Harmonic Influence on Electric Power Cost and Study of Harmonic Electricity Price

Wang Yongjun, Yue Chaoyuan (Institute of Systems Engineering, Huazhong University of Science and Technology, Wuhan 430074, Hubei, China) There have been some researches on the mechanism of hazards and effects, but there are few studies on the effects of harmonics on the cost and income of power companies and harmonic power prices. . Discuss the influence of harmonics on the cost of electricity, theoretically analyze the influence of harmonics on the measurement of the electric energy meter, formulate harmonic electricity price calculation model according to two kinds of pricing standards, and provide theoretical basis for the electric power company to make harmonic charges.

With the development of science and technology, the rapid growth of new types of electrical equipment (such as electronic devices, switching power supplies, and speed control devices) has greatly increased social productivity on the one hand, and on the other hand has connected a large number of nonlinear loads to the grid. The power grid is heavily polluted and power quality is degraded. At present, harmonics, negative sequence, and flicker have become three major hazards in the power system, which seriously threatens the safe and economical operation of the power grid and the safety of electricity for the majority of users. Harmonic pollution is particularly serious. In general, harmonics will reduce power quality, cause metering errors, and generate large reactive power. This will increase losses and temperature rises in power equipment and transmission lines, reduce the lifespan of power supply equipment, threaten the safe operation of the power grid, and provide power supply costs for large power grids. In addition, with the vigorous development of power electronics technology, the capacity of converter devices in modern industrial production equipment is also increasing, and the number is increasing. These non-linear loads will also generate a large amount of harmonic currents into the grid.

At present in China, the issue of harmonics is gradually being valued by people.

Harmonic control in power systems is a new and interdisciplinary problem that needs to be studied urgently. Its causes, mechanisms for damage and impact, the formulation of measurement and evaluation standards, calculation and analysis methods, and measures for comprehensive governance The exploration of such aspects should be continuously deepened. This article analyzes the influence of harmonics on the cost of electricity and the analysis of the metering influence of the meter, and establishes a harmonic electricity price calculation model based on two pricing standards, which provides a theoretical basis for the power company to perform harmonic charges.

1 The Harm of Power Harmonics The current harmonic sources in China are mainly some rectifier equipment, such as the rectification equipment of chemical and smelting enterprises, various regulators and electric locomotives. For example, electric locomotives not only generate harmonics but also asymmetric loads, and their location and operating conditions will change over time. The arc furnace is also a source of harmonics, and its variation is very irregular, especially in the melting period, its harmonics are more serious. In addition, with the development of science and technology, new types of electrical equipment will be rapidly added, which may be a factor that can cause serious harmonic pollution in the future.

At present in China, the harm caused by harmonics has been basically recognized by everyone. Many also pointed out that the pollution caused by harmonics has been very serious in our country. For example, there are currently 2 large-scale steelmaking plants in Wuxi, about 15 small and medium-sized steelmaking plants, and a total capacity of 338 arc furnaces (4 for 0t, 3 for 20t, 4 for 10t, and 25 for 5t and below). Mainly distributed in the 110, 35, 10kV side of each substation. The annual electric power consumption of electric arc furnaces increased from 6 hours in 1990 to 120.5 billion kW-h at the end of 1993. The annual average annual depletion rate of 27.7% accounts for 18% of the annual electricity consumption in the region. It is a large electricity consumer in the region. As a non-linear load, the pollution caused by the harmonic current injected into the power grid by the electric arc furnace is becoming increasingly serious. Due to harmonics caused by the distance protection of the wrong signal and malfunction, capacitance over-current tripping, transformer ferromagnetic audio and electrical equipment damage and other phenomena occur from time to time, a serious threat to the safe and economic operation of the grid.

In addition, East China Power Grid 500kV Luosuo line operation caused 220kV2774 line current waveform distortion, resulting in the line high-frequency phase difference protection can not be put into operation, the reason is: harmonic resonance and grid structure, a strong source of harmonics will of course It will cause some damage to the power grid, and a not too strong harmonic source will also cause resonance conditions due to improper coordination of grid parameters, causing serious damage to the operation of the power grid.

Harmonic waves have various degrees of influence and harm on various electrical equipment. From the engineering point of view, it mainly manifests in the following aspects.

a. The main influence of harmonics on motors and transformers is to cause additional iron loss and copper loss, so that the temperature rise of the equipment is too high and the insulation strength is reduced; secondly, vibration is generated and noise is emitted, and long-term vibration will cause metal fatigue and mechanical damage; Harmonics can also cause harmonic overvoltages.

b. Harmonic amplification can exacerbate harmonic harm. Harmonic amplification is harmonics injected by a harmonic source. Its frequency is in the resonance region near the resonant point of the network, and it stimulates partial resonance of the inductor and capacitor. When harmonics cause system resonance, the consequences are very serious, harmonic voltage rises, harmonic current is large, causing relay protection misoperation and causing equipment damage.

c Harmonic interference to relay protection and automatic devices. The interference of harmonics on relay protection and automatic devices can be classified into three categories: first, the interference generated by harmonics based on positive sequence quantities; second, the interference caused by harmonics based on negative sequence quantities; and third, the harmonics alone Generated interference. Electrified railways, electric arc furnaces and other harmonic sources are also negative sequence power supplies. The harmonic interference superimposed on the negative sequence content has a very serious impact on relay protection and automatic devices.

2 The influence of harmonics on the cost and revenue of the power company The above has only explained the influence and harm of harmonics on various electrical equipment from an engineering perspective. In fact, the harm of harmonics to the power system not only manifests itself in engineering but also in economics. Harmonic hazards have been a lot of research as an engineering problem, but almost no one has done any research on the economic aspects of this issue. Harmonics not only affects various electrical equipment, but also causes the grid to increase the cost of power supply to users. It also causes errors in the power meter due to the presence of harmonics, causing the meter reading to be inconsistent with the actual load used, affecting the company’s revenue. . Specifically, the impact of harmonics on the cost and revenue of power companies is mainly reflected in five aspects.

2.1 Harmonic waves cause various losses to increase power costs Harmonic currents must generate additional losses in transmissions of transformers, motors, and lines. The harmonic resistance Rh of the windings is larger than the fundamental resistance Ri due to the skin effect of the current. The additional harmonic losses generated by h-th harmonic current for Rh=R\ is the harmonic current content in Ah windings.

From the above equation, it can be seen that each additional harmonic loss is proportional to the square of the harmonic current and the square root of the number of harmonics.

The measured data of an electric appliance manufacturing company in Japan show that when the transformer Ih reaches 0.1 In, the loss of the transformer is greater than the rated loss by 10%. For the electrified railway such an impact harmonic source, harmonic power loss due to harmonics It's even bigger. For example, an area caused resonance due to the 5th harmonic injected into the power grid by the electrified railway, causing the 3rd and 5th harmonic losses of electrified railways to be injected into the power grid to amount to 190kW, accounting for 1.9% of the average fundamental wave load of 10MW and 2.2 additional losses. Some electrical equipment capacity makes the power variable cost rise. The iron core in the electrical equipment will cause core loss in the core coil under the action of the alternating magnetic flux and generate a large amount of heat. The core loss consists of two parts: eddy current loss and hysteresis loss.

Practice has proved that in the normal operation of the motor and transformer, eddy current loss is 2 to 3 times smaller than the hysteresis loss, it may be set to 2.5 times. Therefore, under the condition that the terminal voltage is kept constant, the iron loss caused by the nth harmonic is the one, and P0 is the iron loss under the fundamental wave condition. The value can be found in the national standard on the performance of electrical steel.

1.7T magnetic induction, 50Hz, iron loss per unit mass as shown in Table 1.

The measured data of the Xuedian traction station in the background harmonics test report of the power supply system of the Harbin-Dalian railway electrification retrofit system was used, and the actual iron loss calculation was performed using the DQ120-27 cold-rolled silicon oriented steel as an example. The actual calculation results are shown in Table 2. Table 1 Cold Rolled Oriented Silicon Steel Loss Table Maximum Iron Loss - 27 Cold Rolled Oriented Silicon Steel Actual Iron Loss Table Harmonic Times Permissible Harmonic Current / A Three-term Maximum Harmonic Current / A Yes No Exceeding the standard is whether or not the mass per unit core iron core harmonic loss / (W°kg | visible higher harmonics significantly exceeded the situation, harmonics on the occupation of electrical equipment capacity is very significant. With the number of harmonics plus the number of The use of harmonics has gradually increased the occupation of the capacity of electrical equipment. Harmonic overweight has caused significant iron loss, and at the same time, the heat output of electrical equipment has made the motor unable to work at rated power, that is, iron loss has taken up a large amount of electrical equipment capacity. Excessive waves will cause the cost of electricity to rise.

23 Harmonic Reduction of Lifetime of Electrical Equipment Increases Fixed Cost of Electricity Because the insulation structure used in electrical equipment is mostly composed of a variety of insulation materials, the insulation grade of electrical equipment is the material with the lowest heat resistance among the main insulation materials it uses. decided. Because the existence of harmonics makes the heat of various electrical equipment exceed the design heat level, it will greatly reduce the life of insulating materials and reduce the service life of electrical equipment.

The operating temperature has a great influence on the life of the insulating material. For example, the lifetime t(a) of Class A insulation material has the following relationship with the use temperature of 9(C): 2718. This shows that the life of insulation material decreases exponentially with temperature. Calculated according to the test data a=.88, the insulation life is shortened by half for each 8C high temperature. It can be seen that the temperature has a great influence on the insulation life.

24 Harmonic Influence on Relay Protection and Automatic Devices In the devices that cause power system accidents that are affected by harmonics in the power system of our country and cause faults or performance degradation, relay protection and automatic devices are the most common. As a result of the influence of harmonics in electrified railways, especially in traction substations, individual relay protection and automatic devices can start up to one hundred times or more in a quarter, resulting in erroneous trips resulting in large-scale blackouts. The accidents are not uncommon. Whether in 220kV, 330kV, or 500kV power grids, harmonic protection affects line protection or transformer protection, causing false start or false tripping. The harmonics originate from electrified railways or converter transformers. In some areas, the background harmonics will be amplified to cause some relay protection malfunctions under the condition that the harmonic compensation is caused by the complementary capacitor bank. The influence of harmonics on relay protection and automatic devices seriously threatens the security and economic operation of the grid. The losses caused by accidents caused by it are sometimes invaluable.

2.4 Harmonics Cause Electric Meter Measurement Error Impact Electric Power Company's Revenue Electric Energy Meter Accurate measurement of electric energy is the basis for fair collection and payment of electricity charges. In addition to considering the influence of harmonics on the cost of electricity, the influence of harmonics on the metering is also a factor that cannot be ignored when calculating the electricity price. The influence of harmonics on metering is mainly manifested in two aspects.

It is difficult to truthfully reflect the serious harmonics problem in real power grids. For example, users of electric locomotives, steel mills, etc., generate severe current waveform distortions, and the power meter will generate large errors. The traditional electrical energy measurement is based on a linear load. The voltage and current at both ends are assumed to be sinusoidal waveforms. Inductive power meters are widely used today and are designed to operate at power frequency conditions. In theory, only the same frequency voltage and current can constitute power. Power frequency voltage (current) and harmonic current (voltage) do not generate power. However, due to the non-linearity of the ferromagnetic components of the inductive power meter, when the power frequency voltage (or current) of a pure sinusoidal waveform is input, there will be some harmonics in the windings and the disks of the watch.

Therefore, when one of the input voltages and currents contains harmonics, although the true power of the subharmonic in the circuit is zero, in the energy meter it is the same as the input pure sinusoidal power frequency due to distortion. Frequency harmonic components interact to form false harmonic power, causing a random or positive or negative error in the meter.

On the other hand, the current usually passes through the transformer before entering the meter. When the higher harmonics enters the meter through the transformer, a large error will occur and the actual power consumption cannot be accurately reflected.

The declining frequency characteristics of the watt-hour meter Harmonic voltages and currents of the same frequency constitute the harmonic power and the corresponding harmonic energy. However, due to the falling frequency characteristics of the inductive meter, the rpm of the disk under harmonic power is lower than that of the same frequency. The speed is much lower. The Northwest Electric Power Experiment Research Institute conducted harmonic influence tests on two single-phase induction power meters. The results show that the ratio of the rotational speed of the harmonic power of the same power meter to the response of the fundamental power is approximately 3 times: Harmonics are 0.65 harmonics and 0.47 harmonics are 0.28. In general, due to their declining frequency characteristics, conventional induction watt-hour meters have been unable to accurately measure higher harmonic energy. In recent years, there have been several research institutes in China that have conducted studies on the effects of harmonics on the metering of electricity meters, and have done a lot of actual measurements. From the results of actual measurement, the magnitude of harmonic power determines the magnitude of the error generated by harmonics on the meter. The greater the harmonic power, the greater the error generated on the meter. This is the main reason for the measurement error of the meter. Under the conditions of certain voltage and current harmonic content, the direction of harmonic power also affects the magnitude of the error of the energy meter. When the harmonic power and the fundamental power are in the same direction or in opposite directions, the error of the energy meter is the largest. The positive and negative errors depend on the direction of the harmonic power. When the harmonic power is injected into the user end from the power grid, the error of the meter is a positive error; when the harmonic power is injected into the power grid from the user end, the meter error is a negative error.

Take the third harmonic as an example to test the effect of harmonic power on the meter error: 180 (the harmonic load is injected into the grid by the simulated load) (0 is the relative angle between the harmonic component and the fundamental wave) Table 3 3rd Harmonic Energy Meter The influence of the error on the digital electromagnetic type can use the same method to obtain the influence of other higher harmonics on the error of the energy meter. The error curve of (Pn) (n=2, 3, 4) is plotted under the above conditions.

Errors can be estimated from the error curves generated by the single harmonics. For the error caused by the load containing more complex harmonic components on the energy meter, the total error curve can be obtained by the principle of superposition based on the error curve plotted by a single harmonic. After tests, it is proved that the estimated value is basically the same as the actual measured value.

3 Harmonic Electricity Price The cost of a power company is the basis for setting the price. The electricity prices of various users should truly reflect the cost of power supply and provide users with appropriate price signals.

The impact of the book is implicit in the electricity tariffs that the power company sells to all users. This is similar to the situation where a few factories discharge wastewater into rivers and all residents along the river need to pay sewage charges. In this way, a reasonable tariff plan should reflect the mutual influence of harmonics on the power company's revenue and costs. Therefore, the cost accounting standard should be the most basic standard for establishing the electricity price model, and it is also in line with the relevant national policies.

As mentioned earlier, the increasing harmonic pollution in the power grid greatly affects the cost and revenue of the power company. Therefore, in the future, the pricing of electricity must consider the impact of harmonics on the cost of electricity. At present, we should formulate a new electricity price calculation method in light of China's national conditions, conduct harmonic charging for users of large harmonic sources, strengthen the study of the effects of harmonics on the cost and income of power companies, and formulate harmonic electricity prices, thereby forcing large harmonic sources. The reduction of harmonic emissions by users and the realization of harmonic control of power by economic means may be one of the most effective measures for harmonic control.

The impact of higher harmonics on the cost and revenue of power companies is mainly reflected in five aspects. The first four aspects are difficult to accurately estimate, and punitive pricing standards for these effects are taken into account in the harmonic electricity price; and for harmonics The measurement error of electric energy meter has been extensively tested in China. The error can be estimated by the measured data and reflected in the harmonic electricity price according to the cost accounting pricing standard.

According to the punitive pricing standards and cost accounting pricing standards, the following harmonic power price calculation formula is proposed: Pb unified sales price; Ki penalty coefficient, when the harmonic is stationary, Ki = 0.2; when the harmonic is fluctuating, Ki = 0.3; When the harmonic content causes the system parameter harmonic K2 harmonics to estimate the error of the energy meter, it can measure the total harmonic power to check the error curve to select the value of K2.

Harmonic electricity price calculation model should be divided into the following two cases.

Many power equipments have certain harmonics. Their power consumption is different, and each harmonic voltage, harmonic current, and harmonic power contained in the power equipment are different. Is it necessary to use all the power equipment with harmonics? It is neither reasonable nor feasible to charge fees for equipment with very small harmonic content. Therefore, there must be a certain standard for harmonic charges. Harmonic charges should only be used when certain harmonic indicators exceed the standard. For this reason, harmonic 2Un.In limits are used as harmonic charging standards.

For the setting of harmonic charging standard 2Un In limits according to the national standard GB/T1454993, there is a permissible value table for the harmonic current injected into the common connection point, see Table 4 according to Table 4 we can calculate the number of corresponding harmonics The voltage content rate limit table is shown in Table 5. The effect of harmonics on the power supply cost is the result of the harmonic voltage and harmonic current. Therefore, the voltage and current product Un/n of each harmonic is taken as the evaluation harmonic. The indicators of the wave's influence on the power supply cost are shown in Table 6. Since the harmonic contents of different harmonics of different harmonic power supplies have different characteristics, we use 2UnVn as the standard for punitive charges for harmonic power supplies. Table 7. For the sake of simplicity, simple and easy 2UnIn standards can be developed for different types of harmonic users. For example, for the harmonic load of the AC electric arc furnace, 2nd, 3rd, 4th, 5th, and 7th harmonics can be calculated. In value; 3,5,7,9,11,13,15 harmonic 2Un.In values ​​can be calculated for electrified railway harmonic loads.

05 is to consider the use of certain measuring equipment to charge a load containing harmonics, put a certain amount of work, therefore, to be included in the additional charges of harmonic charges, temporarily calculated as a result of metric errors less 5% of charges.

Table 4 Harmonic current allowable values ​​injected into common connection points Standard voltage reference Short 3203717191528132512141121 Table 5 Harmonics voltage limits of utility grids Standard voltage reference Short 380V voltage class load Mainly civilian-oriented, even standard voltage/kV reference short circuit Capacity/MVA Harmonic Order and Harmonic Voltage Current Product/kVA Standard Voltage/kV Reference Short-circuit Capacity Harmonic Order and Harmonic Voltage Current Product/kVA Standard Voltage/kV Reference Short-circuit Capacity Harmonic Order and Harmonic Voltage Current Product/kVA Standard voltage reference short-circuit capacity/MVA industrial load is also mainly used internally by users. Therefore, in the early stage of harmonic charges, it may not be included in the harmonic charging standard limit table.

4 Conclusions From an economic point of view, it is necessary to consider the influence of harmonics on the cost and revenue of the power company. The harmonic power price model and harmonic charging standards determined according to the two pricing standards can be used as the basis for charging to harmonic sources. Harmonic charges are a kind of power compensation and additional electricity charges for power companies. This is just economic compensation. Economic compensation is not the purpose of harmonic control. The ultimate goal of harmonic control is to reduce the harmonic source to the power system and its power users. Harmonic pollution.