What happens if there is water in the transformer oil?

Water mixed into transformer oil will seriously affect its performance and may cause equipment failure. The specific impacts and hazards are as follows:

Deterioration of electrical performance

1. Decreased insulation strength

- Water significantly reduces the breakdown voltage:

• When the water content is 50 ppm, the breakdown voltage drops by about 35%

• When the water content is 100ppm, the breakdown voltage may be halved

- Typical case: A 220kV transformer caused a bushing flashover accident due to excessive water content in the oil (78ppm)

2. Increased dielectric loss

- The tanδ value increases exponentially with water content:

| Water content (ppm) | tanδ (90℃) |

|------------|-----------|

| 10 | 0.002 |

| 50 | 0.008 |

| 100 | 0.015 |

Changes in chemical properties

1. Accelerated oil aging

- Water catalyzes oxidation reaction, and the acid value (KOH) growth rate increases by 3-5 times

- For every 10 ppm increase in water, the oil life is shortened by about 15%

2. Damage to solid insulation

- When the water content of cellulose insulation paper exceeds 1.5%:

• Tensile strength decreases by 50%

• The degree of polymerization (DP) decays by ≥100 per year

Risk of mechanical failure

1. Intensified partial discharge

- Water vaporization produces bubbles, which trigger PD under the action of the electric field

- Measured data: When the water content is greater than 30 ppm, the partial discharge increases by 2 orders of magnitude

2. Hidden dangers of low-temperature operation

- At freezing temperature (-40℃):

• Freezing water freezes and causes an oil channel blockage

• Volume expansion may damage the radiator

Typical failure modes

1. Insulation failure

- Short circuit between winding turns

- Flashover on the surface of the bushing

2. Corrosion of metal parts

- Water reacts with sulfides to generate H₂SO₄

- Case: A transformer in a power station produces Cu₂S deposits due to copper winding corrosion

3. Gas relay malfunction

- False gas signal generated by water evaporation

Hazard level assessment

| Water content (ppm) | Hazard level | Recommended measures |

|------------|---------|---------|

| ＜15 | Normal | Routine monitoring |

| 15-30 | Note | Strengthen detection |

| 30-50 | Warning | Planned treatment |

| ＞50 | Danger | Immediate treatment |

Special note: When the water content in the oil exceeds the standard, the following should be detected simultaneously:

1. Dissolved gas in the oil (pay special attention to the H₂ content)

2. Acid value and interfacial tension

3. Water content of solid insulation (calculated by oil-paper equilibrium curve)

Prevention suggestions: Install an intelligent online micro-water monitoring system to monitor the changes in water content in the oil in real time, and automatically start the vacuum oil filter device when the water content approaches the warning value. For important transformers, it is recommended to perform chromatographic analysis of oil moisture at least once a year.