Toshiba

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Power Transformer


Power Transformer

Overview

To cope with the increase in electrical power demand, power transformer capacity is increasing. In particular, the capacity of generator transformers for thermal and nuclear power stations have become considerably high. TOSHIBA manufactured generator transformer of 200MVA in 1958, 430MVA in 1963, 680MVA in 1967, and 1100MVA in 1973, which broke the Japanese record for the largest capacity of all time. In 1996 TOSHIBA made and delivered the world largest capacity generator transformer of 500kV and 1450MVA for a nuclear power station.
500kV transformer Three-phase transformer
TOSHIBA had begun development of 500kV transformers and completed and shipped its first 500kV transformer from Japan for the Canadian electric authorities in 1967. Further in 1971, TOSHIBA provided Japan's first 500kV Auto-transformer of 1000MVA bank for connecting 500kV and 275kV networks. During the same period in 1976, Auto-transformers of 1500MVA bank were also been delivered. TOSHIBA occupies a very high status in the world for manufacturing experience of 500kV transformers with a cumulative capacity of 500kV transformers amounting to approximately 200GVA.

Core

Three-phase transformers usually employ a three-leg core. Where transformers to be transported by rail are of large capacity, a five-leg core is used to keep them within the height limitation for transport. A two-leg core is well known for single-phase transformers A three-leg core is also used for single-phaes transformers. A four-leg core and a five-leg core construction are usually used in large-capacity single-phase transformers.
Core
High-grade, grain-oriented silicon steel strip is used for the core materials. The main and side legs of the core are tightly bound by glass-fiber tapes to achieve low noise and low no-load loss. The clamp which supports the core has a plate configuration and is fastened and fixed together with the yoke of the core by glass-fibre tape. The same method is also applied to the main legs.

Windings

TOSHIBA has two standard types of high voltage winding structures; a high-series capacitance disc winding and a turn shield continuous disc winding. Their use depends upon the winding specifications. Both have excellent characteristics to lightning surges and their reliability is highly regarded by domestic and foreign utilities. A continuous disc winding can be used for medium voltage winding. Helical winding, wound by multi parallel conductors, is applied for low voltage and heavy current winding. And Tap windings utilize a layer winding or a twin disc winding.
Layer WindingLayer
Winding
Continuous WindingContinuous
Winding
Continuous WindingContinuous
Winding

Insulation Structure

TOSHIBA has developed original computer softwares for analysing transient potential oscillations in transformer windings and electric fields of the winding configurations. Using this software analysis, engineers can comprehend exactly the electric field distribution in the winding configuration. Insulation design is then performed precisely from such analysis. Oil gaps between windings, winding end and grounded electrodes are subdivided finely by pressboards. These so called multi barrier insulation structure provides a high dielectric strength and presents reliable and stable insulation performance.
Insulation Structure

Leakage Flux Measures

With the increase in transformer capacity, the leakage flux also rises, causing increased stray loss or local overheating. For large-capacity transformers, it becomes very important from the standpoint of improved reliability to thoroughly comprehend leakage flux and to take measures to minimize stray loss. At TOSHIBA, careful measures against leakage flux are taken on the basis of the results of computer-aided analysis on leakage flux distribution and eddy current loss on each part of the transformer by fully utilizing our wide experience in producing an extensive number of large-capacity transformers. Generally made of mild steel, tanks and other structural members have high permeability and are liable to induce leakage flux concentration. Thus, the tank inner surface is provided with a laminated shield made of silicon steel strips to prevent leakage flux from penetrating the tank, thus reducing eddy current loss in steel members.
Leakage Flux Measures Leakage Flux Measures

Short Circuit Strength

Transformer windings are severely affected by electromagnetic force due to short-circuit currents passing through the windings. As the inner winding is exposed to buckling force, the core supports it securely and further bonded transposed-stranded conductors are used to improve its hardness. For the outer winding, half-hardened copper conductors are used. Hamakawasaki Operations has one of the world's-largest short-circuit testing facilities and has conducted many short-circuit testings on large power transformers. Moreover, short-circuit tests have been conducted on actual 250MVA 500kV power transformer by KEMA in the Netherlands. It passed the tests successfully and its short- circuit strength has been acknowledged worldwide.
Short Circuit Strength 250MVA 500kV power transformer

Low-Noise Technologies

TOSHIBA supplies low-noise transformers of the world's highest grade, making free use of newly developed low-noise technologies and computer-aided noise analysis.
Low-Noise Technologies
Low-Noise Technologies
Compact low-noise transformers are made by adopting newly developed VC sound insulators and plastic-fan unit coolers.
Low-Noise Technologies
Boundary noise can be precisely predicted even in the complex configuration of land by 3D noise analysis

Manufacturing Engineering

Dust Control
Mixing of not only metallic powders, but also all sorts of dust and foreign particles may lead to partial discharge in power transformers. Core and coil are therefore assembled in a dust-free shop where the dust-falling rate is checked daily. In particular, winding operations are carried out in an enclosed space in a dust-free shop.
Winding Machines
Large capacity disc windings are wound by vertical winding machines, which enable windings to be made with high efficiency and high quality without influence of copper conductors weight.
Winding Machines
Drying and Filled with Deaerated Oil
In the core-type transformer, the core-and-coil assembly is independent of the tank, so that the assembly is allowed to completely dry. When drying the core-and-coil assembly, Toshiba's innovative vapor phase drying method is used, in which special oil vapor is sprayed on the assembly to utilize latent heat produced when the oil vapor condenses. Since heating is effected deep inside evenly and quickly, the assembly can be completely dried without causing damage to the insulation. When a core-and-coil assembly has been installed in a tank, the tank is evacuated to a high vacuum state to remove reabsorbed humidity on the insulation surface and voids in impregnated insulation; then it is filled with deaerated oil under the high vacuum.
Drying and Filled with Deaerated Oil

Products Lists

  • Power Transformer
  • Gas Insulated Transformer
  • Medium or small capacity gas insulated transformer
  • Large capacity gas insulated transformer
  • TOSHIBA ASA Transformer
  • Shunt Reactor
  • Converter Transformer
  • Large Capacity Furnace Transformer
  • Phase Shifting Transformer


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