1. Introduction The S6 and S7 series 6kV power transformers used by Qilu Company account for over 90% of its total applications. Having operated continuously for nearly 20 years, these transformers exhibit high no-load losses and are currently suffering from severe oil leakage that is difficult to repair. This causes environmental pollution and energy waste, and also poses safety hazards. Currently, the S9 series is widely used in 6.3–10 kV power transformers in China, and the S11 series is now available as an option in the domestic market. Since 1994, under the leadership of the Three Committees and Three Departments, Shenyang Transformer Institute has developed four varieties: SH-160, 200, 315, and 500 kVA. In 1998, Shanghai Zhixin Electric Company introduced design and process technologies from GE and AlliedSignal, becoming the only professional manufacturer of amorphous alloy transformers in China. Currently, there are over 30 companies producing amorphous alloy transformers in China. 2. Characteristics of Amorphous Alloy Cores Low losses, especially low no-load losses; low noise, especially low no-load noise; fully sealed, preventing transformer oil from contacting outside air, meeting maintenance-free requirements; meets the requirements of ring-type power supply, with no exposed live parts, ensuring safe operation. The use of amorphous core composite distribution transformers is an ideal development direction. The no-load loss of amorphous alloy distribution transformers is 70%–80% lower than that of silicon steel sheets. The thickness of ordinary silicon steel sheets is 0.35mm, 0.30mm, 0.27mm, 0.23mm, and 0.18mm. The thickness of silicon steel sheets is closely related to the eddy current loss and hysteresis loss of the transformer; reducing the thickness of silicon steel sheets by half reduces iron losses by 3/4. The thickness of amorphous alloy core sheets is only 0.025mm, significantly less than that of ordinary silicon steel sheets, thus offering a significant advantage in reducing iron losses. The efficiency of amorphous alloy cores can reach up to 99.4%, while the efficiency of ordinary silicon steel sheet transformers is around 96%. 3. Status of Transformers to be Replaced: The No. 1 PVC unit originally had eight 1600kVA transformers and two 800kVA transformers. Under normal circumstances, each pair of transformers supplies two low-voltage busbars as a backup, operating separately. The capacity of any transformer must meet the load requirements of both busbars. The two S7-800kVA transformers primarily supply lighting, with a daytime load of only 3.5%, close to no-load. The two 1600kVA transformers supply emergency fans, with a load factor of only 13%. The six 1600kVA transformers supply the unit's motors; according to the initial design, each transformer has sufficient capacity to operate at full load on both busbars. During normal operation, the load factor of each transformer is between 26% and 32%. As can be seen from the above examples, the two 800kVA transformers operate close to no-load during the day, with their main power loss being iron loss (voltage-dependent and constant). Iron loss also accounts for a large portion of the total losses of the 1600kVA transformers. 4. Comparison of Transformer Losses: The main performance indicators of the S11 stacked core distribution transformer are shown in Table 1. The performance of the amorphous alloy transformer is shown in Table 2. The load losses of the amorphous alloy transformer are basically similar to those of the S11 transformer. 5. Evaluation of Transformer Energy Efficiency: Internationally, there are many methods for evaluating transformer energy efficiency. All methods require comparing transformer prices and their loss costs. In the late 1970s in the United States, due to rising energy prices, many power companies began requiring that the transformers they designed should have a minimum service life cost, thus giving rise to the Total Cost of Ownership (TOC) method. The TOC method became an industry standard in the United States in 1981. Purchasing transformers according to the TOC standard has been used ever since. The TOC method sums the initial cost of the transformer and the equivalent present value of loss costs, expressing the total cost of the purchased transformer. The Total Cost of Ownership (TOCEFC) method (hereinafter referred to as TOC) uses the Equivalent First Cost (EFC) to evaluate the economic benefits of transformers. The relevant standards of the National Electrical Manufacturers Association of the United States, namely the US NEMATPl-1996 standard, were referenced and combined with the actual situation in China. (1) Total Ownership Cost (TOC) The total ownership cost (TOC) is the sum of the initial investment of the transformer and its loss cost during its service life. The total ownership cost method compares the total ownership costs of transformers with different efficiency levels and prices, and selects the transformer efficiency level according to the lowest total ownership cost. (2) Formula for calculating TOC TOC=C+A•NL+B•LL Where, NL is the rated no-load loss or iron loss of the transformer (kW); LL is the rated load loss or copper loss of the transformer (kW); A is the capital cost per kilowatt of no-load loss during the transformer's life (yuan/kW); B is the capital cost per kilowatt of load loss during the transformer's life (yuan/kW); C is the initial cost of the transformer, which can be used when comparing schemes (yuan). (3) Determination of calculation parameters 1) Transformer no-load loss NL and load loss LL Transformer no-load loss NL and load loss LL both include rated active power loss and take into account the active power loss of its reactive power on the power grid. The no-load loss and load loss are calculated according to the following formula: Where, is the rated no-load active power loss of the transformer, i.e. iron loss, kW; is the rated excitation power of the transformer, kvar; is the rated load active power loss of the transformer, i.e. copper loss, kW; is the rated load leakage magnetic power of the transformer, kvar; K is the reactive economic equivalent, which is taken according to the position of the transformer in the power grid. Generally, k=0.1 kW/kvar can be taken; is the transformer no-load current (%); is the transformer impedance voltage (%); is the transformer rated capacity (kVA). The A coefficient is the capital cost per unit no-load loss during the transformer's life, yuan/kW, and the B coefficient is the capital cost per unit load loss during the transformer's life, yuan/kW. The A and B coefficients are very important for transformer buyers to understand the value of transformer no-load loss and load loss. Once the values ​​of A and B are determined, evaluating the total cost of the transformer becomes simple and easy. For power companies and non-power companies, the determination of coefficients A and B differs slightly. Coefficients A and B are functionally related to the transformer's no-load loss and load loss, showing a functional relationship with energy costs and capacity costs. For power companies, the energy cost and capacity cost per unit loss are more complex due to the investment and operation methods throughout the entire power generation, transmission, and distribution process, requiring research and formulation by power company professionals. For example, comparing the total ownership cost of S9-800/10 and S7-800/10 transformers, with a service life of 20 years: Solution: ① Calculate the loss values, including reactive power, of the SBH1l-800 type, 800 kVA transformer: No-load loss = 380W; Load loss = 7500W. ② Similarly, the loss values ​​for S7-800: No-load loss: S7 = 2.5kW; Load loss: S7 = 13.49kW. ③ Transformer no-load and load loss costs (service life 20 years) No-load loss cost: A•NLS9-0.38A for amorphous transformer, A•NLNT=2.5A for S7 transformer Load loss cost: B•LL39=7.5B for amorphous transformer, B•LLS7=13.49B for S7 transformer ④ Transformer unit price: S9 is 63,640 yuan, S7 is 55,340 yuan. ⑤ Total Cost of Ownership (TOC) over a 20-year lifespan: TOC Amorphous = Amorphous Price + 0.38A + 7.5B = Amorphous Price + 18,495 + 132,510 = 151,005 + Amorphous Price TOCS7 = S7 Price + 2.5A + 13.49B = S7 Price + 121,680 + 238,341 = S7 Price + 360,021 According to relevant data, A = 48,672 yuan/kW, B = 17,668 yuan/kW. After comparison, TOC Amorphous is significantly lower than TOCS7. From the above comparison, the no-load loss of the obsolete S7 and S6 transformers is far greater than that of current energy-saving transformers, with the reduction in no-load loss of amorphous alloys being particularly significant. Currently, the load rate of the 10 transformers used in our company's plant is relatively low. Selecting energy-saving transformers with lower no-load loss will greatly reduce power loss, resulting in significant economic benefits. Recent statistics show that the use of amorphous alloy transformers has resulted in a significant reduction in operating costs, which is quite substantial for enterprises seeking to improve efficiency and reduce costs. (Article sourced from "Energy Saving Innovation 2006 – Proceedings of the First National Electrical Energy Saving Competition")