RU2025017C1 - Method of control over mode of power transmission - Google Patents

Abstract

FIELD: electrical power engineering. SUBSTANCE: line transformers are connected in series on ends of power line. Shunting reactors are placed into their excitation windings to control voltage in line by control over excitation of line transformers. Voltage is set depending on power transfer which corresponds to preset drain of reactive power to power systems. EFFECT: improved reliability of control. 1 dwg

Description

 The invention relates to the electric power industry and can be used to automatically control the power transmission mode determined by its load and voltage on the high-voltage line (VL).

 A device for controlling the voltage on the overhead line as a function of its load, in which the secondary winding of the regulating transformer (RT) is connected to the excitation winding (OV) of the linear transformer (RT) through a controlled source of reactive power (IRM) [1]. The device controls the longitudinal component of the voltage and the longitudinal capacitance introduced into the overhead line. The device diagram includes two transformers, an IRM, a reactor, and other elements. A large number of components complicates the circuit and reduces the reliability of its operation.

 It is also known a device for controlling the voltage of the network, in which, in order to simplify the excitation winding of the LT is powered by the voltage of the network and connected in series with the IRM [2]. The change in the longitudinal and transverse components of the voltage introduced into the overhead line by means of LT is carried out by regulating the conductivity of the IRM, consisting of a capacitor and a controlled reactor (UR). When regulating in the current of the SD, harmonics arise, which requires special devices to suppress them. This is a disadvantage of this device.

 A device for controlling the voltage of an overhead line is known, in which the OB of a linear transformer is connected to the overhead line voltage in series with a capacitor. The additional voltage introduced into the overhead line by means of an RT is determined by the value of the capacitor capacitance and the parameters of the RT. RT voltage regulation is not performed, which is a disadvantage of the device. In addition, it is difficult to use a system on an extra-high voltage overhead line due to the direct connection of capacitors to the overhead line voltage.

 The purpose of the invention is to increase the efficiency of controlling the overhead line voltage and reactive power.

 This is achieved by regulating the EMF of sequential (linear) transformers included in the cut-off of the overhead line at its starting and receiving ends. The excitation winding of the LT is switched on to the overhead line voltage and connected in series with the shunt reactor. The change in the magnetization magnetization flux RT is made by switching the branches of the field winding. The EMF of the linear winding, proportional to the magnetizing magnetizing magnetization, changes the voltage of the overhead line. The law of voltage regulation of overhead lines is determined by those tasks that are set before the control system of the power transmission mode.

- P

sinλ ,
(1) где Р_н - натуральная мощность ВЛ; λ - волновая длина ВЛ. В случае малой нагрузки (S < P_н) ВЛ генерирует избыточную мощность, которая должна поглощаться ШР. Осуществляется компенсация примерно 60-80% зарядной мощности ВЛ Q_вл.з = -Р_нx xsin λ. По мере изменения нагрузки ВЛ ШР отключаются (включаются) с помощью высоковольтных выключателей (ВВ). При этом колебания напряжения не должны превышать 2-3% и определяются по формуле Δ U = =Q_p/S_к, где S_к - мощность к.з. в точке подключения реактора; Q_p - мощность одного реактора в группе.As you know, the reactive power generated (consumed) by overhead lines is determined by its load and is expressed by the formula
Q _ow =

- P

sinλ,
(1) where R _n is the natural power of the overhead line; λ is the wavelength of the overhead line. In the case of a small load (S <P _n ), the overhead line generates excess power, which should be absorbed by SR. Compensation is carried out for approximately 60-80% of the overhead charging power Q _ow.w = -P _n x xsin λ. As the load changes, the overhead lines of the SR are switched off (on) using high-voltage switches (BB). In this case, voltage fluctuations should not exceed 2-3% and are determined by the formula Δ U = Q _p / S _k , where S _k is the short-circuit power. at the connection point of the reactor; Q _p is the power of one reactor in the group.

 The experience of operating power systems has shown low efficiency of using SRs due to limitations on the number of permissible explosive commutations, through which SRs are connected to the overhead line. As a result, ballasts do not turn off at high overhead lines, which increases the loss of active power and reduces the transmission capacity. In addition, the switching of the SR causes voltage fluctuations that exceed the permissible level. Therefore, it is necessary to reduce the unit power of the SR, which is not economically feasible.

 The use of controlled shunt reactors (CSR) increases the efficiency of OHL regulation. However, thyristor power control of the CSR causes the generation of higher harmonics, the suppression of which requires additional expensive filtering equipment. In addition, CSRs are still under development; their serial production has not been mastered by domestic industry.

VL reactive power generation is determined by its load s and the value of the VL natural power R _n (Equation (1)). The natural power P _{n is} proportional to the square of the overhead line voltage U ² _ow and is determined by the expression P _n = U ² _ow / Z _in , where Z _in is the wave impedance of the overhead line. The generated overhead capacitive power Q _{is N} = -P x xsin λ can be effectively controlled by varying the voltage U _is. To implement a deep change in the voltage of the overhead line according to the technology of the proposed method, RTs are used, which are included in the cut of the overhead line. In the voltage regulation mode of the overhead line U _v VL excitation will be provided by the SR current. The reactive current of the SR, passing along the winding of the LT, excites a magnetic flux in its steel, which generates an EMF in the linear winding of the LT. With a constant current of the SR, the magnitude of this EMF can be changed by changing the transformation coefficient of the LT (switching the branches of the field winding).

 For LT it is customary to distinguish between pass-through and own power. Through passage power is meant the power of the circuit, in the cut of which the LT is included. The relative value of the own power is equal to the relative value of the emf of the light source. The regulation of LT can be carried out according to the same schemes as the regulation of transformers with on-load tap-changers. The reactance of an RT, referred to the line voltage, is small and usually amounts to about 2%. Power losses in them do not exceed 0.5% of the throughput power. The data presented refer to RT with a value of EMF (additional voltage) of the order of 15%.

 The excitation winding RT is usually powered by a special control transformer (RT) with on-load tap-changer. In the proposed technical solution, there is no need for RT, since the excitation winding of the RT is supplied from overhead lines or buses of the transmitting (receiving) power system. In this case, the excitation current (SR current) is determined mainly by the resistance of the SR and the voltage at the power point. The reduced RT resistance along the excitation winding is small and amounts to about 3-5%.

Power LT _lt S = Δ ^E. I _{ow is} determined by the magnitude of the range of variation of the EMF Δ E and the overhead current I _ow .

The current SHR I _SH forms the magnetization _MDF F and the corresponding magnetic induction B in steel LT. EMF Δ E = 4.44 is induced in the linear winding of the LT ^. f ^{. B.} H xx W ₁ , where f is the current frequency I _w ; N-active section of the magnetic circuit defined by the calculated power S LT _lt; W ₁ - the number of turns of the linear winding, the value of which is determined by the value of the magnetic induction B. When the voltage is constant at the point of connection of the circuit, the excitation winding of the LT-SR magnetic induction B depends only on the number of turns of the excitation winding W ₂ , since the magnetization MDS is F = I _w x xW ₂ , and the current I _wd can be taken constant.

 The drawing shows a diagram of an implementation of a method for controlling a power transmission mode.

 The circuit contains buses 1 of the transmitting power system, high voltage line 2, buses 3 of the receiving power system, linear transformers 4, linear windings of LT 5, field windings of LT 6, shunt reactors 7, switching devices 8 under load of the branches of the excitation winding 6, voltage sensor 9, overhead voltage line 9, sensor 10 active power of the overhead line, the setpoint switch 11 of the overhead line parameters, the overhead line control unit 12, the remote control channel 13.

 The system operates as follows.

 Transmission bus 1 and bus 3 of the receiving power system are connected by OHTL 2, in the cut of which windings 5 are connected at the transmitting and receiving ends. Field windings of LT 6 are powered by OHL or bus of the transmitting (receiving) power system. In series with the windings 6, shunt reactors 7 are turned on. The LTs have devices 8 for switching the branches of the windings 6. The overhead line voltage and load are fixed by sensors 8 and 9. The calculated overhead line parameters and power system mode parameters are determined in the control unit 11. The overhead line mode control unit 12 generates control lines the impact on the change in position of the devices 8 depending on the magnitude of the overhead line voltage, its load and the overhead line and power system parameters. The control actions on the device 8 switching branches under load LT of the receiving end of the overhead line are transmitted through channels 13 telecontrol.

The current _ШР I _шр , passing through the excitation winding, creates magnetization MDS in steel LT, which causes the appearance of magnetic induction B and EMF in the linear winding E _ow . Sign EMF E _ow negative, the voltage of the overhead line decreases. This applies to the transmitting node of the overhead line. In the receiving node, the EMF of the LT has the opposite sign, since the overhead line voltage must be increased to the voltage value of the buses of the receiving power system. The regulation of the emf of the transmitting and receiving nodes of the overhead line is done by switching the branches (on-load tap-changer type) of the field windings.

,
(2) где φ_н - угол сдвига фаз; а_к, а_х - коэффициенты потерь активной мощности короткого замыкания и холостого хода соответственно; Р_вл - активная мощность в начале ВЛ. Расчеты показывают, что оптимальное напряжение, вычисленное по (2), достигает максимально допустимого уровня при нагрузке S = (0,3-0,4) ^. P_н.Studies have shown that in order to reduce active losses and limit the drain of capacitive power into power systems, the voltage on the overhead line must be proportional to the root of the active power. In this case, the voltage at the beginning of the overhead line should change in the expression
U _ow.opt =

,
(2) where φ _n is the phase angle; and _to , and _x are the loss coefficients of the active power of the short circuit and idle, respectively; R _ow - active power at the beginning of the overhead line. Calculations show that the optimal voltage calculated according to (2) reaches the maximum allowable level at a load S = (0.3-0.4) ^. P _n

(3)
В зависимости от поставленных задач управления режимом ВЛ могут изменяться и законы регулирования напряжения ВЛ.It can be shown that for a given value of the drain of capacitive power in the power system Q _{c, the} voltage at the beginning of the overhead line should vary according to
U _ow =

(3)
Depending on the tasks assigned to control the overhead line, the laws of regulating the overhead line voltage can also change.

 The control unit 12 in accordance with the adopted laws of voltage regulation (according to formulas (2), (3) or other dependencies) generates control actions on the device 8 switching branches. The control of the LT of the receiving end of the overhead line is carried out through the channel 11 telecontrol.

 To implement the proposed technical solution, linear transformers should be equipped with an automatic branch switching device. Domestic plants produce automatic voltage regulators for transformers such as BAURPN and ART-1N. A device of the type ART-1H automatically controls the electric drives of the transformer branch switch. The device has a voltage control path, a control and monitoring unit, a clock pulse generator and a device for introducing an external change in the voltage setting. With a simple law of voltage regulation, for example proportional to one or two parameters, the control circuit can be based on a standard on-load tap-changer. If more complex processing of information is required (according to formulas (2), (3), etc.), taking into account a number of system parameters, then the development of a control action should be assigned to a computer (analog or digital), which are currently supplied large substations 500-750 kV.

 Thus, according to the proposed technology, a deep change in the overhead line voltage according to a given law is made by linear transformers with automatically controlled excitation. The shunt reactor load current is used as the excitation. The regulation of the excitation is carried out by automatically changing the number of turns streamlined by the indicated current. The proposed control principle greatly simplifies the installation of deep voltage regulation of overhead lines, increases the efficiency of regulation and the efficiency of power transmission.

Claims (1)

METHOD OF CONTROL OF THE ELECTRIC TRANSMISSION MODE, including a high-voltage line with linear transformers included in its cut in the sending and receiving units, the field windings of which are connected to the line through reactance, according to which the voltage of the high-voltage line is changed by regulating the excitation of linear transformers, characterized in that they additionally measure the value power flow along the line P _ow and determine the value of voltage on the line U _l corresponding to a given value of the drain react net power in the connected power systems Q _c , as
U _l =

Q _c +

,
where Z _in - wave impedance of the line;
λ is the wavelength of the line,
measured value of the current line voltage U _Lt, compare it to U _l and U _Lt <U _l increased, and if U _Lt> U _l reduce the line voltage to a value U _L by appropriately changing the number of turns of the winding excitation linear transformers as well as reactances use shunt reactors.

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