blow transformer

Detailed Explanation and Countermeasures of Transformer Explosion (Blow Transformer)

Combined with American standards and practical application scenarios:

 I. Definition and Types

"Blow Transformer" refers to the phenomenon where due to faults in the transformer, internal arcs, overheating, or a sudden

 increase in pressure occur, leading to the rupture of the outer shell, sparks, smoke, and even explosions. Common types include:

- **Residential Distribution Transformer** (such as a 480V/240V single-phase transformer)

- **Industrial Transformer** (such as a 2.4kV-34.5kV three-phase transformer)

- **Power Transformer** (used for power grid transmission)

 II. Common Causes (with American Standard Basis Attached)

 1. Overload

- **Reasons**:

  - The load exceeds the rated capacity (for example, when residential air conditioners and electric vehicle charging piles operate

 simultaneously).

  - **NEC 450.3**: The load of the transformer shall not exceed 100% of the rated power (short-term overload needs to comply with 

the temperature rise standard).

- **Consequences**: Overheating of the winding → Decomposition of the insulating oil → Increase in internal pressure.

 2. Short Circuit Fault

- **Reasons**:

  - Aging of the winding insulation, invasion of small animals, and wear of the cables (About 15% of transformer failures in the

 United States are caused by squirrels every year).

  - **IEEE C57.12.00**: The transformer needs to be able to withstand a short-circuit impact of 3-10 times the rated current.

- **Consequences**: The instant large current causes the winding to deform and arc discharge.

 3. Insulation Failure

- **Reasons**:

  - Contamination of the insulating oil (moisture, impurities), and aging due to high temperature (the insulation grade is lower 

than the ambient temperature).

  - **UL 1561**: The insulating oil of the transformer needs to pass the dielectric strength test (≥30kV).

- **Case**: During the wildfires in California in 2024, 3 transformers caught fire due to insulating oil leakage.

 4. Lightning Strike and Overvoltage (Surge)

- **Data**: About 22% of transformer failures in the United States are caused by lightning every year (as statistically analyzed by IEEE).

- **Protection**:

  - **NEC 285**: A surge protector (SPD) needs to be installed, and the discharge current ≥10kA.

  - **IEEE C62.11**: The distance between the lightning arrester and the transformer needs to be <15 meters.

 5. Manufacturing Defects

- **Typical Problems**: Poor winding welding, design defects of the radiator (such as GE recalling 1000 transformers in 2023).

 III. Fault Signs and Emergency Handling

 1. Early Warning Signals

 2. Emergency Steps (Standards of American FirstEnergy Corporation)

1. **Power Off**: Immediately disconnect the high and low voltage side circuit breakers of the transformer (preferably use remote control).

2. **Isolate the Site**: Set a safe distance (for high-voltage transformers, it needs to be ≥10 meters), and hang a "Danger" sign.

3. **Extinguish the Fire**: Use a dry powder fire extinguisher (Class ABC), and do not use water (when the insulating oil is burning).

4. **Report**: Notify the power company (such as Florida Power & Light) and the fire department (refer to the NFPA 70E standard).

 IV. Preventive Measures (Classified by Scenarios)

 1. Residential Distribution Transformer

- **Model Selection**:

  - Capacity: Calculate according to the residential load (1.2-1.5 times the peak power, for example, a 50kVA transformer supplies 20 households).

  - Brands: Cooper Power Systems and Eaton are recommended.

- **Installation**:

  - **NEC 110.26**: The distance between the transformer and the building needs to be ≥3 meters (to prevent the spread of fire).

  - Grounding: Adopt **Ufer grounding** (steel bars in the concrete + grounding rod), and the resistance <5Ω.

 2. Industrial Transformer

- **Monitoring System**:

  - Install an **online oil chromatograph analyzer** (such as GE D60) to detect fault gases such as H₂ and CH₄ in real time.

  - Temperature sensor: Set the threshold at 105°C (trigger an alarm if exceeded, IEEE C57.91 standard).

- **Maintenance**:

  - Replace the insulating oil every 2 years (ASTM D3487 standard), and check the DC resistance of the winding.

 3. Outdoor Transformer

- **Protection Level**:

  - **NEMA 3R** (rainproof) or **NEMA 4X** (anti-corrosion), and install a bird protection net (aperture <5cm).

- **Environment**:

  - There should be no weeds or combustibles around (in line with the NFPA 70B "Electrical Equipment Maintenance Standard").

 V. Relevant Standards and Regulations

 VI. Analysis of Fault Cases

**The Transformer Explosion Incident in a Miami Apartment in 2024**

- **Reasons**:

  - Severe unbalance of the three-phase load (single-phase load accounts for 85%) leads to the drift of the neutral point.

  - Failure to regularly detect the load balance as required by **NEC 210.10**.

- **Lessons**:

  - Install an **automatic load balancing device** (such as ABB PCS 100).

  - Mandatorily replace old transformers (>20 years old).

**Conclusion**: The explosion of transformers needs to be prevented through **appropriate model selection, regular maintenance,

 and overvoltage protection**. When a fault occurs, follow the NEC and NFPA standards to cut off the power and isolate the site.

 In the American market, brands such as **Cooper Power** and **Eaton** that have passed the UL certification are recommended. 

Pay attention to the compliance of grounding and the environment during installation.