The shutdown had been planned for months. At one of the largest petrochemical plants in Saudi Arabia, every contractor was on a strict timeline. The work had to be done right, and it had to be done fast.

For Petrozone International, this job was about more than just transformer maintenance. It was about executing a complex, high-risk operation with precision, ensuring that the plant’s Generator Step-Up Transformer (GSUT) was fully serviced, tested, and ready for reliable operation.

There was no margin for error. The entire process had to be completed step by step, in the right sequence, without a single delay.

At the center of the job was this massive transformer:

  • Voltage: , 18KV/230KV,
  • MVA:165/220MVA (ONAN/ONAF)
  • Cooling Method: ONAN/ONAF
  • Vector Group: YNd1
  • Frequency: 60Hz
  • Phase: 3
  • Main Tank Oil Capacity: 60,000 Liters

This was a high-voltage, high-capacity machine, and our job was to bring it back to top condition.

Step 1: Setup And Safety Measures

Before any work could begin, the site had to be prepared. Safety was the first priority.

🔹 Spill containment measures were put in place—no oil leaks were allowed.
🔹 Barriers were set up around the work zone to keep unauthorized personnel away.
🔹 All tools and filtration machines were checked and positioned for smooth execution.

With everything secure, we were ready to begin.

Step 2: Oil Filtration Of Transformer Main Tank

Transformer oil is the lifeblood of the system. Over time, it absorbs moisture, collects impurities, and loses its insulating strength.

The first major task was to filter the oil in the transformer’s main tank.

How we did it:
✔ Connected high-efficiency oil filtration machines to the main tank.
✔ Started oil circulation and ran multiple filtration cycles.
✔ Performed Breakdown Voltage (BDV) tests at each stage to monitor progress.

By the end of the process, the oil was fully purified and its insulation strength was restored.

Step 3: Oil Filtration Of OLTC Chamber

The On-Load Tap Changer (OLTC) is one of the most critical parts of the transformer. It allows voltage adjustments under load, but its oil also degrades over time.

To ensure smooth OLTC operation, we:

✔ Drained the old oil and stored it safely.
✔ Ran multi-cycle filtration to remove contaminants.
✔ Refilled the OLTC chamber with fresh, filtered oil.

This step ensured smooth switching operations and extended the life of the OLTC unit.

Step 4: Preparing For Electrical Testing – Opening HV Cable Chambers

Before electrical testing could begin, we had to open the high-voltage (HV) cable chambers.

 Why was this important?
Since the HV cable chambers were oil-filled, the oil had to be drained into an external transformer tank before opening the chamber. This ensured a controlled environment where the high-voltage links could be safely accessed.

✔ Drained the HV cable chamber oil to prevent spills.
✔ Carefully opened the chamber and disconnected HV links.
✔ Inspected connections for any signs of overheating, corrosion, or insulation damage.

With everything checked and verified, the transformer was now ready for electrical testing.

Step 5: Comprehensive Electrical Testing

Now came the most critical part of the job—verifying the transformer’s health through electrical testing. Every test had to be done systematically, leaving nothing to chance.

 Tests performed:
✔ General inspection and physical checks
✔ Mechanical verification of all parts
✔ Insulation Power Factor Tan δ and Capacitance Test (Winding & Bushings)
✔ Insulation Resistance Test (IR)
✔ Winding Resistance Test (WR)
✔ Polarization Index (PI)
✔ Transformer Turns Ratio (TTR)
✔ Magnetic Balance Test
✔ Magnetizing Current Test
✔ Terminal Tightness Check

Every result was recorded and compared against manufacturer standards. The transformer passed every test, confirming it was in excellent condition.

Step 6: Final Filtration Of Hv Cable Chamber Oil

Once electrical testing was complete, the HV cable chamber oil had to be restored.

This was a delicate step. Any moisture trapped inside the cable chamber could lead to insulation failure.

How we did it:
✔ The drained oil was filtered separately using high-efficiency machines.
✔ The HV cable chamber was kept under vacuum to remove any residual moisture.
✔ The filtered oil was refilled carefully, ensuring no contamination.
✔ The chamber was sealed and rechecked for leaks.

With this step done, the HV cable chamber was now fully restored and ready for operation.

Step 7: Final Oil Analysis & System Checks

Before declaring the job complete, we conducted a final oil analysis for:

✔ Transformer Main Tank
✔ HV Cable Chamber
✔ OLTC Chamber

A Dissolved Gas Analysis (DGA) was performed to detect any hidden faults. Results came back clear, confirming that the transformer was ready for re-energization.

🔹 Final leak checks were done.
🔹 Oil levels were verified.
🔹 Worksite was cleaned and all tools were removed

Final Result – A Transformer Back In Prime Condition

After days of nonstop, round-the-clock execution, the transformer was ready.

  • Oil restored to peak insulation strength.
  • Electrical tests passed with top results.
  • HV cable chamber serviced, dried, and sealed.
  • No leaks, no delays, no issues.

When the plant’s engineers re-energized the transformer, it hummed back to life, carrying the full load without a hitch.

The job was a success.

What This Means For Maintenance Teams

If you’re running a plant, your transformers are either being maintained properly, or they’re heading for failure.

Ask yourself:
🔹 Are your transformers being serviced with this level of detail?
🔹 Do you know the condition of your HV cable chambers?
🔹 Has your oil been tested for BDV and DGA recently?

If you hesitate to answer, then it’s time to get in touch with Petrozone International.

When It Comes To Transformer Maintenance, We Get It Done Right

At Petrozone International, we don’t just maintain transformers—we bring them back to life with precision, efficiency, and zero compromise on quality.

Want to know more about our transformer maintenance services? Click here  

Need to contact Petrozone? Get in touch here

Power your plant with confidence. Maintain your transformers with Petrozone.