Please share the Tan-Delta test results you're referring to. I need to see the actual data to provide specific and helpful feedback.However, based on your general description and understanding, here's a breakdown of potential issues and considerations when interpreting Tan-Delta results on MV cables

General Guidelines and Concerns (Without seeing your data):
Your Understanding is Correct

You are generally correct in your assessment of typical Tan-Delta values for new and aged MV cables.

New Cables (< 0.001 or < 0.1%)

These values indicate very low insulation losses and excellent cable condition.

Monitoring Zone (0.001 - 0.005 or 0.1% - 0.5%)

Values in this range suggest some degree of insulation degradation, contamination, or moisture ingress. Monitoring and trend analysis are crucial. The rate of change is often more important than the absolute value.

Concern Zone (> 0.005 or > 0.5%)

Values exceeding this threshold indicate significant insulation degradation and require investigation. Potential actions include more frequent testing, offline diagnostic tests (VLF Tan Delta, PD), and potentially cable replacement planning.

Factors Influencing Tan-Delta

Several factors besides cable age and insulation condition can influence Tan-Delta readings:

Cable Type and Construction

Different cable types (e.g., XLPE, EPR) have inherent variations in Tan-Delta values, even when new. Knowing the cable type is critical.

Operating Voltage

Tan Delta typically increases with Voltage. The test voltage should be known.

Temperature

Tan-Delta is highly temperature-dependent. Test results should be corrected to a standard temperature (e.g., 20°C) for comparison. If temperatures weren't recorded, the results are significantly less useful.

Frequency

Test performed at 50/60 Hz.

Key Considerations When Analyzing Your Results (Once you provide them)


Cable Type

What type of MV cable is it (XLPE, EPR, PILC, etc.)? This is the most critical piece of information.2.

Cable Age and History

How old is the cable? Has it been subjected to any known overloads, surges, or environmental stresses? This history is very important.3.

Operating Voltage

At what voltage is the cable operated?4.

Test Voltage

What voltage was the Tan-Delta test performed at? (This is usually specified as a fraction of the cable's rated voltage.)5.

Test Frequency

What frequency was used for the test (e.g., 50 Hz, 60 Hz, VLF)?6.

Temperature Correction

Were the Tan-Delta values temperature-corrected? If so, to what temperature? If not, what were the ambient and cable temperatures during the test?7.

Phase Balance

Are the Tan-Delta values relatively consistent across all three phases (if it's a 3-phase cable)? Significant imbalance between phases could indicate localized problems in one phase.8.

Trend Analysis

Have Tan-Delta tests been performed on this cable previously? If so, what is the trend? A rapidly increasing Tan-Delta is far more concerning than a stable value, even if it's slightly above the "new cable" threshold.9.

Connection details

Are the cable terminations and joints properly made? Any issue with these can give misleading reading.10.

Other Test Data

Are there other tests that have been performed on the cable that can be reviewed (Partial Discharge or Insulation Resistance).

What to Look For in the Results You Provide



Absolute Tan-Delta Values

The primary indicator.

Temperature

Crucial for accurate interpretation.

Test Voltage

Essential for comparison with standards and other tests.

Frequency

Essential for comparison with standards and other tests.

Trend Data (if available)

Past test results for comparison.

Any Notes or Comments

The testing technician's observations can be valuable.

Recommendations (Before you provide data)


Gather All Information

Collect as much information as possible about the cable's history, operating conditions, and the testing procedure.2.

Consult Standards

Refer to relevant standards (e.g., IEEE 400.2, IEC 60502) for guidance on interpreting Tan-Delta results for your specific cable type and voltage class.
3.

Consult with Experts

If you have significant concerns, consult with a qualified cable testing or power systems engineer. They can provide a more detailed analysis and recommendations based on your specific situation.

Once you provide the Tan-Delta test results, I can give you more specific and targeted advice. Flag for review