PROPER SAMPLING of Dielectric Liquid

Sampling is a critical element in predictive maintenance rather than reactive maintenance.
- Predictive Maintenance: Involves understanding the current state of apparatus to preempt failures and outages.
- Reactive Maintenance: Involves responding to failures after they have occurred.
Objectives of Sampling:
- To identify early faults in the apparatus, particularly insipient faults.
- Example: Arcing may be signaled by as little as one part per million of acetylene.
- To assess the quality of new liquid or existing stored liquids.
- Common Issue: Contamination from improper handling during transfers.
- Minimize outages by conducting planned maintenance rather than dealing with unexpected failures.
- Maintenance planning can lead to improved reliability of equipment.
- Ensure safety for staff, contractors, and the public by identifying hazardous conditions.
- For instance, high gassing levels can pose substantial risks if not managed properly.
- Maintain relationships with insurance providers and work to reduce premiums through effective asset management.

A good sample is integral for accurate analysis and understanding of the equipment condition.
The sampling process should avoid contamination, which can lead to misleading results and public relations issues.
- Impacts of Contamination:
- Poor sampling can lead to poor public perception if issues arise, potentially leading to negative media coverage.

Valves: Central to the sampling process and can impede obtaining a clean sample.
- Contamination often occurs due to debris settling at the bottom near the valve.
- To obtain a clean sample, it’s essential to analyze the bulk insulation rather than residue collected at the valve.

The container used for sampling affects the sample quality.
- Compatibility of the container and any lid used is significant as reactions may occur that can alter sample integrity.
- Atmospheric Influence: High humidity days are unfavorable for sampling because oils can absorb moisture quickly.
Tubing Memory: Oil may diffuses into tubing (elastomers), leading to contamination if the same tubing is used across multiple samples.

Preparatory Steps: Sample operation conducted by a technician referred to as Harry.
- Harry begins by recording nameplate information, crucial for contextual analysis:
- Temperature rise (e.g., 55°C or 65°C), type of transformer, preservation system, manufacturer details, and construction materials (oil, ester, silica).
Safety Precautions: Always check valves to avoid unnecessary oil spillage during the sampling process.
Tools for Sampling:
- Requires PPE (Personal Protective Equipment) like lab coats and nitrile gloves (latex not suitable for oil).
- Use of plumbing tools to effectively access sampling points without making a mess.

Harry flushes the valve with at least two quarts of oil to ensure that contaminants are cleared.
- Key consideration: Flush out any materials trapped behind valve components.

Sample Filling:
- Harry fills sample bottles to about a third volume and swirls for homogenization before transferring to waste.
- Ensures a final fill to the shoulder of the sample bottle for sufficient material without risking hydraulic pressure issues.
Syringe Sampling:
- The last sample taken for maximum purity. It involves checking syringe integrity and pre-wetting to create a seal.
Importance of expelling bubbles to prevent interference in later analysis; nitrogen levels are an essential consideration post-sampling.

Cleanup after sampling is as critical as the sampling itself.
Inspect for any leaking oil and ensure all utilities and equipment are returned to original condition to avoid future hazards.
Document Cleanliness: All areas should be left cleaner than found, emphasizing safety.

Sampling duration should be approximately twenty minutes to ensure proper procedures are followed.
Refer to established guidelines (e.g., ASTM D923, IEC methods) for sampling procedures to standardize practices.
- Note: Differences in valve types may exist based on geographic manufacturing standards.
Tests Impacted by Sampling Quality:
- Key tests such as dielectric strength, water content, and dissolved gas analysis can yield false results if contamination or improper methodologies are applied.

Choose containers based on compatibility and required volume for specific tests.
- Avoid plastics that contaminants and perform poorly in chemical tests. Favor glass and aluminum to avoid issues.
Review specific volume requirements based on the tests, e.g., dielectric strength requests may require a larger sample than standard tests.
Materials for Sampling:
- Adequate equipment must be on hand before sampling to ensure successful operations.
- Essential items: Carboy for waste oil, rags, absorbent pads, plumbing tools, proper PPE, and new tubing.
Important: Pre-planning for materials that can’t be interchanged between types of oils (natural esters vs. mineral oils).

Assess surrounding areas for hazards prior to sample collection.
- Check for wildlife, leaks, and environmental factors that could impact safety.
Proper handling and disposal of waste materials must adhere to environmental regulations, especially in sensitive areas.

Comprehensive data recording during sampling helps in achieving accurate lab results:
- Document transformer characteristics and environmental parameters.
- Ensure clarity on the reason for sampling and any changes observed (e.g., transformer trips, routine checks).
Laboratory Information Management Systems (LIMS):
- Once serial numbers are entered, track sample history effectively without need for repeated documentation each time.
- Final sample forms should reflect detailed information for reactive adjustments in the laboratory.