How Does ASTM D1816 Apply to New Insulating Oil?

This is Part 6 of a seven-part series on dielectric breakage voltage testing in insulating transformer oils. Part 5 covered the factors that cause ASTM D1816 values to vary and what drives result inconsistency across samples and test conditions. Here we will examine D1816 applications for new oil, oil being processed for installation, and oil in newly commissioned transformers. Part 7 will complete the discussion of standard dielectric breakdown voltage methods, examining IEC 60156 and its applications.

Evaluating New Oil Against IEEE C57.106

ASTM D1816 dielectric breakdown voltage testing plays an important role in the evaluation of new insulating oil across three distinct stages: as received from the supplier, after processing for installation in equipment below 230 kV, and after processing for installation in equipment at 230 kV and above.¹ IEEE Standard C57.106-2015 provides the governing acceptance criteria for each stage, with minimum D1816 values specified for both the 1 mm and 2 mm gap settings.²

New Oil As Received From the Supplier

Per Table 1 of C57.106-2015, the minimum acceptable D1816 values for new mineral insulating oil as received from the supplier are 20 kV at the 1 mm gap setting and 35 kV at the 2 mm gap setting. Oil that does not meet the minimum for the selected gap setting should be rejected. D1816 is a particularly important acceptance criterion for bulk oil shipments, where storage and transport conditions can introduce contamination that may not be apparent through visual inspection alone.

Processed Oil Prior to Energizing

Values for processed oil are higher than those for oil as received because new oil undergoes vacuum treatment and filtration to remove suspended particles, moisture, and dissolved gases before equipment is filled. This processing elevates the dielectric breakdown voltage, and the acceptance thresholds reflect that expectation.

An important field consideration applies at both voltage classes below and above 230 kV: D1816 values will decline somewhat when new oil is introduced into equipment during filling. When testing oil in the field after processing, values above the published minimums will be required in order for the filled equipment to meet the standard at energization.

Equipment Below 230 kV

Per Table 2 of C57.106-2015, minimum D1816 values for new oil processed for equipment below 230 kV, prior to energizing, are as follows:

• ≤ 69 kV: 25 kV (1 mm gap) / 45 kV (2 mm gap)
• > 69 kV and < 230 kV: 30 kV (1 mm gap) / 52 kV (2 mm gap)

Equipment at 230 kV and Above

Per Table 3 of C57.106-2015, minimum D1816 values for new oil processed for equipment at 230 kV and above, prior to energizing, are as follows:

• ≥ 230 kV and < 345 kV: 32 kV (1 mm gap) / 55 kV (2 mm gap)
• ≥ 345 kV: 35 kV (1 mm gap) / 60 kV (2 mm gap)

Why Higher Voltage Classes Require Higher Minimums

The progressive increase in D1816 minimums across voltage classes reflects the heightened consequences of contamination at higher operating voltages. Contamination degrades the dielectric performance of insulating oil in direct proportion to the electrical stress it must withstand — making thorough contamination removal both more critical and more measurable at higher voltage classes. A higher D1816 value is the direct result of more complete contamination removal, and the standard’s escalating thresholds enforce that requirement.

Summary:

• Three distinct acceptance stages apply to new oil under IEEE C57.106-2015: as received from the supplier, processed for equipment below 230 kV, and processed for equipment at 230 kV and above — each with its own D1816 minimums.
• As-received minimums are 20 kV (1 mm gap) and 35 kV (2 mm gap) — oil failing these thresholds should be rejected regardless of source.
• Processed oil thresholds are higher because vacuum treatment and filtration elevate dielectric breakdown voltage by removing particles, moisture, and dissolved gases prior to filling.
• Field testing after processing requires values above published minimums — ASTM D1816 values decline during equipment filling, so in-field measurements must exceed the standard’s thresholds to ensure compliance at energization.
• Higher voltage class equipment carries stricter minimums — the consequences of residual contamination scale with operating voltage, and the escalating D1816 thresholds enforce progressively more complete contamination removal.

References:

¹ Standard Test Method for Dielectric Breakdown Voltage of Insulating Liquids Using VDE Electrodes, ASTM D1816-12(2019), ASTM International, West Conshohocken, PA, 2019.

² IEEE Guide for Acceptance and Maintenance of Insulating Mineral Oil in Electrical Equipment, IEEE Std C57.106-2015 (Revision of IEEE Std C57.106-2006), IEEE, Piscataway, NJ, 2016.

In This Series:

• Part 1: How Are Dielectric Breakdown Voltage Tests Standardized?
• Part 2: What Does ASTM D877 Actually Detect — and When?
• Part 3: How D1816 Became the Standard for Dielectric Breakdown Testing
• Part 4: How Do You Interpret ASTM D1816 Results Accurately?
• Part 5: How Do You Diagnose a Failed ASTM D1816 Result?
• Part 6: How Does ASTM D1816 Apply to New Insulating Oil?
• Part 7: How Does IEC 60156 Compare for Dielectric Breakdown Testing?