Calculation of technical losses in the line 10 sq. Thesis: Losses of electricity in distribution networks
METHODS FOR CALCULATION OF POWER LOSSES
When transmitting electricity from the buses of power plants to consumers, part of the electricity is spent on heating conductors, creating electromagnetic fields and other effects associated with alternating current. Most of these costs, which will be referred to as energy losses in the future, are for heating the conductors.
The term “energy loss” should be understood as the technological consumption of electricity for its transmission. It is for this reason that instead of the term “energy loss” in reporting documents power systems use the term “ technological consumption of electricity during transmission through electric networks”.
In a line operating with a constant load and having active power losses ΔР, power losses over time t will be
If the load changes during the year, then the energy losses can be calculated in various ways.
The most accurate method for calculating energy losses ∆W- this is their determination according to the load schedule of the branch, and the calculation of power losses is carried out for each stage of the schedule. This method is called the graphical integration method. When calculating for each hour, an hourly calculation of electricity losses is obtained.
There are daily and annual load schedules. On fig. 7.3 shows summer and winter daily schedules of active and reactive loads.
Rice. 7.3. Load curves: a - winter daily; b - summer daily;
c - by duration
The annual schedule is built on the basis of typical daily schedules for the spring-summer and autumn-winter periods. This is an example of an ordered graph, i.e. one in which all load values are arranged in descending order (Fig. 7.3). As a result, get annual schedule load, which shows the duration of work at a given load. Therefore, such a graph is called duration schedule.
Annually load schedule it is possible to determine the energy losses for the year. To do this, determine the loss of power and electricity for each mode.
After calculating the power losses in each mode, the total power losses for the year are obtained, all losses are summarized under different modes
, (7.7)
where ΔР i- power loss on i-th stage of the load schedule;
Δt i– duration i-th stage of the load schedule.
The value of power loss is found by the relation
where Si- full power i- th stage of the load schedule;
U i is the line voltage across i- th stage of the load schedule.
Loss of power and electricity in the transformer over time Δt i:
;
,
where ΔР to and ΔР x– losses respectively in copper and steel of the transformer;
S 2 i– load on the secondary side of the transformer on i-th stage of the schedule;
S nom- rated power of the transformer.
With k parallel identical transformers
. (7.9)
Electricity loss per year
. (7.10)
Depending on the degree of uniformity of the load curve, the number of transformers connected in parallel k may be different.
Dignity method for determining losses according to the load curve is high precision. The disadvantage of the method should be considered the lack of information about the load curves for all branches of the network. In addition, the desire for calculation accuracy causes an increase in the number of steps in the load curve, and this, in turn, leads to an increase in the complexity of the calculation.
One of the most simple methods loss determination is the calculation of electricity losses by time of greatest loss. From all modes, the mode in which the power loss is the greatest is selected. Calculating this mode, get the power loss in it ΔР nb. Energy losses per year are found by multiplying these power losses by the time of greatest losses τ :
The time of greatest losses is the time during which, when operating with the greatest load, the loss of electricity would be the same as when operating according to the actual load schedule:
where N- number of load steps.
It is possible to establish a connection between the losses of electricity and the electricity received by the consumer.
The energy received by the consumer in a year is equal to
where Rnb– the maximum power consumed by the load;
T nb- this is the time in hours for which, when working with the greatest load, the consumer would receive the same amount of electricity as when working on a real schedule.
Rice. 7.4. Definition ∆W according to the load schedule and τ :
a – line equivalent circuit; b, d – three-stage and multi-stage load curves; c, e - three-stage and multi-stage graphs S2
From the graphs shown in Fig. 7.4 shows that the values τ and T nb generally do not match. For example, T nb represents the abscissa of a rectangle whose area is equal to the area of the three-step graph in Fig. 7.4, b or a multi-stage graph in fig. 7.4, g.
Let's build a graph S 2 = f(t)(Fig. 7.4, c). Let's assume that the power loss i-th stage of the graph is approximately determined by the rated voltage, i.e. instead of (7.8) we will use the following expression
Given that r l / = const, It should be noted that the loss of electricity over time Δt i are equal on a certain scale.
Electricity losses per year on a certain scale are equal to the areas of the figures in Fig. 6.4, c and e.
The time of greatest loss τ is the abscissa of a rectangle whose area is equal to the area of the three-step graph in Fig. 7.4, in or multi-stage graph in fig. 7.4, d. Similarly to (7.13), we obtain
.
Busy time from (7.13)
.
Electricity losses in transformers are calculated by the formula
, (7.14)
where
T = 8760 h is the number of hours in a year.
The expression can be applied only with a constant number of transformers connected in parallel, i.e. K = const.
Because the power consumption Р ~ I×cosφ, and the power loss ΔР ~ I 2, then the discrepancy between the values of the time of the greatest load becomes obvious T nb and the time of greatest losses τ (Fig. 7.4). There are empirical formulas relating τ and T nb. For a number of characteristic loads, it is possible to build dependences by calculation τ = f (T nb, cosφ) shown in Fig. 7.5.
Rice. 7.5. Dependencies τ from T nb and cosφ
The procedure for calculating losses using the τ method, i.e. according to the time of greatest losses, the following:
1) find the time of the greatest load using the annual schedule;
2) from graphic dependencies τ = f (T nb, cosφ) given in reference literature, find the time of greatest losses;
3) determine the losses in the maximum load mode ΔР nb;
4) by ratio ΔW = ΔР nb × τ find the energy loss per year.
The method of calculating the greatest losses in time was one of the most common before the widespread introduction of computers. The method is based on the assumptions that the maximum energy losses in the network element correspond to the maximum load of the system and the graphs of active and reactive powers are similar, i.e. cosφ = const. When using empirical dependences of τ on T nb and cosφ the configuration of load curves is only partially taken into account. The assumptions made lead to large errors in this method. In addition, using the τ method, it is impossible to calculate losses in lines with steel wires, the resistance of which is variable.
Further improvement in the accuracy of loss calculation led to the development of the method τ P and τ Q . With this method, in magnitude ΔР nb the power losses from the flow of active and reactive power through the network are separated.
The calculated ratio has the form
ΔW = ΔP P × τ P + ΔP Q × τ Q ,
where ΔР р, ΔР Q- components of power losses from the flow of active and reactive power through the network.
Introduction
Literature review
1.2 Load power losses
1.3 No-load losses
1.4 Climate losses of electricity
2. Methods for calculating electricity losses
2.1 Methods for calculating electricity losses for various networks
2.2 Methods for calculating electricity losses in distribution networks 0.38-6-10 kV
3. Programs for calculating electricity losses in distribution electrical networks
3.1 The need to calculate the technical losses of electricity
3.2 Application of software for calculating electricity losses in distribution networks 0.38 - 6 - 10 kV
4. Regulation of electricity losses
4.1 The concept of the loss standard. Methods for setting standards in practice
4.2 Loss specifications
4.3 The procedure for calculating the standards for electricity losses in distribution networks 0.38 - 6 - 10 kV
5. An example of calculating electricity losses in distribution networks 10 kV
Conclusion
Bibliography
Introduction
Electrical energy is the only type of product that does not use other resources to move it from the places of production to the places of consumption. For this, part of the transmitted electricity itself is consumed, so its losses are inevitable, the task is to determine their economically justified level. Reducing electricity losses in electrical networks to this level is one of the important areas of energy saving.
During the entire period from 1991 to 2003, the total losses in the energy systems of Russia grew both in absolute terms and as a percentage of electricity supplied to the grid.
The growth of energy losses in electrical networks is determined by the action of quite objective laws in the development of the entire energy sector as a whole. The main ones are: the trend towards the concentration of electricity generation at large power plants; continuous growth of loads of electrical networks, associated with a natural increase in loads of consumers and a lag in growth rates bandwidth networks on the growth rates of electricity consumption and generating capacities.
In connection with the development of market relations in the country, the importance of the problem of electricity losses has increased significantly. The development of methods for calculating, analyzing power losses and choosing economically feasible measures to reduce them has been carried out at VNIIE for more than 30 years. To calculate all components of electricity losses in the networks of all voltage classes of AO-energos and in the equipment of networks and substations and their regulatory characteristics, a software package has been developed that has a certificate of conformity approved by the CDU of the UES of Russia, the Glavgosenergonadzor of Russia and the Department of Electric Grids of RAO "UES of Russia".
Due to the complexity of calculating losses and the presence of significant errors, in recent times special attention is paid to the development of methods for normalizing power losses.
The methodology for determining loss standards has not yet been established. Even the principles of rationing have not been defined. Opinions on the approach to rationing range widely - from the desire to have an established fixed standard in the form of a percentage of losses to control over "normal" losses with the help of ongoing calculations according to network diagrams using appropriate software.
According to the received norms of electricity losses, tariffs for electricity are set. Tariff regulation is entrusted to the state regulatory bodies FEK and REC (federal and regional energy commissions). Energy supply organizations must justify the level of electricity losses that they consider appropriate to include in the tariff, and energy commissions should analyze these justifications and accept or correct them.
This paper considers the problem of calculating, analyzing and normalizing electricity losses with modern positions; the theoretical provisions of the calculations are presented, a description of the software that implements these provisions is given, and the experience of practical calculations is presented.
Literature review
The problem of calculating electricity losses has been worrying power engineers for a very long time. In this regard, very few books on this topic are currently being published, because little has changed in principle device networks. But it produces enough a large number of articles where old data are clarified and new solutions are proposed for problems related to the calculation, regulation and reduction of electricity losses.
One of the latest books published on this topic is Zhelezko Yu.S. "Calculation, analysis and regulation of electricity losses in electrical networks" . It most fully presents the structure of electricity losses, loss analysis methods and the choice of measures to reduce them. The methods of normalization of losses are substantiated. Described in detail software, which implements methods for calculating losses.
Earlier, the same author published the book "Selection of Measures to Reduce Electricity Losses in Electric Networks: A Guide for Practical Calculations". Here, the greatest attention was paid to methods for calculating electricity losses in various networks and the use of one or another method depending on the type of network, as well as measures to reduce electricity losses, was justified.
In the book Budzko I.A. and Levina M.S. "Power supply of agricultural enterprises and settlements" the authors examined in detail the problems of power supply in general, focusing on distribution networks that feed agricultural enterprises and settlements. The book also provides recommendations on organizing control over electricity consumption and improving accounting systems.
Authors Vorotnitsky V.E., Zhelezko Yu.S. and Kazantsev V.N. in the book "Electricity losses in electrical networks of power systems" considered in detail general issues related to reducing electricity losses in networks: methods for calculating and predicting losses in networks, analyzing the structure of losses and calculating their technical and economic efficiency, planning losses and measures to reduce them.
In the article by Vorotnitsky V.E., Zaslonov S.V. and Kalinkini M.A. "The program for calculating the technical losses of power and electricity in distribution networks 6 - 10 kV" describes in detail the program for calculating the technical losses of electricity RTP 3.1 Its main advantage is ease of use and easy-to-analyze conclusion of the final results, which significantly reduces personnel labor costs for calculation.
Article Zhelezko Yu.S. "Principles of regulation of electricity losses in electrical networks and calculation software" is devoted to the actual problem of regulation of electricity losses. The author focuses on the purposeful reduction of losses to an economically justified level, which is not ensured by the existing practice of rationing. The article also makes a proposal to use the normative characteristics of losses developed on the basis of detailed circuit calculations of networks of all voltage classes. In this case, the calculation can be made using the software.
The purpose of another article by the same author entitled "Estimation of electricity losses due to instrumental measurement errors" is not to clarify the methodology for determining the errors of specific measuring instruments based on checking their parameters. The author in the article assessed the resulting errors in the system for accounting for the receipt and release of electricity from the network of an energy supply organization, which includes hundreds and thousands of devices. Special attention paid to the systematic error, which at present is an essential component of the loss structure.
In the article Galanova V.P., Galanova V.V. "Effect of the quality of electricity on the level of its losses in the networks" paid attention to the actual problem of the quality of electricity, which has a significant impact on the loss of electricity in the networks.
Article by Vorotnitsky V.E., Zagorsky Ya.T. and Apryatkin V.N. "Calculation, rationing and reduction of electricity losses in urban electrical networks" is devoted to clarifying existing methods for calculating electricity losses, rationing losses in modern conditions, as well as new methods for reducing losses.
The article by Ovchinnikov A. "Electricity losses in distribution networks 0.38 - 6 (10) kV" focuses on obtaining reliable information about the operation parameters of network elements, and above all about the load of power transformers. This information, according to the author, will help to significantly reduce the loss of electricity in networks of 0.38 - 6 - 10 kV.
1. Structure of electricity losses in electrical networks. Technical losses of electricity
1.1 Structure of electricity losses in electrical networks
When transferring electrical energy losses occur in each element of the electrical network. To study the loss components in various elements network and assess the need for a particular measure aimed at reducing losses, an analysis of the structure of electricity losses is performed.
Actual (reported) electricity losses Δ W Rep is defined as the difference between the electricity supplied to the network and the electricity released from the network to consumers. These losses include components of a different nature: losses in network elements that are purely physical in nature, the consumption of electricity for the operation of equipment installed at substations and ensuring the transmission of electricity, errors in fixing electricity by metering devices and, finally, theft of electricity, non-payment or incomplete payment meter readings, etc.
Ministry of Industry and Energy Russian Federation(Ministry of Industry and Energy of Russia)ORDER
O b approval of the methodology for calculating standard (technological) losses of electricity in electric networks
In pursuance of paragraph 2 of Decree of the Government of the Russian Federation of February 26, 2004 N 109 and paragraph 3 of Decree of the Government of the Russian Federation of December 27, 2004 N 861, I order: 1. Approve the proposed method for calculating standard (technological) losses. 2. To impose control over the execution of this order on the Deputy Minister of Industry and Energy of the Russian Federation A.G. Reus. Minister V.B. Khristenko
APPROVED
Order of the Ministry of Industry and Energy of Russia
Methodology for calculating standard (technological) losses of electricity in electrical networks
I. General provisions
1. The methodology is designed to calculate the standards for technological losses of electrical energy in the electrical networks of organizations engaged in the transmission of electrical energy through electrical networks. 2. Standards for technological losses of electricity calculated according to this method are used when calculating the fee for services for the transmission of electricity through electric networks. 3. Standards for technological losses of electricity in the planning period can be calculated: - on the basis of data on circuits, network loads and the composition of operating equipment in the planning period, using loss calculation methods established by this methodology; - based on the standard characteristics of process losses calculated in accordance with this methodology based on loss calculations in the reporting (base) period. In the absence of a regulatory characteristic, it is allowed to determine the loss standards in the planning period based on the calculations of losses in the reporting (base) period, changing the load losses in proportion to the square of the ratio of electricity outputs to the network in the planning and base periods, and idle losses - in proportion to the power (quantity) of operating equipment in the planning and base periods. 4. Terms and definitions a) Actual (reported) electricity losses - the difference between the electricity supplied to the network and the electricity released from the network, determined according to the data of the electricity metering system. b) Electricity metering system - a set of measuring complexes that measure the supply and output of electricity from the network and include measuring current transformers (CT), voltage (VT), electric meters, connecting wires and cables. Measuring complexes can be combined into an automated electricity metering system. in) Technological losses of electricity - the sum of technological losses during the transportation of electricity and losses in the sale of electricity. G) Technological losses during the transportation of electricity - the sum of two components of losses: - losses in the lines and equipment of electrical networks due to physical processes occurring during the transmission of electricity in accordance with the technical characteristics and modes of operation of lines and equipment ( technical losses ); - electricity consumption for own needs of substations. e) Losses in the sale of electricity - the sum of losses due to errors in the electricity metering system, and losses due to theft of electricity, the perpetrators of which have not been identified. Note. Losses caused by theft of electricity are not a technical characteristic of the electrical network and the electricity metering system, and their standards are not considered in this methodology. e) Technical losses - the sum of three components of losses in the lines and equipment of electric networks: - losses depending on the load of the electric network ( load losses ); - losses depending on the composition of the included equipment ( semi-permanent losses ); - losses depending on weather conditions. g) Electricity consumption for own needs of substations - electricity consumption required to ensure operation technological equipment substations and livelihoods of service personnel. h) Losses of electricity due to errors in the electricity metering system - the total imbalance of electricity, due to the technical characteristics and modes of operation of all measuring complexes for the receipt and release of electricity. and) Standard for technological losses of electricity - technological losses of electricity (in absolute units or as a percentage of the established indicator), calculated in accordance with this methodology for operating modes, technical parameters of lines, network equipment and electricity metering systems in the period under review. to) Regulatory method for calculating load losses of electricity - a method that uses the entire amount of available information about the circuits and loads of networks of a given voltage when calculating losses. With an increase in the equipment of networks with means of measuring and operational control of modes, it is recommended to use more accurate methods from their list established by the methodology. l) Normative characteristic of technological losses of electricity - dependence of the standard of technological losses of electricity on the structural components of the receipt and supply of electricity.II. Methods for calculating normative (technological) losses during the transportation of electricity
5. Methods for calculating load losses 5.1. Load losses of electricity for a period of T hours (D days) can be calculated by one of five methods, depending on the amount of information available about the schemes and loads of networks (methods are arranged in order of decreasing calculation accuracy): 1) operational calculations; 2) settlement days; 3) medium loads; 4) the number of hours of the greatest power losses; 5) estimation of losses based on generalized information about circuits and network loads. Power losses in the network when using methods 1 - 4 for calculating electricity losses are calculated on the basis of a given network scheme and the loads of its elements, determined by measurements or by calculating the loads of electrical network elements in accordance with the laws of electrical engineering. Electricity losses according to methods 2 - 5 must be calculated for each month of the billing period, taking into account the network scheme corresponding to this month. It is allowed to calculate losses for settlement intervals, including several months, in which network schemes can be considered as unchanged. Electricity losses for the billing period are determined as the sum of losses calculated for the months (calculated intervals) included in the billing period. 5.1.1. The method of operational calculations consists in calculating the losses of electricity according to the formula:Where n- number of network elements; D t- the time interval during which the current load I ij i-th network element with resistance R i, take unchanged; m- number of time intervals. The current loads of the network elements are determined on the basis of data from the dispatch lists, operational measuring systems (OIC) and automated systems electricity metering and control (ASKUE). 5.1.2. The calculation day method consists in calculating electricity losses according to the formula:
Where D W- electricity losses per day of the billing month with the average daily electricity supply to the grid W average day and the configuration of the load graphs in the nodes, corresponding to the control measurements; k l - coefficient taking into account the effect of losses in the armature of overhead lines and is taken equal to 1.02 for lines with a voltage of 110 kV and above and equal to 1.0 for lines of lower voltages; - coefficient of the form of the schedule of daily electricity supply to the network (a schedule with a number of values equal to the number of days in a month control measurements); D eq j - equivalent number of days in j-th calculated interval, determined by the formula:
, (3)
Where W mi - supply of electricity to the network in i-th month with the number of days D mi ; W m.r - the same, in the billing month; N j is the number of months in the j-th calculation interval. When calculating electricity losses per month D equiv j = D mi . Losses of electricity for the calculated day D W day is defined as the sum of power losses calculated for each hourly interval of the calculated day. Electricity losses in the billing period are determined as the sum of losses in all billing intervals of the year. It is allowed to determine the annual losses of electricity based on the calculation of D W days for winter day control measurements, taking in the formula (3) N j = 12. The coefficient is determined by the formula:
, (4)
Where W i - supply of electricity to the network for the i-th day of the month; D m is the number of days in a month. In the absence of data on the supply of electricity to the network for each day of the month, the coefficient is determined by the formula:
, (5)
Where D p and D n.r - the number of working and non-working days in a month ( D m = D p+ D n.r); k w - the ratio of the values of energy consumed on the average non-working and average working days k w = W n.p / W p . 5.1.3. The average load method consists in calculating electricity losses according to the formula:
, (6)
Where D R cp - power losses in the network at average node loads over the calculated interval; - coefficient of the form of the graph of the total load of the network for the calculated interval; k k - coefficient taking into account the difference in the configurations of the active and reactive load graphs of various branches of the network; T j - the duration of the j-th calculation interval, h. The form factor of the graph of the total load of the network for the calculation interval is determined by the formula:
Where P i - the value of the load on i-th stage graphics duration t i , hour; m- the number of graph steps on the calculated interval; R cp - average network load for the calculated interval. Coefficient k k in formula (6) is taken equal to 0.99. For networks 6 - 20 kV and radial lines 35 kV instead of the values P i and R cf in formula (7), the current values of the head section can be used I i and I cf. In this case, the coefficient k k is taken equal to 1.02. It is allowed to determine the coefficient of the shape of the graph for the calculated interval according to the formula:
, (8)
Where is the coefficient of the form of the daily schedule of the day of control measurements, calculated by the formula (7); - coefficient of the form of the schedule of monthly electricity supplies to the network (a schedule with the number of values equal to the number of months in the calculation interval), calculated by the formula:
, (9)
Where W m i - supply of electricity to the network for i-th month settlement interval; W cf. month - the average monthly supply of electricity to the network for the months of the settlement interval. When calculating losses for a month In the absence of a load schedule, the value is determined by the formula:
The fill factor of the graph of the total load of the network k h is determined by the formula:
, (11)
Where W o - electricity supply to the network during time T; T max - the number of hours of using the maximum network load. The average load of the i-th node is determined by the formula:
Where W i - energy consumed (generated) in i-th node during T. 5.1.4. The method of the number of hours of the greatest power losses consists in calculating the losses of electricity according to the formula:
, (13)
Where D R max - power loss in the mode of the maximum load of the network; t o - the relative number of hours of the greatest power losses, determined from the graph of the total network load for the calculated interval. The relative number of hours of the greatest power losses is determined by the formula:
, (14)
Where R max - the largest value from m values R i in the calculated interval. Coefficient k k in formula (13) is taken equal to 1.03. For networks 6 - 20 kV and radial lines 35 kV instead of the values R i and R max in formula (14), the current values of the head section can be used I i , and I max. In this case, the coefficient k k is taken equal to 1.0. It is allowed to determine the relative number of hours of the greatest power losses for the calculated interval according to the formula:
, (15)
Where t c is the relative number of hours of the greatest power losses, calculated by formula (14) for the daily schedule of the day of control measurements. The values of t v and t N are calculated by the formulas:
, (16)
, (17)
where W m.r - supply of electricity to the network in the billing month. When calculating losses per month t N = 1. In the absence of a load schedule, the value of t o is determined by the formula: 5.1.5. Loss estimation method based on generalized information about network schemes and loads consists in the calculation of electricity losses based on the dependencies of losses on the total length and number of lines, total power and number of equipment obtained on the basis of technical parameters of lines and equipment or statistical data. 5.2. Electricity losses should be calculated for typical operating and maintenance schemes. AT calculation scheme all elements of the network, the losses in which depend on its mode (lines, transformers, high-frequency barriers of high-frequency communication, current-limiting reactors, etc.), must be turned on. 5.3. Estimated values of active resistance of wires of overhead lines (VL) R n is determined taking into account the temperature of the wire t n ,°C, depending on the average ambient temperature for the billing period t in and current density in the wire j, A/mm 2:
R n= R 20 [ 1+0.004(t in -20+8.3j 2 F/300) ] , (19)
Where R 20 - standard reference resistance of a wire with a cross section F, mm 2 , at t n = 20°С. Note. In the absence of data on medium density current for the billing period in each element of the electrical network take the calculated value j \u003d 0.5 A / mm 2. 5.4. Losses of electricity in the connecting wires and busbars of substation switchgear (SPPS) are determined by the formula:
Where F- average section of wires (tires); L- total length of wires (tires) at the substation; j- current density. In the absence of data on the parameters used in formula (20), estimated losses in SPPS are taken in accordance with the table. Clause 1 of Appendix 1 and classify them as conditionally permanent losses.5.5. Electricity losses in measuring current transformers (CTs) are determined by the formula:
, (21)
Where D PТТnom - losses in ТТ at rated load; b ТТav - the average value of the current load factor of the CT for the billing period. In the absence of data on the parameters used in formula (21), the calculated losses in the CT are taken in accordance with Table. Clause 3 of Appendix 1 and classify them as conditionally permanent losses. 6. Regulatory methods for calculating load losses 6.1. Regulatory method calculation of load losses of electricity in networks 330 - 750 kV is a method of operational calculations. 6.2. Normative methods of calculation load losses of electricity in networks 35 - 220 kV are: - in the absence of reverse energy flows through interconnections 35 - 220 kV - the method of settlement days; - in the presence of reverse energy flows - the method of average loads. In this case, all hourly modes in the billing period are divided into groups with the same directions of energy flows. Calculation of losses is carried out by the method of average loads for each group of modes. In the absence of data on energy consumption at 35 kV substations, it is temporarily allowed to use the method of the largest power losses for calculating losses in these networks. 6.3. Normative method of calculation load losses of electricity in networks of 6 - 20 kV is the method of average loads. In the absence of information on energy consumption at TS 6 - 20 / 0.4 kV, it is allowed to determine their loads by distributing the energy of the head section (minus energy at the TS, where it is known, and losses in the network 6 - 20 kV) in proportion to the rated powers or coefficients maximum load of TS transformers. In the absence of electric meters on the head sections of 6-20 kV feeders, it is temporarily allowed to use the method of the largest power losses for calculating losses in these networks. 6.4. Normative method of calculation load losses of electricity in 0.38 kV networks is a method for estimating losses based on the dependencies of losses on generalized information about circuits and network loads, described below. Losses of electricity in the line 0.38 kV with a cross section of the head section F g, mm 2, supply of electrical energy to the line W 0.38, for the period D, days, calculated by the formula:
, (22)
Where L eq - equivalent line length; tg j - reactive power factor; k 0.38 - coefficient taking into account the nature of the distribution of loads along the length of the line and the uneven loads of the phases. The equivalent line length is determined by the formula:
L eq = L m +0.44 L 2-3 +0,22 L j , (23)
Where L m - line length; L 2-3 - length of two-phase and three-phase branches; L j - length of single-phase branches. Note. The main is understood as the greatest distance from the 0.4 kV busbars of the distribution transformer 6 - 20 / 0.4 kV to the most remote consumer connected to a three-phase or two-phase line. Intra-house networks of multi-storey buildings (up to electricity meters) include branches of the corresponding phase in the length. In the presence of steel or copper wires in the trunk or branches in the formula (23) substitute the lengths of the lines determined by the formula:
L \u003d L a + 4L c + 0.6L m, (24)
Where L a, L with and L m - lengths of aluminum, steel and copper wires, respectively. Coefficient k 0.38 is determined by the formula:
k 0.38 = k and (9.67 - 3.32d p - 1.84d p), (25)
Where d p is the share of energy supplied to the population; k and - coefficient taken equal to 1 for the 380/220 V line and equal to 3 for the 220/127 V line. When using formula (22) to calculate the losses in N lines with total lengths of highways L m å , two-phase and three-phase branches L 2-3 å and single-phase taps L 1 å the average supply of electricity in one line is substituted into the formula W 0,38 =W€0.38 / N, where W 0.38 å - total energy release in N lines, and the average section of the head sections, and the coefficient k 0.38 determined by formula (25) is multiplied by the coefficient k N , taking into account the disparity in the lengths of the lines and current densities in the head sections of the lines, determined by the formula
k N \u003d 1.25 + 0.14 d p (26)
In the absence of data on the duty cycle of the graph and (or) the reactive power factor, take k h = 0.3; tg j=0.6. In the absence of accounting for electricity supplied in the 0.38 kV line, its value is determined by subtracting from the energy supplied to the 6 - 20 kV network, losses in lines and transformers 6 - 20 kV and the energy supplied to TP 6-20 / 0, 4 kV and 0.38 kV lines, which are on the balance of consumers. 7. Methods for calculating conditionally constant losses 7.1. Conditionally permanent power losses include: - no-load losses in power transformers (autotransformers) and arc extinguishing reactor transformers; - losses in equipment, the load of which is not directly related to the total load of the network (adjustable compensating devices); - losses in equipment having the same parameters for any network load (unregulated compensating devices, valve-type arresters (RV), surge arresters (OPN), high-frequency connection devices (UVCH), instrument voltage transformers (VT), including their secondary circuits, electric meters 0.22 - 0.66 kV and insulation power cables). 7.2. Idle power losses in a power transformer (autotransformer) are determined on the basis of the no-load power losses D given in the passport data of the equipment. R x, according to the formula:
, (27)
Where T p i is the number of hours of operation of the equipment in i-th mode; U i - voltage on the equipment in the i-th mode; U nom - rated voltage of the equipment. The voltage on the equipment is determined by measurements or by calculating the steady state of the network in accordance with the laws of electrical engineering. 7.3. Electricity losses in a shunt reactor (SR) are determined by formula (27) based on the power losses D given in the passport data R R. It is allowed to determine the losses in the SR based on the data in Table. Clause 1 of Annex 1. 7.4. Electricity losses in a synchronous compensator (SC) or a generator switched to the SC mode are determined by the formula:
Where b Q is the coefficient of maximum load of the SC in the billing period; D R nom - power loss in the nominal load mode of the SC in accordance with the passport data. It is allowed to determine the losses in the SC based on the data in Table. Clause 2 of Annex 1. 7.5. Electricity losses in static compensating devices (CU) - capacitor banks (BC) and static thyristor compensators (STK) - are determined by the formula:
D W KU \u003d D r ku S ku T r, (29)
Where D R ku - specific power losses in accordance with the passport data of the CU; S ku - KU power (for STK it is taken according to the capacitive component). In the absence of passport data, the value of D rku is taken equal to 0.003 kW / kvar for BK, 0.006 kW / kvar for STK.7.6. Electricity losses in valve arresters, surge arresters, HF connection devices, voltage measuring transformers, electric meters 0.22 - 0.66 kV and insulation of power cables are accepted in accordance with the data of equipment manufacturers. In the absence of manufacturer's data, the calculated losses are taken in accordance with Appendix 1 to this Methodology. 8. Methods for calculating losses depending on weather conditions 8.1. Losses depending on weather conditions include three types of losses: - to the corona; - from leakage currents through insulators of overhead lines; - electricity consumption for ice melting. 8.2. Electricity losses per corona are determined on the basis of data on specific power losses given in table. 1, and about the duration of weather types during the calculation period. At the same time, periods of good weather (for the purposes of calculating corona losses) include weather with a humidity of less than 100% and ice; to periods of wet weather - rain, sleet, fog. Table 1 . Specific power losses per corona.
|
VL voltage, support type, number and cross section of wires in phase |
Power loss per corona, kW / km, in weather, |
dry snow |
frost |
220st - 1 ´ 300 |
220st/2-1 ´ 300 |
220zhb-1 ´ 300 |
220gb/2- 1 ´ 300 |
110st-1 ´ 120 |
110st/2-1 ´ 120 |
110zhb-1 ´ 120 |
110gb/2-1 ´ 120 |
|
VL voltage, kV, number and cross section of wires in phase |
Specific electricity losses per corona, thousand kW/km, per year, in the region |
220st - 1 ´ 300 |
220st/2-1 ´ 300 |
220zhb-1 ´ 300 |
220gb/2- 1 ´ 300 |
110st-1 ´ 120 |
110st/2-1 ´ 120 |
110zhb-1 ´ 120 |
110gb/2-1 ´ 120 |
K u cor \u003d 6.88 U 2 rel - 5.88 U rel, (30)
Where U rel - the ratio of the operating voltage of the line to its nominal value. 8.6. Losses of electricity from leakage currents in the insulators of overhead lines are determined on the basis of data on specific power losses given in Table 3, and on the duration of weather types during the billing period. According to the effect on leakage currents, weather types should be combined into 3 groups: 1 group - good weather with humidity less than 90%, dry snow, frost, ice; Group 2 - rain, sleet, dew, good weather with humidity of 90% or more; Group 3 - fog. Table 3. Specific power losses from leakage currents through insulators of overhead lines
|
weather group |
Power losses from leakage currents through insulators, kW/km, for overhead lines with voltage, kV |
0,103 | 0,953 | 1,587 |
|
Region number |
Losses of electricity from leakage currents through insulators of overhead lines, thousand kWh/km per year, at voltage, kV |
|
Number of wires in a phase and section, mm 2 |
The total cross section of the wires in the phase, mm 2 |
Estimated electricity consumption for melting ice, thousand kWh / km per year, in the area on ice: |
III. Methods for calculating losses due to errors in the electricity metering system
10. Losses of electricity due to errors in the electricity metering system are calculated as the sum of the values determined for each metering point for the supply of electricity to the network and the output of electricity from the network according to the formula:D W account \u003d - (D tt b + D TN + D q b - D U t + D mid) W / 100, (31)
Where D tt b - current error of CT,%, at current load factor b TT; D t - TN error modulo voltage,%; D q b - error of the transformer circuit for connecting the meter,%, with a current load factor b TT; D c - counter error, %; D U tn - voltage loss in secondary circuit TN, %; W- energy recorded by the meter for the billing period. 10.1. The error of the transformer circuit for connecting the meter is determined by the formula:
D q b = 0.0291 (q I b - q U) tg j , (32)
Where q I b is the angular error of the CT, min, with a current load factor b TT; q U - angular error of HP, min; tg j - reactive power factor of controlled connection. 10.2. The CT current load factor for the billing period is determined by the formula:
, (33)
Where U nom and I nom - rated voltage and current of the primary winding of the CT. 10.3. The error values in formulas (31) and (32) are determined on the basis of metrological verification data. In the absence of data on the actual errors of the measuring systems, it is allowed to calculate the losses of electricity due to the errors of the electricity metering system in accordance with Appendix 3 to this Methodology.
IV. Methods for calculating the regulatory characteristics of technological losses of electricity
11. The normative characteristic of technological losses of electricity is determined on the basis of the calculation of losses in the base period by the methods set forth in sections II and III of this methodology, and is used to determine the standard of losses for the planning period. 11.1. The normative characteristic of technological losses of electricity has the form:Where W i (j) - values of indicators (income and output of electricity) reflected in the reporting; n- number of indicators; W o - supply of electricity to the network; D- the number of days of the calculation period, which corresponds to the specified energy values; BUT, AT and With- coefficients reflecting the components of losses: BUT ij and B i - load losses, With post - conditionally permanent losses, With pg - losses depending on weather conditions, With s.n - electricity consumption for own needs of substations, AT Uch - losses due to errors in the electricity metering system. 11.2. The standard characteristic of load power losses in closed networks is determined on the basis of a pre-calculated characteristic of load power losses, which has the form:
, (35)
Where P i(j) - power values corresponding to the indicators reflected by the formula (34); a ij and b i - coefficients of the normative characteristics of power losses. 11.3. The conversion of power loss characteristic coefficients into electric power loss characteristic coefficients is carried out according to the formulas:
, (36)
11.4. For the components of the regulatory characteristic, containing products of energy values, the value is calculated by the formula:
, (38)
Where k f i and k f j - shape coefficients of the i-th and j-th graphs of active power; r ij - correlation coefficient of the i-th and j-th graphs, calculated according to the OIC data. In the absence of calculations r ij accept . 11.5. Coefficient C post is determined by the formula
C post \u003d D W post / D, (39)
Where D W post - conditionally permanent losses of electricity in the base period. 11.6. Coefficient C pg is determined by the formula
C po = D W po /D, (40)
Where D W post- electricity losses depending on weather conditions in the base period. 11.7. The coefficient C s.n is determined by the formula
C s.n = W s.n / D, (41)
Where D W s.n - electric power consumption for own needs of substations in the base period. 11.8. Coefficient AT uch is determined by the formula
B account \u003d D W account / W about, (42)
Where D W uch - losses due to errors in the electricity metering system in the base period. 11.9. The normative characteristic of load losses of electricity in radial networks has the form:
, (43)
Where W U - supply of electricity to the network with voltage U behind D days; BUT U - coefficient of the normative characteristic. 11.10. Coefficient A U of the normative characteristic (43) is determined by the formula:
, (44)
Where D W n U - load losses of electricity in the network with voltage U in the base period. 11.11. Odds BUT and With(C post, C pog and C s.n.) for radial networks of 6 - 35 kV as a whole, according to their values calculated for the lines included in the network (A i and C i), they are determined by the formulas:
, (45)
Where W i - supply of electricity to the i-th line; Wå - the same, to the network as a whole; n- the number of lines. Odds A i and Сi, must be calculated for all lines of the network. Their determination based on the calculation of a limited sample of lines is not allowed. 11.12. Coefficient BUT for networks of 0.38 kV is calculated by formula (43), in which as D W nU substitute the value of the total load losses in all lines 0.38 kV D W n 0.38 calculated by formula (22) taking into account formula (26).
Appendix 1
(technological) losses
electricity in electrical networks
Estimated electricity losses in equipment
1. Table A.1. Electricity losses in shunt reactors (SR) and connecting wires and busbars of substation switchgear (SPPS)|
Type of equipment |
Specific energy losses at voltage. kV |
SR, thousand kWh/MVA per year |
SP PS, thousand kWh/ substation per year |
|
Type of equipment |
Energy losses, thousand kWh per year, at the rated power of the SC, MVA |
SC |
|
Type of equipment |
Electricity losses, thousand kWh/year. at equipment voltage. kV |
RV | opn |
|
Section, mm 2 |
Electricity losses in cable insulation, thousand kWh/km per year, at rated voltage. kV |
Appendix 2
to the Methodology for calculating regulatory
(technological) losses
electricity in electrical networks
Distribution of territorial entities of the Russian Federation by regions for the purposes of calculating losses depending on weather conditions
|
Region number |
Territorial entities included in the region |
Republic Sakha-Yakutia, Khabarovsk Territory | Areas : Kamchatka, Magadan, Sakhalin. | Republic : Karelia, Komi | Areas : Arkhangelsk, Kaliningrad, Murmansk | Areas : Vologda, Leningrad, Novgorod, Pskov | Republic : Mari-El, Mordovia, Tataria, Udmurtia, Chuvash | Areas : Belgorod, Bryansk, Vladimir, Voronezh, Ivanovo, Kaluga, Kirov, Kostroma, Kursk, Lipetsk, Moscow, Nizhny Novgorod, Orel, Penza, Perm, Ryazan, Samara, Saratov, Smolensk, Tambov, Tver, Tula, Ulyanovsk, Yaroslavl | Republic : Dagestan, Ingushetia, Kabardino-Balkaria, Karachay-Cherkess, Kalmykia, North Ossetia, Chechnya Territories: Krasnodar, Stavropol | Areas : Astrakhan, Volgograd, Rostov | Republic Bashkiria | Areas : Kurgan, Orenburg, Chelyabinsk | Republic : Buryatia, Khakassia | The edges : Altai, Krasnoyarsk, Primorsky | Areas : Amur, Irkutsk, Kemerovo, Novosibirsk, Omsk, Sverdlovsk, Tomsk, Tyumen, Chita |
Appendix 3
to the Methodology for calculating regulatory
(technological) losses
electricity in electrical networks
Calculation of losses caused by errors in the electricity metering system
Clause 3.1. Electricity losses due to errors in the electricity metering system are determined on the basis of data on accuracy classes TT - K TT, TN - K TN, counters - To cf, coefficients of the current loading of the CT - b TT and service life of meters after the last verification - T pov, years. The following dependences of the average errors of CTs, VTs and meters are used only to calculate the total underestimation for the electrical network as a whole. These dependencies are not allowed to be used to adjust the meter readings at a particular metering point. Clause 3.2. Losses of electricity due to errors in the electricity metering system are calculated as the sum of the values determined for each metering point for the supply of electricity to the network and the output of electricity from the network according to the formula:Where D tt i , D t i and D mid i - average errors of CT, VT and counter,%, in i-th point accounting; W i - energy recorded by the meter at the i-th metering point for the billing period. Clause 3.3. The average error of the CT is determined by the formulas: for a CT with a rated current I rated 1000 A: at b CT 0.05 D CT = 30( b TT - 0.0833) To TT; (A.2) at 0.05< b TT 0.2 D TT = 3.3333 ( b TT - 0.35) To TT; (A.3) at b CT > 0.2 D CT = 0.625 ( b TT - 1) To TT; (A.4) for CTs with rated current I nom more than 1000 A:
, (A.5)
Clause 3.4. The average error of the VT (taking into account the losses in the connecting wires) is determined by the formula:
, (A.5)
Clause 3.5. The average error of the induction meter is determined by the formula:
, (A.7)
Coefficient k take equal to 0.2 for induction meters manufactured before 2000, and 0.1 for induction meters manufactured after this period. When determining the normative underestimation, the value T
Power losses in network elements.
Calculation of power losses in power lines.
Calculation of power losses in power transmission lines with a uniformly distributed load.
Calculation of power losses in transformers.
The given and calculated loads of consumers.
Calculation of electricity losses.
Measures to reduce power losses.
Power losses in network elements
For a quantitative characteristic of the operation of the elements of the electrical network, its operating modes are considered. Work mode- this is a steady electrical state, which is characterized by the values of currents, voltages, active, reactive and apparent powers.
The main purpose of calculating modes is to determine these parameters, both to check the admissibility of modes, and to ensure the efficiency of the operation of network elements.
Determining the values of currents in the elements of the network and voltages in its nodes begins with building a picture of the distribution of the total power over the element, i.e. with the definition of capacities at the beginning and end of each element. This pattern is called flow distribution.
When calculating the power at the beginning and at the end of an electrical network element, the power losses in the element resistances and the influence of its conductivities are taken into account.
Calculation of power losses in power lines
Active power losses in the PTL section (see Fig. 7.1) are due to the active resistance of wires and cables, as well as the imperfection of their insulation. The power lost in the active resistances of a three-phase power transmission line and spent on its heating is determined by the formula:
where 
full, active and reactive currents in power transmission lines;
P, Q, S- active, reactive and apparent power at the beginning or end of the power transmission line;
U
R- active resistance of one phase of the power transmission line.
Losses of active power in the conductance of the power transmission line are due to the imperfection of the insulation. In air transmission lines - the appearance of a corona and, to a very small extent, current leakage through insulators. In cable transmission lines - the appearance of conduction current and its absorption. Losses are calculated according to the formula:
,
where U- linear voltage at the beginning or end of the power transmission line;
G– active conductivity of the LEP.
When designing overhead power transmission lines, the power loss to the corona tends to be reduced to zero by choosing such a wire diameter when the possibility of a corona is practically absent.
Reactive power losses in the PTL section are due to inductive resistances of wires and cables. The reactive power lost in a three-phase transmission line is calculated similarly to the power lost in active resistances:
The charging power of the power transmission line generated by capacitive conduction is calculated by the formula:
,
where U- linear voltage at the beginning or end of the power transmission line;
B- reactive conductivity of the LEP.
Charging power reduces the reactive load of the network and thereby reduces power losses in it.
Calculation of power losses in a lep with a uniformly distributed load
In the lines of local networks ( 
) consumers of the same power can be located at the same distance from each other (for example, light sources). Such transmission lines are called lines with a uniformly distributed load (see Fig. 7.2).
In a uniformly loaded three-phase alternating current line with a length L with total current load I current density per unit length will be I/L. With linear active resistance r 0 active power losses will be:
If the load were concentrated at the end, then the power loss would be defined as:
.
Comparing the given expressions, we see that the power losses in the line with a uniformly distributed load are 3 times less.
During the design of electrical networks and systems with low currents, calculations of voltage losses in cables and wires are often required. These calculations are necessary in order to select the cable with the most optimal. At wrong choice conductor, the power supply system will fail very quickly or not start at all. To avoid possible errors, it is recommended to use the online voltage loss calculator. The data obtained using the calculator will provide a stable and safe work lines and networks.
Causes of energy loss in the transmission of electricity
Significant losses occur as a result of excessive dissipation. Due to excess heat, the cable can become very hot, especially under heavy loads and incorrect calculations of electricity losses. Under the influence of excess heat, damage to the insulation occurs, creating a real threat to the health and life of people.
Losses of electricity often occur due to too long cable lines, at high power loads. In the case of prolonged use, the cost of paying for electricity increases significantly. Incorrect calculations can cause equipment malfunctions, for example, burglar alarm. Voltage losses in the cable acquire importance when the power supply of the equipment has low DC voltage or alternating current, rated from 12 to 48V.
How to Calculate Voltage Loss
To avoid possible problems the online voltage loss calculator will help. Data on the length of the cable, its cross section and the material from which it is made are placed in the table of initial data. For calculations, information about the load power, voltage and current will be required. In addition, the power factor and temperature characteristics of the cable are taken into account. After pressing the button, data on energy losses in percent, indicators of conductor resistance, reactive power and voltage experienced by the load appear.
The basic calculation formula is the following: ΔU=IxRL, in which ΔU means the voltage loss on the calculated line, I is the consumed current, determined mainly by the parameters of the consumer. RL reflects the resistance of the cable, depending on its length and cross-sectional area. It is the last meaning decisive role power loss in wires and cables.
Opportunities to reduce losses
The main way to reduce cable losses is to increase its cross-sectional area. In addition, it is possible to shorten the conductor length and reduce the load. However, the last two methods cannot always be used, due to technical reasons. Therefore, in many cases, the only option is to reduce the resistance of the cable by increasing the cross section.
A significant disadvantage of a large cross section is a noticeable increase in material costs. The difference becomes noticeable when cable systems stretch to long distances. Therefore, at the design stage, you must immediately select a cable with desired section, for which you will need to calculate the power loss using a calculator. This program is of great importance when drawing up projects for electrical work, since manual calculations take a lot of time, and in the mode online calculator The calculation takes just a few seconds.