RU2508584C1 - Automatic adjustment method of arc-suppression reaction coil - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: method consists in creation on a network neutral in its normal operating mode of an artificial potential from a generator of variable non-industrial frequency and measurement of parameters of the outline of zero network sequence based on the found frequency of resonance of fixed inductance of a reaction coil with the network capacity, and at occurrence of single-phase fault to ground - in recording of a measurement result, deactivation of the variable frequency generator and resonant adjustment of an arc-suppression reaction coil in compliance with the results of the last measurement, supplemented by the fact that as an arc-suppression reaction coil there used is a single-phase controlled reaction coil of a transformer type with short-circuit voltage of 100% between windings, and its resonant adjustment in the single-phase short-circuit mode in compliance with the earlier found values of capacitance current of the network is performed by selection of the required inductance resistance at outputs of secondary winding by means of a switchboard and a set of sufficient amount of resistances with values pro rata to the first numbers of ascending power series 2n, which can be connected to outputs of secondary winding of the reaction coil in series with possibility of shunting with the corresponding switch of the switchboard of any of them.

EFFECT: improving accuracy and quick action of adjustment of ASRC, including in modes of arcing short circuits, at simultaneous provision of harmonicity of compensation current.

3 dwg

Description

The present invention relates to the field of electrical engineering, in particular, to devices for compensating capacitive currents of single-phase earth faults in electric networks with an insulated neutral voltage of 6 ... 35 kV, and can be used to accurately measure the expected capacitive current of earth faults and subsequent resonant tuning of arc suppression reactors (DGR) at the time of a fault. The technical result consists in increasing the accuracy and speed of adjustment of the GDR, including in the modes of arc faults, while ensuring the sinusoidality of the compensation current, simplifying and cheapening the design of the reactor.

At present, plunger reactors and reactors with magnetization of the magnetic circuit are used as smoothly and automatically controlled arc suppression reactors to compensate for capacitive currents during single-phase earth faults (OZZ) in electric networks of 6-35 kV with isolated neutral [1]. Both have advantages and significant drawbacks, therefore, research and development continues, aimed both at improving existing designs and at creating devices of a different operating principle, which combine linear characteristics and a small composition of the higher harmonics of plunger reactors with the absence of moving elements and speed characteristic for a magnetoacoustic resonance with bias.

In recent years, in high-voltage electric networks, as a three-phase reactive power control device, both controlled transformer-type shunt reactors (USHRT or magnetic flux switching reactors) and STK or other converting devices using thyristors for smooth regulation of current consumption are already used [2] .

Transformer-type reactors (or reactors with magnetic flux switching) are a three-phase transformer with a short circuit voltage increased to 100% between the primary and secondary windings. When the secondary winding is shorted, the rated reactive power with the rated current in the primary winding is consumed, and when the secondary winding is opened, the open circuit power is close to zero and corresponds to the open circuit current of a conventional transformer. Three-phase thyristor converters for the full reactor power connected to the terminals of the secondary winding are used to smoothly control the primary winding current and the consumed reactive power. When working with intermediate values of power consumption, when the thyristors are open part of the period of the network frequency, odd harmonics appear in the reactor current, which are used to reduce filters.

Therefore, a solution in the form of a GDR based on such a single-phase reactor (single-phase two-winding transformer with a short-circuit voltage between windings of 100%) and with a thyristor converter at the terminals of the secondary winding for smooth adjustment of the compensation current seems to be effective. However, this raises a number of unresolved technical problems, which are listed below and can be solved using the invention:

- unsatisfactory harmonic composition of the consumed GDR current, since with conventional thyristors with natural switching, its distortions are unacceptably high, and when using PWM modulation at high frequency, losses, cost and switching effects on the valves increase;

- the impossibility of using widely used devices for measuring and regulating plunger GDRs (adjustment to the maximum neutral voltage) or magnetizable GDRs (automatic adjustment system for compensation type SANK with resonant frequency search), because in the absence of a short to ground and the corresponding current through the converter, its valves are in undefined semiconducting state with unstable resistance in the secondary circuit of the reactor;

- for the same reason, a GDR based on a single-phase USRT (or a controlled reactor with magnetic flux switching) does not provide accurate compensation in single repetitive SCR modes with a short duration (up to one period) and a large duty cycle, since unlike a fixed-inductance plunger reactor, the first moment of the OZZ does not have such a reactor;

- lack of redundancy and reliable protection against overvoltages of the controlled semiconductor converter, providing regulation of the compensation current, which reduces the reliability of the device as a whole;

- the impossibility of identifying a damaged feeder in the OZZ mode in the simplest way using the existing maximum current protection.

The aim of the claimed invention is to provide accurate measurement of the network capacity and subsequent automatic control of the arcing reactor in a single-phase circuit with a given accuracy while ensuring speed, sinusoidal current of the reactor and simplifying its design compared to three-phase CCRTs controlled by thyristor converters of high power, size and cost.

Closest to the proposed invention is a method of controlling an extinguishing reactor with magnetization using an automatic compensation adjustment system (SANK), which in normal operation of the network provides regular measurement of capacitive current by scanning the neutral generator with a variable frequency with stabilized magnetization of the GDR, and in the OZZ mode by the controller to the control angles of the thyristor converter puts the reactor in the mode of accurate compensation with a given value then and [3]. However, such systems of automatic compensation of the OZZ current are not without some of the disadvantages listed above, in particular, they are characterized by a non-sinusoidality of the compensation current and a significant compensation error in the modes of arc faults with high duty cycle, due to the inertia of such reactors, as well as overshoot and oscillation of the integral channel of the controller.

The above goal and technical result is achieved in the proposed invention by the fact that the method of automatic tuning of an arcing reactor included in the neutral of the supply transformer, which consists in creating an artificial potential on the network neutral in the normal mode of its operation from an alternating non-industrial frequency generator and measuring the parameters of the zero-sequence circuit based on the found resonance frequency of the fixed inductance of the reactor with the network capacity according to the formula:

, где $$I_{s\mathrm{but}m}=\left(I_{dgR}+I_{b\mathrm{but}s}\right){(\frac{f_{\mathrm{fifty}}}{f_p})}^2$$

where

I _deputy - the expected capacitive current with a metal single-phase earth fault;

I _dgr is the known value of the current of the extinguishing reactor in this section of tires;

I _bases - the known current value of a parallel-connected unregulated basic arc suppression reactor (in its absence, this value is zero);

f ₅₀ - rated industrial frequency of the network (for Russia, 50 Hz);

f _p is the found resonance frequency of the inductance of the connected arcing reactors with the current network capacity to ground; and at the moment of a single-phase earth fault — storing the measurement result, turning off the variable frequency generator and resonant tuning of the arc suppression reactor in accordance with the result of the last measurement, is supplemented by the use of a transformer type single-phase controlled reactor with short-circuit voltages between the windings 100 %, and its resonant tuning in the single-phase circuit mode in accordance with the previously found value of the capacitive current of the network is selected by selecting the necessary inductance at the terminals of the secondary winding using a switch and a set of a sufficient number of resistances with values proportional to the first numbers of the power series 2 ⁿ , which can be connected to the terminals of the secondary winding of the reactor in series with the possibility of bypassing any of them with the corresponding switch key, or in parallel with the possibility connecting the corresponding switch keys with the required set of resistances, while the fixed value the inductive reactance of the reactor for measuring the capacitive current of the network in the normal mode of operation is provided by the same switch by shorting the secondary winding of the reactor to a short-circuit or by a given inductive resistance, and the possibility of the selective action of the maximum current protection at the time of the occurrence of an SCR is provided by the same switch due to short-term overcompensation with a short-circuit secondary winding or due to the active component of the reactor current with short-term connection to the output m secondary winding resistance.

To clarify the claimed method, Fig. 1 shows a structural functional diagram of an arc suppression reactor based on a magnetic flux switching reactor 2 (single-phase USRT) connected to a network with isolated neutral via connection transformer 1. A network of 6, 10 or 35 kV, in the general case mixed (air-cable) has a distributed capacitance to the ground, which must be compensated with the help of the GDR to minimize the current of a single-phase earth fault.

The first of the technical problems - the sinusoidality of the GDR current - can be solved in three different ways, the first two of which involve controlling the reactor using a semiconductor converter (PP) at the terminals of the secondary winding:

- the traditional use of the filter of the most powerful odd canonical harmonics (3, 5, 7), connected to the secondary winding of the GDR parallel to the PP;

- the use in the PP of fully lockable high-frequency thyristors or transistors to form a pulse-width modulation (PWM) sinusoidal current curve without the use of filters;

- rejection of continuous smooth regulation by changing the control angle of the semiconductor converter using instead a commutation of a set of inductive resistances at the terminals of the secondary winding.

Using filters of the most powerful odd harmonics is the simplest, proven in other applications, and therefore a reliable solution. In particular, it is precisely the 5–7 harmonics filters that are used in 110 kV and 400 kV ACHRs already in operation, as well as in traditional STK. However, the most powerful third harmonic and multiples of it are excluded from the mains current of the indicated devices in a circuit way, for example, by connecting the secondary windings of a three-phase group into a triangle. Therefore, the relative required filter power for three-phase devices will be significantly lower. In addition, such a solution for a single-phase extinguishing reactor means complicating and increasing the cost of the design as a whole due to additional filters with a capacity of about 30% of the nominal power of the GDR, and in this regard, reducing the control range of the extinguishing reactor, since the filter capacitor battery produces reactive power at the first harmonics (fundamental frequency 50 Hz) and current in the primary circuit.

The second option using fully controllable thyristors or transistors, which allows to ensure the sinusoidality of the current consumption due to PWM, can be significantly more expensive than the first, because, for example, power IGBT modules are several times higher in cost than conventional thyristor cells of converters with natural switching. In addition, active losses will increase significantly with the corresponding addition of the active component in the compensation current and the need for more serious measures to cool the converter. Such modules, compared with conventional thyristors, allow less current and voltage overloads, therefore, a large redundancy for redundancy and serious protection against switching overvoltages are required.

The simplest, and therefore cheaper and more reliable is the third option - regulation of the GDR by the magnitude of the inductive resistance at the terminals of the secondary winding. In this case, the converter (pos. 3 of FIG. 1) is replaced by a set of inductive resistances with a switch controlled by SANK for a given accuracy of compensation of the changing capacitive current of the network. A set of resistances with switches on the terminals of the secondary winding can be switched on in parallel (Fig.1-a), or in series (Fig.1-b). The second option is more preferable for two reasons: firstly, the desired total resistance is selected by a simple arithmetic sum (linearly, and not inversely, as with parallel connection), and secondly, unloading any resistance for the required set is never accompanied by a complete break windings and corresponding overvoltage on its terminals and on the switch.

Figure 1. Connection (a) or unloading (b) with the switch keys of the required set of inductive resistances at the terminals of the secondary winding of the GDR.

1 - a transformer with a neutral output and a secondary "triangle" winding (or a zero sequence filter of the FMZO type) for connecting an AGR;

2 - single-phase transformer with a short circuit voltage 100% - the electromagnetic part of the GDR with magnetic flux switching;

3 - a switch at the terminals of the secondary winding of the GDR with a set of the required number of inductive resistances (chokes) and switches providing parallel (a) or serial (b) connection of the desired set of resistances.

4 - automatic control system of the type SANK, providing a mode of continuous measurement of the current capacity of the network, detection of OZZ, switch management.

The number of switched resistances, in addition to using the corresponding different values in accordance with the selected SANK algorithm, can be further reduced by reducing the adjustment range of the GDR. The three-phase USRT, as well as the magnetization-controlled SSR, has a practical depth of regulation from idle (1% of rated current) to rated power (about a hundred or 1: 100). And such a range is really necessary for three-phase shunt reactors continuously operating in variable load electrical networks. To compensate for the capacitive current in the OZZ modes, in most cases, a sufficient range is 1: 5, and for specific substations it is often even less. Accordingly, with a regulation depth of 50 ... 80% of the rated power with a given accuracy, a smaller number of inductive resistances and corresponding switch keys will be required.

A magnetic flux switching resonance generator (based on a single-phase USRT) operates in the above circuit variants as follows. All the problems mentioned earlier - the current measurement of the capacitive current of the network, the response of the GDR to single faults, protection against switching overvoltages, and the selective action of current protections - are solved by switch 3 connected to the terminals of the secondary winding of the reactor with a set of inductive resistances (chokes), which is in normal conditions the network keeps the circuit constantly on with minimal (zero) or close to it resistance.

In both variants of the circuit, in the normal network operation mode, SANK 4 continuously measures the capacitive current of the network based on a comparison of the current network capacity with the constant inductance of the GDR 2, which is determined by the minimum (zero) resistance at the terminals of its secondary winding using the switch 3. At the same time, SANK 4, as in the well-known analogue of the invention, constantly scans the network with its variable-frequency generator through the signal winding of the DGR (or through an additional low-power transformer in the circuit with minimum resistance) and, based on the maximum voltage of the neutral voltage, finds the resonance frequency of the known and constant reactor inductance 2 with a capacity change of 6, 10 or 35 kV when changing feeders.

Further, the expected capacitive current OZZ and the corresponding setting for switch 3 are determined in SANK 4 by the relation [3], which follows from the equality of the inductance of the GDR 2 and the network capacity at the found resonant frequency, different from the industrial one, and lying at the minimum shunt resistances connected by the switch 3 to winding of the reactor 2, in the range of 60 ... 90 Hz or more:

, где $$I_{\mathrm{at}\mathrm{from}t}=((I_{dgR}+I_{b\mathrm{but}s}){(\frac{f_{\mathrm{fifty}}}{f_p})}^2-I_{b\mathrm{but}s})$$

where

I _dgr is the known current value of a controlled arc suppression reactor on a given section of tires with a fixed partial or full shunting of its secondary winding;

I _bases - the known value of the current in parallel connected unregulated base reactor (in its absence, this value is zero);

f ₅₀ - rated industrial frequency of the network (for Russia, 50 Hz);

f _p is the apparent resonance frequency of the inductance connected to the section of reactors with the current capacity of the network to ground;

I _mouth - the current setting (and corresponding inductive resistance) found in SANK 4 for the regulator-switch 3 of the controlled arc suppression reactor 2.

If any 033 occurs, including a stable metal or arc single with a short duration and a long duty cycle, at the first moment, the DGR 2 with a shunted secondary winding has a constant inductance close to nominal and provides inertialess compensation of the inrush of capacitive current in the first period (half period). At the same time, SANK 4 switches from the current measurement mode to the control mode, turning off the variable frequency generator, transferring the current (inductance) of the DGR 2 to the desired value with the appropriate set of resistances using switch 3 during the first period of the network frequency (or after a specified period of time) .

Ensuring the detection of a damaged feeder (selective action of conventional current protection) is easily achieved by delaying the transition from the minimum shunt resistance to the required one, or by turning on a separate circuit with active resistance in the circuits of Fig. 1. Thus, switching the secondary winding of the considered GDR short or through active resistance makes it possible to identify a damaged feeder by simple current protection due to overcompensation or by the short-term active component of the OZZ current from the reactor.

Currently, mathematical modeling of the considered methods and algorithms for controlling the GDR on the basis of a controlled single-phase reactor with magnetic flux switching has been performed. Figure 2 shows the oscillograms of the GDR adjustment by unloading the series resistances in the secondary winding circuit (according to the circuit in Figs. 1-6), which confirm the high speed of the GDR, the sinusoidal current of the compensation, and the absence of overvoltage during switching. Modeling of the GDR modes was carried out in the NRAST program, which for many years has been used to study controlled reactors.

Figure 2. Oscillograms of the currents and voltages of the GDR when tuning by switching inductive resistances in the secondary circuit.

On the oscillograms from top to bottom: OZZ current, capacitive component of the OZZ current, GDR compensation current, induction in the GDR magnetic circuit core, resistance current in the secondary winding circuit, voltage at its terminals, neutral voltage (to GDR).

As switches with rated parameters up to 1000 V, 500 A, a wide range of devices can be used from vacuum chambers, gas-insulated switches and power transistor modules to automatic machines and contactors with remote control.

The accuracy of regulation depends on the accuracy of the SANK measurements (the error does not exceed 2%) and the selected step of the switched chokes, that is, their number. For example, if we take seven chokes based on a power series 2 ⁿ with values of 1, 2, 4, 8, 16, 32, 64 millegenes, which allow changing the resistance at the terminals of the secondary winding through 0.314 Ohms from zero to 40 Ohms, then for an GDR with a power of 480 kVar in a 10 kV network, we obtain the control characteristic shown in Fig. 3.

Figure 3. Dependence of the GDR current on the inductance of the inductor at the terminals of the secondary winding

With a non-linear (inverse-dependent) control characteristic, the selected step of 0.001 mH (or 0.314 Ohm) allows for regulation on the steepest initial section with a step of about 2 A or with a maximum error of 1.5%. Together with the measurement error, this means for the specified reactor a deviation from the resonance tuning of not more than three amperes with the practical absence of higher harmonics and an active component in the compensation current.

The number of chokes with switches can be reduced to six if the control range is limited to 20 Ohms (with a minimum capacitive current of 033 per section, as a rule, more than 40% of the nominal current of the GDR) and then to five (2, 4, 8, 16, and 32), if double the tuning step and, accordingly, increase the maximum possible deviation of the reactor current from the preset SANK set point to plus or minus two amperes. With 4 chokes of 2, 4, 8 and 16 mH, the available control range will be from 50 to 100%.

It should be noted that there is another variant of the algorithm with the transition from the next measurement of the capacitive current of the network to the required GDR inductance specified on the basis of this measurement until 033 occurs. Then, switching for the next set of chokes will occur in the absence of voltage on the reactor and its secondary winding, and when If a short circuit occurs, the reactor will immediately provide an accurate compensation mode. However, in this case, the measurement mode is somewhat more complicated, since after each switching of the reactors, the next search for the resonant frequency will occur with a new, albeit also predefined, reactor inductance. In this case, the required range of the variable frequency generator will be wider with the possibility of moving into an area close to the network frequency (50 Hz). In the latter case, a transition to another nearest combination of throttles with some overcompensation or undercompensation will be required. In the case of the unlikely coincidence of the next measurement with the occurrence of 033, the switching is blocked and the GDR comes into operation with the inductance established on the basis of the previous measurement.

Here it is necessary to clarify that the search for the resonant frequency for measuring the capacitive current of the network is carried out in the SANK for a time of the order of 1.5 ... 2 minutes and is repeated continuously (or with a given regularity). The search is carried out by sequentially passing the estimated range of the resonance frequency (either by the "golden section" method) against the background of a beating of two frequencies in the received signal of the network neutral bias voltage - the network frequency of 50 Hz (with the usual presence of some "natural" neutral bias) and variable frequency from the probing network SANK generator. In the zone of close frequencies, if the resonance frequency differs from the industrial one by less than 1 Hz, the beat period tends to infinity, increasing the time and measurement error. Therefore, the SANK algorithm provides in such cases (at resonance frequencies of plus or minus 2 Hz from the network frequency) a transition to another reactor inductance in the measurement cycle corresponding to a difference between frequencies of the order of 10 Hz. Thus, the proposed method allows you to:

- create high-tech devices that allow combining the positive qualities of plunger and magnetizable GDR: linearity of characteristics, sinusoidal current, deep control range and speed with the simultaneous absence of mechanical moving elements, expensive converters and filters;

- switching the secondary winding of the GDR short, to inductive reactance or with a given time to active resistance, makes it possible to accurately measure the network capacitance, the correct operation of the GDR in single-circuit modes, protection against switching overvoltages, selective operation of zero-sequence current protection, and in the presence of the necessary set of inductive resistances with a switch - fine-tuning the reactor in resonance with the network capacity without using a converter;

- the exclusion of powerful thyristor converters for regulating the compensation current simplifies and cheapens the design of the reactor, increases its reliability, and also provides a sinusoidal current of the reactor in the entire load range without the use of filters.

The proposed method for controlling the switching of inductive resistances (inductors) at the terminals of the secondary winding of a GDR with magnetic flux switching is quite simple, reliable, and with the number of such inductors with switches from 5 to 7, it is possible to obtain the necessary control accuracy for reactors with power from 300 to 840 kVar and higher.

Literature:

1. Features of arc suppression reactors with magnetization and methods for their improvement. Aliev R.G., Dolgopolov A.G., Dolgopolov S.G. Power Engineer, No. 8, 2012

2. Controlled Reactors - Technology Overview. Dolgopolov A.G., Sokolov S.E. Electrical Engineering News, No 3 (75), 2012

3. Dolgopolov A.G. A method for automatically setting an extinguishing reactor. RF patent №2222857 Publ. Bull №3, 2004

Claims (1)

A method for automatically adjusting an arcing reactor included in the neutral of a supply transformer, which consists in creating an artificial potential in the normal mode of its operation from an alternating non-industrial frequency generator and measuring the parameters of the zero sequence circuit of the network based on the found resonance frequency of the fixed reactor inductance with the network capacity according to the formula :
$$I_{s\mathrm{but}m}=\left(I_{dgR}+I_{b\mathrm{but}s}\right){(\frac{f_{\mathrm{fifty}}}{f_p})}^2,$$

where I _Deputy - the expected capacitive current with a metal single-phase earth fault;
I _dgr is the known value of the current of the extinguishing reactor in this section of tires;
I _bases - the known current value of a parallel-connected unregulated basic arc suppression reactor (in its absence, this value is zero);
f ₅₀ - rated industrial frequency of the network (for Russia, 50 Hz);
f _p is the found resonance frequency of the inductance of the connected arcing reactors with the current network capacity to ground;
and at the time of the occurrence of a single-phase earth fault - storing the measurement result, turning off the variable frequency generator and resonant tuning of the arcing reactor in accordance with the result of the last measurement, characterized in that a transformer-type single-phase controlled reactor with a short circuit voltage between windings 100 is used as an arcing reactor %, and its resonant tuning in the single-phase circuit mode in accordance with the previously found value of the capacitive current of the network lyayut selection required inductive impedance at the terminals of the secondary winding via a switch and set a sufficient number of resistances with values proportional to the number of degrees of a number 2 ^n, which may be connected to the terminals of the secondary reactor winding in series with the ability to bypass the corresponding key switch of any of them, or in parallel, with connecting the corresponding switch keys with the required set of resistances, while the fixed values the inductive reactance of the reactor for measuring the capacitive current of the network in the normal mode of its operation is provided by the same switch by shorting the secondary winding of the reactor to a short-circuit or to a given resistance, and the possibility of the selective action of the maximum current protection at the time of the occurrence of the SCR is provided by the same switch due to short-term overcompensation with a short-circuited secondary or due to the active component of the reactor current with short-term connection to the terminals of the secondary quipment resistance.

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