Common Faults Detected by Transformer Winding Resistance Testing

Transformer Winding Resistance Testing (TWRT) is a powerful diagnostic tool that plays a critical role in detecting underlying faults in transformers. While other tests like insulation resistance or oil analysis are important, TWRT is uniquely capable of identifying issues that can lead to catastrophic failures if left undetected. In this article, I’ll cover the top 5 deadly transformer faults that only Transformer Winding Resistance Testing can detect, and explain why early detection is vital for maintaining transformer reliability and preventing costly downtime.

1. Internal Winding Short Circuits

How TWRT Detects Winding Short Circuits

An internal winding short circuit occurs when two turns of the winding come into direct contact due to insulation failure. This can result in an uneven distribution of electrical current, causing excessive heating, localized damage, and, eventually, catastrophic failure.

Why It’s Dangerous

Winding short circuits are one of the most dangerous transformer faults because they often start small but can quickly escalate. Left undetected, they can cause overheating, which may lead to complete transformer failure or even fire. Transformer Winding Resistance Testing detects these faults by measuring an increase in resistance in the affected winding.

Personal Anecdote: During a routine test on a power transformer at a substation, the resistance values on one phase were slightly elevated compared to the others. Upon closer inspection, we found that a short circuit had occurred between two winding turns. Early detection allowed us to intervene before the transformer suffered irreversible damage.

2. Loose or Damaged Connections

How TWRT Detects Loose or Damaged Connections

Loose or damaged connections between the windings and terminal leads can increase resistance at the connection points. Over time, this can lead to localized overheating, which further degrades the connection and can lead to equipment failure.

Why It’s Dangerous

Loose connections are dangerous because they often go unnoticed until the transformer is exposed to heavy load conditions. As the connection weakens, it can cause arcing, leading to high heat and potentially damaging the entire transformer. TWRT can detect these issues early by identifying abnormally high resistance readings in specific phases.

Personal Anecdote: I once witnessed a transformer fail during peak load because a damaged terminal connection caused excessive resistance. During a post-failure analysis, we found that TWRT could have identified this issue months earlier had it been performed. Since then, I’ve made it a practice to include TWRT as a regular maintenance task, especially for critical transformers.

3. Winding Deformation or Displacement

How TWRT Detects Winding Deformation

Winding deformation typically occurs due to mechanical stress, such as a severe fault, short circuit, or transportation damage. This can cause the windings to shift or deform, affecting their resistance and leading to uneven current distribution.

Why It’s Dangerous

Winding deformation is particularly hazardous because it can lead to insulation breakdown and create internal short circuits, significantly increasing the risk of a transformer failure. TWRT is highly effective at detecting these shifts by comparing the resistance values between windings. Sudden or unexpected changes in resistance values often indicate physical changes in the winding structure.

Personal Anecdote: After a transformer was subjected to a mechanical shock during installation, TWRT revealed a noticeable increase in the resistance of one winding. Upon further inspection, we discovered that the winding had been displaced, and immediate corrective action was taken to prevent future failure.

4. Open Circuits in the Winding

How TWRT Detects Open Circuits

An open circuit in the winding occurs when there is a break in the electrical path, usually due to a broken wire, poor soldering, or mechanical damage. Transformer Winding Resistance Testing can quickly detect open circuits by showing an infinite or very high resistance value, indicating a complete break in the continuity of the winding.

Why It’s Dangerous

An open circuit can lead to severe operational inefficiencies or complete transformer failure. When the winding is interrupted, the transformer cannot effectively transfer electrical energy, causing severe disruption in the power supply. TWRT is the best method for detecting open circuits, as it directly measures the continuity of the winding.

Personal Anecdote: During a commissioning test of a transformer that had recently undergone refurbishment, TWRT revealed that one of the windings had an open circuit. Without this test, the transformer would have been energized and could have caused an immediate fault, leading to severe damage and extended downtime.

5. Deteriorating Insulation Between Windings

How TWRT Detects Insulation Breakdown

Insulation deterioration between windings can lead to electrical faults like partial discharge or arcing, causing damage to both the transformer’s insulation system and its windings. As insulation weakens, the winding’s resistance can increase, which Transformer Winding Resistance Testing detects early on.

Why It’s Dangerous

Deteriorating insulation is a critical issue that often progresses slowly but has potentially catastrophic consequences. If insulation failure occurs, the result is typically an internal short circuit, leading to transformer failure. TWRT can reveal early signs of insulation degradation by identifying small but steady increases in resistance values over time.

Personal Anecdote: In one instance, TWRT detected a gradual increase in winding resistance over a series of tests. By investigating further, we found that the insulation was starting to degrade due to thermal stress. The early warning allowed us to plan a scheduled shutdown for repairs, avoiding a failure during peak load periods.

Conclusion

Transformer Winding Resistance Testing is a vital tool in detecting the early signs of potentially catastrophic transformer faults. From internal winding short circuits to deteriorating insulation, these issues can be detected long before they lead to major failures. By incorporating TWRT into your regular maintenance routine, you can prevent costly downtime, extend the lifespan of your transformers, and ensure the reliability of your power system.

As an electrical testing expert, I’ve seen firsthand how catching these faults early with TWRT has saved transformers from irreparable damage. In the fast-paced and high-stakes environment of the electric power industry, proactive testing is key to avoiding devastating failures and maintaining efficient operations.