperature, humidity, and corrosive factors. The insulation system must be designed to withstand long-term operation under rated voltage and temperature, and have sufficient insulation margin to prevent insulation breakdown and short circuits. First, the winding insulation thickness must be strictly calculated according to the rated voltage and insulation level, and the insulation layer should be uniform and dense to avoid partial discharge. For epoxy resin cast windings, vacuum pressure impregnation (VPI) technology should be adopted to ensure that the insulation material fully fills the gaps between the winding conductors, eliminating air bubbles and improving insulation performance. For Nomex paper insulation windings, multiple impregnations with solvent-free varnish should be performed to enhance insulation density and moisture resistance.
In addition to the main insulation between windings and between windings and the core, the匝间 insulation and interlayer insulation of the windings must also be strengthened. The匝间 insulation should be selected according to the voltage between turns, and materials with high dielectric strength and good thermal stability should be used to prevent匝间 short circuits. The interlayer insulation should be designed with reasonable thickness and structure to withstand the interlayer voltage and avoid insulation aging caused by heat accumulation. It is also necessary to consider the insulation protection of the lead wires and terminals, which should be covered with flame-retardant and insulating sleeves, and the connection points should be tightly fixed to prevent poor contact and arcing. Regular insulation resistance testing and partial discharge testing should be incorporated into the design verification process to ensure that the insulation system meets the requirements of long-term safe operation in petrochemical environments.
Thermal management is a key challenge in the design of explosion-proof dry-type transformers for petrochemical plants, as the sealed explosion-proof shell limits heat dissipation, and the high ambient temperature in petrochemical plants (often 40℃ or higher) further exacerbates heat accumulation. Excessive temperature rise not only reduces the service life of the transformer but also may trigger the ignition of flammable media around the equipment. Therefore, the design must adopt effective heat dissipation measures to ensure that the temperature rise of the transformer does not exceed the limit specified by the standard (usually 100K for F-class insulation, 125K for H-class insulation).
Common heat dissipation methods for explosion-proof dry-type transformers include natural air cooling (AN) and forced air cooling (AF). For small-capacity transformers (below 100kVA), natural air cooling can be adopted by optimizing the shell structure, such as designing heat dissipation fins on the shell surface to increase the heat dissipation area. For large-capacity transformers (above 100kVA), forced air cooling is required, which involves installing explosion-proof fans inside the shell to accelerate air circulation and enhance heat dissipation. The fans must be explosion-proof type (Ex d) to ensure that they do not generate sparks during operation. Additionally, the heat dissipation system should be designed with redundancy, such as installing multiple fans that can work alternately, to avoid heat dissipation failure due to single fan damage. The temperature of the windings and core should be monitored in real-time, and when the temperature exceeds the set threshold, the fans should automatically start, and an alarm signal should be sent to the control system to prevent overheating.
Environmental adaptability design is essential to ensure that explosion-proof dry-type transformers can operate stably in the harsh environment of petrochemical plants. First, the transformer should have a high protection level, usually IP54 or higher, to prevent dust, water, and corrosive media from entering the shell. For areas with high dust concentrations (such as crushing workshops, material storage areas), the protection level can be increased to IP65, and a dust-proof cover and dehumidification device can be added to prevent dust accumulation and condensation. Second, the transformer should be designed to resist mechanical vibration, as petrochemical plants often have large mechanical equipment (such as pumps, compressors) that generate strong vibration, which may cause loose windings, core displacement, or damage to the shell joint surface. The base of the transformer should be equipped with shock-absorbing rubber pads or steel structure reinforcement, and the windings should be tightly bound with epoxy glass ribbons to enhance mechanical stability.
Corrosion resistance is another important aspect of environmental adaptability. Petrochemical plants often have corrosive gases such as H₂S, SO₂, and Cl₂, which can corrode the transformer shell, windings, and other components. Therefore, the shell should be treated with anti-corrosion coating (such as epoxy resin coating, fluorocarbon coating), and the internal components should be made of corrosion-resistant materials. For coastal petrochemical plants, the transformer should also be designed to resist salt spray corrosion, and stainless steel materials or special anti-salt spray coatings should be used. Additionally, the transformer should be equipped with a condensation prevention device, such as a built-in heater, which automatically starts when the ambient temperature is below 5℃ or the humidity is higher than 85% to prevent condensation on the surface of the windings and core, which would reduce insulation performance.
Compliance with international and domestic standards is a mandatory requirement for the design of explosion-proof dry-type transformers for petrochemical plants, as non-compliant equipment may pose serious safety hazards and fail to pass industry inspections. Internationally, the main standards include IEC 60079 series (explosive environments), IEEE C57.12.01 (dry-type transformers), and ATEX 2014/34/EU (EU explosion-proof certification). Domestically, the key standards are GB/T 3836 series (explosive environment electrical equipment) and GB 1094.11 (dry-type transformers for explosive environments). The design must strictly follow the requirements of these standards, including explosion-proof type selection, shell parameters, insulation level, temperature rise limit, and test methods.
In addition, the transformer must pass strict certification tests, such as explosion-proof performance test, insulation test, temperature rise test, and mechanical strength test, to obtain relevant certification certificates (such as CE certification for the EU market, CCC certification for the Chinese market, UL certification for the North American market). It is worth noting that the latest version of the standards has higher requirements: for example, IEC 60079-0:2023 strengthens the requirements for the whole life cycle safety management of equipment, and GB/T 3836.1—2021 adds special clauses for high-risk environments, requiring the shell material to have a tensile strength of not less than 550 MPa and an impact toughness of not less than 27 J (-20℃). The design should keep pace with the update of standards to ensure long-term compliance.
Intelligent monitoring and protection design is an important trend in the modern design of explosion-proof dry-type transformers for petrochemical plants, which can improve the operational reliability of the equipment and reduce the risk of accidents. The transformer should be equipped with a comprehensive monitoring system, including temperature sensors (PT100), humidity sensors, current and voltage sensors, and partial discharge sensors. These sensors can real-time collect operating parameters such as winding temperature, core temperature, ambient humidity, load current, and partial discharge intensity, and transmit the data to the centralized control system through IoT connectivity.
The monitoring system should have functions such as over-temperature alarm, over-current alarm, under-voltage alarm, partial discharge alarm, and humidity alarm. When an abnormal parameter is detected, the system can automatically send an alarm signal to the operation and maintenance personnel, and take corresponding protective measures (such as starting the cooling fan, cutting off the power supply) to prevent the situation from worsening. Additionally, the system should support remote monitoring and management, allowing operation and maintenance personnel to check the operating status of the transformer in real-time through mobile phones or computers, perform predictive maintenance, and reduce on-site maintenance frequency, which is particularly important for petrochemical plants with high-risk and difficult-to-access areas. The intelligent monitoring system should also comply with the requirements of IEC 61850 communication protocol to realize seamless integration with the plant’s intelligent power management system.
In conclusion, the design of explosion-proof dry-type transformers for petrochemical plants is a comprehensive and rigorous process that requires full consideration of explosion-proof performance, material selection, insulation design, thermal management, environmental adaptability, standard compliance, and intelligent monitoring. Each design link is closely related to the safety and stability of the transformer and the entire petrochemical production system. By strictly following the above considerations, adopting advanced design concepts and technologies, and complying with relevant international and domestic standards, explosion-proof dry-type transformers can effectively prevent explosion and fire hazards, ensure the safe and stable operation of petrochemical plants, and provide reliable power support for the petrochemical industry’s high-quality development. With the continuous upgrading of petrochemical technology and the increasing requirements for safety and environmental protection, the design of explosion-proof dry-type transformers will continue to develop in the direction of high reliability, high efficiency, intelligence, and green energy conservation.
