What Is Acidity (TAN) Testing

Learn how TAN (Total Acid Number) testing works for transformer oil. Discover step-by-step methods, acceptable values, common mistakes, and how Wrindu testers ensure accurate acidity analysis.

Transformer oil doesn’t stay the same forever. Over time, heat, oxygen, and contaminants cause the oil to degrade and form acidic compounds. That’s why Acidity (Total Acid Number, TAN) testing is an essential part of transformer oil analysis.

This guide explains what TAN is, why it matters, and how to test it step by step in a simple, practical way.

Click the image to know more about Insulating Oleic Acid Value Tester.

What Is Acidity (TAN) in Transformer Oil?

Total Acid Number (TAN) measures the amount of acidic substances in transformer oil.

It is expressed as:
mg of KOH (potassium hydroxide) required to neutralize 1 gram of oil

Higher TAN values indicate more oil degradation.

Why Is TAN Testing Important?

As transformer oil ages, oxidation produces acids that can harm both the oil and solid insulation.

High acidity can lead to:

  • Sludge formation
  • Reduced cooling efficiency
  • Corrosion of metal parts
  • Insulation deterioration

Regular TAN testing helps detect early-stage oil aging before serious damage occurs.

What Causes Acidity in Transformer Oil?

Several factors contribute to increasing acidity:

  • Oxidation due to high operating temperatures
  • Exposure to air (oxygen)
  • Moisture contamination
  • Presence of metal catalysts (like copper)

Over time, these factors accelerate chemical breakdown.

How Does the TAN Test Work?

TAN testing is based on a neutralization reaction:

  • The oil sample is mixed with a solvent
  • A base solution (usually KOH) is added
  • The amount of base needed to neutralize the acids is measured

The result reflects the oil’s acidity level.

How Do You Perform TAN Testing Step by Step?

1. How Do You Prepare the Sample?

  • Collect a clean oil sample
  • Avoid contamination from water or dust
  • Measure a precise amount for testing

2. How Is the Solvent Added?

  • Mix the oil with a neutral solvent (often alcohol-based)
  • This helps dissolve acidic compounds

3. How Is the Titration Performed?

  • Add KOH solution gradually
  • Stir continuously during the process
  • Use an indicator or automatic sensor to detect the endpoint

4. How Is the Endpoint Determined?

  • In manual testing: color change indicates neutralization
  • In automatic testing: the instrument detects the endpoint electronically

5. How Is TAN Calculated?

  • The system calculates the amount of KOH used
  • The result is expressed as mg KOH/g oil

What Is a Good TAN Value?

Typical guidelines:

  • New oil: very low TAN (close to 0)
  • In-service oil: gradual increase over time
  • High TAN: indicates significant aging and possible need for oil treatment or replacement

Standards vary, but values above 0.1–0.2 mg KOH/g often require attention.

What Factors Affect TAN Test Accuracy?

To ensure reliable results, consider:

  • Clean sample handling
  • Accurate measurement of reagents
  • Proper calibration of equipment
  • Avoiding exposure to air during testing

How Wrindu Testers Stand Out

Wrindu TAN testers are built to deliver accurate, fast, and consistent acidity measurements for transformer oil.

Key Advantages:

1. Automated Titration System
Reduces human error and ensures repeatable results.

2. High Detection Accuracy
Sensitive sensors detect precise neutralization points.

3. Easy Operation
User-friendly interface simplifies testing procedures.

4. Fast Testing Speed
Quick analysis improves maintenance efficiency.

5. Standards Compliance
Designed to meet ASTM and IEC requirements for TAN testing.

With Wrindu testers, operators gain reliable insight into oil aging and condition.

What Are Common Mistakes in TAN Testing?

Avoid these issues:

  • Using contaminated samples
  • Incorrect reagent concentration
  • Poor mixing during titration
  • Misreading the endpoint in manual tests

These can lead to inaccurate acidity measurements.

FAQs About Acidity (TAN) Testing (Q&A)

Q1: What does a high TAN value indicate?

A: It indicates oil oxidation and aging, which can lead to sludge formation and insulation damage.

Q2: How often should TAN testing be done?

A: Typically during routine maintenance, especially for older transformers or those under heavy load.

Q3: Can high acidity be reduced?

A: Yes. Oil reclamation or filtration processes can reduce acidity levels.

Q4: What is the difference between TAN and pH?

A: TAN measures total acidic content in oil, while pH measures acidity in water-based solutions. They are not directly comparable.

Q5: Is automatic TAN testing better than manual testing?

A: Yes. Automatic systems improve accuracy, reduce operator error, and provide consistent results.

Q6: What happens if acidity is ignored?

A: It can lead to insulation failure, reduced cooling efficiency, and ultimately transformer breakdown.

Final Thoughts

Acidity (TAN) testing is a key indicator of transformer oil health and aging. By monitoring TAN levels regularly, operators can take early action to prevent costly failures.

Using advanced tools like Wrindu testers ensures accurate diagnostics and better long-term asset management.

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