How To Opt for Dry-Type Or Oil-Immersed Transformers: Scenario-Based Selection Criteria

I. Introduction

1.1 The Importance of Medium and High-Voltage Transformers

Medium and high-voltage transformers serve as the backbone of power transmission and distribution systems, enabling the safe and efficient conversion of voltage levels to meet industrial, commercial, and public infrastructure needs. As a leading brand in the medium and high-voltage transformer industry, JZP has established a solid reputation for reliability, technical innovation, and tailored solutions. The correct selection between dry-type and Oil-Immersed Transformers directly impacts system stability, operational safety, maintenance costs, and long-term return on investment—making it a critical decision for project planners and engineers.

1.2 Purpose of the Article

This article aims to provide a comprehensive, scenario-driven framework for selecting JZP’s dry-type or oil-immersed medium and high-voltage transformers. By analyzing technical differences, application scenarios, and real-world cases, readers will gain practical insights to align transformer type with specific project requirements, ensuring optimal performance and value.

II. Overview of JZP Medium and High-Voltage Transformers

2.1 Introduction to JZP Brand

With decades of experience in the power equipment industry, JZP has emerged as a trusted provider of medium and high-voltage transformers (voltage range: 10kV-220kV, capacity: 315kVA-250MVA). The brand is committed to technological advancement, integrating advanced materials, intelligent monitoring systems, and eco-friendly designs into its product lineup. JZP’s transformers are widely adopted in power grids, industrial parks, commercial complexes, and renewable energy projects globally, earning recognition for their high efficiency, low failure rate, and compliance with international standards (IEC, ANSI, GB).

2.2 Basic Concepts of Medium and High-Voltage Transformers

Medium and high-voltage transformers operate on the principle of electromagnetic induction, transferring electrical energy between circuits at different voltage levels while maintaining frequency consistency. Key components include the iron core (providing magnetic flux path), windings (conducting current and inducing voltage), insulation system (preventing electrical breakdown), and cooling structure (dissipating heat generated during operation). In power systems, these transformers bridge the gap between high-voltage transmission lines and medium-voltage distribution networks, or between medium-voltage sources and low-voltage end-users, ensuring stable power supply for critical operations.

III. Technical Differences Between Dry-Type and Oil-Immersed Transformers

3.1 Enclosure Design

Dry-Type Transformers feature an open or semi-enclosed structure, with iron cores and windings exposed or protected by a dust-proof casing. This design eliminates the risk of oil leakage and simplifies visual inspection. In contrast, oil-immersed transformers adopt a fully sealed steel tank filled with insulating oil, providing superior protection against external contaminants (dust, moisture, corrosive gases) but requiring strict leakage prevention measures. JZP’s dry-type transformers use corrosion-resistant materials for enclosures, while its oil-immersed models incorporate double-sealing technology to enhance durability.

3.2 Lead Configuration

Dry-type transformers utilize silicone rubber bushings, which offer excellent insulation performance, flexibility, and resistance to high temperatures (up to 155°C). These bushings are ideal for indoor environments with limited space, as they occupy less vertical clearance. Oil-immersed transformers, on the other hand, employ porcelain bushings—known for their robustness, creepage resistance, and suitability for high-voltage applications (above 110kV). JZP’s porcelain bushings undergo strict quality control to ensure reliability in harsh outdoor conditions, such as strong winds and heavy pollution.

3.3 Insulation and Cooling Methods

Dry-type transformers rely on resin insulation (epoxy resin casting or vacuum pressure impregnation), which is non-flammable, self-extinguishing, and free of toxic fumes. Cooling is typically achieved through natural air convection (AN) or forced air cooling (AF) for higher capacity models. Oil-immersed transformers use mineral oil or natural ester oil as both insulation and cooling medium—oil circulates through the tank and radiators (or cooling fans) to dissipate heat. JZP’s resin-insulated dry-type transformers meet F/H class insulation standards, while its oil-immersed products feature high-quality insulating oil with excellent oxidation resistance and dielectric strength.

3.4 Capacity and Voltage Ratings

Dry-type transformers are generally designed for medium voltage (10kV-35kV) and medium capacity (315kVA-20MVA), making them suitable for distribution applications. Their capacity is limited by heat dissipation efficiency in enclosed spaces. Oil-immersed transformers cover a wider range: voltage up to 220kV and capacity up to 250MVA, catering to high-voltage transmission and large-scale industrial needs. JZP offers customized solutions for both types, with dry-type transformers optimized for compactness and oil-immersed models engineered for high load capacity and long-term stability.

IV. Scenario-Based Selection Criteria

4.1 Indoor Scenarios

4.1.1 Commercial Buildings (Malls, Office Towers)

Commercial buildings demand space-saving, fire-safe transformers with low noise levels. Dry-type transformers are the preferred choice here: their compact design fits into basement electrical rooms or floor-mounted cabinets, and resin insulation eliminates fire hazards associated with oil leakage. JZP’s dry-type transformers operate at noise levels below 60dB, ensuring a comfortable environment for occupants. Additionally, their low maintenance requirements align with the operational needs of commercial facilities, where downtime must be minimized.

4.1.2 Crowded Public Spaces (Hospitals, Schools, Theaters)

Safety is paramount in crowded areas, making dry-type transformers indispensable. Unlike oil-immersed models, they do not pose fire or environmental risks in the event of insulation failure. Hospitals, in particular, require uninterrupted power supply—JZP’s dry-type transformers with AF cooling systems maintain stable performance under fluctuating loads, supporting critical medical equipment. Schools and theaters benefit from their non-toxic insulation materials, ensuring compliance with strict safety regulations for public venues.

4.1.3 Special Indoor Environments (Basements, Underground Garages)

Basements and underground spaces often suffer from poor ventilation, high humidity, and limited access. Dry-type transformers excel in these conditions: their sealed windings resist moisture absorption, and natural air cooling eliminates the need for complex ductwork. JZP’s dry-type transformers are equipped with moisture-proof coatings and corrosion-resistant components, ensuring reliable operation in environments with relative humidity up to 95% (non-condensing). Their lightweight design also simplifies installation in confined spaces.

4.2 Outdoor Scenarios

4.2.1 Independent Substations

Independent substations require high-voltage, large-capacity transformers with robust outdoor performance. Oil-immersed transformers are ideal here: their sealed tank design protects internal components from rain, dust, and temperature extremes, while oil cooling enables efficient heat dissipation for high-capacity operation (up to 250MVA). JZP’s oil-immersed transformers for substations feature weather-resistant casings, explosion-proof devices, and online monitoring systems, ensuring 24/7 reliability in remote or harsh outdoor locations.

4.2.2 Open Factory Premises

Factories with open outdoor areas prioritize cost-effectiveness, high load capacity, and easy maintenance. Oil-immersed transformers offer a lower total cost of ownership compared to dry-type models for large-capacity applications (above 20MVA). Their simple cooling structure (radiator fins + natural oil circulation) reduces maintenance needs, while JZP’s optimized design minimizes energy loss (no-load loss ≤ 0.3% of rated capacity). Additionally, oil-immersed transformers can be installed directly on concrete foundations without the need for specialized enclosures, saving space and installation costs.

4.2.3 Hot and Humid Climates

In regions with high temperatures (above 40°C) and high humidity (e.g., tropical areas), transformer cooling and insulation performance are critical. Oil-immersed transformers perform well here due to the high heat capacity of insulating oil, which maintains stable operating temperatures even in extreme heat. For projects requiring indoor installation in hot and humid climates, JZP’s dry-type transformers with forced air cooling (AF) or water cooling (WF) systems provide an alternative, ensuring temperature rise stays within IEC limits (≤ 100K for F-class insulation).

4.3 Special Application Scenarios

4.3.1 Data Centers

Data centers require ultra-reliable transformers with low noise, high efficiency, and fast fault recovery. Dry-type transformers are preferred for indoor data center environments, as they eliminate oil leakage risks and operate quietly (≤ 55dB). JZP’s dry-type transformers for data centers feature low no-load loss (≤ 0.25%) and high short-circuit withstand capacity, ensuring stable power supply for critical IT equipment. For large-scale data centers with outdoor power rooms, oil-immersed transformers with low noise designs (equipped with soundproof enclosures) are also available, offering high capacity and energy efficiency.

4.3.2 Railway and Rail Transit

Railway systems demand compact, shock-resistant transformers with excellent electromagnetic compatibility (EMC). Dry-type transformers are suitable for on-board or wayside applications due to their lightweight, compact design, and resin insulation’s resistance to vibration (up to 3g acceleration). JZP’s rail-specific dry-type transformers meet EN 50124-1 standards for EMC and fire safety, ensuring no interference with train control systems. Their sealed structure also protects against dust and moisture in tunnel or outdoor rail environments.

4.3.3 Wind and Solar Power Plants

Renewable energy plants require transformers that can handle fluctuating loads, voltage variations, and outdoor environmental stress. Oil-immersed transformers are widely used in wind and solar farms due to their high efficiency (up to 99.7%), large capacity (up to 100MVA), and resistance to outdoor elements. JZP’s renewable energy-specific oil-immersed transformers feature low-voltage ride-through capability, harmonic suppression technology, and corrosion-resistant coatings for coastal or desert locations. For small-scale solar plants with indoor installations, dry-type transformers offer a compact, eco-friendly alternative.

V. Case Studies of JZP Transformer Applications

5.1 Successful Application Cases

5.1.1 JZP Dry-Type Transformers in a High-Rise Building

Project Background: A 50-story office tower in Shanghai required a reliable Power Distribution solution for its basement electrical room (space: 8m × 5m), with strict fire safety and low noise requirements.

Solution: JZP supplied three 10kV/0.4kV dry-type transformers (capacity: 2500kVA each, F-class insulation, AN/AF cooling). The transformers’ compact design (length × width × height: 2.8m × 1.5m × 2.2m) fit the limited space, while resin insulation met the building’s fire code (GB 50016-2014). Low noise operation (< 58dB) ensured compliance with office environment standards.

Operation Results: The transformers have been in service for 5 years with zero failures. Average energy efficiency is 99.2%, reducing annual electricity costs by 12% compared to conventional models. User feedback highlights easy maintenance and stable performance during peak load periods (8:00-18:00 daily).

5.1.2 JZP Oil-Immersed Transformers in a Large-Scale Factory

Project Background: A petrochemical factory in Guangdong needed a high-voltage power supply solution for its production line (rated voltage: 35kV, total load: 80MVA), with outdoor installation and 24/7 operation requirements.

Solution: JZP provided four 35kV/6kV oil-immersed transformers (capacity: 20MVA each, ONAN cooling, mineral oil insulation). The transformers featured explosion-proof pressure relief valves, online oil temperature monitoring, and corrosion-resistant casings to withstand the factory’s high-temperature (up to 42°C) and dusty environment.

Operation Results: The transformers have operated continuously for 3 years with a failure rate of 0%. Energy loss is 0.5% of rated capacity, saving the factory approximately 1.2 million kWh of electricity annually. The sealed design has prevented oil leakage, ensuring environmental compliance with local regulations.

5.2 Summary of Application Experience

From the above cases, key factors for selecting JZP transformers include: aligning insulation and cooling methods with environmental conditions (e.g., dry-type for indoor/fire-sensitive areas, oil-immersed for outdoor/large-capacity needs); matching capacity and voltage ratings to load requirements; and prioritizing safety and efficiency standards relevant to the application (e.g., low noise for commercial buildings, EMC for railways). JZP’s customization capability—such as tailored cooling systems, insulation classes, and monitoring functions—ensures optimal compatibility with diverse project scenarios.

VI. Selection Recommendations and Precautions

6.1 Key Pre-Planning Considerations

• Power Requirements: Calculate rated capacity, voltage level, and load characteristics (stable vs. fluctuating) to determine transformer type. For loads above 20MVA or voltage above 35kV, oil-immersed transformers are more cost-effective.
• Space and Environment: Evaluate installation location (indoor/outdoor), space constraints, temperature, humidity, and fire safety regulations. Indoor/crowded areas require dry-type transformers; outdoor/large-scale projects benefit from oil-immersed models.
• Budget and Lifespan: Consider initial investment, energy efficiency, and maintenance costs. Dry-type transformers have higher upfront costs but lower maintenance needs; oil-immersed transformers offer lower initial costs for large capacities but require periodic oil testing/replacement.

6.2 Post-Installation Maintenance Considerations

• Dry-Type Transformers: Conduct annual visual inspections (windings, bushings, cooling fans), clean dust from cooling surfaces, and test insulation resistance (≥ 100MΩ at 1kV). JZP’s dry-type transformers have a maintenance interval of 2-3 years for core and winding checks.
• Oil-Immersed Transformers: Perform quarterly oil sampling (test dielectric strength, water content, and acidity), inspect radiators for blockages, and check for oil leaks. JZP recommends oil replacement every 8-10 years or when quality indicators exceed IEC limits.
• Monitoring Systems: Invest in intelligent monitoring (temperature, humidity, partial discharge) for critical applications. JZP’s smart transformers integrate IoT sensors, enabling remote real-time monitoring and predictive maintenance.

6.3 Compatibility with Other Equipment

Ensure the selected transformer is compatible with upstream (generators, transmission lines) and downstream (switchgear, inverters) equipment. Key compatibility factors include: voltage regulation range (±2.5% or ±5%), short-circuit withstand capacity (≥ 25kA for 10kV), and connection type (flange, cable terminal). JZP provides technical support to verify compatibility with third-party equipment, ensuring seamless system integration.

VII. Conclusion

7.1 Recap of Key Points

Selecting between JZP’s dry-type and oil-immersed medium and high-voltage transformers requires a scenario-driven approach: dry-type transformers are optimal for indoor, fire-sensitive, or space-constrained environments (commercial buildings, data centers, railways) due to their safety, compactness, and low noise; oil-immersed transformers excel in outdoor, large-capacity, or cost-sensitive applications (substations, factories, renewable energy plants) thanks to their high efficiency, robust performance, and cost-effectiveness. Technical factors—insulation class, cooling method, capacity, and voltage rating—must align with project-specific requirements, while maintenance needs and equipment compatibility should be considered for long-term reliability.

7.2 Industry Outlook

The medium and high-voltage transformer industry is evolving toward higher efficiency, intelligence, and eco-friendliness. JZP is at the forefront of this trend, investing in research and development of low-loss amorphous core transformers, biodegradable natural ester oil-immersed transformers, and AI-powered smart monitoring systems. As renewable energy integration and urbanization accelerate, the demand for scenario-specific transformer solutions will grow—JZP remains committed to delivering innovative, reliable products that meet the changing needs of global customers, while adhering to strict environmental and safety standards.