Oil-Immersed Transformer Voltage Parameter Table: Key Selection Guide

2025-07-15 18:08 | By: ZTELEC-www.ztelecgroup.com | 147click

Choosing the correct voltage parameters for oil-immersed transformers is essential for ensuring long-term stability, energy efficiency, and safety. As a core component of the power grid, the transformer's voltage selection directly impacts system performance and equipment lifespan. This guide outlines critical voltage characteristics and selection logic based on real-world applications.

oil-immersed transformer voltage

1. Voltage Level Matching: Grid and Load Side

Grid-Side Voltage

The transformer’s primary voltage should match the nominal voltage of the supply network—commonly 10kV, 20kV, or 35kV. Voltage fluctuation ranges (typically ±10%) must be considered.

In rural areas or remote terminals, voltage may drop significantly. In such scenarios, a transformer with a broader tapping range is necessary to compensate.

Load-Side Voltage

The low-voltage side—such as 0.4kV or 6.3kV—must align with the rated voltage of the electrical load. For sensitive or precision equipment, it's critical to reserve a margin for voltage regulation to prevent instability or performance issues.

2. Tap Changer Selection: Voltage Fluctuation Control

A tap changer adjusts the transformer's turns ratio to stabilize output during input voltage variations.

For applications with large voltage fluctuations (such as photovoltaic grid connections), select a tap range of ±10%. For stable industrial power environments, a ±5% tap range is typically sufficient.

On-load tap changers are preferred for systems that require dynamic voltage adjustment without shutdown.

3. Insulation Design: Withstand Environmental and Electrical Stress

The transformer must handle both power frequency voltage and lightning impulse voltage beyond system operating levels.

High-Altitude Considerations

At elevations above sea level, air insulation performance drops—approximately 10% per 1000 meters. In these cases, reinforce insulation or adjust ratings accordingly.

Dirty and Humid Environments

In polluted or moist conditions, increase creepage distance, use higher insulation grades, or select sealed designs to maintain insulation reliability.

transformer parameter table

4. Short-Circuit Impedance: Balancing Efficiency and Protection

Impedance Type	Range	Advantages	Disadvantages	Application
High Impedance	6–10%	Reduces fault current, protects downstream devices	Higher operational losses	Urban substations, industrial networks
Low Impedance	4–6%	Better efficiency, improved voltage regulation	Higher short-circuit current	Rural or small-scale systems

5. Typical Transformer Selection Process

Step 1: Confirm the existing grid voltage and evaluate potential upgrades over the next 5–10 years.

Step 2: Analyze load characteristics, including startup impact and harmonic content.

Step 3: Calculate short-circuit capacity and ensure alignment with system protection devices.

Step 4: Adjust design for environmental factors such as altitude, pollution level, and ambient temperature.

6. Pitfalls to Avoid During Selection

Do not select transformers based solely on nominal voltage. Always evaluate the actual voltage fluctuation range to ensure performance under all conditions.

Overdesign—such as excessive insulation or an overly wide tap range—can increase capital cost without delivering proportional operational benefit. However, underdesigning may lead to system instability and expensive retrofits later.

Voltage parameter selection for oil-immersed transformers is a systematic engineering task that involves coordination between grid-side voltage, load-side requirements, tap changer range, insulation strength, short-circuit impedance, and environmental factors.

Only by applying a comprehensive and scenario-based approach can users select transformers that offer reliable, cost-effective, and long-term performance. For complex configurations or high-voltage systems, always consult a professional transformer engineer to ensure optimal selection.