DueWater heater transformeroutlet short circuit, resulting inTransformerThere are many causes of internal failures and accidents. They are also more complex. They are related to factors such as structural design, raw material quality, technical level and operating conditions, but the choice of magnet wire is the key. From recent years onWater heater transformerAccording to the analysis of the accident and the analysis of the accident, the reasons related to the electromagnetic wire are roughly as follows.
1.AccordingWater heater transformerThe static theoretical design of the selected electromagnetic wire is completely different from the stress acting on the electromagnetic wire during actual operation.
2.At present, the calculation procedures of various manufacturers are based on ideal models, such as uniform distribution of leakage magnetic fields, the same number of turns diameter and equal phase forces. Actually,Water heater transformerThe leakage magnetic field is not uniformly distributed. The iron yoke part is relatively concentrated, and the magnet wire in this area also bears a large mechanical force; the transposition line will change the direction of force transmission due to the climbing in the transposition position, thereby generating torque. Due to the elastic modulus of the cushion, the axial unequal spacing of the spacer blocks will delay the resonance of the alternating force generated by the leakage of the alternating magnetic field. This is the fundamental reason why the iron core is deformed in the corresponding parts of the yoke, swivel seat and voltage regulating tap.
3.When calculating the short-circuit resistance, the effect of temperature on the bending and tensile strength of the magnet wire is not considered. The short-circuit resistance designed at room temperature does not reflect the actual working conditions. According to the test results, the temperature of the magnet wire to its yield limit ≥0.2Has a big impact. As the temperature of the magnet wire increases, its bending strength, tensile strength and elongation250°Cratio of bending strength and tensile strength50°CWhen low10%, while the elongation decreases40more than%. InWater heater transformerIn actual operation, under the rated load, the average winding temperature can reach105°C, the hot spot temperature can reach118°C. Usually,Water heater transformerThere is a reclosing process during operation. Therefore, if the short circuit point cannot disappear temporarily, it will be in a short time (0.8s) Withstand the second short-circuit impact, but due to the first short-circuit current impact, the winding temperature will rise sharply. AccordingGB1094The maximum allowable temperature is250°C. At this time, the short-circuit resistance of the winding has been greatly reduced. This is why most short-circuit accidents areWater heater transformerCause of occurrence after re-closing.
4.Using ordinary transposition line, the mechanical strength is poor, easy to be short-circuit mechanical force, easy to deform, the strand is loose, and the copper is exposed. When an ordinary transposed conductor is used, this part will generate a large torque due to the large current and the steep transposition. At the same time, due to the combined effect of amplitude and axial leakage magnetic field, the wire pie at both ends of the winding will also be produced. A larger torque will cause deformation.