Transformer selection method based on loss reduction efficiency of island region

Abstract

In order to overcome the deficiencies and existing problems of the prior art, the transformer selection method based on the loss reduction efficiency of the island area is used for mathematical modeling of the equivalent circuit of the transformer; the transformer model is used to calculate the island area power distribution network loss generated by different models of transformers; the transformer loss generated by different models of transformers under different capacity and load rate conditions is calculated, and the most suitable transformer model for the island area power distribution network is compared and analyzed; the selected transformer is placed back into the model, the geographical adjustment parameters brought by the island area are added, and the loss reduction benefit is judged whether it covers the transformer replacement cost; finally, it is decided whether to replace the selected model of transformer or to select the transformer model again. The present application considers that the voltage grade of the island area power distribution network is high, the load rate is not high, and many influences brought by the natural environment, and selects the transformer model which can effectively reduce the loss of the island power distribution network.

Description

Technical Field

[0001] This invention belongs to the field of power system energy conservation and loss reduction technology, and in particular, it is a transformer selection method based on loss reduction efficiency in island areas. Background Technology

[0002] With the continuous development of my country's power grid, the power loss of the grid itself is also staggering. The main source of this power loss is the loss in power lines and transformers. Transformers, as electrical equipment in the power system that converts and distributes power, have a significant impact on grid losses depending on their selection. Therefore, many existing technologies focus on reducing losses through transformer selection. For example, the invention patent CN201611040237.8, "Transformer Energy Saving and Loss Reduction Adaptability Assessment Method," discloses a method for assessing transformer energy saving and loss reduction adaptability. Traditional transformer life-cycle cost calculations use estimated or average values ​​for load and operating time, ignoring additional losses caused by heavy loads or peak loads; simultaneously, operational losses and ring network losses are generally ignored, leading to underestimation of transformer losses. This invention uses a graded assessment of economic and energy-saving indicators as a means of evaluating transformer adaptability. It proposes an improved method for calculating transformer losses using hours as the time window and an annual comprehensive indicator evaluation time window, forming a two-dimensional method for assessing transformer operational adaptability from an energy saving and loss reduction perspective. This invention considers the correction of safety losses due to the non-parametric characteristics of transformers, and uses hours as a time window to improve the accuracy of cycle cost and loss calculations. It evaluates the adaptability of transformers from two-dimensional standards of economy and energy saving. While this technical solution is indeed universally applicable in conventional situations, it is not suitable for island regions. my country's island regions have unique geographical locations, numerous islands, and dispersed loads. Aquaculture, fisheries, and related light industries and services exhibit significant seasonality, and their load growth is not rapid. Therefore, it is necessary to consider these characteristics, as well as the transformer's loss reduction efficiency, to select a suitable transformer type. Summary of the Invention

[0003] To overcome the shortcomings and problems of existing technologies, this invention provides a transformer selection method based on loss reduction efficiency in island regions. By establishing a transformer loss reduction model based on the application scenario of island regions, the model simulates the operating conditions of different transformer models under different capacities and load rates, thereby enabling the selection of the appropriate transformer model after loss reduction. After selection, the model is re-entered to determine whether the overall replacement cost is lower than the loss reduction benefits, ultimately making a decision. This avoids the problem of neglecting other operating factors when focusing solely on loss reduction.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: a transformer selection method based on loss reduction efficiency in island regions, further comprising the following steps:

[0005] Step 1: Perform mathematical modeling for the equivalent circuit of the transformer;

[0006] Step 2: Calculate the distribution network losses in the island area caused by different types of transformers based on the transformer model, and analyze the impact of transformer selection on the distribution network losses in the island area.

[0007] Step 3: Calculate the transformer losses of different transformer models under different capacities and load rates, and compare and analyze to determine the most suitable transformer model for the island area distribution network;

[0008] Step 4: Place the selected transformer back into the model, add the geographical adjustment parameters brought by the island region, and recalculate to determine whether the loss reduction benefits cover the transformer replacement cost.

[0009] Step 5: Based on the calculation results in Step 4, decide whether to replace the selected transformer model or select a new transformer model.

[0010] Preferably, the geographical location information of the island area where the transformer is located is obtained, and the geographical adjustment parameters for step 4 are obtained based on the geographical location of the transformer.

[0011] Preferably, the geographical adjustment parameters are parameters formed based on the temperature, humidity, and corrosion information collected at the location of the transformer, and on the costs incurred in maintenance.

[0012] Preferably, in step 2, modeling is performed for both two-winding and three-winding transformers, and the transformer loss model is as follows:

[0013]

[0014] In the formula, P 0i P represents the no-load loss of the i-th distribution transformer; Ki S represents the short-circuit loss of the i-th distribution transformer; i S represents the apparent power of the i-th transformer; Ni K represents the rated capacity of the i-th transformer; T This represents the load fluctuation coefficient. Based on this model, the losses generated by the transformer under ideal operating conditions can be accurately calculated.

[0015] Preferably, when the secondary winding is referred to the primary winding, R T X is a resistor. T For reactance, G T For conductivity, B T For susceptance, the above parameters are calculated as follows:

[0016]

[0017]

[0018]

[0019]

[0020] In the formula, △P K U is the increment of transformer short-circuit loss; ΔP0 is the increment of transformer no-load loss; U K % represents the short-circuit voltage percentage; I0% represents the no-load current percentage, U N For the rated voltage, S N This is the rated power. A simplified formula facilitates calculation.

[0021] Preferably, when the tertiary winding is referred to the primary winding, the electrical parameters of the three-winding transformer are obtained based on the transformer's capacity ratio, short-circuit loss, and no-load loss:

[0022]

[0023]

[0024] In the formula, R T1 R T2 R T3 X represents the resistance of each winding. T1 X T2 X T3 For the reactance corresponding to each winding, ΔP S1 , △P S2 , △P S3 U represents the short-circuit loss corresponding to each winding; S1 % and U S2 % and U S3 % represents the percentage of short-circuit voltage corresponding to each winding, U N For the rated voltage, S N For rated power, the formulas for calculating the conductance and susceptance of a three-winding transformer are the same as those for a two-winding transformer.

[0025] Preferably, in step 4, after selecting the transformer model, the number of transformers in the substation before and after the replacement is reset to n1 and n2 respectively. Then, the actual loss reduction that can be achieved by this replacement is:

[0026]

[0027] In the formula, P 0i P represents the no-load loss of the i-th distribution transformer; Ki S represents the short-circuit loss of the i-th distribution transformer; i S represents the apparent power of the i-th transformer; Ni K represents the rated capacity of the i-th transformer;T This is the load fluctuation coefficient.

[0028] Preferably, when calculating the loss of each transformer, the corresponding geographical adjustment parameter should be added. This is to obtain accurate information on the actual loss reduction.

[0029] Therefore, compared with existing technologies, this invention takes into account the high voltage level, low load rate, and numerous impacts of the natural environment in island distribution networks, and selects transformer models that can effectively reduce losses in island distribution networks. The selected transformer models are then incorporated into the model with environmental parameters to accurately calculate energy-saving and loss-reduction benefits, thereby determining whether replacement is necessary. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the overall process of the transformer selection method for reducing losses in island areas based on the present invention.

[0031] Figure 2 This is a simplified circuit diagram of a dual-winding transformer, illustrating the transformer selection method for reducing losses in island regions based on the present invention.

[0032] Figure 3 This is a simplified circuit diagram of a three-winding transformer, based on the transformer selection method for reducing losses in island regions according to the present invention.

[0033] Figure 4 This is a schematic diagram comparing the losses of transformers with the same capacity but different load rates, based on the transformer selection method for reducing losses in island regions according to the present invention. Detailed Implementation

[0034] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0035] Different transformer selection requirements apply to different situations. For example: (1) In rural areas where residents live in scattered locations and the load is mainly single-phase, single-phase transformers are preferred, and they should be evenly connected to the three-phase lines; (2) When the low-voltage load has large time-varying or seasonal differences and the average load rate is relatively low, amorphous alloy distribution transformers or on-load tap-changing transformers can be selected; (3) In distribution areas with large load and voltage fluctuations, on-load tap-changing distribution transformers can be selected. In island areas, many transformers in infrastructure were not designed with these issues in mind during initial installation. Although they can still be used, they have caused significant losses and waste. In such cases, it is necessary to consider whether to replace the transformer. Replacing a transformer mainly involves two points: 1. Which model of transformer to use for replacement. 2. When to replace it. There are many solutions for reducing transformer losses in the existing technology, but this does not mean that transformer replacement is necessary to achieve loss reduction. This invention provides a theoretical basis for transformer replacement.

[0036] In this embodiment, as Figure 1 As shown, this invention, based on the generally high voltage levels of power grids in island regions, mathematically models the equivalent circuits of commonly used two-winding and three-winding transformers. The main components of a power transformer are the windings and the iron core (magnetic core). Its primary function is to adjust voltage and control power flow within a certain range, meeting the requirements for safe operation of the power grid under any background and condition. Iron loss and copper loss constitute the main losses of a transformer. Iron loss, also known as no-load loss, includes eddy current loss and hysteresis loss; its magnitude is related to the supply voltage and the iron core material. Copper loss, also known as short-circuit loss, includes basic copper loss and additional copper loss; its magnitude is related to impedance and current.

[0037] like Figure 2 As shown, after the secondary winding is referred to the primary winding,

[0038] When the secondary winding is referred to the primary winding, R T X is a resistor. T For reactance, G T For conductivity, B T For susceptance, the above parameters are calculated as follows:

[0039]

[0040]

[0041]

[0042]

[0043] In the formula, △P K U is the increment of transformer short-circuit loss; ΔP0 is the increment of transformer no-load loss; UK % represents the short-circuit voltage percentage; I0% represents the no-load current percentage, U N For the rated voltage, S N This is the rated power.

[0044] Since part of the reactance is imaginary, therefore Figure 2 The part involving complex number calculations is denoted as j. The impedance of the line is R + jX, and the admittance is G + jB. Impedance and admittance are reciprocals of each other. Both j and -j are obtained through complex number calculations.

[0045] Based on the practical considerations of this invention, the power grid voltage level in island areas is generally high, therefore three-winding transformers account for a large proportion. A simplified circuit for a three-winding transformer is as follows: Figure 3 As shown. When the tertiary winding is referred to the primary winding, the electrical parameters of the three-winding transformer are obtained based on the transformer's capacity ratio, short-circuit loss, and no-load loss:

[0046]

[0047]

[0048] In the formula, R T1 R T2 R T3 X represents the resistance of each winding. T1 X T2 X T3 For the reactance corresponding to each winding, ΔP S1 , △P S2 , △P S3 U represents the short-circuit loss corresponding to each winding; S1 % and U S2 % and U S3 % represents the percentage of short-circuit voltage corresponding to each winding, U N For the rated voltage, S N For rated power, the formulas for calculating the conductance and susceptance of a three-winding transformer are the same as those for a two-winding transformer.

[0049] Similarly, since some reactances are imaginary, therefore Figure 3 The part involving complex number calculations is denoted as j. The impedance of the line is R + jX, and the admittance is G + jB. Impedance and admittance are reciprocals of each other. Both j and -j are obtained through complex number calculations.

[0050] The losses in a power distribution network mainly originate from lines and transformers. Among these, transformers, as electrical devices that convert and distribute electrical energy in the power system, have a significant impact on network losses depending on their selection. Transformer losses consist of no-load losses and load losses.

[0051] Based on the analysis of the transformer model, the transformer loss model is shown in the following equation:

[0052]

[0053] In the formula, △A0 is the total no-load loss, △A K For the total load loss, P 0i P represents the no-load loss of the i-th distribution transformer; Ki S represents the short-circuit loss of the i-th distribution transformer; i S represents the apparent power of the i-th transformer; Ni K represents the rated capacity of the i-th transformer; T This is the load fluctuation coefficient.

[0054] As can be seen from the transformer loss model, changing the transformer model mainly changes its no-load loss P. 0i and short-circuit loss P Ki Given the transformer models and related parameters before and after replacement, the losses ΔA1 of the ordinary transformer and ΔA2 of the energy-saving transformer can be calculated. The energy savings from replacing a single transformer are shown in the following formula:

[0055] △A Z =△A1-△A2

[0056] Distribution transformers are classified into three energy efficiency levels, with Level 1 having the lowest energy consumption. The no-load and load losses of all levels of oil-immersed and dry-type distribution transformers must comply with the relevant regulations in the "Energy Efficiency Limits and Energy Efficiency Levels for Three-Phase Distribution Transformers". Traditional dry-type transformers use silicon steel as their core material. This material results in significant losses under no-load conditions, greatly wasting electrical energy. Currently, the most mainstream energy-saving distribution transformers are energy-saving oil-immersed silicon steel transformers and amorphous alloy transformers. Oil-immersed silicon steel transformers are classified into S7, S9, S11, S13, and S15 series based on loss performance; the S7 and S9 series are now obsolete. Amorphous alloy transformers combine energy efficiency and economy, and are also available in dry-type and oil-immersed types. A notable feature of amorphous alloy transformers is their low no-load loss, which aligns with national industrial policies and the requirements for energy conservation and emission reduction in power grids. They are distribution transformers with ideal energy-saving performance and are particularly suitable for areas where low-voltage power loads vary significantly in time periods or seasonally and where the average load factor is relatively low.

[0057] Due to the unique geographical location of island areas, the large number of islands, and the dispersed load, the aquaculture and related light industries and services exhibit significant seasonality, resulting in slow load growth. Therefore, amorphous alloy distribution transformers or on-load tap-changing transformers are more suitable for use in island areas. In this embodiment, an amorphous alloy distribution transformer is selected.

[0058] The losses caused by transformers are related not only to the transformer model but also to its capacity and number. A larger transformer capacity results in greater no-load losses; conversely, a smaller transformer capacity leads to significantly increased load losses when the load is too high, or even overloaded. Therefore, selecting the appropriate transformer capacity and number based on the actual load variation range can effectively reduce energy consumption and losses. This involves choosing the appropriate transformer model.

[0059] Since transformer selection affects the power grid, this paper compares the energy-saving capabilities of the most commonly used oil-immersed transformers to lay the foundation for subsequent transformer selection. The transformer parameters are shown in the table below.

[0060] Table 1 Relevant parameters of oil-immersed transformers

[0061]

[0062] The data in the table shows that for transformers of the same model, the larger the capacity, the greater the no-load loss and load loss. Therefore, transformer capacity must be considered when selecting a transformer. When comparing the losses of transformers with the same capacity but different load rates, a transformer with a rated capacity of 1250kVA is uniformly selected for the loss comparison under different load rates. The loss calculation is as follows: Figure 4 As shown.

[0063] from Figure 4 It is known that the higher the load rate, the greater the active power loss of any type of transformer. When the load rate is the same, among the transformers mentioned above, the SH15 type transformer has the greatest potential for loss reduction. With a transformer capacity of 1250kVA, if the S11 and S13 transformers are replaced with SH15 type transformers, the loss reduction rates under different load rates are shown in the table below.

[0064] Table 2 Loss Reduction Rate under Different Load Rates

[0065]

[0066] As shown in the table, replacing the S11 and S13 transformers with amorphous alloy transformers resulted in the highest loss reduction rate at a load rate of 20%. The lower the load rate, the lower the loss reduction rate. Therefore, using amorphous alloy transformers in low-load scenarios offers better loss reduction performance.

[0067] Under the premise of meeting the requirements for power supply reliability, the number and capacity of transformers in the substation can be reasonably selected and implemented in accordance with the relevant provisions of the guidelines. Assuming that the transformer configuration of the substation meets the reliability requirements before and after optimization, and disregarding the parallel and separate operation of transformers, and assuming that the number of transformers in the substation before and after optimization are n1 and n2 respectively, the loss reduction that can be achieved before and after optimization is:

[0068]

[0069] In this process, it's important to note that the results calculated by the computer are ideal values. To be more realistic, a geographical adjustment parameter corresponding to each transformer needs to be added when calculating the loss of each transformer. The geographical location information of the island region where the transformer is located is obtained, and the geographical adjustment parameter is derived based on this location. This geographical adjustment parameter is formed based on temperature, humidity, and corrosion information collected at the transformer's location, and the costs incurred in maintenance. This parameter is obtained according to the actual situation, and the final loss reduction value is calculated and converted into actual economic benefits. This economic benefit is then compared with the cost of replacing the amorphous alloy distribution transformer used in this embodiment to determine whether transformer replacement is necessary.

[0070] In this embodiment, the benefits from the corresponding loss reduction rate are sufficient to cover the cost of replacing the amorphous alloy transformer. Therefore, it can be determined that the corresponding transformers will be replaced with new amorphous alloy transformers one by one within 3 months. This invention utilizes natural laws to provide technical support for this replacement.

[0071] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. All equivalent changes made to the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A transformer selection method based on loss reduction efficiency of island regions, characterized by, Further comprising the following steps: Step 1: Mathematical modeling for the equivalent circuit of the transformer; Step 2: According to the transformer model, calculate the island area power distribution network loss generated by different types of transformers, analyze the influence of transformer selection on the island power distribution network loss; Step 3: Calculate the transformer loss generated by different types of transformers under different capacity and load rate conditions, and compare and analyze the transformer type most suitable for the island area power distribution network; Step 4: Put the selected transformer back into the model and add the geographical adjustment parameters brought by the island area where it is located to recalculate whether the loss reduction benefit covers the cost of transformer replacement; Step 5: According to the calculation result of step 4, decide whether to replace the selected type of transformer or reselect the transformer type; The geographical adjustment parameter is a parameter formed based on the cost of maintenance and treatment according to the temperature, humidity and corrosion degree information collected at the location of the transformer; In step 2, the double-winding and three-winding transformers are modeled, and the loss model of the transformer is: ； wherein is the total no-load loss, is the total load loss, is the no-load loss of the i-th distribution transformer; is the short-circuit loss of the i-th distribution transformer; is the apparent power of the i-th transformer; is the rated capacity of the i-th transformer; is the load fluctuation coefficient; In step 4, after selecting the transformer model, the number of transformers in the substation before and after replacement is respectively reset and The actual loss reduction achieved by this replacement is: ； wherein is the no-load loss of the i-th distribution transformer; is the short-circuit loss of the i-th distribution transformer; is the apparent power of the i-th transformer; is the rated capacity of the i-th transformer; is the load fluctuation factor.

2. The transformer sizing method based on island area loss efficiency reduction of claim 1, wherein, Obtain the geographical location information of the island area where the transformer is located, and obtain the geographical adjustment parameter for step 4 according to the geographical location of the transformer.

3. The transformer sizing method based on island area loss efficiency reduction of claim 1, wherein: When the secondary winding is reduced to the primary winding, is the resistance, is the reactance, is the conductance, is the susceptance, the above parameters are calculated as follows: ； ； ； ； wherein is the transformer short circuit loss increment; is the transformer no-load loss increment; is the short circuit voltage percentage; is the no-load current percentage, is the rated voltage, is the rated power.

4. The transformer sizing method based on island area loss efficiency reduction of claim 1, wherein: When the three-winding transformer is reduced to the primary side winding, the electrical parameters of the three-winding transformer are obtained according to the capacity ratio, short-circuit loss and no-load loss of the transformer: ； ； wherein, , , is the resistance of each winding, , , is the reactance of each winding, , , is the short circuit loss of each winding; , , is the short circuit voltage percentage of each winding, is the rated voltage, is the rated power, the conductance and susceptance calculation formula of three winding transformer is the same as that of two winding transformer.

5. The transformer sizing method based on island area loss efficiency reduction of claim 1, wherein, When calculating the loss of each transformer, the geographical adjustment parameter corresponding to the transformer needs to be added.

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