Okay, let's break down the situation with the partial discharge on your dry-type transformer. Based on your description and the available tests, here's an assessment and some recommendations

1. Severity and Serviceability
Partial Discharge (PD) is a concern. Any partial discharge, especially surface PD, indicates insulation degradation. It means the dielectric strength of the insulation is being compromised. Over time, this will erode the insulation and lead to a fault. 200 Mohm IR is low. 200 Megohms on a 20kV/6.6kV transformer is lower than desirable. While the PI of 2.5 is acceptable, the low IR suggests the insulation is already compromised. Generally, for a transformer of this voltage class, you'd want to see IR values in the Gigaohm range. Pictures are essential. You mention you have pictures. Please share those! The visual appearance of the PD site (tracking, carbon deposits, location) is critical for judging the severity. Combined, the PD and low IR indicate a problem. The transformer's insulation is under stress and degrading. Can it be kept in service? This is a judgment call with risk. Based on your limited testing, I would be hesitant to recommend long-term continued service without more thorough diagnostics. If you keep it in service, it must be under increased observation (more on that below). The decision depends on: Criticality

How critical is this transformer to your operation? What are the consequences of a failure (downtime, safety, etc.)?

Load

Is the transformer lightly loaded or heavily loaded? Higher load stresses the insulation more.

Monitoring

Your ability to monitor the PD and other parameters.

2. Following PD Progress (Without Tan Delta)

Without tan delta testing, your options are limited, but here's what you can do: Regular Visual Inspections

This is crucial. Look for:

Increased PD activity

Is the PD more frequent, louder, or brighter? (Ideally, do this in the dark).

Tracking

Are there signs of carbon tracking across the surface? (Black, sooty deposits). This is a very bad sign.

Ozone Smell

Partial discharge generates ozone. A persistent ozone smell near the transformer is a red flag.

Changes in IR

Monitor IR values at regular intervals (e.g., weekly or monthly). A decreasing IR is a critical warning.

Overheating

Use a thermal imager to scan the transformer's surface, especially the area around the PD. Localized hot spots can indicate insulation breakdown.

Audible Noise

Listen for changes in the PD noise. Is it getting louder or more constant? Use a stethoscope or acoustic PD detector (if available) to pinpoint the source.

Temperature Monitoring

If possible, monitor the transformer's operating temperature. Higher temperatures accelerate insulation degradation.

Consider an Offline PD test (if possible). This will provide more detailed information about the partial discharge activity.3. Epoxy Repair Epoxy Can Be Effective (But With Caveats)

Specially formulated epoxy resins can be used to encapsulate and suppress surface PD on dry-type transformers.

Important Considerations



Root Cause

The epoxy only addresses the symptom (surface PD). You need to understand and, if possible, address the underlying cause. This might be: Surface contamination (dust, moisture, pollutants) Manufacturing defect Insulation aging Overvoltage stress

Surface Preparation is Critical

The area must be thoroughly cleaned and prepared before applying the epoxy. This typically involves: De-energizing and isolating the transformer. Cleaning with a suitable solvent to remove grease, oil, and contaminants. Abrading the surface to provide a good bond for the epoxy.

Epoxy Selection

Use a high-quality, electrically insulating epoxy specifically designed for this purpose. It should have good adhesion, dielectric strength, and thermal conductivity.

Application

Follow the epoxy manufacturer's instructions carefully. Proper mixing, application thickness, and curing are essential.

Professional Application is Recommended

Ideally, this type of repair should be done by a qualified technician experienced in transformer repair.

It's a Patch, Not a Cure

Epoxy repair is often a temporary solution. It might extend the transformer's life, but it doesn't guarantee long-term reliability.

Potential Problems with Epoxy



Masking the Problem

The epoxy can hide the underlying problem, making it harder to detect future degradation.

Stress Concentration

If not applied correctly, the epoxy can create stress concentrations that lead to new PD sites.

Incompatibility

The epoxy might not be compatible with the existing insulation, leading to further problems.*

My recommendation is to consult with a transformer repair specialist. They can assess the damage and recommend the best course of action. If the epoxy repair is not done properly, it can lead to more serious problems.4. Recommendations1. Share Pictures

Please provide the pictures of the PD. They are very important for assessing the severity.2.

Offline PD Test (if possible)

Get a proper offline PD test done by a qualified company. This will give you a much better picture of the extent and nature of the PD.3.

Contact a Transformer Specialist

Consult with a reputable transformer repair or service company. They can provide a more detailed assessment and recommend appropriate repair or replacement options.4.

Increased Monitoring (If Keeping in Service)

If you decide to keep the transformer in service, implement a rigorous monitoring program as described above.5.

Budget for Replacement

Even if you repair the transformer, start budgeting for a replacement. The PD indicates that the insulation is aging, and the transformer's lifespan is likely reduced.6.

Review Operating Conditions

Are there any factors contributing to the PD (overvoltage, harmonics, load imbalances, environmental issues)? Addressing these can help prevent future problems.

In summary, the partial discharge and low IR reading are concerning. You need more information to make a fully informed decision about whether to keep the transformer in service. Consult with a specialist, get more testing done, and implement a rigorous monitoring program if you continue to operate it. Flag for review