What Are the Causes of Loose Transformer Cores?

If there is no binding adhesive (or if the adhesive fails), the causes are as follows:

(1) The burrs around the edges of the silicon steel sheets are too large, and the stacking seam gaps do not meet the specified requirements.

(2) Errors in the stacking sequence (e.g., missing sheets or overlapping joints) result in the core not being compressed tightly enough after stacking.

(3) Waviness or bending in the silicon steel sheets prevents the core from being clamped securely after pressing.

(4) Poor-quality epoxy resin glass-fiber tape used for binding the yoke and core, improper binding techniques, insufficient binding tension, or failure to cure into a solid structure can all lead to loose binding, aging of the binding hoops, and subsequent faults, ultimately causing the core to loosen.

(5) The clamping bolts are not tightened sufficiently, or anti-loosening washers are not installed. During operation, electromagnetic vibrations cause the bolts to loosen, which in turn loosens the core and can also cause the grounding copper shunts to fall off.

(6) If the clamping bolts are not tightened properly or if there is slight vibration noise, the bolts can be retightened using a large wrench until the noise ceases. If the noise persists, further measures must be taken.

(7) If noise is generated by a few missing sheets, overlapping joints, waviness, bending, or damaged silicon steel sheets, the clamping bolts can be retightened, or paper shims can be added before retightening. If the noise stops, no further action is needed. Otherwise, the core must be disassembled to re-select the silicon steel sheets and re-stack and press the core. When selecting the sheets, the standard stacking pattern of two sheets per layer must be strictly followed; any instances of single-sheet or three-sheet stacking must be corrected to two sheets. Sheets of uniform thickness should be selected. Bent, damaged, or severely wavy sheets must be discarded. Sheets with excessive burrs must be re-deburred; they can only be re-stacked once the burr height is reduced to less than 0.03 mm.

(8) For faults involving damaged, aged, or loose epoxy resin glass-fiber tape binding hoops, the binding must be completely redone using qualified materials. During the binding process, temporary steel hoops must first be applied to clamp the core tightly. After the tape is wound to the required thickness, it must be baked and cured into a solid structure before the temporary steel hoops are removed.