If the transformer core becomes loose, how does the current change?

The core becomes loose, resulting in increased losses, higher current flow, and abnormal noises.

A loose core should cause an increase in magnetic resistance, which in turn means an increase in magnetic flux. As a result, more power conversion is required; this may be reflected as an increase in current, and the oil temperature of the transformer should rise as well.

This post was last edited by jjli618 on 2010-7-1 14:25. 1. Reasons for loose core 　　(1) Large burrs around the silicon steel sheets, and the gap between the layers does not meet the requirements. 　　(2) There are defects in the discs, resulting in empty spaces or overlaps, which prevents the core stacks from being compressed tightly. 　　(3) The iron chips are wavy and curved, preventing a tight fit after lamination. 　　(4) Poor quality of the epoxy resin fiberglass tape used for binding the iron yoke and core, improper manufacturing processes, insufficient binding tension, and failure to form a solid unified structure all lead to loose binding, aging of the binding straps, and malfunctions, resulting in the core becoming loose. 　　(5) The fastening bolts of the clamp are not tightened, or anti-loosening washers are not used; as a result, they become loose after vibration caused by electromagnetic forces, which in turn loosens the core and causes the grounding copper plates to fall off. Treatment methods: (1) If the fastening bolts of the clamping pieces are not tightened properly or there is slight vibration noise, use a large wrench to tighten the bolts again until the noise disappears; if the noise persists, further measures need to be taken. 　　(2) In cases where silicon steel sheets with a few empty spots, overlaps, waves, bends, or damages produce noise, the fastening bolts can be tightened again, or cardboard shims can be added before tightening. If the noise disappears, that’s sufficient. Otherwise, the core must be disassembled, the silicon steel sheets re-selected, and the core reassembled and pressed. When selecting silicon steel sheets, they should be stacked in pairs; if one sheet is accidentally used or if they are stacked in threes, they must all be changed to being stacked in pairs ； Select laminations with the same thickness ； Discard bent sheets, fragments, and silicon steel sheets with severe waviness ； Silicon steel sheets with large burrs need to have their burrs removed again; they can be stacked once the burr size is less than 0.03 millimeters. 　　(3) For faults such as damage, aging, and loosening of epoxy resin fiberglass tape bindings, they must all be re-bound, with the requirement that the materials used are qualified. During binding, first secure it with temporary steel hoops; once a certain thickness has been achieved, dry and cure it. After it has hardened into a solid mass, remove the temporary steel hoops. Changes in excitation current: 1) The magnetic flux density is inversely proportional to the cross-sectional area of the core. Looseness leads to an increase in the lamination factor, while an insufficient number of laminations directly results in a decrease in the cross-sectional area; both scenarios cause an increase in the magnetic flux density. The saturation of the transformer core increases; in severe cases, this can lead to an increase in THDU (waveform distortion). 2) As the magnetic flux density rises, the W/kg value of the core also increases, resulting in higher iron losses. Additionally, irregular stacking of the laminations increases magnetic resistance, leading to higher local magnetic flux densities and thus greater iron losses. 3) The no-load current increases, including an increase in the iron loss current as well as the excitation current. After the excitation current increases, the reactive power of the transformer rises, while the power factor decreases