66 kV Oil-Immersed Power Transformer Selection Guide | Structure, Performance & Application Analysis

Time：2025-12-5    Auther：ZTelec-www.ztelectransformer.com

How to Choose the Most Suitable 66 kV Oil-Immersed Power Transformer for Your Power Project?

In large industrial substations, energy infrastructure, and modern transmission and distribution networks, 66 kV oil-immersed power transformers have become the mainstream choice due to their high reliability, long service life, and excellent heat dissipation capabilities. Selecting the right transformer model based on operating environment and load characteristics is essential for ensuring safe and stable operation. This article provides a detailed and systematic analysis from the perspectives of core structure, application scenarios, and key selection criteria.

Core Structural Features of 66 kV Oil-Immersed Transformers

1. Core Structure

The core is made of high-quality grain-oriented silicon steel sheets, using either laminated or wound-core structures. Its main advantages include low loss and low noise, strong resistance to magnetic saturation during grid fluctuations, and high operational efficiency that reduces long-term energy consumption.

2. Windings and Conductor Materials

Two conductor materials are widely used in 66 kV transformers:

Copper Windings: Excellent conductivity, strong short-circuit resistance, and long service life.

Aluminum Windings: Lightweight and cost-effective, ideal for projects with tight budget constraints.

The windings are designed with multi-layer cylindrical or continuous structures to enhance mechanical strength and short-circuit withstand capability.

3. Insulation System

The composite insulation structure consists of premium transformer oil, DDP, TIV, and high-density pressboard. It delivers high dielectric strength, strong electrothermal stability, and reliable long-term operating performance under heavy loads.

4. Cooling Structure

Common cooling methods include:

ONAN (Oil Natural Air Natural): Suitable for stable-load applications, featuring simple structure and low maintenance.

ONAF (Oil Natural Air Forced): Equipped with cooling fans to enhance heat dissipation, ideal for fluctuating or high-load operating conditions.

Selecting the appropriate cooling class improves overload capability and overall transformer stability.

How to Select the Most Suitable 66 kV Oil-Immersed Transformer?

1. Define Core Requirements

Capacity: Determine based on the maximum load plus a recommended 20% reserve margin.

Voltage: Confirm the primary 66 kV level and corresponding secondary voltage.

Installation Environment: Consider whether the transformer is used indoors or outdoors and evaluate temperature, humidity, and altitude conditions.

2. Confirm Key Performance Parameters

Energy Efficiency Level: Prefer Level-1 high-efficiency transformers to reduce operational losses.

Cooling Method: Choose ONAN or ONAF based on load fluctuation patterns.

Short-Circuit Impedance: Typical values range from 6% to 10% depending on system requirements.

Protection Level: Outdoor installations should meet IP55 or higher.

3. Important Selection Considerations

Winding Material: Copper windings are recommended for better durability and performance.

Protection Configuration: Essential devices include Buchholz relay, oil thermometer, and pressure relief valve.

Monitoring Functions: Selecting models with online monitoring interfaces enables intelligent management and predictive maintenance.

4. Evaluate Supplier Qualifications

Prioritize suppliers with strong R&D capability and proven engineering experience in 66 kV transformer manufacturing.

Verify certifications such as ISO 9001 and review application cases.

Evaluate the coverage and responsiveness of their after-sales service network.

5. Conduct a Comprehensive Cost Assessment

Compare initial procurement costs and long-term operational costs, including annual no-load and load losses. Also estimate long-term maintenance and service expenses to ensure cost-effectiveness.

Typical Application Scenarios of 66 kV Oil-Immersed Power Transformers

66 kV transformers are widely used in:

Urban and regional substations.

Industrial and mining enterprise transmission systems.

Large EPC power engineering projects.

New energy facilities such as PV plants, wind farms, and power stations.

Critical infrastructure such as expressways and data centers.

Selecting a properly matched 66 kV oil-immersed power transformer directly influences equipment stability, operational lifespan, and overall economic efficiency. Buyers should comprehensively assess structural features, performance parameters, application scenarios, and supplier qualifications to ensure optimal performance. For technical support including model selection, insulation configuration, drawings, transportation, and installation guidance, feel free to contact us—we provide reliable and professional solutions for your power engineering projects.