RU2023337C1 - Method of automatic limiting of power transfer in intersystem power line - Google Patents

Abstract

FIELD: electrical power engineering. SUBSTANCE: power transfer P_st is measured at start of intersystem power line, setting P_tr of transfer is found at P_st>P_tr, power of regulating power stations in function of this deviation is changed. Optimum value of transfer is determined by conditions of minimal losses of power P_los with P_st<P_los, voltage in power line is changed to voltage V_nom determined by minimum of power losses preventing its decrease below

Description

 The invention relates to the electric power industry and can be used to automatically limit the power flow of intersystem power transmission.

 There is a method of automatically limiting the flow, in which the setting of the limiting flow changes as a function of the load mode of other power transmissions of the power system [1]. When adjusting the setting, the change in the parameters of the power system, affecting the limit of the static stability of the intersystem power transmission (MSE), by which the flow is limited, which reduces the efficiency of using the method, is not taken into account.

 There is also a system for automatically limiting the power flow, in which the setting is changed taking into account the parameters of the power system that affect the stability limit of the ITU [2]. The limit setting is corrected without taking into account the current amplitude value of irregular flow fluctuations, which reduces the reliability of the ITU.

 In another known method of automatic flow limitation, the limiting setpoint is determined taking into account the current values of the MSE static stability limit and the amplitude of irregular flow fluctuations [3]. The stability limit is determined on the model of the current mode of the power system, and the amplitude of irregular flow fluctuations is determined by the mean square deviation of the flow calculated from the results of measurements of the parameters of irregular fluctuations in the power flow of the ITU. The setting is made without taking into account the operational parameters of the ITU, depending on its load and the voltage values at the nodes adjacent to the power systems, which reduces the cost-effectiveness of the ITU. The flow of capacitive currents through ITU elements in low load conditions causes additional losses of active power. The problem is much more complicated when using ITU high natural power. The generation of charging power of such lines becomes comparable with their natural power, which complicates the task of regulating the voltage and drain of reactive power.

, где U_н - напряжение, замеренное в начале ВЛ, φ_н - заданный угол сдвига фаз в начале ВЛ, а_н, в_н - коэффициенты потерь активной мощности короткого замыкания и холостого хода ВЛ. При выполнении условия Р_п < Р_поосуществляют изменение напряжения в начале ВЛ до оптимального значения по потерям активной мощности, определяемого выражением U_но=

, путем изменения коэффициентов трансформации трансформаторов, связывающих ВЛ с энергосистемами. В процессе изменения напряжения корректируют уставку ограничения по текущим параметрам σ и Р_пр.To increase the economy and reliability of the ITU in low-load conditions, automatic control of the voltage on its high-voltage line (VL) as a function of a changing power flow is required. In the model the current mode of the power system, taking into account the voltage levels VL endpoints, determine the limit of static stability MSER _pr. At the same time, the power flow is measured at the beginning of the power line R _p and the current value of the mean square deviation of the power flow σ is determined from the measurements. It is then determined flow setpoint limit P _y = (p _ave - 3σ) / (K _n + 1),
where K _n - standard safety factor of the stability of power transmission,
and comparing the value of the power flow R _p with the setting R _y . In the event that the overflow P _p exceeds the set limit, P _y changes the capacity of the regulatory power plants (RES) as a function of the deviation obtained. At the same time, the decrease in the overflow R _{p is} recorded for its optimal value, determined by the minimum power loss in the overhead line P _by = U $\genfrac{}{}{0ex}{}{\text{2}}{\text{n}}$ Cos

where U _n is the voltage measured at the beginning of the overhead line, φ _n is the specified phase angle at the beginning of the overhead line, and _n , in _n are the loss coefficients of the active power of the short circuit and the open circuit of the overhead line. When the condition P _n <P carried _by a voltage change at the beginning of VL to an optimal value for the active power losses, _but defined by the expression U =

, by changing the transformation ratios of the transformers that connect the overhead lines to the power systems. In the process of changing the voltage adjusting the current limit setpoint parameters σ and P _ave.

 The drawing shows a diagram of a method for automatically limiting the flow of power.

The circuit contains a sensor 1 for the amount of power overflow, a setpoint 2 for the overflow restriction settings, an element 3 for comparing the overflow with the setpoint, a setpoint correction unit 4, a unit 5 for determining the mean square deviation of the overflow from the limit setpoint, a unit 6 for generating a control action for the overflow limit, distribution unit 7 control action between separate distribution zones, block 8 determining the limit setting, block 9 determining the limit of static stability of power transmission, bus 10 of the transmission power system, bus 11 p receiving power system, transformer 12 for transmitting a power system with overhead lines, transformer 13 for connecting a receiving power system with overhead lines, a high-voltage power line 14, automatic regulator 15 for the transformation ratio of the transformer, remote control channel 16, measuring transformer 17 for overhead voltage, sensor 18 for overhead voltage, sensor 19 coefficient power cosφ _n , block 20 for determining the optimal VL power loss, comparison unit 21, master 22 of the maximum allowable voltage change at the start of the overhead line, control unit 23 influencing the change in the transformation coefficient of the communication transformer, block 24 determine the optimal voltage loss at the beginning of the overhead line.

 The system of automatic flow restriction operates as follows.

The sensor 1 measures the power flow R _p in the overhead line, the value of which is compared in element 3 with the set value (set limit for the flow), which is set by the switch 2. The deviation of the flow from the set value from element 3 is fed to the input of the block 6 for forming a control action for the flow limit in accordance with the accepted, for example, proportional-integral control law. Block 7, this control action is distributed between the individual distribution networks connected to the flow restriction system. According to a number of measurements of the overflow R _p in block 5, the value of the mean square deviation of the overflow σ is determined. The value of the limit of the static stability of the power transmission P _{ol is} calculated in block 9, which is a model of the current mode of the power system, taking into account the voltage levels in the starting and receiving nodes of the overhead line. The value of the limit R _CR is determined in accordance with the current values of the overflow R _p , voltage at the beginning of the overhead line U _n and other parameters of the power system mode, on which the value of the limit R _PR depends. The voltage at the beginning of the overhead line 14 is measured by the transformer 17 and is fixed by the sensor 18. The setting of the flow restriction P _y is determined by the expression P _y = (P _CR - ΔP) / (1 + K _n ),
where Δ P = 3 σ is the amplitude of irregular fluctuations in the flow, K _n is the standard safety factor of the stability of power transmission. With the help of block 4, the setpoint of setter 2 is corrected in accordance with the current value P _y determined by block 8.

, где U_н - напряжение ВЛ, замеренное в ее начале, φ_н - заданный угол сдвига фаз в начале ВЛ, ф_н, b_н - коэффициенты активных потерь мощности короткого замыкания и холостого хода ВЛ, получаемые из обобщенных постоянных четырехполюсника, замещающего электропередачу. Текущее значение Р_по вычисляется в блоке 20 по параметрам U_н, φ_н и коэффициентам a_н, b_н, вводимым в этот блок заранее. Фазовый угол φ_нопределяется заданным режимом ВЛ по реактивной мощности. Текущее значение U_н фиксируется датчиком 18. В блоке 21 производится сравнение оптимальной величины перетока Р_по с его текущим значением Р_п и при выполнении условия Р_п < Р_по вырабатывается разрешающий сигнал, поступающий на вход блока 23, который формирует управляющее воздействие на изменение коэффициента трансформации трансформатора связи 15 для установления оптимальной величины напряжения в начале ВЛ по выражению:
U_но=

Напряжение U_но определяет минимум потерь активной мощности в ВЛ при текущем значении перетока мощности Р_п. Угол сдвига фаз φ_н в начале ВЛ должен быть опережающим для создания режима выдачи реактивной мощности в конце линии. Параметр cosφ_н является заданной величиной, которая определяется требуемым режимом ВЛ по передаче реактивной мощности. Вычисленное значение U_но поступает на вход блока 23, в котором производится сравнение с предельно допустимым минимальным значением U'_но, определяемым допустимым изменением предела устойчивости при снижении напряжения U_н в начале ВЛ. При соблюдении условия U_но > U'_но и наличии разрешающего сигнала от блока 21 в блоке 23 вырабатывается управляющее воздействие на изменение коэффициента трансформации трансформатора связи 12. Автоматический регулятор 15 переключает ответвления обмотки трансформатора 12 в соответствии с управляющим воздействием блока 23, благодаря чему в начале линии 14 устанавливается оптимальное напряжение U_но. От регулятора 15 по каналу телеуправления 16 передается сигнал на регулятор 15 трансформатора 13, соединяющего ВЛ с шинами 11 приемной энергосистемы. При этом производится согласованное переключение ответвлений обмотки трансформатора 13 с учетом режима работы приемной энергосистемы. Снижение напряжения на ВЛ ограничивается задатчиком 22. При выполнении условия U_но ≅ U'_но на выходе блока 23 появляется фиксированное управляющее воздействие, соответствующее напряжению U'_но, определяемому с учетом ограничения по изменению предела устойчивости Р_пр.The value of the optimal overflow R _according to the conditions of the minimum loss of active power in the overhead line is determined by the expression P _{according to} = U $\genfrac{}{}{0ex}{}{\text{2}}{\text{n}}$ Cosφ _n

, where U _n is the overhead line voltage measured at its beginning, φ _n is the specified phase angle at the beginning of the overhead line, f _n , b _n are the coefficients of active power losses of short circuit and open circuit of the overhead line obtained from the generalized four-terminal constants replacing the power transmission. The current value of P _is calculated in block 20 according to the parameters U _n , φ _n and the coefficients a _n , b _n introduced in this block in advance. The phase angle φ _n is determined by the specified overhead line mode by reactive power. Current value U _n fixed sensor 18. At block 21 compares the optimum value _of P flow with its current value R _n and, when the condition P _n <P produced _by allowing the signal applied to the input of block 23, which generates a manipulated variable to change the ratio transformation of the communication transformer 15 to establish the optimal voltage value at the beginning of the overhead line by the expression:
U _but =

The voltage U _but determines the minimum loss of active power in the overhead line at the current value of the power flow R _p . The phase angle φ _n at the beginning of the overhead line must be leading in order to create a regime for reactive power output at the end of the line. The parameter cosφ _n is a given value, which is determined by the required overhead line mode for reactive power transmission. The calculated value of U _but arrives at the input of block 23, in which a comparison is made with the maximum permissible minimum value of U ' _but determined by the permissible change in the stability limit with a decrease in voltage U _n at the beginning of the overhead line. Subject to the condition U _but > U ' _but also the presence of the enable signal from block 21, in block 23, a control action is generated to change the transformation coefficient of the communication transformer 12. Automatic controller 15 switches the branches of the transformer winding 12 in accordance with the control action of block 23, so at the beginning line 14 sets the optimal voltage U _but . From the controller 15 through the telecontrol channel 16, a signal is transmitted to the controller 15 of the transformer 13, connecting the overhead line with the buses 11 of the receiving power system. In this case, a coordinated switching of the branches of the winding of the transformer 13 is made, taking into account the operating mode of the receiving power system. The voltage reduction on the overhead line is limited by the setpoint 22. When the condition U _but ≅ U ' _but at the output of block 23 is met, a fixed control action appears corresponding to the voltage U' _but determined taking into account the restrictions on the change in the stability limit P _ave .

The implementation of the method of automatically limiting power flow allows you to significantly reduce the loss of active power in the overhead line in the mode of reduced power transmission load. In addition, the problem of compensation of excess capacitive power generated by overhead lines in this mode is partially or completely eliminated. The power flow restriction setting is adjusted depending on the current value of the parameters σ and Р _pr , which increases the reliability of power transmission in the entire range of its loads.

Claims (1)

METHOD OF AUTOMATIC LIMITATION OF POWER TRANSFER OF INTER-SYSTEM POWER TRANSMISSION, according to which, on the model of the current mode of the power system, taking into account the voltage values at the end nodes of the high-voltage line, the limit of the static stability of the power transmission P _pr is measured, the value of the power flow at the beginning of the power transmission line P _p is determined from the measurement data the value of the mean square deviation of the power flow σ, then the setting of the flow restriction is determined
P _y = (P _pp - 3σ) / (K _n + 1),
where K _n - standard safety factor for the stability of power transmission,
compare the value of the overflow P _p with the limit setting P _y and if the overflow P _p exceeds the settings P _y , the power of the regulating power plants is changed as a function of the deviation obtained, characterized in that they additionally record the decrease in the flow P _p for its optimal value, determined by the minimum power loss in the high-voltage power lines
P _by = U $\genfrac{}{}{0ex}{}{\text{2}}{\text{n}}$ cosφ _n -

,
where U _n - voltage measured at the beginning of the line;
φ _n - a given phase angle at the beginning of the line;
a _n , b _n - the loss coefficients of the active power of the short circuit and idle line
when the condition P _n <P carried _by a voltage change at the beginning of a line to an optimal value of the active power losses defined by the expression
U _but =

·

,
by changing the transformation coefficients of the transformers connecting the high-voltage line to the power systems, while in the process of changing the voltage, the limit setting for the current parameters P _pp and σ is _adjusted , and the voltage U _{but is} limited to the minimum allowable value U $\genfrac{}{}{0ex}{}{\text{1}}{\text{n}}$ _about , determined by the acceptable level of the limit of static stability P _PR

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