RU55223U1 - REACTIVE POWER COMPENSATION DEVICE - Google Patents

Abstract

The utility model relates to the field of electrical engineering and, in particular, to electrical devices designed to control the modes of AC power lines (power lines). it can be used for longitudinal or transverse compensation of reactive power. The power line reactive power compensation device comprises a synchronous compensator (SC), a SC exciter, an SC excitation automatic control unit, an SC stator operating mode sensor connected to its information inputs to an SC excitation automatic control unit, an asynchronous electric motor kinematically connected to the SC shaft and equipped with a control winding connected through a switch to a starting rheostat. An induction motor exciter was introduced into the device, supplying its control winding, an automatic control unit for the excitation of the asynchronous electric motor, and rotor angular position sensors and operating parameters of the stator circuit of the asynchronous electric motor, the outputs of which are connected to the information inputs of the automatic control unit for the excitation of the asynchronous electric motor. The objective of the utility model is to provide regulation of reactive power and stable operation of the SC in a wide range of voltage changes on the stator winding of the SC. The utility model has developments aimed at providing the ability to regulate the flow of active power with longitudinal compensation of power lines, minimizing power losses in the device and simplifying its operation, including the start-up process. 4 C.p.F., 2 ill.

Description

Technical field

The utility model relates to the field of electrical engineering and, in particular, to electrical devices designed to control the modes of AC power lines (power lines). It can be used for longitudinal or transverse compensation of reactive power. The preferred area of application of the utility model is the longitudinal compensation of power lines with the function of controlling the magnitude and direction of the flow of active power.

State of the art

To compensate for reactive power (longitudinal and transverse), various devices are used [1], including those made on the basis of electromechanical synchronous compensators (SC), which are able to provide high reliability, resistance to impulse disturbances in power lines, and high quality of the generated voltage. Currently, such devices are advisable to use for compensation capacities in the range of 100-1000 MVA.

A device is known for compensating the reactive power of power lines containing a synchronous compensator, its exciter, an automatic excitation control unit equipped with sensors of operating parameters (voltage, active and reactive power of the stator circuit) of a synchronous compensator, the outputs of which are connected to the information inputs of the regulator, and an asynchronous motor kinematically coupled with a synchronous compensator shaft and equipped with a control winding connected through a switch to a starting rheostat [2].

The causative agent of the SC together with the automatic excitation control unit is configured to maintain a given reactive power or voltage at the connection point of the SC (transverse compensation) or with the ability to control the power flow of power transmission lines (longitudinal compensation).

The induction motor in the device [2] has a power of 5-10% of the power of the SC and is used to accelerate it. Together with the starting rheostat, it provides the unit’s start-up up to a sub-synchronous speed, which is favorable for the power system (and SC), followed by the inclusion of a compensator in the network by means of self-synchronization and disconnecting the electric motor from the network.

The circuit of the device [2] is simple, reliable enough, has high efficiency and electromagnetic compatibility, high overload capacity.

The disadvantage of the device [2] is that it does not ensure the stability of the SC when the voltage across the stator winding of the SC varies over a wide range. The limits of the reactive power consumed by the synchronous compensator are limited by its nominal parameters, however, under conditions when the mains voltage varies widely (to zero), the range of the reactive power consumed, in which the synchronous compensator works stably, is narrowed. This disadvantage of the device [2] is especially evident when using the device for longitudinal compensation, when the process of regulating the flow of active power through power lines is accompanied by a change over a wide range of voltage on the stator winding of the SC. Under reduced voltage, the electromagnetic moment of the compensator becomes insufficient to maintain it in a rotating state and ensure its static and dynamic stability.

The induction motor in the device [2] is not able to compensate for fluctuations due to its natural moment characteristic

the shaft of the unit, due to violations of the stability of the SC in the above modes, even if it is not disconnected from the network after starting the SC.

In addition, when changing the shear angle between the current vector in the power transmission line and the longitudinal axis of the compensator from 90 el. the angle in the shaft of the compensator (and the electric motor) will change and along the chain network - electric motor - compensator - the network will transmit active power in one direction or another, loading the electric motor and the compensator with active currents. This leads to additional losses in both machines and to overload of the accelerating motor, since its power is significantly less than the power of the SC.

Utility Model Essence

The objective of the utility model is to provide regulation of reactive power and stable operation of the SC in a wide range of voltage changes on the stator winding of the SC.

A device for reactive power compensation of a power transmission line (transmission line) contains a synchronous compensator, a synchronous compensator exciter, a unit for automatically controlling the synchronous compensator excitation, a mode sensor for the stator circuit of a synchronous compensator, connected to the information inputs of a synchronous compensator automatic control unit for excitation, an asynchronous motor kinematically coupled with synchronous compensator shaft and equipped with a control winding second, connected through a switch to the starting resistors. An induction motor exciter was introduced into the device, supplying its control winding, an automatic control unit for the excitation of the asynchronous electric motor, and rotor angular position sensors and operating parameters of the stator circuit of the asynchronous electric motor, the outputs of which are connected to the information inputs of the automatic control unit for the excitation of the asynchronous electric motor.

This solves the problem by creating asynchronous electric motor automatically adjustable additional torque on the shaft SK.

The following development of the utility model is provided.

The device can be equipped with an active power flow sensor for the power transmission line, the output of which is connected to an additional information input of the synchronous compensator excitation automatic control unit.

This allows you to adjust the flow of active power in the longitudinal compensation of power lines.

The unit for automatically controlling the excitation of an asynchronous electric motor can be made in the form of a two-channel controller for active and reactive power, while the active power control channel is capable of damping rotor vibrations and correcting the angular position of the rotor field vector in a steady state, and the control channel for reactive power - with the ability to maintain a given reactive power of the stator winding of an induction motor, and introduced a current sensor single and transverse axes of the control winding of an induction motor, connected by its outputs to an additional information input of the unit for automatically controlling the excitation of the induction motor.

This minimizes the loss of electricity in the device.

An asynchronous electric motor can be made in the form of a brushless cascade of electrical machines equipped with a symmetrical two-phase longitudinal-transverse control winding.

This allows you to simplify the operation of the device, especially in combination with brushless execution of the pathogen synchronous compensator.

The starting rheostat can be made in the form of an induction current-limiting element, the resistance of which changes automatically as a function of the frequency and magnitude of the current flowing through it.

This improves reliability and simplifies the startup process of the device.

Brief Description of the Figures

Figure 1 presents the functional diagram of the utility model, taking into account its development, connected to power lines for longitudinal compensation with the function of controlling the flow of active power.

Figure 2 presents the functional diagram of the control unit for the excitation of an induction motor used in the composition of the proposed device.

Utility Model Implementation

Figure 1 shows:

- synchronous compensator 1;

- pathogen 2 compensator 1;

- block 3 automatic control of the excitation of the compensator 1;

- an asynchronous electric motor 4 kinematically connected by a shaft 5 with a compensator 1;

- sensor 6 of the angular position of the rotor of the electric motor 4;

- pathogen 7 of the electric motor 4;

- block 8 of the automatic regulation of the excitation of the electric motor 4, which feeds its control winding 9, which is connected through the switch 10 to the starting rheostat 11;

- sensors 12 and 13 of the operational parameters of the stator circuits of the compensator 1 and the motor 4, connected to the information inputs of blocks 3 and 8, respectively.

Figure 1 also shows the installation inputs of blocks 3 and 8, designed to enter the appropriate settings.

When using the device for longitudinal compensation, its function is to maintain a given flow of active power through power lines. Figure 1 shows the used in this case, the sensor 14 of the flow of active power transmission lines. In this case, the setpoint P ₀ is applied to the installation input of block 3 according to the active power flow in the line, and the signal from sensor 14 is sent to the additional information input of block 3.

When using the device for lateral compensation of power lines, it is connected in parallel with it (the stator circuits of the compensator 1 and motor 4 are connected to the line 15 via switches). In this case, the function of the device is to maintain a given reactive power at the output of the compensator 1 or a given voltage at the point of connection to the line. In this case, the corresponding setpoint Q ₀ for reactive power or the set U ₀ for voltage is applied to the installation input of block 3.

In both cases, the settings p ₀ and q ₀ are set at the installation inputs of block 8, setting the desired operating mode of motor 4 (for more details, see below).

In addition, figure 1 shows the elements of the equipment of the substation, providing the appropriate connection of the compensation device with line 15: switches 16 and 17, as well as matching transformers 18 and 19. To the low voltage windings of transformers 19 and 18 are connected the stator windings of compensator 1 and motor 4 A switch 20 is provided at the substation for shunting the low voltage winding of the transformer 19 included in the cut line 15.

The output of the current sensor 21 is connected to one of the information inputs of block 8 along the longitudinal and transverse axes of the control winding 9 of the asynchronous electric motor.

In the functional diagram of block 8 (figure 2), two control channels are used: active and reactive power. The input signals of block 8 are the reference signals p ₀ and q ₀ , the current value p and q of the stator of the electric motor 4, the signal Uδ from the sensor 6 and the signal U of the _network voltage. Input signals are supplied to the controller 22 active

power and reactive power regulator 23. In the active power control channel behind the regulator 22, the angle switch 24 is turned on, the offset angle between the signal U of the _network carrying information about the phase of the voltage of the network and the signal U _δ from the sensor 6. The outputs of the regulators 25 coordinate receive the output signals of the regulators 24 and 23, and also the conversion signals Sinδ and Cosδ generated in the functional node 26. The output signals of the converter 25, together with the negative feedback signals i _fq and i _fd for currents in the longitudinal and transverse axes of the control winding of the electric motor 4, coming from the dates Chik 21 (see figure 1), are fed to the output regulators 27 and 28. The control voltages U _fd and U _fq formed by the regulators 27 and 28 serve to control the pathogen 7 supplying the control winding of the electric motor 4.

The electric motor 4 may have a multiphase, for example three-phase, control winding or be made in the form of a brushless cascade of electrical machines equipped with a symmetrical two-phase longitudinal-transverse control winding. The last embodiment of the motor 4 allows you to simplify the system of its excitation, consisting of blocks 7 and 8, and to increase its reliability.

With a three-phase control winding on an electric motor 4, blocks 3 and 8 can be made in the form of a three-phase cycloconverter according to the zero scheme, and with a symmetric two-phase longitudinal-transverse control winding, in the form of two reversible controlled bridge rectifiers.

The causative agent 2 of the compensator 1 can be made, for example, in the form of a thyristor controlled bridge rectifier or in the form of a brushless electric machine.

The device can be used for longitudinal or lateral compensation.

In the longitudinal compensation mode, the device operates as follows (see figure 1).

In the initial state, the switches 16 and 17 are open, and the transformer 19, included in the cut line 15, is shunted on the low voltage side by the switch 20.

Suppose that in line 15 there is some kind of overflow P of active power, which, in particular, can be equal to zero.

The start of the compensator 1 is carried out by the electric motor 4 when the exciters 2 and 7 are turned on after the switches 16, 17 are turned on and the switch 20 is turned off. The asynchronous motor 4 is started using the rheostat 11 with the switch 10 closed. The starting torque must be sufficient to overcome the starting moment and the necessary acceleration the mass of the unit, the compensator 1 is the engine 4. At a sub-synchronous speed controlled by block 8, the signals for inclusion in operation are automatically generated by the signals of the sensor 6 of the angular position Lok 8, exciter 7, the forming voltage to the control winding 9 of the motor 4 on its longitudinal and transverse axes and for disabling the switch 10.

Block 8 is made according to a two-channel control circuit (see figure 2) and works as follows.

The controllers 22 and 23 generate signals proportional to the deviations of the current values of p and q measured by the sensor 13 from the values set at rates p ₀ and q _0, respectively.

The adjuster 24 of the angle δ adjusts the speed of the unit to synchronous. After that, the switch 17 is turned on, the switch 20 is turned off and the exciter 2 of the compensator 1 is put into operation. In block 3, the compensator excitation control signal is generated as a function of the current value of the power flow P in line 15 and the setpoint P ₀ .

Depending on the angle of shift between the emf vector of the compensator 1 and the current vector in line 15 at the moment, a braking or accelerating moment may occur on the shaft 5, which will lead to an overflow

active power along the network - electric motor - compensator - network circuit. In this case, block 8 using the controller 22 (see figure 2) installed in the channel for regulating the excitation by active power, acts on the pathogen 7 and shifts the vector of the electromagnetic field generated by the rotor winding of the electric motor 4 relative to the rotor itself and thus reduces the overflow power in line 15 to the setpoint value p ₀ in steady state.

In this case, the function of damping the rotor vibrations and correcting the angular position of the rotor field vector in the steady state is carried out as follows.

In dynamic modes caused by disturbances in line 15, an electromagnetic moment arises on shaft 5. Exciters 2 and 7 simultaneously participate in damping deviations of its angular position, trying to reduce these deviations to zero. Since such disturbances, as a rule, are short-term, the electric motor 4, even of a significantly lower power than the compensator 1, is capable of effectively damping these disturbances due to the overload capacity in time.

To the new steady state of the compensator 1 with the changed value of the angle of the rotor position, the control unit 8 adjusts, according to the integral law, the angle of shift of the rotor field vector until the active power of the motor stator reaches the set point p ₀ .

The setpoint p ₀ can be selected on the basis of active losses only in the electric motor 4 or taking into account compensation of the total losses of the unit. In this case, the active losses in the compensator 1 are completely covered by the electric motor 4.

In the channel for regulating the excitation by reactive power, block 8, using the regulator 23 (see Fig. 2), acts on the pathogen 7, ensuring that the given reactive power of the stator winding of the asynchronous electric motor 4 is maintained.

The setpoint q ₀ no of reactive power can be selected based on the condition of minimizing losses in the copper of electric motor 4 (cosφ = 1).

The operation of the compensator 1 in the mode with negative excitation, as well as at low voltage values on the stator winding, is associated with a sharp decrease in the margin of static and dynamic stability. In these modes, operation stability is practically only ensured by the appropriate control in block 8 of the electromagnetic moment of the electric motor 4, which makes it possible to ensure the operability of the compensator 1 in the longitudinal compensation device with deep regulation of the power flow in the power transmission line.

When connecting the proposed compensation device to the power transmission lines according to the transverse compensation scheme, the induction motor 4 is controlled by the exciter 7 and block 8 in the same way, and block 3 provides stabilization of reactive power or voltage at the point of connection to line 15 at the level of the corresponding setpoint applied to its installation input (see above). Moreover, all the mentioned positive properties of the compensation device are preserved, and the synchronous compensator 1 acquires the properties of an asynchronized compensator with a transverse winding, which is only located outside the compensator 1 in the motor housing 4.

In fact, the electric motor 4 with the exciter 7 and the control unit 8 accelerates and holds the compensator 1 when the voltage is lowered and functions as an active flywheel damping vibrations of the active power (angle θ) under dynamic disturbances in the system.

The electric motor 4 can be made in the form of a brushless asynchronous machine or in the form of a brushless cascade of electrical machines equipped with a symmetrical two-phase longitudinal-transverse control winding. This will simplify the operation of the device, especially in combination with brushless execution of block 2.

The rheostat 10 can be made in the form of an induction current-limiting element, the resistance of which changes automatically as a function of the frequency and magnitude of the current flowing through it [3]. This improves reliability and simplifies the startup process of the device.

Information sources

1. Kochkin V.I., Nechaev O.P. The use of static reactive power compensators in electric networks of power systems and enterprises. Moscow, ENAS, 2000.

2. E.Ya. Gurevich. Synchronous compensators. SEI., M.-L., 1958 (p. 137).

3. UK application No. 2075271 for CL. IPC H 01 F 27 / 24.1981

Claims (5)

1. A device for compensating reactive power of a power line (transmission line) containing a synchronous compensator, a pathogen of a synchronous compensator, a unit for automatically controlling the excitation of a synchronous compensator, a sensor for the operating parameters of the stator circuit of a synchronous compensator, connected to the information inputs of a unit for automatically controlling the excitation of a synchronous compensator, an asynchronous motor kinematically connected with the shaft of the synchronous compensator and equipped with a control an outlet connected via a switch to a starting rheostat, characterized in that an asynchronous electric motor exciter is introduced, supplying its control winding, an automatic control unit for the induction electric motor excitation, and rotor angular position sensors and operating parameters of the stator circuit of the asynchronous electric motor, the outputs of which are connected to the information inputs of the automatic block regulation of the excitation of an induction motor. 2. The device according to claim 1, characterized in that it is equipped with a sensor for active power flow of the power transmission line, the output of which is connected to an additional information input of the unit for automatically controlling the excitation of a synchronous compensator. 3. The device according to claim 1, characterized in that the unit for automatically controlling the excitation of the induction motor is made in the form of a two-channel controller for active and reactive power, while the control channel for active power is made with the possibility of damping the rotor vibrations and adjusting the angular position of the rotor field vector in steady state, and the control channel for reactive power - with the ability to maintain a given reactive power of the stator winding of an induction motor For, and introduced a current sensor along the longitudinal and transverse axes of the control winding of the induction motor, connected by its outputs to the additional information input of the unit for automatically controlling the excitation of the asynchronous motor. 4. The device according to claim 1, characterized in that the induction motor is made in the form of a brushless cascade of electrical machines equipped with a symmetrical two-phase longitudinal-transverse control winding. 5. The device according to claim 1, characterized in that the starting rheostat is made in the form of an induction current-limiting element, the resistance of which changes automatically as a function of the frequency and magnitude of the current flowing through it.