The concept of power system load schedules and electricity tariffs. The concept of power system load schedules and electricity tariffs Peak of technical capabilities
Based on the shape of the load graphs, five groups of industrial load, household consumption, electric transport, street lighting, and agricultural needs are distinguished. Due to one- and two-shift enterprises, the industrial load is reduced at night and in the evening.
Municipal consumption increases significantly in the morning and evening, the evening peak is longer. Transport traffic has peaks in the morning and evening hours. Street lighting has a maximum at night. Agricultural consumption schedules are quite uniform with seasonal changes in its value.
The total load schedule is obtained by hourly addition of the loads of all consumers for typical winter and typical summer months
Fig.1 Summary of load on a winter day.
Fig.2 Total load graph in summer days.
The winter schedule has 2 peaks (Figure 1), the summer - 3 (Figure 2), which is explained by longer daylight hours (lighting is turned on after the end of work at single-shift enterprises and a decrease in transport traffic).
Summer loads are lower in absolute value.
To determine the annual demand for electricity, an annual schedule of load durations is used (Figure 3)
Fig. 3 Annual graph of load duration and annual graph of monthly maximums (Fig. 4).
Fig.4 Annual graph of monthly maximums.
The duration of the load is determined by summing it over 210 winter days and 155 summer days. The area under the annual load duration curve determines the total annual electricity demand.
2. Methods for covering electrical load peaks
Due to the significant unevenness of the electrical load during the day, an important task is to rationally cover relatively short-term but significant load peaks. Based on the number of hours of maximum load use, a distinction is made between base, half-peak and peak units. For base power plants, the maximum load use is 6000 - 7500 hours per year, for half-peak and peak power plants - 2000 - 6000 and 500 - 2000 hours, respectively.
Since existing CPPs and CHPPs are not able to fully cover the variable electrical load schedule, special half-peak and peak units should be developed and put into operation.
When designing base power plants, first of all, the requirement is high thermal efficiency, which determines increased capital investments.
For thermal power plants operating a relatively small number of hours per year (peak and half-peak), the main requirement is high maneuverability and low capital investment, although sometimes this is achieved at the expense of reduced thermal efficiency.
Let's look at the main ways to cover electrical load peaks
1. The use of hydroelectric power plants due to the ease of starting, stopping and changing the load is in the best possible way
2. Use of the power reserve of conventional steam turbine power units operating in the mode of frequent starts and stops.
3 The use of highly maneuverable units, such as peak and half-peak steam turbines, gas turbines and steam-gas pumped storage power plants. Pumped storage power plants pump water from the lower reservoir to the upper one during periods of minimum electrical loads, consuming energy from the network, and during periods of maximum loads they operate like hydroelectric power plants.
4. Use of temporary overload of steam turbine thermal power plants due to regime measures (changes in steam parameters in front of the turbine, shutdown of the high pressure pump, etc.)
5. Energy storage by filling gas storage facilities for compressed air, which is then used in gas turbine units, heat accumulation in the form of hot water and electricity in electric batteries
To facilitate the passage of electrical load peaks, you can use load graph leveling, which is understood as an active influence on the consumption mode, leading to a reduction in load peaks. The achievement of these goals is achieved by increasing the shifts of work of enterprises using incentive night tariffs for electricity, creating unified energy systems due to different times of maximum load in areas with different geographical longitudes, the presence of regulator consumers, the hours of operation of which are determined by the energy system.
Figure 5. Annual graph of the duration of the utility load.
Great value to determine the operating modes of thermal power plants and boiler houses when designing heat supply systems, it has an annual schedule, but the duration of the utility load (Figure 5). It shows the change in heating load, which includes heat for heating and hot water supply, from its maximum value to its minimum throughout the year.
To construct an annual schedule, it is necessary to know the duration of different outside air temperatures during the heating period for a given climate zone where a thermal power plant or boiler house is being built, determine the hourly heat consumption for heating, ventilation and hot water supply, depending on the outside air temperature, construct a network temperature graph (Fig. 6 ) according to the temperature, schedule and duration of each flow rate, construct an annual schedule of heat supply.
Fig 6. Network temperature graph.
In order to stimulate the rational use of fuel and energy resources, seasonal prices for natural gas and seasonal tariffs for electric and thermal energy, tariffs for these types of energy differentiated by time of day and day of the week, as well as other forms of incentives are established in the manner determined by the government of the Republic of Belarus .
An important point economic incentive for energy saving is the transition from single-rate to two-rate and zone tariffs, allowing to smooth out the national load curve. This leads to increased energy efficiency at the stage of production of electrical and thermal energy. The graph (Fig. 7) clearly shows that it is extremely profitable for the consumer to reduce the load during the hours when the tariff in the power system is maximum.
Fig.7 Daily electricity consumption (curve 1) and tariff differentiated by time of day (curve 2) for an electrometallurgical plant in Germany
Tariffs for electrical energy (power) are systems of price rates by which payments for electrical energy (power) are made.
Two-part tariff - a tariff for industrial and equivalent consumers, providing for a basic payment (for the contractual or actual value of the highest half-hour combined active power consumed during the hours of maximum load of the power system) and an additional payment (for the actual amount of active energy consumed) for the billing period.
The main payment of a two-rate tariff is the price of 1 kW of the contractual or actual value of the highest active power consumed, accepted in accordance with the declaration on the level of tariffs for electrical energy supplied by the republican unitary electric power enterprises of the Belenergo concern.
Additional payment of a two-part tariff - the price of 1 kWh of active energy consumed, accepted in accordance with the declaration.
3.3. Power system power balance
Balance provides for correspondence (equality) between income and expenses. The power balance is built separately for active and reactive power.
The active power balance of the energy pool at time t can be presented in the following form:
where i is the serial number of the power plant; j - serial number of the energy interconnection transmitting active power to the one under consideration; i is the serial number of the energy pool receiving active power from the one under consideration.
The incoming part of the active power balance includes the total available active power of power plants
the same amount of active power received from other
energy associations
The consumption part of the active power balance consists of the maximum active load of a given
Losses in electrical networks
energy association Nmax(t), consumption of active power for own needs, the amount of active reserve power and active power supplied toother energy networks,
A similar expression can be written for the reactive power balance:
3.3.1. Expense part of the balance
To draw up a power balance, graphs of electrical loads are used, displaying changes in power consumption during the period of time under consideration. Load graphs can express the power consumption regime of individual enterprises, sub-sectors, districts, regional and integrated energy systems. The operating modes of power plants depend on the modes of electricity consumption: the main equipment of power plants, power lines and transformer substations. Power consumption modes can be presented in the form of tables or graphs. Electrical load graphs are considered for both active and reactive loads. The discrepancy between the configurations of these graphs is determined by differences in the modes of consumption of active and reactive power certain types consumers.
Depending on the duration of the period under consideration, there are:
daily, weekly, monthly and annual load schedules;
winter, spring, summer and autumn.
When planning loads, standard (averaged) schedules are used. They are compiled for different groups of consumers (industrial, agricultural, municipal) and given periods of time. In a typical graph, each load ordinate is the arithmetic mean value for the period under consideration.
Load curves are characterized by: configuration; maximum, average and minimum loads; the ratios of these loads.
Typical graphs of power system loads for a day, week, month, year are shown in Fig. 3.1.
Rice. 3.1. Daily load schedule
Daily chart indicatorspower system loads. To analyze the participation of generating capacities in covering the daily load schedule of the power system, three parts are distinguished: peak, half-peak and base.
Rice. 3.2. Components of the daily load schedule:
I, II, III - peak, half-peak, baseline
The daily schedule of the electrical load of the power system is characterized by a minimum Rtt, average R Wed , maximum
The following relationships are considered: fill factor of the daily schedule
where E day is daily energy consumption, million kWh/day; E p - potential energy consumption; average load
P av = E day /24
minimum load factor
α min =Рmin/Рmax.
Indicators (β day and α min reflect the power consumption regime and make it possible to compare and analyze graphs of different scales.
An increase in the share of housing, communal and agricultural loads, and a reduction in night shifts lead to a decompression of schedules. Increasing the share of continuous production and improving equipment utilization leads to tighter schedules. The values of the graph indicators depend on the structure of the industry, climate and other factors. Thus, according to different associations, α min and β days (for December 1991) had the values presented in table. 3.1.
Creation of integrated energy systems, use of two-part tariffs for electricity consumption, commissioning of consumer-regulators (for example, operation of a pumped-storage power station in pumping mode), increasing the shift ratio of enterprises, artificial displacement
Table 3.1
Regional indicators of power consumption for the month
|
Association | ||
|
North-West Center South |
0,84 0,86 0,89 |
The weekly graph of electrical loads displays load fluctuations by day of the week, mainly due to weekends and holidays. In addition to load fluctuations within individual weeks, there are
There are fluctuations between weeks caused by changes in the duration of daylight hours and an increase in load. Within each month, weekly electricity consumption is not the same:
Rice. 3.5. Annual load charts
Rice. 3.6. Changing the fill factor values of the daily chart
The weekly power consumption graph is shown in Fig. 3.3. Monthly graphs of the electrical load of the power system (Fig. 3.4) display the fluctuation of the average weekly load by week of the month. Annual graphs of electrical load show fluctuations in average monthly R srms or average monthly regular maximums – Рсрмеs, regular highest monthly maximums P maxi , absolute monthly maximums R" tah by month of the year (Fig. 3.5).
The main indicators of the annual schedule are:
Rice. 3.3. Weekly power consumption chart
Rice. 3.4. Monthly load charts
annual schedule fill rate
Where R max month i is the maximum load of the power system for each month; R max year i is the annual maximum load of the power system; R max average year - average annual maximum load;
growth rate, characterizing the increase in the maximum load of the year under review compared to the previous one,
Where R tah1 i , R tah i 2 - maximum monthly loads in January and December of the year under review.
If Kr = 1, then the annual load schedule of the power system is called static, If Kr >1 - dynamic, reflecting intra-annual load growth;
annual number of hours utilization of the maximum load of the energy system
where E gods is the amount of energy consumed by the energy system per year; P max c - maximum system load.
Indicator A c characterizes the estimated number of hours at which the annual electricity demand is covered at a constant load. It can be defined as the product of the number of hours in a year and the filling factors of the daily, weekly, monthly and annual load schedules (Fig. 3.6), h:
where β week and β months are the fill rates of the weekly and monthly load schedules, respectively.
If the value is known h c , found by using the coefficients of unevenness of load graphs, then the annual maximum electrical load of the power system can be determined in the following form:
Calculation and construction of combined graphs of electricalpower system loads. There are several methods for constructing daily power system load schedules. For schedules for the near future, with a slight change in the structure of electricity consumption, the method of analogies is used, in which the reporting schedule with the necessary clarifications is taken as a basis. To construct graphs for a more distant future, as well as for new rapidly developing energy systems, the following are used: integral, synthesized methods and the method of generalized characteristics, which is most widespread.
The method of generalized characteristics, developed at the Energosetproekt and ENIN institutes named after. G.M. Krzhizhanovsky, uses characteristics to determine the number of hours of use of the maximum load of the energy system, depending on the area of location, the share of household electricity consumption and the number of hours of use of the maximum industrial and transport load of energy supply. This makes it possible to determine the maximum load of the power system for a typical winter and summer day. Based on typical energy interconnection load schedules and daily load indicators, the power system load schedule is calculated for winter and summer days.
The annual schedule of monthly maximum loads can be expressed by the following equation, MW:
where a l is the ratio between the summer and winter maximum electrical load; / - serial number of the month; P" max 12 - daily maximum load in December of the year preceding the year under consideration.
As a rule, σ month = 0.96...0.97; β day varies by month and can be determined when constructing an auxiliary chart
In addition to this graph, an annual graph of average monthly loads is constructed to balance the energy and fuel of the system. To construct it, annual graphs of maximum monthly loads and coefficients of daily and monthly unevenness are used:
1cm. rice. 3.6), using (β day.l, β day . 3 for a specified number of hours of maximum use of a system located in a specific geographic area. The failure of the annual schedule of maximum monthly loads (mainly in the spring-summer period) is used to carry out major types of equipment repairs.
The coincidence in time of production and consumption of electricity, and therefore the impossibility of “working at the warehouse”, determines the need to create power reserves in energy systems in operation. The main task of redundancy in the energy sector is to ensure maximum reliability and uninterrupted power supply, as well as stability of quality energy parameters both in the event of emergency failure of units and during planned capital and routine repairs of equipment. Disruption of the electrical supply leads to economic damage to both consumers and the energy system itself. The presence of a system-wide power reserve, which is maneuvered by the dispatch service of the power system, and the creation of large power interconnections significantly increases the reliability of power supply to consumers.
Required power reserve of the power system N p consists of the following types of reserves: load N r.load, emergency - N equal > repair N rrem, national economic N r.nx , those.
Load reserve is necessary to maintain a given frequency level in the system during irregular load deviations (fluctuations). The amount of the reserve depends on the scale and characteristics of consumers and varies within the following limits: 4...5% for power systems with a maximum load of 3...5 million kW; 1... 1.5% for systems with a load exceeding 25...30 million kW. The load reserve must be constantly ready for use and placed on units operating with some underload from large power plants with highly maneuverable equipment, primarily hydroelectric power plants).
The approximate value of the load reserve is calculated using the following formula:
where P max p is the regular (calculated) maximum load (mathematical expectation of the weighted average maximum load of the power system on normal working days, which are Tuesday, Wednesday, Thursday and Friday), MW.
The emergency reserve compensates for the reduction in power caused by emergency downtime of equipment due to its damage and is intended for the rapid commissioning of generating capacities into each other.
Total installed power of the power system
Maximum operating power of the power plant;
Power reserve;
Backup power of electric
exchanged as a result of accidents at the station and in power lines. The amount of emergency reserve should be taken based on the total power of the entire power system, the number of units installed at power plants, and be no less than the power of the largest unit in the system.A repair reserve is necessary in the power system to carry out scheduled preventative repairs (major and current) of the main equipment of power plants without disconnecting consumers and reducing the reliability of power supply.
The national economic reserve involves providing energy for new facilities commissioned ahead of schedule or for excess energy needs of existing enterprises. The value of this reserve power is taken equal to 1...2% of the expected maximum load of the energy interconnection.
On Tuesday, August 8, the Ministry of Energy reported that electricity consumption in Crimea broke the record set in 2012 due to the heat. This was due to the heavy use of air conditioners during the peak holiday season. To cope with energy shortages during peak consumption hours, it was previously decided to introduce temporary shutdown schedules (GVO).
In particular, on the evening of August 7, after the introduction of the GVO, more than 108,000 people in Crimea and Sevastopol remained without electricity for about 2 hours.
Krasnodar region rushes to the rescue
In a number of districts of the Krasnodar Territory, according to the recommendations of the Ministry of Energy, electricity will be cut off, Gazeta.ru reported on Wednesday, August 9, citing the press service of the regional administration. As stated in the message, which has already been removed from the administration’s website, the electricity supply will be turned off “to stabilize power flows, prevent damage to equipment and disrupt the stability of parallel operation of the power system of the Crimean Peninsula with the Unified Energy System of Russia, accompanied by the satisfaction of the needs of a significant part of consumers in the Republic of Crimea.”
Restrictions on power consumption were to be made in an amount of up to 110 MW in the period from 20:00 to 23:00. They were supposed to remain without electricity in Novorossiysk, Anapa and Gelendzhik, as well as in the Crimean, Abinsky, Slavyansky, Krasnoarmeysky and Temryuksky districts of the Krasnodar Territory.
The Ministry of Energy denied that the department gave recommendations on the introduction of gas water supply in the Krasnodar Territory.
They also explained that the rolling blackout schedule during peak load hours was introduced only in the territory of the Republic of Crimea. “In connection with the current situation in the Republic of Crimea, a rolling blackout schedule was introduced during peak load hours. At the same time, the Russian Ministry of Energy did not give recommendations on introducing a schedule for temporary blackouts in the Krasnodar Territory. The information published on the administration’s website is erroneous and will be removed from the site in the near future,” RNS quotes a statement from the Ministry of Energy.
Meeting
Russian Energy Minister Alexander Novak held a meeting in Yalta on issues of power supply to consumers in the Krasnodar Territory and the Republic of Crimea. According to the minister, the power consumption record was broken in the regions for several days in a row.
Alexander Novak
Minister of Energy of the Russian Federation
On August 7, electrical power consumption in Crimea exceeded the historical maximum load and amounted to 1,249 MW, which is 70 MW higher than the summer maximum. And in the Kuban energy system, the historical maximum was 5,032 MW, which is 433 MW higher than the maximum recorded in July 2016.
Among the main reasons for the current situation, the head of the Ministry of Energy named the increase in electricity consumption by industrial enterprises, the development of the resort and recreational complex of the regions and the increase in household load due to the use of air conditioners due to abnormally high temperatures. The consequence of this was a sharp change in the structure of active and reactive power consumption in power systems.
SO UESAt the meeting, they noted the fact that out of 284 diesel generator sets (DGS) with a total capacity of at least 109.6 MW (122 MW including Sevastopol), provided for by the regulations for the transfer of consumers to decentralized power supply to cover the emerging power shortage, only 75 DGS were included with a total capacity of 18.3 MW.
Alexander Novak ordered to carry out extraordinary inspections of power lines, notify the population about the possible use of GVO and explain the need for the measures taken, and also temporarily prohibited carrying out unscheduled and planned renovation work backbone network and any work at power plants with upper class voltage 110 kV and above. In addition, an instruction was given to the Council of Ministers of the Republic of Crimea to bring into working order all diesel generator sets necessary to cover the power shortage as soon as possible.
Peak technical capabilities
According to the System Operator, the abnormal heat (with the average air temperature exceeding the norm by almost 10ºС for this time of year) led to the fact that the IPS of the South has exhausted the technical capabilities to ensure the current level of electricity consumption in Crimea and Kuban. By 18:00 on August 7, the power flow across the energy bridge reached maximum values- about 800 MW, while solar power plants, which provide part of the consumption in the Crimean energy system, reduced their power to zero in the evening.
SO UES In addition to new historical highs in the power systems of Crimea and Kuban (the latter has recorded record power consumption values for the entire period of its existence for three days in a row), consumption in the Stavropol Territory and the Astrakhan Region is breaking records for maximum power. It is logical that the UES of the South as a whole set a new record for power consumption. During the daytime maximum load hours on August 8, power consumption in this IPS reached 15,754 MW, which is 6% (907 MW) higher than the maximum recorded on July 18, 2016.
An increase in electricity and power consumption and a change in the ratio of active and reactive power consumed due to the specific consumption structure caused by hot weather led to a decrease bandwidth electrical connections and the depletion of active and reactive power reserves in the energy systems of the Unified Energy System of the South, the CO recognized. The only way to ensure stable operation of the power system is to introduce GVO, which will avoid long-term failure of equipment, overload of power lines and network equipment and reduction of voltage in the network below the minimum permissible values, the operator also said in a statement.
SO UES According to Kommersant, all “systemically important” capacities are included. Inter RAO clarified that the Dzhubginskaya and Sochinskaya TPPs are loaded, and OGK-2 said that the CO gave the command to turn on 1.6 GW (i.e. 6 out of 8 units) at the Novocherkasskaya GRES, 2.1 GW (7 of 8 units) at the Stavropol State District Power Plant and 250 MW (both units) at the Adler Thermal Power Plant. There are 3 units in operation at the Rostov NPP (about 3 GW). Rosseti explained that “maximum reliable power supply schemes” have been created in Kuban’s networks; when the CO makes a decision on introducing GVO, the company “will carry out the appropriate command.”
Lack of capacity
For stable operation of the energy system, 4 additional mobile gas turbine power plants (MGTS) with a capacity of 22 MW each will be supplied to Crimea, said a member of the Russian State Duma Committee on Energy, former First Deputy Prime Minister Crimean government Mikhail Sheremet. According to him, MGTS will be used until the commissioning of two thermal power plants under construction.
Mikhail Sheremet
Deputy, member of the State Duma Committee on Energy
A decision was made to create a powerful energy fist so that the electricity shortage that we are experiencing due to abnormal heat can be overcome painlessly. We have a huge number of ARIPs [autonomous sources backup power- Central Power Plant], from which a small cluster is formed, which in total will give us another 80-90 MW, which will cover the electricity shortage. Moreover, 4 more MGTS are being transferred, which will solve pressing problems. Their power is standard, 22 MW each.
However, the problem is not only the lack of generation, but also the Taman energy system as a whole. The southwestern region of the Kuban energy system is traditionally included in the list of problem points of the UES of Russia. The Ministry of Energy and the CO recognize from year to year that failures are possible here. The situation also worsened after the annexation of Crimea: it was necessary to create from scratch a power supply system for the peninsula on the Russian side, but so far only the Kerch energy bridge has been built.
As the press service of the SO reported to RIA Novosti, the organization considers it very important to comply with the deadlines for commissioning the 500 kV Rostovskaya-Taman transmission line, which will significantly increase the reliability of the region’s energy supply, and to announce a competition and construction of a power plant in Taman. The need to build a power plant in the southwest of the Krasnodar Territory has been discussed in SO for a long time, even before Crimea became part of Russia, warning of the threat of a disruption in power supply.
However, the 940 MW station still does not have an investor (the competition was declared invalid), and the overhead lines should only be completed by the end of the year. At the same time, as Kommersant previously wrote, the introduction of networks for projects in Taman (railway approaches to the Kerch Bridge and the port) is constantly shifting, and the supply pattern is changing. It is planned that the Ministry of Energy may announce a competition for the construction of the power plant this summer.
Work to stabilize the situation is underway not only in the Krasnodar Territory, but also in Crimea itself: according to RIA Novosti, by September an additional 20 MW of power will be commissioned on the peninsula, and by the end of the year - about 150 MW more.
According to forecasters, extremely high temperatures in the region will continue until the end of the week.
