1,000+ Electrical Transformers (7.2–34.5 kV, 25–3000 kVA) — UL Evaluated, Certificate of Compliance Available — In Stock & Ready to Ship from Houston, CA & Florida. Contact Us Today!
At Daelim Belefic, we have been developing, manufacturing and improving our transformers for over 15 years. Our transformer solutions have reached over 30 countries, on all continents. In places with demanding working environments and the need for high reliability, our hermetically sealed transformers are the ideal solution.
Whether deployed in remote locations, extreme temperature conditions, offshore platforms, or demanding industrial environments, this type of transformer proves essential for reliable and efficient operation. By using hermetically sealed transformers, you get a device that protects itself and your investment with reduced need for intervention from your maintenance team.
Daelim Belefic’s hermetically sealed transformer range covers a wide range of distribution and power applications. The design complies with all major global standards. The table below shows a full list of technical parameters of our transformers:
Transformer Parameter | Specification / Range |
Rated power | 30 kVA to 20 MVA (customized transformers available beyond this range) |
Rated voltage (HV) | Up to 44000 V |
Rated voltage (LV) | 230 V – 6600 V |
Frequency | 50 / 60 Hz |
Cooling method | ONAN (smaller units) – OFAF (higher ratings) |
Tank design | Corrugated wall, fully hermetic enclosure without conservator and breather |
Insulation class | Usually Class A |
Insulation medium | Mineral oil per IEC 60296 Biodegradable ester fluid available on request |
Winding material | Copper is standard. Aluminium available on request |
Temperature operation range | −25 °C to +45 °C (arctic and tropic conditions available on request) |
Noise level | ≤55 dB at 1m distance (ultra low noise transformer available on request) |
Service life | 25-30 years under normal operating conditions |
Applicable standards | IEC – ANSI/IEEE – CSA – AS/NZS |
All capacities and data listed in the table represent standard ratings of hermetically sealed transformers. If your project requirements go beyond the listed parameters, our engineering team is ready to support you—tailored, project-specific solutions are one of our key strengths.
Every hermetically sealed transformer manufactured by Daelim Belefic is engineered with a single objective – delivering superior performance in demanding environments while minimizing maintenance requirements. The key technical features include:
Feature | Customer Benefit |
Fully sealed corrugated transformer tank | ● The corrugated walls of the transformer tank ribs adapt to changes in oil volume. ● No need for a preservative and silica gel breather. ● Significantly reduces the risk of internal tank contamination from air, moisture, and external impurities. ● Stable oil quality and characteristics throughout the service life ● Extended service life to 25-30 years
|
Cold-rolled grain-oriented silicon steel core | ● Reduces losses in the transformer core ● Saving tens of thousands of dollars in electricity over the transformer lifecycle ● Lower temperature of the transformer core slows down thermal aging |
Precision-wound copper windings with thermally upgraded insulation | ● Copper windings resistant to continuous heating up to 105°C ● Maintaining insulation integrity through thousands of thermal cycles ● Short circuit resistance designed according to IEC 60076-5 |
Transformer cooling (ONAN standard, ONAF optional) | ● Natural cooling requires no power supply or maintenance ● On larger units, ONAF cooling is used, but with the preservation of the hermetic characteristics of the transformer |
FR3 Biodegradable ester fluid | ● Improved fire protection (buildings, underground installations) ● Significantly higher flash point ● FR3 fluid absorbs moisture from the insulation system – extending the service life |
When reliability is critical and maintenance is limited, hermetically sealed transformers are the logical solution. Designed for demanding environments such as renewable energy plants, heavy industry or isolated installations – these transformers will ensure consistent performance, lower operating costs and less downtime.
With solutions from Daelim Belefic, you get a transformer engineered to unlock maximum performance exactly where it matters most.
Daelim Belefic has extensive experience in renewable energy projects – solar and wind power plants. In the range of up to 30 MVA, hermetically sealed transformers are the ideal solution for these often isolated systems. They are made to withstand higher stress and cyclic loading while preserving the integrity of the insulation system. Also, the highly efficient design has fewer losses during off-peak periods when the output of renewable power plants is reduced.
In heavy industrial plants, high electrical loads are combined with atmospheric contamination – metal and coal dust, acid fumes, sulfur compounds, etc. Hermetically sealed transformers are highly resistant to the ingress of these contaminants. Daelim Belefic has delivered dozens of transformers to date for various environments – chemical processing plants, mines, cement and steel plants where continuity of operation is essential.
The absence of a conservator makes hermetically sealed transformers more compact than equivalent conservator-type transformers. This is an important advantage in urban environments, underground applications and generally locations where space is limited. Our transformers, combined with low noise levels and the option of biodegradable ester fluid as an insulating material, meet high safety standards and requirements.
Salt-saturated air is one of the most aggressive accelerators of transformer insulation and tank degradation. In coastal substations, oil and gas offshore platforms, hermetically sealed transformers prevent oil contamination and any other atmospheric contact. Together with our hot-dip galvanized or marine-grade epoxy coating, these transformers are intended for offshore wind power substations, port authority distribution networks of coastal industrial facilities around the world.
In desert regions, daytime ambient temperatures regularly exceed 45°C. In addition to the extreme heat and hot, dry air, the atmosphere also contains fine dust particles. The corrugated walls of the hermetically sealed tank control the expansion of the oil at high temperatures, and the seal prevents the ingress of air and dust. Daelim Belefic supplies such transformers to large-scale solar farms and gas and oil processing plants.
When a transformer is located at the end of a distribution line hundreds of kilometers long, the cost-effectiveness of maintaining a conservator-type transformer drops significantly. The hermetic type of transformer allows for safety and minimal maintenance. Install the transformer and return after a few years to find it working flawlessly. Such transformers are regularly supplied in rural electrification projects, agricultural systems, and for powering remote telecommunications towers.
Daelim Belefic’s engineering team approaches each project as an opportunity for long-term cooperation, not just a catalog selection of the final solution. Thus, the range of our capacities is very wide, and we can adapt to the following dimensions:
Feature | Custom Options |
Voltage | ● Any HV/LV combination within our equipment range |
Capacity | ● 30 kVA to 20 MVA is standard ● All above is available upon request |
Insulation | ● Mineral oil (IEC 60296) ● FR3 biodegradable ester fluid ● Synthetic ester fluid |
Cooling | ● ONAN standard cooling ● ONAF for larger units |
Extreme temperature configurations | ● Arctic-rated designs for -55°C to tropical ambient at +50°C |
Smart monitoring package | ● Oil/winding temperature indicator, oil level gauge, Pressure relief device, factory-wired control box, SCADA integration |
Voltage regulation | ● OCTC (off-circuit tap changer) ● OLTC (on-load tap changer) |
Bushing configuration | ● Porcelain ● Polymer ● Epoxy-resin |
The core laminations and windings of hermetically sealed transformers are manufactured using modern and controlled materials, with emphasis on dimensional accuracy and insulation integrity. The design practice of such transformers focuses on reducing losses and mechanical stress in accordance with applicable IEC/ANSI standards.
Our transformers are made of fully welded steel construction, with built-in corrugated ribs that are useful during the thermal expansion of the insulating material. Seal integrity and transformer performance are verified by factory oil leakage testing to ensure complete tightness. The surface of the transformer tank is prepared with coatings that ensure long-term protection against corrosion and external influences.
Core-coil assemblies are dried using controlled processes to remove moisture from insulation materials. Transformer oil filling is conducted under controlled conditions to minimize air entrapment, and oil quality is verified through standard electrical and chemical tests in line with international standards.
Daelim Belefic operates under an established quality management framework in accordance with ISO 9001 rules. Design, procurement and final testing controls are established throughout the production process. All of our company’s products comply with major global standards such as IEC and ANSI/IEEE. Quality control can be summarized as follows:
Hermetically sealed transformers manufactured in Daelim Belefic are prepared for delivery with the main focus on protection, reliability and project readiness. Each unit is factory-sealed and securely packed to minimize any risk of contamination and mechanical damage.
For larger units and long distances, sea freight is the standard transport method, with detailed container securing calculations provided for ISO 20′ and 40′ containers. In the case of oversized equipment, out-of-gauge heavy-lift solutions are carefully coordinated to ensure safe handling and compliance with transport regulations.
For time-critical projects, air freight options are available for smaller units, with packaging specifically engineered to withstand the additional stresses of air cargo handling. In addition, road and rail transport are also available for closer destinations.
To ensure smooth customs clearance and project execution, Daelim Belefic provides complete export documentation, including commercial invoices, packing lists, bills of lading, certificates of origin, test reports, and any required inspection certificates.
Each of our delivered transformers comes with an appropriate warranty and additional services backed by years of experience. Over the years, we have built a team that protects the total cost of ownership of your project and investment.
On-site support – If necessary, our team provides field services. It includes on-site installation supervision, commissioning, troubleshooting, and maintenance support for supplied equipment.
Contact us with your required capacity, voltage level, operating environment and required standards. With the Daelim Belefic team, you will receive a fast, expertly supported design that will meet all your needs.
Whether you need a hermetically sealed transformer for a renewable energy project, industrial systems or remote applications, we will help you choose the right configuration from the start.
Our team ensures transformers that have full compliance with international standards, while optimizing performance, reliability and reducing operating costs. Each of our configurations is designed to match real operating conditions.
Under normal operating conditions, without significant damage or failures, our transformers are designed to last at least 25-30 years. Since the oil is preserved in a sealed tank, there is no requirement for periodic testing, filtration or oil replacement.
Recommended maintenance is quite simple – annual external visual inspection, inspection of the tank, bushings, condition of the cooling devices if the transformer has them. In addition, it is necessary to check the condition of the monitoring devices and inspect the protective relays.
Yes. Daelim Belefic has CSA certification and UL/cUL listings for transformers intended for the North American market. Also, our transformers can be manufactured according to the IEC 60076 standard with CE marking, intended for the European market. When requesting a quote, you only need to specify the target market and the standards that the transformer needs to meet. Our team will do the rest.
Yes. The IEC 60076-1 standard defines service conditions at altitudes up to ≤1,000 m and temperatures between −25°C and +40°C. Daelim Belefic regularly supplies hermetically sealed transformers that are designed for operation at altitudes above 4,000 m, arctic temperatures down to −55°C and tropical and desert conditions up to +45°C.
When inquiring, please specify the altitude and ambient temperature minimum/maximum so that we can determine the appropriate operating parameters.
Hermetically sealed transformers have certain disadvantages. Reduced flexibility for maintenance and inspection of the transformer, and certain cooling limitations for higher power ratings. However, these disadvantages are less significant compared to the advantages – low maintenance, good insulation condition during service life and stable overall performance.
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