How to prevent Transformer Sudden Short-Circuit Failure?

—Analyzing Short-Circuit Resistance Verification and Structural Reinforcement Solutions

 

In power grid systems and industrial distribution, "transformer sudden short-circuit leading to winding deformation and insulation breakdown" has become a global challenge for electrical equipment reliability. According toIEEE C57.12.00 statistics, short-circuit current impacts can subject windings to electromagnetic forces exceeding 100 kN, causing 40% of transformers to fail after their first short-circuit event. This article systematically explains short-circuit resistance verification processes and structural reinforcement technologies based on international standards likeIEC 60076-5 und  IEEE C57.12.90, supported by cross-regional engineering validation data.

 

Inhalt

1. Destruction Mechanism and Risk Quantification of Short-Circuit Current

● Electromagnetic Force Impact of Short-Circuit Current

(1)Short-Circuit Current Calculation and Electromagnetic 

Force Generation When a short-circuit occurs on the transformer’s secondary side, the primary current surges to 10–25 times its rated value, determined by the transformer’s impedance voltage percentage (%).

 

 

Formel:

 

Variablendefinitionen:

· : System rated voltage

·: Impedance voltage percentage (typical range: 4%–12%)

·: Transformer rated current

 

Ejemplo: A 1000 kVA transformer with Z%=6% and I_Nenn = 1443A has a short-circuit current of:

 

(2)Direct Mechanical Damage from Electromagnetic 

Forces Per the Lorentz force formula, electromagnetic forces between adjacent winding conductors are:

 

Variablendefinitionen:

·: Leakage flux density (0.5–1.2 T, determined by winding spacing and current)

·:Short-circuit current

·: Conductor effective length

 

Ejemplo:If B=0.8T and L=2m, the force is: F=0.8×24,050×2=38,480N(≈38.5kN)

 

Fehlermodi:

·Axiale Kompression: High-voltage windings experience inward pressure, leading to inter-turn insulation crushing.

·Radiale Ausdehnung: Low-voltage windings expand outward, causing support strut fractures and eventual collapse.

 

● Thermal Effects and Insulation Degradation

(1) Joule Heating Mechanism:

Short-circuit current generates heat via winding resistance:

 

Variablendefinitionen:

·R: Winding resistance (Ω)

·t: Short-circuit duration (typically ≤2 seconds)

·c: Specific heat capacity (copper: 385 J/kg·K)

·m: Conductor mass

Ejemplo: For a 50 kg copper conductor with AIsc =24kA and t=1s:

 

(2)Insulation Failure Process:

·Thermische Zersetzung: Epoxy resin carbonizes when temperatures exceed 105°C (Class A insulation limit).

 

·Dielectric Strength Reduction: Insulation paper breakdown voltage drops 5%–8% per 10°C rise (IEC 60076-5).

 

·Inter-Turn Short Circuits: Partial discharge inception voltage falls from 15 kV to below 6 kV, causing permanent damage.

 

2.International Standards for Short-Circuit Resistance Verification

● IEC 60076-5:Dynamic Stability Testing Core standard for transformers ≤35 kV.

(1)Testprozedur:

·Pre-short-circuit state:Apply rated current; monitor temperature and vibration.

 

·Short-circuit impulse:Apply symmetrical current at 75% tap position for 0.25 seconds.

 

·Repeat three times to assess cumulative damage.

 

(2)Bestehenskriterien:

·Reactance change ≤2%

 

·Winding deformation ≤1.5 mm (measured via laser displacement sensors).

 

● IEEE C57.12.90:Mechanical Strength Validation Key standard for large-capacity transformers in North America.

(1)Anforderungen:

Capacity (kVA)	Short-Circuit Cycles	Axial Force Limit (kN)
≤ 2500	3	80
2501-10,000	2	150
> 10,000	1	300

 

(2)Testmethoden:

·Static pressure simulation using hydraulic cylinders (60-second hold).

 

·Vibration frequency sweep (10–2000 Hz); natural frequency shift ≤5%.

 

3. Structural Reinforcement Solutions for Enhanced Short-Circuit Resistance

● Optimized Winding Support Systems

(1)Verstärkungstechniken:

·Epoxy-Resin Impregnated Struts: 

Glass-fiber-reinforced epoxy (bending strength ≥350 MPa, 4× stronger than wood) reduces radial deformation from 3.2 mm to 0.8 mm.

·Axial Compression Systems: 

Disk spring assemblies (preload ≥50 kN) mitigate  axial compression, increasing withstand cycles from 1 to 3 (per IEC 60076-5).

 

(2)Leistungsvergleich:

 

Parameter	Traditionelle	Verstärkt
Axial Deformation (mm)	3.2	0.8
Short-Circuit Cycles	1	3

 

● Core and Clamping Structure Enhancements

(1)Verstärkungstechniken:

·Low-Hysteresis Silicon Steel: 23ZDKH90 steel reduces core vibration energy transfer by 40%, avoiding resonance (ISO 10816-3 compliant).

 

·Multi-Layer Welded Clamps: Q345B steel (yield strength 345 MPa, 47% higher than Q235) absorbs 300 kN axial forces (meets IEEE C57.12.90).

 

(2)Mechanische Eigenschaften:

Werkstoff	Streckgrenze (MPa)	Damping Ratio (ξ)
Q235 Stahl	235	0.02
Q345B Stahl	345	0.05

 

Zusammenfassend

Conclusion Modern transformers reinforced viaIEC 60076-5 und IEEE C57.12.90 standards can withstand ≥50 kA short-circuit currents (IEC Level 4). Global cases show a 70% reduction in annual failure rates (ABB 2023 Whitepaper). For customized solutions, contact our technical team for simulation, testing, and validation services.

 

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