What are the oil-immersed transformer monitoring
Date: July 14, 2025 09:26:08
The monitoring of oil-immersed transformers can be categorized into "Electrical quantity monitoring + Oil system monitoring + Mechanical/environmental condition monitoring + Online intelligent diagnostics" There are 12 core indicators in four sections. Daily operation, preventive testing and online monitoring are all centered on these items.
1. Electrical quantity and temperature rise monitoring
| Monitoring projects |
Methods/Sensors |
Limit or criterion |
Major Abnormal Signs |
| Winding hot spot temperature |
Fluorescent fiber optic or thermal simulator |
≤ 78 K (hot spot temperature rise) |
Localized overheating, turn-to-turn short circuit |
| Top oil temperature |
Platinum Resistors / Fiber Optics |
≤ 55 K (natural cooling) |
Oil degradation, heat dissipation failure |
| Load Current & Voltage |
Secondary CT/PT |
real time value |
Overload, three-phase unbalance |
| Core ground current |
clamp-on ammeter |
≤ 0.1 A (empirical value) |
Multi-point grounding of the iron core |
2. Oil system monitoring
| Monitoring projects |
Methods/Sensors |
Limit or criterion |
Major Abnormal Signs |
| oil level |
Magnetic Flap/Float |
Reservoir scale ±10 % |
Oil leaks, sudden temperature changes |
| Oil Chromatography (DGA) |
Online Chromatograph |
H₂, C₂H₂, CH₄, C₂H₄, CO, CO₂ Concentrations and gas production rates |
Discharge, overheating, insulation deterioration |
| Water content in oil |
Coulomb method/fiber optic humidity |
≤ 25 mg/L (500 kV) |
Dampness of insulation |
| oil breakdown voltage |
Offline Sampling |
≥ 50 kV (500 kV class) |
Oil Deterioration |
3. Mechanical and environmental condition monitoring
| Monitoring projects |
Methods/Sensors |
Limit or criterion |
Major Abnormal Signs |
| partial discharge |
UHF/Ultrasound/High Frequency CT |
≤ 300 pC (apparent discharge) |
Insulation defects, air bubbles |
| cooling system |
Current, Vibration, Flow |
Fans and oil pumps operate normally |
Insufficient heat dissipation, clogged oil lines |
| Gas Relay |
Reed switch/fiber optic |
Zero gas, no light gas alarm |
Internal discharge, oil leakage |
| pressure relief valve |
Mechanical indicators/sensors |
No movement, no fuel injection marks |
High internal pressure |
| vibration and noise |
Accelerometers/sound level meters |
≤ 85 dB(A) |
Loose iron core, deformed windings |
4. Online integrated diagnostic platform
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data fusion: Real-time data such as temperature, oil chromatography, local discharge, load, etc. are sent to the background AI diagnostic model to realize:
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Failure mode recognition (discharge, overheating, moisture, etc.)
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Remaining life assessment
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Dynamic Load Guidance (boosts utilization by 10-15 %)
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communications protocol: IEC 61850, Modbus-TCP, MQTT, support for cloud/edge computing.
On-site implementation of recommendations
| take |
Required items |
Optional items |
| Main transformers 220 kV and above |
Fluorescent fiber optic winding temperature measurement + in-line DGA + UHF localized discharge |
Microwater in oil online, core grounding online |
| 110 kV distribution substation |
Top oil temperature + online DGA |
Fluorescent fiber optic winding temperature measurement |
| Newly built power stations |
Integrated intelligent control cabinet (with all online modules built-in) |
Drone infrared inspection docking |
"Temperature + Oil and Gas + Local Discharge" Is the oil-immersed transformer monitoring the "three big things", the rest of the project according to the voltage level, importance and investment intensity of flexible configuration.
