[Abstract] Distribution transformers often become unusable due to excessive losses during long-term use, representing a significant waste of resources. Reusing these old transformers can effectively reduce resource waste, improve their utilization rate, and is also crucial for environmental protection. This article mainly introduces relevant methods and measures for converting high-loss transformers into low-loss transformers for reference.
Keywords: Transformer; High-loss to low-loss retrofit; Core winding
I. Analysis of High-Loss Transformer Retrofitting
During the rapid development of my country's power industry, the total installed power capacity has reached a world-leading position. The achievements in power engineering are not only evident but have also made significant contributions to my country's socio-economic development. In the power system, transformers are crucial electrical equipment, essential for power plants, substations, and transmission networks. In 2006, my country issued regulations regarding transformer use, including provisions for high-loss transformers, indicating their gradual replacement. In the 1980s, the Chinese government began gradually replacing high-loss transformers with low-loss ones, effectively reducing resource consumption and protecting the environment. Large-scale use of low-loss transformers is underway, with urban and rural power grid upgrades aimed at improving their efficiency. After the introduction of new low-loss transformers, no-load losses have decreased by approximately 8%-15%. Currently, high-loss transformers are gradually being phased out of the Chinese market, and many new energy-saving transformers have become mainstream products. In recent years, in particular, the power grid transformation of various regions in my country has been gradually upgrading high-loss transformers, which is an important foundation for the development of my country's power industry.
If discarded high-loss transformers are not properly processed, the copper, silicon steel sheets, and other materials they contain will cause significant environmental pollution, and this industrial pollution will also impact the natural ecosystem. The indiscriminate dumping of solid waste and the release of exhaust gases and wastewater from dismantling into rivers and land will generate extremely serious pollution, a problem we must currently prioritize.
However, as the transformer industry continues to develop, the use of recycled transformer materials in new transformers can better reduce the environmental pollution caused by transformers. Currently, tens of thousands of high-consumption transformers are gradually being replaced in my country each year, and the remanufacturing of these high-consumption transformers has brought significant pressure and challenges to the market. If recycled transformers and materials can be reused, high-consumption transformers can gradually be transformed into low-loss transformers. This reuse not only saves a significant amount of resources but also effectively reduces energy loss, making a crucial contribution to environmental protection in my country.
II. Measures for Upgrading High-Loss Transformers to Low-Loss Transformers
Several different methods are typically used to upgrade high-loss transformers, including partial or complete transformer replacement. This effectively reduces resource consumption after replacement. Additionally, factors such as transformer load losses also need to be considered. If upgrades are made, the transformer's windings must be improved, requiring timely replacement and adjustment of the original transformer components and wiring. For example, replacing aluminum wires with copper wires, if the transformer core is functioning correctly, will ensure that the density of the silicon steel sheets used in the transformer meets the required standards.
The main process for converting high-loss transformers into low-loss transformers is as follows: First, test the SL7, S7, or S9 type high-energy-consuming transformers that need to be converted to test their no-load loss; based on the no-load loss value of each transformer, redesign the transformers to be converted by reducing the magnetic flux density of silicon steel sheets, increasing the number of turns in the transformer windings, and reducing the transformer capacity, so that they meet the various performance indicators of S11 low-loss transformers.
The dismantled materials will be processed as follows: Old copper wire will be melted down and used for casting copper parts in the production of other products; old transformer oil will be used for lubrication of lathes in the machining workshop; old transformer oil tanks will be scrapped or treated with rust removal, pickling, and painting processes according to their degree of corrosion before being used in remanufactured transformers; old silicon steel sheets will be scrapped if they are of poor quality or severely burned during operation, while those of good quality will be utilized and treated with rust removal and the addition of new silicon steel sheets before being used in the modified transformers. After signing the transformer modification contract and technical agreement with the user, the specific modification plan is as follows: First, based on the transformer modification calculation sheet, design the high-voltage and low-voltage winding drawings of the modified transformer, and perform transformer body assembly, lead wire assembly, and final assembly according to the manufacturing process of a new transformer. After final assembly, pre-shipment tests will be conducted according to the requirements of a newly manufactured transformer to verify the various performance characteristics of the modified transformer. Once the performance meets national standards, the transformer will be approved for shipment. For the core of a high-loss distribution transformer, since K0 and GFe are constant values, reducing the no-load loss P0 requires reducing the value of Pw, which is related to the magnetic flux density of the silicon steel sheets. After the modification, since the core is not replaced and the voltage and frequency remain unchanged, the only way to reduce the no-load loss is to reduce the magnetic flux density in the core, thereby reducing the Pw value of the silicon steel sheets. In practical engineering applications, to better utilize the core, if the no-load loss of the distribution transformer to be modified does not meet the requirements of current low-loss distribution transformers under the original turn potential, temporary no-load testing is conducted by adjusting the number of turns in the low-voltage winding using temporary turns until the no-load performance indicators specified in the current GB/T6451-2008 standard are met.
[Technical Exchange] How to convert a high-loss distribution transformer into a low-loss distribution transformer?
III. Winding Modification of Distribution Transformers
The basic principle of power distribution transformer winding modification is derived from the formula for transformer load loss. In the transformer load loss value, the coil resistance loss accounts for the largest proportion.
During transformer retrofitting, if the conductor is copper, reducing the transformer's P0 and Pk values requires increasing the number of turns in the low-voltage coil. However, due to limitations in window height and width, this necessitates a capacity reduction. When the original transformer material is aluminum wire, a capacity-equal retrofit can be performed based on calculations. Since the resistivity ratio of copper to aluminum at 75℃ is 0.02135/0.0357 = 0.598, replacing aluminum wire with copper reduces the load loss ratio, allowing the cross-sectional area to be reduced to approximately 70% of the original. Therefore, this method not only increases the number of turns and reduces no-load losses but also allows the transformer to meet retrofitting requirements without capacity reduction using conventional methods.
This method involves replacing old transformer cores with new coils, insulation, leads, and components to transform high-loss distribution transformers retired from power grid operation into S11-type low-loss distribution transformers that meet national standards. This fully utilizes the copper wire, silicon steel sheets, transformer oil, and other materials contained in the old transformers. This transformation not only avoids environmental pollution from these materials but also reduces the use of silicon steel sheets and copper, saving a significant amount of raw material consumption annually and contributing to the national initiative to build a resource-saving society.
