Reasons and prevention of winding deformation in transformer faults

Transformer winding deformation is one of the common faults in transformer operation, and its causes are diverse, posing a serious threat to the safe operation of transformers. The following is a detailed analysis of transformer winding deformation:

1、 The main causes of transformer winding deformation

1. Design and manufacturing reasons:

• Unreasonable design, such as insufficient short-circuit strength and poor dynamic stability.

• There are defects or unreasonable factors in the manufacturing process, such as insufficient strength and stiffness of clamping and supporting components, misalignment of coils during assembly, and poor clamping.

2. Short circuit fault during operation:

• Transformers are inevitably subjected to various short-circuit faults during operation. If there are unreasonable parts or insufficient mechanical strength in the structure of the transformer itself, it will cause deformation or displacement of the transformer winding.

• During the short circuit process, the winding experiences complex vibrations composed of inherent and forced oscillations, leading to insulation relaxation, misalignment of spacer blocks, loosening of iron core screws, and ultimately causing deformation of the winding.

3. Impact during transportation:

• The huge dynamic force generated by the impact during transportation can also cause displacement and deformation of the winding.

2、 The main forms and characteristics of transformer winding deformation

1. Overall deformation:

• The displacement of the winding is caused by external forces such as impact, tilt, and vibration during transportation. The size of the deformed winding remains unchanged, but the relative displacement of the iron core changes. The inductance and inter cake capacitance of the winding remain unchanged, while the capacitance to ground changes.

2. Local deformation:

• The local deformation between the pancakes causes some loose wire pancakes to be squeezed under the action of short-circuit electromagnetic force, while others are stretched, resulting in changes in capacitance.

3. Interturn short circuit:

• After a turn to turn short circuit occurs in the winding, the inductance value decreases, the spectral curve changes significantly, the amplitude increases, and some resonance point peaks disappear. But this situation is difficult to capture, and once it occurs, the wire turns will burn out, causing serious damage to the transformer.

4. Wire displacement and deformation:

• When the wire is long and not firmly fixed, displacement and deformation may occur during operation. Wire displacement can cause changes in the capacitance of two ports in the equivalent circuit, thereby affecting the spectral curve.

5. Radial deformation:

• When the winding is subjected to radial force, the internal winding shrinks inward, the diameter decreases, and the inductance decreases. At this point, the distance between the inner and outer windings increases, their capacitance decreases, and the resonance peak in the spectrum shifts towards higher frequencies, resulting in an increase in amplitude.

6. Axial distortion deformation:

• When the gap between transformer windings is large or some of the support rods are displaced, the windings will twist into an S-shape along the axial direction under the action of electromagnetic force. At this point, some inter cake capacitance and ground capacitance decrease.

3、 The hazards of transformer winding deformation

1. Transformer damage:

• Winding deformation may directly cause damage to the transformer and prevent it from continuing to operate.

2. Decreased insulation strength:

• Winding deformation can cause damage to the insulation material or change in insulation distance of transformers, resulting in a decrease in insulation strength. Under long-term normal voltage or overvoltage, it may ultimately lead to insulation breakdown.

3. Decreased mechanical strength:

• After winding deformation, even if the insulation condition is not damaged, the mechanical strength of the coil will decrease. When subjected to a short circuit fault again, it will not be able to withstand the huge electric force and may suffer damage.

4、 Detection and Prevention of Transformer Winding Deformation

1. Testing method:

• Frequency Response Analysis (FRA): By detecting the amplitude frequency response characteristics of each winding of a transformer, it is determined whether the winding has undergone deformation.

• Short circuit impedance method: Determine whether the winding is deformed by testing the changes in leakage inductance in the transformer winding.

• Other methods include low-voltage pulse method, capacitance change method, ultrasonic detection method, vibration method, etc.

2. Preventive measures:

• Strictly control the quality of transformer manufacturing to ensure reasonable design and excellent manufacturing.

• Strengthen the monitoring of transformer operation status, timely detect and handle winding deformation problems.

• Reduce the chance of short circuit on the busbar. Once a short circuit occurs on the busbar side, the protection should cut off the busbar power supply transformer as soon as possible.

• Measurement of frequency response analysis of large transformers in operation, in order to compare with the frequency response analysis results after accidents occur and reasonably determine the degree of transformer winding deformation.