RCM & PM OLTC Overhauling and Leakage Repair on 67MVA Power Transformers N.G SA

Our company delivers professional RCM (Reliability Centered Maintenance) and Preventive Maintenance (PM) services for 67MVA power transformers, focusing on OLTC overhauling and transformer oil leakage repair. These services help National Grid Saudi Arabia reduce failures, avoid shutdowns, and increase transformer lifespan.

What is OLTC and Why Overhauling is Important?

An On-Load Tap Changer (OLTC) is a device inside a transformer that adjusts voltage levels while the transformer is still running. It helps keep electricity stable even when demand changes.

Common OLTC Failure Signs

• Burning smell or carbon contamination
• Overheating or unusual noise
• Slow tap-changing movement
• High contact wear
• Oil contamination due to arcing

Why Overhauling Matters

If the OLTC fails, the transformer can shut down immediately, causing power outages. Overhauling ensures:

• Smooth tap-changing
• Reduced arcing
• Lower risk of internal damage
• Longer transformer life

This is why National Grid Saudi Arabia requires strict OLTC maintenance standards across all major substations.

Scope of Work – 67MVA Transformer Overhauling

Our team followed complete RCM and PM workflows while servicing the 67MVA power transformer for National Grid SA.

OLTC Disassembly & Inspection

We fully opened the OLTC chamber, removed switching components, inspected for carbon deposits, overheating, oil contamination, and worn contacts.

Contact Replacement

Worn and burnt contacts reduce performance. We replaced:

• Fixed contacts
• Moving contacts
• Reversing switch contacts

This ensures smooth and fast switching.

Mechanical Cleaning

All parts were cleaned to remove sludge, carbon, and moisture. This improves oil performance and reduces chances of internal faults.

Switching Mechanism Calibration

We calibrated:

• Tap positions
• Motor drive
• Reversing mechanism

This ensures the OLTC changes taps accurately and safely under load.

• Selector switches

Transformer Leakage Repair (Oil Leakage)

Transformer oil leakage is common in older or heavily loaded units. Oil must remain inside the transformer to cool and insulate internal components.

Types of Oil Leakages

• Gasket leak
• Radiator or cooler pipe leak
• Bushing flange leak
• Valve leak

Causes of Leakage

• Tank welding crack
• Gasket ageing
• Vibration
• Corrosion
• High temperature
• Improper sealing

Complete Leakage Repair Steps

• Identify the leakage source
• Drain and prepare the repair area
• Replace damaged gaskets
• Seal the cracked area
• Tighten all bolts with torque setting
• Perform oil top-up
• Check pressure and vacuum sealing

This guarantees zero leakage after testing.

RCM (Reliability Centered Maintenance) Approach

National Grid Saudi Arabia uses RCM to reduce faults and increase transformer availability.

Why RCM is Important

• Increases system reliability
• Reduces unplanned shutdowns
• Extends OLTC and transformer lifespan
• Improves safety
• Ensures continuous electricity supply

Using RCM, we analyze OLTC failure causes, load cycles, and environmental conditions to plan the best maintenance actions.

Preventive Maintenance (PM) Activities Performed

To meet maintenance standards in Saudi Arabia, our PM activities include:

DGA Testing (Dissolved Gas Analysis)

Detects faults inside oil like arcing, overheating, or insulation breakdown.

IR Thermography

Identifies hotspots on bushings, connections, and OLTC.

OLTC Timing Test

Checks switching speed and mechanical movement.

Oil Filtration & Dehydration

Removes:

• Moisture
• Acidity
• Sludge
• Gas bubbles

Bolts Tightening & Torqueing

Ensures all flanges, valves, and radiators stay leak-free.

These PM tasks ensure the transformer stays in excellent operating condition.

Testing & Commissioning After Overhaul

After completing overhauling and leakage repair, our engineers perform:

Functional Testing

• Manual tap changing
• Motor drive operation
• Selector mechanism test

Load Testing

Checks OLTC performance under real power load.

Final Inspection Checklist

• Oil level and pressure
• No leakage
• Proper temperature
• Correct tap position
• Clean contacts
• Healthy insulation

Only after passing all tests, the transformer is returned safely to operation.

FAQs

1) What is an On-Load Tap Changer (OLTC) and why does it need overhauling?

An On-Load Tap Changer (OLTC) is a critical transformer component that regulates voltage under load conditions. Over time, OLTC contacts and oil degrade due to arcing and continuous operation, making overhauling necessary to maintain grid stability, reduce failures, and increase transformer lifespan.

2)How often should a 67MVA power transformer OLTC be serviced in Saudi Arabia?

For National Grid Saudi Arabia–level installations, OLTC inspection is recommended every 3–5 years, while major overhauling should be performed every 6–8 years, depending on operational load, environmental conditions, and oil test results.

3)What is included in the OLTC overhauling process?

Typical OLTC overhauling includes:

• Mechanical checks and reassembly
• Disassembly and cleaning
• Replacement of carbon contacts
• Inspection of selector and diverter switches
• Oil filtration or oil replacement
• Electrical testing (TTR, IR, BDV,Contact Resistance)

4) What causes oil leakage in power transformers?

Oil leakage usually occurs due to:

• Faulty flange joints
• Thermal expansion
• Worn bushings or conservator tank seals

Improper previous maintenance

5)Why is OLTC and leakage repair important for National Grid Saudi Arabia?

Reliable transformers ensure stable power distribution, reduced downtime, and operational safety. Overhauling and repairing a 67MVA transformer prevents unplanned outages and complies with Saudi National Grid operational standards.

6)How long does transformer OLTC overhauling usually take?

A complete OLTC overhauling and leakage repair for a 67MVA transformer typically takes 1 day, depending on damage, spare part availability, and testing requirements.

7)Do you provide OLTC overhauling and leakage repair services across Saudi Arabia?

Yes, services are available across Riyadh, Dammam, Jeddah, Makkah, Madinah, Tabuk, Abha, and all regions in Saudi Arabia.

8)How do you ensure quality and compliance during transformer maintenance?

We follow IEC standards, National Grid Saudi Arabia maintenance guidelines, and complete all repairs with certified engineers, calibrated tools, and documented test reports.

Final Results & Benefits for National Grid Saudi Arabia

After completing the OLTC overhauling and leakage repair, the 67MVA transformer showed significant improvements:

 Zero oil leakage
 Smooth and fast OLTC switching
 Stable transformer temperature
 Improved voltage regulation
 Reduced risk of sudden shutdowns
 Increased reliability of the power network
 Extended asset lifespan

Thanks to our RCM + PM approach, the transformer is now performing at optimum capacity, supporting National Grid SA operations reliably.