Study of methods and means of voltage regulation. Voltage regulation at substations in rural distribution networks
Formulation of the problem
The purpose of this thesis project is to select branches of transformers of the 10 kV distribution network of the region under consideration on a computer.
Main objectives of the project:
a) improvement computer program MIF1 for the purpose of automating the process of selecting transformer branches on a computer;
b) collection, processing and preparation of data on the 10 kV network of the “L” region;
c) selection and analysis of transformer branches in the 10 kV distribution network of the “L” region on a PC with and without taking into account static characteristics loads;
d) assessment of measures to improve the voltage regime and calculation of technical and economic indicators of the network.
Study of methods and means of voltage regulation
Counter voltage regulation
To provide technical requirements to the voltage regime, it is fundamentally possible to use the following methods:
a) centralized change of voltage mode or voltage regulation on the buses or pins of the power center (CPU);
b) changing or regulating voltage loss values in individual network elements (lines, transformers) or in several network elements (sections) simultaneously;
c) changing or adjusting the transformation ratio of a linear regulator or transformer connected in the network section from the CPU to the power receivers.
Here, change refers to a one-time event carried out on a long period time. This could be: changing the operating position of the regulating branch (RPB) of the transformer, turning on the installation of longitudinal capacitive compensation, turning on an additional line, replacing the cross-section of wires, etc. In this case, the stress regime can be significantly improved. However, the law of stress changes will remain forced, due to changes in loads.
Regulation is understood as a current change in a parameter (voltage, transformation ratio, voltage loss) used to change the voltage regime according to the desired law. This change is usually carried out automatically. Regulatory options are limited in all cases. In each case, the regulatory law must be specifically selected.
When operating a network, the most complete and economical use of all available regulatory capabilities is required. To do this, all automatic control means must have appropriate settings. Under current operating conditions, the matter comes down to monitoring the stress regime and (if necessary) implementing the measures arising from this control. These include: changing the settings of automatic voltage regulators, changing the operating position of the regulating taps of unregulated transformers with off-circuit taps, additional automation of existing control means (if they were not automated before that time), etc. In this case, first of all, the requirements of ensuring a technically permissible voltage regime are met, and then its optimization (to the extent possible) or at least some increase in efficiency.
Depending on the nature of the load change, several subtypes can be distinguished in each of the indicated types of voltage regulation. For example, in centralized regulation Voltage can be divided into three subtypes: voltage stabilization; two-stage voltage regulation; counter voltage regulation.
Stabilization used for consumers with a practically constant load, for example, for three-shift enterprises, where the voltage level must be maintained constant. For consumers with a pronounced two-stage load schedule (for example, for single-shift enterprises), two-stage regulation is used voltage. In this case, two voltage levels are maintained during the day in accordance with the load schedule. In the case of variable load during the day, the so-called counter regulation. For each load value, the voltage loss will also have its own value, therefore, the voltage itself will change with the change in load. To ensure that voltage deviations do not go beyond acceptable values, it is necessary to regulate the voltage, for example, depending on the load current.
The load varies not only throughout the day, but throughout the year. For example, the greatest load during the year occurs during the autumn-winter maximum, and the lowest - in the summer. Counter regulation consists of changing the voltage depending not only on daily, but also on seasonal load changes throughout the year. It involves maintaining high voltage on tires power stations and substations during the period of greatest load and its reduction to nominal during the period of least load.
The transformer is represented as two elements - the transformer resistance and the ideal transformer. The following notations are accepted: U 1 ? voltage on the power center buses; U 2v? voltage on the primary voltage (VN) buses of the district substation; U 2H - voltage on the secondary voltage (LV) buses of the district substation; U 3? consumer voltage.
Voltage on the HV buses of the district substation:
U 2в = U 1? DU 12.
The voltages on the HV and LV buses differ by the amount of voltage loss in the transformer DU t, and, in addition, in an ideal transformer the voltage decreases in accordance with the transformation ratio, which must be taken into account when choosing a control branch.
Percentage deviations are meant for all V and DV on the field of this figure.
In the lightest load mode, reduce the voltage U 2n to a value as close as possible to U nom. In this mode, select the largest standard value n t so that the following condition is satisfied:
U2n.nm? Unom. (2.1)
In the heaviest load mode, increase the voltage U 2n to a value closest to 1.05-1.1U nom. In this mode, select the largest standard value n t so that the following condition is satisfied:
U 2n.nb ? (1.05 - 1.1) U nom. (2.2)
Thus, the voltage at the terminals of consumers, both remote from the power center and nearby, is brought within acceptable limits. With this regulation, in the modes of the highest and lowest loads, the voltage increases and decreases accordingly. Therefore, such regulation is called counter regulation.
For a detailed consideration of counter voltage regulation, we use the equivalent circuit shown in Fig. 5.2, a, where the transformer is represented as two elements - the transformer resistance and the ideal transformer. In Fig. 5.2, and the following designations are adopted: U1 - voltage on the buses of the power center; U2v - voltage on the primary voltage (VN) buses of the district substation; U2н - voltage on the secondary voltage (LV) buses of the district substation; U3 - consumer voltage.
Voltage on the HV buses of the district substation: 
The voltages on the HV and LV buses differ by the amount of voltage loss in the transformer ∆UT, and, in addition, in an ideal transformer the voltage is reduced in accordance with the transformation ratio, which must be taken into account when choosing a control branch.
In Fig. Figure 5.2b shows graphs of voltage changes for two modes: the lowest and highest loads. In this case, the ordinate axis shows the values of voltage deviations as a percentage of the nominal value. Percentage deviations are meant for all V and ∆U in the field of this figure.
From Fig. 5.2b (dashed lines) it is clear that if P t=1, then in the lightest load mode the consumers’ voltages will be higher, and in the heaviest load mode they will be lower permissible value(i.e. deviations U are greater than permissible). In this case, power receivers connected to the LV network (for example, at points A and B) will operate under unacceptable conditions. Changing the transformation ratio of a district substation transformer P t, we change U2H, i.e. we adjust the voltage (solid line in Fig. 5.2,b).
In the lightest load mode, reduce the voltage U2H to a value as close as possible to UHOM. In this mode, select the largest standard value P t so that the following condition is satisfied: U2H.НМ> UHОМ
In the heaviest load mode, increase the voltage U2H to a value closest to 1.05-1.1UHOM. In this mode, select the largest standard value P t so that the following condition is satisfied: U2H.NB >(1.05÷1.1) UHOM
Thus, the voltage at the terminals of consumers, both remote from the power center - at point B, and nearby - at point A, is brought within acceptable limits. With this regulation, in the modes of the highest and lowest loads, the voltage increases and decreases accordingly. Therefore, such regulation is called counter regulation.
23 Voltage regulation at power plants.
Changing the generator voltage is possible by regulating the excitation current. Without changing the active power of the generator, you can change the voltage only within ±0.05UNOM.G, i.e. from 0.95UNOM.G to 1.05UNOM.G
At UNOM.C = 6 kV, the rated voltage of the generator is UNOM.G = 6.3 kV and the control range is 6-6.6 kV. At UNOM.C = 10 kV, the generator voltage is UNOM.G = 10.5 kV and the control range is 10-11 kV.
A deviation of the voltage at the generator terminals by more than ±5% of the nominal leads to the need to reduce its power. This voltage regulation range (±5%) is clearly insufficient.
Therefore, the voltage range of the generator, which is only 10%, is clearly insufficient. Generators of power plants are only an auxiliary means of regulation for two reasons: 1) the range of voltage regulation by generators is insufficient; 2) it is difficult to coordinate the voltage requirements of remote and close consumers.
As the only means of regulation, generators are used only in the case of a system of the simplest type - the station - undistributed load type. In this case, counter voltage regulation is carried out on the buses of isolated power plants of industrial enterprises. By changing the excitation current of the generators, the voltage is increased during peak load hours and reduced during low load hours.
Step-up transformers at power plants TDTs/110 with a rated voltage of the HV winding Uv.nom = 110 kV and part of TDTs/220 cUv.nom = 220 kV, like generators, are an auxiliary means of voltage regulation, because they also have a regulation limit of ±2x2, 5%Uv.nom and with their help it is impossible to coordinate the voltage requirements of close and remote consumers. Step-up transformers TC and TDTs with Uv.nom = 150, 330-750 kV are produced without devices for voltage regulation. Therefore, the main means of voltage regulation are transformers and autotransformers of district substations.
What has been said about counter voltage regulation at a district substation fully applies to voltage regulation at power plants. The latter is easy to understand by replacing it with Fig. 12 - 2 substation substation power plant.
As a rule, counter-voltage regulation in the modes of the highest and lowest loads can be carried out at different branches of the transformers.
For a detailed consideration of counter voltage regulation, we use the equivalent circuit shown in Fig. 5.2, a, where the transformer is similar to Fig. 3.5 is represented as two elements - the transformer resistance and the ideal transformer.
What is the essence of counter voltage regulation and in what cases is it advisable to use it?
With their help, it is impossible to carry out counter voltage regulation, since their transformation ratios are unchanged when the mode changes during the day. Regulation by transformers with off-circuit breakers is used only as a seasonal control. More frequent switching turns out to be an expensive undertaking, since it requires turning off and turning on the equipment, complicates operation and is associated with a sharp increase in the number of maintenance personnel.
If necessary, automatic regulators must provide counter voltage regulation.
What are the considerations for choosing the slope of the counter voltage regulation characteristic?
On the power supply buses, the so-called counter voltage regulation is carried out, which means such regulation when the voltage on the buses of step-down substations increases during peak load hours, and, on the contrary, decreases during minimum load hours. According to the PUE, counter voltage regulation is provided in the range from 1 0 to 1 05 rated network voltage. An increase in voltage during peak load hours is necessary to compensate for the increasing voltage losses in all network elements during such a period.
In electrical systems, according to the current PUE, counter-regulation of voltage on the buses of supply substations of 35 kV and above must be carried out within the range of 0 - 5% of the rated voltage. However, in most cases, the regulation process is carried out in accordance with the load schedule of power systems, which differs, due to the high share of industrial, transport and other consumers, from the schedule of utility loads.
In the simplest case of an autonomous power plant supplying a limited area, counter-regulation of the voltage on its buses can be ensured by changing the excitation of the generators.
As a rule, for a rationally constructed urban distribution network, the use of counter-voltage regulation at the CPU is a comprehensive measure to ensure normalized voltage deviations for the majority of consumers. Therefore, transformers with on-load tap changers must be installed at all substations supplying the distribution network. IN existing networks with transformers without on-load tap-changers, it is possible to install linear regulators with on-load tap-changers in the CPU. On-load tap-changers operate, as a rule, automatically and allow stepwise voltage regulation without disconnecting the load. In table JO-1-10-3 provides the values of the rated voltages of the winding branches of step-down transformers with on-load tap-changers.
It is required to determine: 1) the smallest power of the synchronous compensator that provides counter voltage regulation at the substation, considering that when operating with underexcitation, the synchronous compensator can operate with a load of no more than 50% rated power; 2) the power of a battery of static capacitors that meets the same conditions for voltage regulation at the substation.
Iadd=1.11*530=588.3
The resulting smaller value is divided by the current passing in this power line.
Rice. 5.11. – Current passing in this power line.
The criticality of the ratio of the actual current to the ratio current is indicated by the color intensity, Than brighter color, the more critical the attitude. If Color is not displayed, for example, as in branch 4-6, then the relationship is normal.
The calculation of the current load of transformers is carried out in a similar way, the difference is that 2 currents flow in the branches (higher current and low voltage).
What current will be calculated is specified using the “location” column (HV or LV).
The workspace looks like this:
To perform calculations in this work field, you need to add several columns:
Fig.5.13 – Selecting columns
Fig.5.14.– Show column
Ultimate Workspace as follows:
Rice. 5.15.– Calculation
Using the RastrWin3 PVK, the current loads of transformers and power lines were calculated by setting the equipment currents, as well as the permissible current depending on the temperature using the function setting.
LABORATORY WORK No. 6
CALCULATION OF MODES FOR COUNTER VOLTAGE REGULATION
Goal of the work: obtaining practical skills in calculating the modes of electrical networks with counter voltage regulation in software package RastrWin.
For circuit electrical network shown in Figure 1.1, do the following (for two load values max, min):
1. Draw up a replacement diagram.
3. Create a model for calculating steady-state conditions in the RastrWin software (with setting the parameters of nodes and branches).
4. Perform normal mode calculations.
5. Checkout graphic diagram flow distribution calculation of steady state in the RastrWin software.
7. Draw a graph of voltage losses.
8. Draw a conclusion about the advisability of using the counter-regulation method.
INITIAL DATA
Initial data for drawing up an equivalent circuit for the circuit shown in Figure 1.1:
Table 1
table 2
Nominal parameters of transformers p/st
| Power transformer TMN-6300/35 | ||||||||||
| Nom. power kV*A | Regulation limits | U HV nom kV | U LV nom kV | u CL% | R CL, kW | Р ХХ, kW | I XX, % | R T Ohm | X T Ohm | kVAR |
 | 7,7 | 7,4 | 0,35 | 1,2 | 14,9 |
Figure 6.1 – Network design diagram
Counter voltage regulation method
Voltage regulation is a change in the voltage level at characteristic points of the network using special technical means.
The task of voltage regulation is to ensure normal technical specifications and efficiency collaboration electrical networks and production mechanisms. In the network of each voltage transformation stage, it must be within appropriate limits.
There are several methods of voltage regulation:
Centralized
Voltage stabilization
· Two-stage regulation
· Counter regulation
Local at the consumer
· group
· individual
This paper discusses the method of counter voltage regulation. The essence of the method is to change the voltage depending on the change in the load diagram of the electrical receiver.
According to the counter-regulation method, the voltage on the low-voltage buses of district substations during the period of maximum load should be maintained 5% higher
rated voltage of the supplied network. This figure is given in the PUE (Electrical Installation Rules). Operating experience
shows that the voltage should be increased by 10%, if the voltage deviation at nearby consumers is not
exceeds the permissible value. During the period of minimum load ( R min ≤ R max) the voltage on the 6-10 kV busbars of the substation decreases
up to rated voltage.
Let's consider this method using the following diagram of an electrical network section as an example (Fig. A).
| 1,05 U NOM |
| U NOM |
| 0,95 U NOM |
In maximum load mode, the power center maintains voltage U 1 NB. On tires high voltage PS voltage is lower due to voltage losses in power lines 1. Let's denote this voltage U 2 V. The voltage on the low voltage buses of this substation reduced to the voltage of the higher winding below the voltage U 2 V per voltage loss in the transformer.
If there were no voltage regulation on the substation ( TO t =1), then the actual voltage on the low voltage buses of the substation in relative units would be equal to the voltage. This is the voltage on the buses of electrical receiver A.
Its value satisfies the standards of the PUE. Voltage on the buses of electrical receiver B ( U B without reg.) less voltage on the buses of the electrical receiver. And the amount of voltage loss in power lines 2. Its value does not meet the requirements of the PUE. When regulating voltage ( 
) the voltage on the low voltage buses of the substation is maintained 5% higher than the rated network voltage.
It is impossible to raise the voltage by 10% above the nominal value of the network voltage, because in this case the voltage on the buses of consumer A would not comply with the PUE standards. When regulating the voltage, the voltage on the buses of power receiver B enters the permissible range.
In the minimum load mode, the voltage in the power center is higher, and the voltage losses in the network elements are lower. Therefore, without voltage regulation, both the voltage at consumer A and the voltage at consumer B are higher than the recommended PUE. By changing the transformation ratio, the permissible voltage deviation on the buses of both consumers is ensured.
To regulate voltage by substation transformers, it is possible to change the transformation ratio within 10 - 20%. In this work, on-load voltage regulation (OLTC) is used. The on-load tap-changer is usually installed on the higher voltage winding.
PROGRESS
"Creating a Steady State"
1. For the given electrical network diagram, draw up an equivalent circuit (taking into account active and inductive reactances elements).
3. Create a model for calculating steady-state conditions for maximum and minimum loads in the RastrWin software (with setting the parameters of nodes and branches).
Launch Rastrwin and create new file(Files New Mode OK).
Then fill in the data for the nodes (Open Nodes). Let's set the node numbers, rated voltages (in kV) and names.
Figure 6.2. – Node parameters for maximum loads
Figure 6.3. – Node parameters for minimum loads
Let's set the data for the branches (Open Branches).
To do this, we indicate the numbers of the beginning and end of the branch (it is convenient to use a drop-down list with nodes). We set resistances and transformation ratios (data from point 2).
Figure 6.4. – Parameters of branches for maximum loads
Figure 6.5. – Parameters of branches for minimum loads
4. Perform steady-state calculations.
The circuit parameters for the current task are set. Let's start calculating the steady state. To do this, press the F5 key.
When correct given parameters the mode converges and the following data is displayed in the protocol table:
Figure 6.6. – Calculation of steady state conditions for maximum loads
Figure 6.7. – Steady state calculation for minimum loads
It – iteration number;
Max.sky – value and node number for maximum power imbalance (P or Q);
>V – maximum value and node number for exceeding the voltage in relation to the nominal one – (𝑉𝑉nom⁄)max;
Angle – value and line number for the maximum angle rotation (in degrees). 5. Draw up a graphical flow distribution diagram for calculating the steady state. In PVK RastrWin 3 we will create a graphical diagram. Let's create a new graphics file (Files New Graphics Ok). Let's reproduce the graphical diagram for different load values using “Enter”. The voltage drop on the busbars is within unacceptable limits, which means that one of the control methods must be used. Calculation of mode for counter regulation 6. Adjust the voltage on the low voltage buses according to the law of counter regulation. Using an on-load tap-changer allows you to control the voltage within specified limits. To introduce it into the circuit, we will use the antsapf function. To do this, follow the steps (Open Antsapf Optimization). In the “Antsapfs” table, you need to set the following parameters: · Nbd – number of the transformer regulation type in the database; · Titles – its name (optional); · UI – units of tap pitch (% or kV). If this field is empty, % are assumed; if any character other than % and a space are entered in this field, kV will be assumed; · +/– – antzapf numbering order: · “+” – antsapfs are numbered starting from the maximum positive addition, “–” – from the maximum negative (the default is “+”); · Type – type of regulation. In the raster, when modeling three-winding and auto transformers, you can install 3 control devices on tap changers, tap changers, and VDTs. · Location-Regulating devices can be installed on the HV and MV sides, as well as in the AT neutral. It depends on what formulas will be used to calculate the transformation ratio and permissible winding currents. · Kneutr – number of trunnions in the neutral position (with zero addition), default 1; · V(nr) – voltage of the unregulated stage; · V(reg) – voltage of the regulated stage; · Nanc – number of antsaps with the step specified in the next column; · Step – step size (% or kV depending on the EI field). The order of the Nantz – Step pairs is from the largest minus to the largest plus. An example of filling out the Antangs table for an on-load tap-changer installed in transformers T2-T7 on the HV side and an on-load tap-changer on transformer T1. For RPN2, catalog data was used. On-load tap-changer on the HV side (35/6kV): +/- 12, 1.2%. (Figure 6.5). Figure 6.8. –Antsapf table In order to connect the on-load tap-changer with the transformer, let’s go to the branch tab (Column DB_ants Drop-down menu Select the desired on-load tap-changer). For maximum loads (Figure 6.9). Figure 6.9. – Introduction of regulation in maximum load mode Figure 6.10. – Introduction of regulation in minimum load mode After introducing counter regulation, we recalculate the mode (Mode F5), the parameters of the circuit have also changed. Counter regulation in this work is carried out by changing the number of the on-load tap-changer so that the voltage at the node is within acceptable limits (Column N_ants Enter the required tap-changer). In practice, the command to set the tap is issued by a logic machine and executed by the on-load tap-changer drive. 7. Constructing a voltage graph. Based on the data obtained at the nodes, we construct a voltage graph. To do this, the voltage in the node is compared with the nominal one and set aside as a percentage separately for each stage. Below is an example for a section of circuit: HV “Svobodny” NN “Yuzhnaya” (nodes 1-2-3-8). The percentage deviation of voltage in a node is calculated using the formula below and plotted on the graph: where is the stage voltage in percent; U nom - the nominal voltage value is taken from the standard voltage range; U f - actual voltage in the node. ∆E is calculated as the difference between without regulation and with regulation. ∆E at the second stage is calculated as the sum of the regulated voltage on the first and second transformers. The last value is plotted on the graph. Figure 6.11. – Voltage loss graph at maximum load From this graph it can be seen that regulation in the minimum load mode is not required, however, it was applied to improve the quality of supplied electricity. Under maximum load conditions, energy consumption increased significantly, which means that losses also increased, as can be seen from the graph below. Regulation for this case is necessary. Figure 6.12. – Voltage loss graph at minimum load 8. Draw a conclusion about the feasibility of using the counter regulation method. Figure 6.13. – Graphic diagram (max load) Figure 6.14 – Graphic diagram (min load) Figure 6.15. – Graphic diagram with regulation (max load) Figure 6.16. – Graphic diagram with regulation (min load) LABORATORY WORK No. 6 INFLUENCE OF CSR ON THE STEADY NETWORK MODE Goal of the work: identify the influence of CSR on the steady state of the network in the RastrWin3 PVC. 1. Draw up an equivalent circuit for a given network. 2. Select network elements. 4. Simulate the given network in RastrWin 3 to calculate the steady state. 5. In RastrWin 3 software, create a graphical diagram with the calculation results. 8. Simulate the given network in RastrWin 3 to calculate the steady state. 9. In PVK RastrWin 3, create a graphical diagram with the calculation results. The use of controlled shunt reactors makes it possible to control the operating modes of networks in such a way as to reduce losses and increase the throughput of power lines. This increases the reliability of the system and significantly saves energy during its transmission. Controlled shunt reactors (CSR) are electromagnetic reactors, the inductance of which can be smoothly adjusted using an automatic control system, which allows voltage stabilization on overhead lines with high charging power. In combination with capacitor banks connected in parallel, CSRs are analogues of static thyristor compensators (STC), allowing you to maintain voltage on the lines both in light and heavy load modes. Three types of CSR are used: · CSR controlled by direct current bias using a special control winding. They are a development of JSC ELUR (Russia). The electromagnetic part is produced by JSC "ZTZ" (Ukraine). · CSR controlled by direct current bias through the split neutral of the network winding. Developed by OJSC "HC Elektrozavod". It is designed to compensate for excess charging power and stabilize the voltage in the network. Losses in the new reactor, due to innovative solutions, are more than 30% lower than those of the CSR, which have so far been supplied to the power facilities of PJSC FGC UES. · CSR transformer type, consisting of a two-winding transformer, with a short circuit voltage equal to 100%, and a thyristor group connected to the secondary winding. According to the principle of operation, this type of CSR is fast-acting and is most suitable for objects that require a quick response to network disturbances. Figure 1 shows diagrams for constructing reactors with DC bias. Let's consider the network. In Figure 7.2. A diagram of the electrical network is presented. Fig.7.2. – Electrical network diagram Let's draw up an equivalent circuit for a given network. The most common design diagrams of elements of the electrical power system and expressions for calculating the resistance of their equivalent circuits are given in Appendix 1. Figure 3 shows the equivalent circuit of the electrical network. Fig.7.3 – Electrical network equivalent circuit Equipment data sheets from reference books (tables 2 - 4): table 2 Data for transformer type ATDTsTN-250000/500/220 Table 4 Data for transformer type TDTs-125000/220-U1 Let's calculate the parameters of the transformer ATDTsTN-250000/500/220 U1: Let's calculate the parameters of the transformer TDTs-125000/220-U1: Let's calculate the parameters of the AC-500/64 line: Let's calculate the parameters of the AC-240/32 line: Let's simulate the given network in RastrWin 3. In the conditions of design and operation of electrical networks, it is impossible to control the voltage quality at each power receiver, therefore, when considering the modes of 110-750 kV networks, the voltage quality must be ensured on the secondary voltage buses of 110-750/35-6 kV substations, i.e. in power supply centers of distribution networks. For this purpose, voltage regulation modes and permissible voltage deviations on the secondary voltage buses of substations must be standardized. Voltage modes are selected depending on the nature of the consumers connected to the network and their distance from the power center. In principle, two modes are possible, Fig. 9.6. Voltage stabilization is used when industrial enterprises with a 3-shift work pattern and a flat load schedule are connected to the power center, T m ≥ 5500-6000 h. The law of counter regulation is applied to mixed load, municipal and 1-2 shift enterprises, T m< 5500ч, причем, чем меньше Т м, тем более глубокое требуется регулирование (от 1,0U ном до 1,1U ном). При менее глубоком регулировании напряжение на шинах центра питания должно поддерживаться в диапазоне (1,05-1,1) U ном или (1,0-1,05) U ном. To maintain the required voltage regime in electrical systems, the following principles of voltage regulation are used: · centralized regulation, when the impact is on a large number of network nodes. Such regulation is carried out by generators and transformers of outdoor switchgear of power plants, transformers of large system and regional substations, synchronous compensators; · local regulation is used due to the fact that centralized regulation is not enough to maintain voltage in the required range in all nodes. Such regulation is carried out by transformers of step-down substations and banks of static capacitors; · mixed regulation using both principles. Voltage regulation is carried out: · generators of power plants, in which an increase in the excitation current leads to an increase in EMF and voltage on the generator voltage buses U Г (expressions 9.4, 8.3). Automatic excitation control (ARC) allows you to smoothly regulate the voltage U G or maintain its constant value; · transformers and autotransformers; · compensating devices (synchronous compensators - smoothly, batteries of static capacitors - stepwise); · changing network parameters using longitudinal compensation settings (LPC); · in closed networks - redistribution of active and reactive power flows. Power plant generators are only an auxiliary means of regulation, because they have an insufficient voltage regulation range; in addition, it is difficult to coordinate the voltage requirements of remote and nearby consumers. As the only means of regulation, generators are used only for loads supplied from the generator voltage busbars. Step-up transformers at power plants with a rated voltage of the HV winding of 110-220 kV are also an auxiliary means of voltage regulation, because they have a regulation limit of ±2x2.5% Uvnom, and with their help it is impossible to coordinate the voltage requirements of close and remote consumers. Step-up transformers 330, 500, 750 kV are produced without devices for voltage regulation. Therefore, the main means of voltage regulation are transformers and autotransformers of district substations. Based on their design, there are two types of transformers for step-down substations: · with switching of control branches without excitation, i.e. with disconnection from the network (transformers with PCB); · with switching of control branches under load (transformers with on-load tap-changers). Typically, their control taps are made on the higher voltage side, which has a lower operating current. This makes the operation of the switching device easier.
,
Rice. 7.1. - Schemes for constructing reactors with DC bias
Transformer type S nom, MV A U nom, kV Winding connection diagram and group Uk, %
VN NN
TDTs-125000/220-U1
10,5
Yh/D-11
