Is specialized in designing, manufacturing for power transformers ,furnace transformers and reactor.

Measures to Improve Short Circuit Resistance of Power Transformer

Causes of power transformer short circuit

Measures to Improve Short Circuit Resistance of Power Transformer 1

(1) At present, the calculation program is based on the idealized model of uniform distribution of leakage magnetic field, the same wire turn diameter and equal phase force. In fact, the leakage magnetic field of transformer is not evenly distributed, which is relatively concentrated in the yoke part, and the mechanical force on the electromagnetic line in this area is also large; At the transposition point, the climbing of transposition conductor will change the transmission direction of force and produce torque; Due to the factor of the elastic modulus of the cushion block and the unequal distribution of the axial cushion block, the alternating force generated by the alternating leakage magnetic field will delay resonance, which is also the fundamental reason why the wire cake at the iron core yoke, transposition and the corresponding parts with voltage regulating tapping deforms first.

(2) Ordinary transposition conductor is adopted, which has poor mechanical strength and is prone to deformation, loose strand and copper exposure when bearing short-circuit mechanical force. When using ordinary transposition conductor, due to large current and steep transposition climbing, this part will produce large torque. At the same time, the wire cake at the two ends of the winding will also produce large torque due to the joint action of amplitude and axial leakage magnetic field, resulting in distortion and deformation. For example, there are 71 transpositions of phase a common winding of Yanggao 500kV transformer. Due to the thick ordinary transposition conductor, 66 transpositions have varying degrees of deformation. In addition, Wujing 1L main transformer is also due to the use of ordinary transposition conductor, and the wire cakes at the two ends of high-voltage winding at the iron core yoke have different overturning and exposed wires.

(3) The influence of temperature on the bending and tensile strength of electromagnetic wire is not considered in the calculation of short-circuit resistance. The short-circuit resistance designed under normal temperature can not reflect the actual operation. According to the test results, the temperature of the electromagnetic wire has an impact on its yield limit? 0.2 has a great impact. With the increase of the temperature of the electromagnetic wire, its bending strength, tensile strength and elongation decrease. The bending tensile strength decreases at 250 than at 50 , and the elongation decreases by more than 40%. For the actual transformer, under the rated load, the average winding temperature can reach 105 and the hottest spot temperature can reach 118 . Generally, the transformer has reclosing process during operation. Therefore, if the short-circuit point cannot disappear for a while, it will bear the second short-circuit impact in a very short time (0.8s). However, due to the sharp increase of winding temperature after the impact of the first short-circuit current, the maximum allowable temperature is 250 according to gbl094. At this time, the short-circuit resistance of the winding has decreased greatly, This is why most short circuit accidents occur after transformer reclosing.

(4) The winding is loosely wound, the transposition is not handled properly, and it is too thin, resulting in the suspension of the electromagnetic wire. From the accident damage location, the deformation is mostly seen at the transposition, especially at the transposition of transposition conductor.(5) The use of flexible conductor is also one of the main reasons for the poor short-circuit resistance of transformer. Due to insufficient understanding of this in the early stage, or difficulties in winding equipment and technology, manufacturers are reluctant to use semi-hard conductors, or there are no requirements in this regard in the design. From the perspective of faulty transformers, they are all soft conductors.(6) The clearance of the suit is too large, resulting in insufficient support on the electromagnetic line, which increases the hidden danger to the anti short circuit ability of the transformer.

Measures to Improve Short Circuit Resistance of Power Transformer 2

(7) The preload acting on each winding or gear is uneven, resulting in the jumping of wire cake during short-circuit impact, resulting in excessive bending stress acting on the electromagnetic line and deformation.(8) The winding turns or wires are not cured, and the short-circuit resistance is poor. None of the windings treated by dipping paint in the early stage was damaged.(9) Improper control of the pre tightening force of the winding causes mutual dislocation of the wires of the ordinary transposition wires.

(10) External short-circuit accidents are frequent. The accumulation effect of electrodynamic force after multiple short-circuit current shocks causes electromagnetic wire softening or internal relative displacement, and finally leads to insulation breakdown.Measures to improve short circuit resistance of power transformer1. Short circuit test shall be conducted on the transformer to prevent accidents.

The operation reliability of large transformer first depends on its structure and manufacturing process level, and then carries out various tests on the equipment during operation to master the working conditions of the equipment in time. To understand the mechanical stability of the transformer, we can improve its weak links through short-circuit test, so as to ensure that we know well about the structural strength design of the transformer.2. Standardize the design and pay attention to the axial compression process of coil manufacturing.In the design, the manufacturer shall not only consider reducing the loss and improving the insulation level of the transformer, but also consider improving the mechanical strength and short-circuit fault resistance of the transformer. In terms of manufacturing process, since many transformers use insulating pressing plates, and high and low voltage coils share one pressing plate, this structure requires a high level of manufacturing process. The cushion block shall be densified. After the coil is processed, a single coil shall be dried at constant pressure, and the height of the coil after compression shall be measured.

After the above process treatment, each coil of the same pressing plate shall be adjusted to the same height, and the specified pressure shall be applied to the coil with the oil pressure device during the final assembly, so as to finally reach the height required by the design and process. In the general assembly, in addition to the compression of the high-voltage coil, special attention should be paid to the control of the compression of the low-voltage coil.

recommended articles
Case News
1 What are the advantages and disadvantages of machine winding and manual winding in the manufacture of transformer?The advantages of machine wound transformer are h...
Transformer winding machine is a special equipment used to wind transformer coils. In the process of transformer coil production, winding equipment is divided accord...
Comparison of power transformers:1 What are the advantages and disadvantages of machine winding and manual winding in the manufacture of transformer?The advantages o...
Working principle of power transformerAs for the power transformer, it is a special transformer whose output and input share a set of coils. The step-up and step-dow...
Introduction to working principle of power transformerThe high-voltage winding used in domestic transformers is generally connected into Y connection method, and the...
Operation principle of power transformer1. Operating temperature of transformerDuring the operation of the transformer, copper loss and iron loss will be generated, ...
Inspection during operation of power transformer(1) The on-site meter indication of the upper oil temperature and high and low winding temperature of the transformer...
Maintenance technology of on load tap changer of power transformer1 basic principle and structure of on load tap changer on load tap changer is an electrical device ...
1. Basic working principle of gas protectionWhen a fault occurs inside the power transformer oil tank (including the grounding short circuit through arc resistance c...
Switching power transformer is a power transformer with switch tube. In the circuit, in addition to the voltage conversion function of ordinary transformer, it also ...
no data
As a professional power transformer manufacturer with 20 years of experiences, NINGBO VILLE ENTERPRISE is a combination of Transformer R&D center, production, sales and after sales service, possesses of strong technical strength and excellent manufacturing equipments, as well as modern Office facilities.
no data
Contact person:  GREEN HSU
Contact number:  +86-13906684456 / +86-13867838839
WhatsApp:008613867838839 / 008613906684456

Add: Fl 6, No.C12 Building, Lane 299 Guanghua Rd, Ningbo R&D Park,Ningbo Hi-Tech Zone,China, 315040

Copyright © 2023 NINGBO VILLE ENTERPRISE CO.,LTD. - https://www.villeelectric.com/ | Sitemap