RU2337424C1 - Method of reactive power source control - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: in high-voltage electric networks for compensation of reactive power and stabilisation of voltage. According to the method, three-phase magnetisation-controlled reactor is permanently connected to the mains, and in case voltage deviates from preset value three-phase sectional condenser battery is connected via breakers to the mains or disconnected from the mains. At that connection of every section of three-phase condenser battery is performed with simultaneous performance of the following conditions: U≤U_set and I≤I_min and t-t_n-1≥Δt, disconnection of every section of three-phase condenser battery is carried out with simultaneous performance of the following conditions: U≥U_set and I≥ I_max and t-t_n-1≥Δt, where U - mains voltage at the moment that precedes commutation of condenser battery section, U_set - preset mains voltage, I - reactor current at the moment that precedes commutation, I_min I_max - preset minimum and maximum reactor current, t - moment of commutation time, t_n-1 - moment of time of previous commutation, Δt - setting of commutation delay time.

EFFECT: improvement of mains voltage regulation quality and increase of substation equipment reliability.

1 dwg

Description

The invention relates to the field of electrical engineering, in particular to high-voltage regulated electrical complexes, and can be used in high-voltage electrical networks with a voltage of 110-750 kV to compensate for reactive power and voltage stabilization.

An analogue of the invention is a static thyristor compensator (STK) containing a three-phase power inductance, regulated by sequential thyristor switches, and a capacitor bank connected in parallel with it [1]. In the STK, reactive power is controlled by adjusting the ignition angles of the thyristors and switching (turning on and off) the capacitor bank. However, STK has a number of disadvantages, as he needs cooling, indoors, special maintenance. The control means in it are high-voltage thyristor switches for rated power, which do not allow short-term and emergency overloads that are inevitable in operation. In addition, the STK cannot be performed at a voltage of 110-750 kV, which requires connecting it to an intermediate transformer at full power or to the tertiary winding of existing autotransformers (which is not always possible in existing networks). In both the first and second cases, the efficiency of reactive power regulation on the high-voltage side is significantly reduced. In addition, in the first case, the cost of equipment, installation and operation increases.

The closest reactive power control method is a control method using a reactive power source (IRM), consisting of an adjustable inductance - controlled by magnetizing a three-phase reactor, which is directly connected to a high voltage network, a sectioned capacitor bank, and higher harmonic filters, also connected to a high voltage network voltage with sectioning through switches or to control windings [2]. The IRM is controlled by magnetization using an adjustable rectifier, which is supplied with single-phase voltage from the control windings or from the substation’s auxiliary system, and by switching sections of the capacitor bank.

The prototype IRM control method has a number of advantages compared to the analogue, since it provides an increase in the efficiency of reactive power regulation in high-voltage electric networks and a reduction in the cost of installed equipment. No enclosed spaces and ongoing qualified service are required.

However, it has several disadvantages: increased voltage surges in the network and increased wear of the switching and other electrical equipment of the substation on which the IRM is installed. The reason is that when switching sections of capacitor banks, a “clapping” mode occurs - repeated switching on - turning off the section switches, due to parametric resonance. This is a lengthy transition process, accompanied by repeated long-term power surges in the network that go beyond the limits normalized by the standard. Multiple inrush currents occur when sections of capacitor banks are turned on. Multiple overvoltages also occur - switching and resonant (inductances of the network and reactor with the capacity of the network and capacitor bank). Multiple inrush currents cause large electrodynamic forces, and overvoltage - repeated effects on insulation. This leads to increased wear of the switching and power equipment of the substation. Thus, there is a decrease in the quality of voltage regulation of the network (the main purpose of the IRM installation in the network) and a decrease in the reliability of the substation equipment.

The aim of the invention is to eliminate these drawbacks - improving the quality of voltage regulation of the network and increasing the reliability of substation equipment.

This goal is achieved by the fact that the regulation of the reactive power source, in which the three-phase controlled magnetization reactor is constantly connected to the network, and when the voltage deviates from the set sectionalized three-phase capacitor bank is connected via the circuit breakers to the network or disconnected from the network (that is, commuted), the connection of each section a three-phase capacitor bank is produced while the following conditions are met:

U≤U _ass ,

I≤I _min

tt _n-1 ≥Δt.

The disconnection of each section of a three-phase capacitor bank is performed while the following conditions are met:

U≥U _ass

I≥I _min ,

tt _n-1 ≥Δt.

In the formulas of the switching conditions, the following notations are introduced:

U is the mains voltage at the time preceding the switching (connection or disconnection) of the capacitor bank section;

U _back - set voltage of the network (reactor voltage setting);

I is the reactor current at the time preceding the switching;

I _min - set minimum reactor current (set minimum reactor current);

I _max is the set maximum reactor current (maximum reactor current setting);

t is the instant of switching time;

t _n-1 is the point in time of the previous switching;

Δt - setting delay time switching.

The schematic diagram of the IRM, on the example of which the proposed method is illustrated, is shown in the drawing.

A three-phase bias-controlled reactor 7 is connected to a three-phase network A-B-C through a switch 2 and capacitors of two sections of a capacitor bank 3 and 4 through section switches 5 and b. The magnetization of the control windings of the reactor 1 is carried out through a controlled rectifier 7 - a semiconductor converter (PP), which is regulated by the automatic control system 8 (ACS). The Converter 7 is powered by an alternating three-phase voltage ("≈") from the control windings (or tertiary windings of the reactor) or from the auxiliary system of the substation. System 8 is powered by alternating and direct current (“≈” and “=”) and receives information about the magnitude of the reactor current from current transformers 9 and the network voltage from voltage transformers 10. The reactor switch 2 and the sectional switches 5 and 6 of the capacitor bank are switched by command from self-propelled guns 8.

The reactor 1 may be a three-phase or in the form of a three-phase group of three single-phase reactors. The converter can carry out both separate (phase-by-phase) and simultaneous (immediately three phases) magnetization.

The proposed method of managing the IRM is as follows.

The magnetization controlled reactor 1 by circuit breakers 2 is connected to a three-phase network A-B-C with voltage U. Before this switching on, control system 8 sets the voltage U of the network specified for regulation (stabilization), _rear , minimum reactor current I _min , maximum reactor current I _max and a time delay Δt between adjacent switching sections of the capacitor banks (turning on or off the switches 5 and 6).

With a small load of the network or its absence (at night) in the network there is an excess of reactive power due to capacitive currents of the distributed capacity of the high-voltage network to the ground. As a result, the voltage in the network increases above a predetermined voltage U _back , which is fixed by voltage transformers 10 and system 8, which generates a command for converter 7 to increase the bias current of reactor 1. As a result, the current of reactor 1 increases (up to the maximum current I _max ), the IRM goes over into the consumption mode of automatically regulated reactive power and automatic voltage stabilization in the network. In this case, the system 8 monitors the voltage change due to load fluctuations in the network, increasing or decreasing the bias current of the reactor 1.

With a further increase in the load in the network, a lack of reactive power occurs, system 8, responding to a decrease in voltage U≤U _ass and checking the condition of the reactor current is less than the minimum I≤I _min , gives a command to turn on the section switch 5 - to connect one section of the capacitor bank to the network 3, putting the IRM into reactive power generation mode.

At maximum network load conditions again arise U≤U _back and I≤I _min . In this case, if the previous switch was turned on earlier by a time not less than the time Δt, i.e. if the third condition tt _n-1 ≥Δt is met, system 8 gives the command to turn on the sectional switch 6 - to connect the second section of the capacitor bank 4 to the network, putting the IRM in reactive power generation mode up to the maximum (at the minimum reactor current). Typically, the time interval Δt is 1-10 minutes, depending on the parameters of the IRM and the network.

With a decrease in load (switching to night time), an excess of reactive power and an increase in voltage occur in the network. It is required from the IRM to switch from the mode of reactive power output to the regime of reactive power consumption. Therefore, self-propelled guns 8 generates commands to increase the reactor current and to turn off sections of the capacitor bank. Shutdown is performed each time when three conditions are met simultaneously: U≥U _ass , I≥I _max and tt _n-1 ≥Δt.

Each connection to the capacitor network is accompanied by a surge and a surge in the network due to the inertia of current regulation controlled by magnetization of the reactor, which has a certain speed (in the presence of forcing, the time constant for gaining or resetting the power is a fraction of a second, in the absence of a few seconds). Each disconnection of capacitors from the network is also accompanied by an abrupt decrease in the network voltage. However, if three switching conditions are met simultaneously, this remains almost invisible on the network. The reason is that system 8 immediately after the occurrence of a voltage surge gives a command to change the bias current of the reactor (and, consequently, the mains current of the reactor). As a result of this, within fractions of a second in the presence of a magnetization forcing function in the reactor or within a few seconds in the absence of this function, an IRM with adjustable inductance - reactor 7 - returns the system to a voltage close to the initial one.

Failure to comply with one of the three conditions may create unfavorable IRM operation modes. For example, if the condition for the delay of the subsequent switching after the previous tt _n-1 ≥Δt is not met, then after the next switching on of the capacitor bank section, the resulting short-term power surge is taken by system 8 as a command to turn off this section of the battery. And if there is no time delay Δt, then a shutdown will occur, and then the system 8 will receive a signal about a decrease in voltage, and if there is no delay, the section will be connected again. Conditions arise for the “clapping” mode, which would not exist if the time delay Δt were observed, during which all transients decay. Thus, the proposed method of regulation ensures the elimination of the "clapping" mode when switching sections of capacitor banks — repeated switching on and off of sectional switches due to parametric resonance. This is a lengthy transition process, accompanied by repeated long-term power surges in the network that go beyond the limits normalized by the standard for the quality of electric energy. Application of the proposed method reduces switching and resonant overvoltages (inductances of the network and reactor with the capacity of the network and capacitor bank) arising from surges in current and voltage. Due to the decrease in the number of inrush currents, the level of influence of electrodynamic forces on the structural elements of electrical equipment is reduced, and due to the decrease in the number of overvoltages, repeated effects on insulation are reduced. This leads to reduced wear of the switching and power equipment of the substation. Thus, there is an improvement in the quality of voltage regulation of the network (the main purpose of the IRM installation in the network) and an increase in the reliability of substation equipment.

The proposed method has several advantages over similar methods of regulating the IRM: it reduces voltage surges in the network and the deterioration of switching and other electrical equipment of the substation on which the IRM is installed.

The efficiency of the new method of regulating the IRM and its advantage over the known methods are confirmed by calculations, mathematical modeling, test results of similar devices, if necessary, the results of this work can be additionally provided. In the near future, it is planned to manufacture prototypes of IRM for serial production using the proposed method.

Literature

1. Static thyristor compensators for power systems and power supply networks. Bortnik I.M. et al. Electricity, 1985, No. 2.

2. Patent for the invention of the Russian Federation No. 2282912 according to the application No. 2004121712, the priority of the invention July 16, 2004. Published from 08/27/2006 in the Bul. Number 24.

Claims (1)

A method of regulating a reactive power source, in which a three-phase bias controlled magnetization reactor is constantly connected to the network, and when the voltage deviates from a predetermined three-phase sectioned capacitor bank, they are connected through the circuit breakers to the network or disconnected from the network, characterized in that each section of the three-phase capacitor bank is connected while fulfillment of conditions U≤U _ass , I≤I _min tt _n-1 ≥Δt, disconnection of each section of a three-phase capacitor bank is carried out while fulfilling the conditions U≥U _ass I≥I _max , tt _n-1 ≥Δt, where U is the mains voltage at the time preceding the switching of the capacitor bank section, U _ass is the set mains voltage, I is the reactor current at the time preceding the switching, I _min is the set minimum reactor current, I _max is the set maximum reactor current, t is the moment switching time, t _n-1 is the time instant of the previous switching, Δt is the setting of the switching delay time.