CN201797318U - Reactance Adjustable Reactive Power Compensator - Google Patents

Abstract

A reactance-adjustable reactive power compensator comprises an adjustable reactor and a capacitor bank. The adjustable reactor and the capacitor bank are parallelly connected onto a circuit after being serially connected with each other, the adjusting reactor adopts a magnetic valve dry-type iron core reactor, and is mainly used for restraining power harmonics and limiting switching-on inrush current when in high and low voltage power grid reactive power compensation, and the reactor leads reactance rate to meet certain requirements so as to achieve the best harmonic restraining effect by means of adjusting inductive reactance value of the reactor according to conditions of power harmonics, so that functions of not only compensating power grid reactive power but avoiding changing effect of restraining certain harmonic.

Description

Reactance adjustable reactive power compensator

technical field

The utility model relates to an adjustable reactance reactive power compensator for suppressing grid harmonics and limiting closing inrush current during dynamic compensation of reactive power of high and low voltage grids. the

Background technique

At present, both at home and abroad have accumulated relatively rich experience in reactive power compensation and harmonic control, and there are relatively mature products at home and abroad. Reactive power compensation usually adopts the method of switching capacitors, and harmonic control usually uses wireless Harmonic control is achieved by using a source or an active filter. The passive filter is mainly composed of a reactor and a capacitor in series, which has the advantage of being easy to design, but its filtering effect depends on the impedance characteristics of the system. Although active power filters have great technical advantages that passive filters do not have, it is not realistic to completely replace passive filters in power systems at present, because compared with passive filters, active The high cost of power filters is the main reason for limiting the popularization and use of active power filters. Therefore, passive filters are still widely used at present. the

Due to the complex load conditions of the power grid, most power grids need to perform reactive power compensation and harmonic control at the same time, so two sets of devices are required. Moreover, directly connecting capacitors in parallel to the power grid for reactive power compensation will generate a certain amount of noise on the power grid. Harmonic amplification, series reactors in the circuit of parallel capacitors is a very effective and feasible method to solve the problem of harmonic amplification. If the reactance rate of the reactor is selected properly, the effect of higher harmonics can be suppressed. Therefore, the current reactive power compensation devices in the domestic power grid connect fixed reactors in series with the capacitor circuit, which can not only compensate the reactive power in the power grid, but also suppress the harmonics in the power grid. In the actual power grid, the load is constantly changing, and the power factor is also changing at any time. In order to adapt to the changing power factor of the power grid, it is required to use multiple groups of capacitors to switch in groups to achieve the purpose of dynamically compensating the power factor of the power grid. If the number of capacitor groups changes, but the inductance value of the reactor remains unchanged, the effect of harmonic suppression will not be achieved, and the effect of harmonic amplification may also occur. In order to achieve both power compensation and grid harmonic suppression, multiple sets of reactors are usually used in series with multiple sets of capacitors. The disadvantage of this method is that multiple sets of reactors are required, which increases equipment investment and floor space. the

Through the above analysis and the actual operation of the power grid, the reactance adjustable reactive power compensator can realize the compensation and filtering effect of reactive power compensation and harmonic control, which can not only reduce equipment investment, but also reduce the equipment footprint. At the same time, the dual effects of reactive power compensation and harmonic control are realized. Therefore, the dry-type iron core reactor with adjustable reactance rate has very important practical application value. the

Utility model content

The technical problem to be solved by the utility model is the inductive reactance value of the series reactor, that is, the reactance rate can be continuously adjusted within a certain range, so as to automatically adjust when the grid harmonics and reactive power change, so that the reactive power compensation and Harmonic suppression achieves the best effect, and can reduce equipment investment and equipment footprint. the

In order to solve the above technical problems, the utility model provides an adjustable reactance reactive power compensator for suppressing harmonics and limiting inrush current during reactive power compensation of high and low voltage power grids. the

The adjustable reactance reactive power compensator includes an adjustable reactor and a capacitor bank; the adjustable reactor and capacitor bank are connected in series and connected in parallel on the line. the

The capacitor bank of the reactance adjustable reactive power compensator includes multiple sets of switches and multiple sets of capacitors; each switch and each capacitor are connected in series and then connected in parallel to form a capacitor bank. the

The adjustable reactor of the adjustable reactance reactive power compensator consists of a reactor coil and a reactor core. The saturation degree of the magnetic circuit changes the inductive reactance value of the reactor. the

The switch of the reactance adjustable reactive power compensator can be an AC contactor, a thyristor or a composite switch; if the switch is an AC contactor, a fuse is connected in series in the AC contactor circuit to protect the switch. the

The utility model has positive effects: (1) The inductive reactance value of the reactor is continuously adjusted by adjusting the saturation degree of the magnetic circuit of the reactor iron core, so that the reactance rate is 0.1-1%, 4.5%-6% and 6%- 12% or other ranges are continuously adjustable, which can meet the best suppression effect on grid harmonics when grid harmonics change. (2) The reactance-adjustable reactive power compensator of the utility model can be combined with the capacitor bank arbitrarily to keep the reactance rate unchanged, realize the reactive power compensation of the grid, and keep the function of suppressing harmonics unchanged. (3) The reactor coil and iron core of the reactance-adjustable reactive power compensator of the utility model are made of epoxy casting, which can be either dry-type natural cooling or oil-immersed cooling, and is easy to install.

Description of drawings

Fig. 1 is the connection diagram of the adjustable reactor and capacitor bank of embodiment 1

Fig. 2 is the composition schematic diagram of the capacitor bank of embodiment 1

Fig. 3 is the schematic diagram of the adjustable reactor of embodiment 1

Fig. 4 is the schematic diagram of the shunt capacitor device connected to the bus bar and the single-phase value circuit of embodiment 1

Fig. 5 is the series-parallel resonance schematic diagram of embodiment 1

Detailed ways

See Fig. 1 and Fig. 2, the reactance adjustable reactive power compensator of the present embodiment, comprises adjustable reactor 1 and capacitor bank 2; Adjustable reactor 1 and capacitor bank 2 are connected in parallel on the line after being connected in series; Capacitor bank 2 comprises Multiple sets of switches 2-1 and multiple sets of capacitors 2-2; each switch 2-1 and each capacitor 2-2 are connected in series and then connected in parallel to form a capacitor bank. The adjustable reactor 1 of this embodiment is composed of a reactor coil 1-1 and a reactor core 1-2. The reactor core 1-2 adopts a variable section, and the section of the iron core is reduced by a small section in the middle of the iron core. , by changing the saturation degree of the small cross-section magnetic circuit to change the inductance value of the reactor, as shown in Figure 3 is the structure and circuit diagram of the magnetic valve adjustable reactor. The main iron core of the reactor is split into two halves, each with a cross-sectional area of A _y and a length of l~l _t . The difference is that each half of the iron core has a small section with a length of l _t and an area of A _yt (A _yt <A _y ). The four windings with the number of turns of N/2 are symmetrically wound on the two half-core legs respectively. The upper and lower windings on each half of the iron core have a tap with a tap ratio of δ=N ₂ /N, and thyristors K _P1 and K _P2 are connected between them. After the upper and lower windings of different iron cores are cross-connected, they are connected to the power grid in parallel, and the freewheeling diodes are straddled on the cross terminals. It can be seen from Figure 2 that if K _P1 and K _P2 are not conducting, according to the symmetry of the winding structure, there is no difference between the reactor and the no-load transformer at this time. When the power supply is in the positive half cycle, the thyristor K _P1 bears the forward voltage, and K _P2 bears the reverse voltage. If K _P1 is triggered to be turned on (that is, two points a and b are at the same potential), the power supply will provide DC control voltage and current to the circuit through the winding with _N2 turns after autotransformation by the winding with a voltage ratio of δ. Similarly, if K _P2 is triggered to be turned on during the negative half cycle of the power supply, a DC control voltage and current will also be generated, and the direction of the control current is the same as that when K _P1 is turned on. In a power frequency cycle of the power supply, the turn-on of the thyristors K _P1 and K _P2 plays the role of full-wave rectification, and the diode plays the role of freewheeling. Changing the firing angles of K _P1 and K _P2 can change the size of the control current, thereby changing the saturation of the reactor iron core, and adjusting the capacity of the reactor smoothly and continuously. It can be seen from Fig. 1 that the iron core magnetic path of the magnetic valve type adjustable reactor has a larger area (area A _y , length ll _t ) and a smaller area (area A _yt , length l _t ) in series made. Because in the entire capacity adjustment range of the magnetic valve type adjustable reactor, the working state of the large-area section iron core is always in the unsaturated linear region of the magnetic circuit, and its reluctance is relatively small compared to the small-area l _t- section iron core, so it is ignored. It can be seen that the magnetic circuit of the magnetic valve-type adjustable reactor is a "valve-type" structure. When the small-section iron core with an area of A _yt is completely saturated, it is equivalent to all the magnetic valves being closed, and the magnetic resistance is the largest. At this time, the entire magnetic circuit is like An air gap with area A _y and length l _t (it should be noted that the core segment with area A _y is not saturated at this time). And when the small cross-section iron core segment with area A _yt is in the unsaturated linear region, the reluctance is very small, the magnetic force lines almost completely pass through it, and the magnetic valve is fully opened. In other cases, part of the magnetic flux will pass through the air gap with an area of A _y -A _yt , and the other part will pass through the small-section iron core segment. The reluctance of the former is linear, and the reluctance of the latter is nonlinear. Therefore, the reactor The magnetic circuit consists of two parallel reluctances.

Selection of single-phase capacity of series reactor: as shown in Figure 4, the device is connected to the busbar, and its capacitor bank is connected in series with the reactor. Generally, the three-phase is connected in a star-shaped neutral point without grounding, and the capacity of each phase is equal. 4 single-phase value loop representation. _The rated reactance rate of the device can be calculated by the following formula, namely: K=X _L /X _C , where U _C ＝I _C X _C , U _L ＝IC X _L , Q _L ＝U _L I _L ＝I _L ² X _L ＝KI _C ² X _C ＝KQ _C

It can be obtained that the single-phase capacity of the series reactor is equal to the single-phase capacity of the capacitor bank multiplied by the rated reactance rate K of the device. the

Selection of reactance rate K of series reactor: Parallel harmonic resonance: In power system, parallel capacitor bank is installed to compensate reactive power and increase voltage level. However, adding a parallel capacitor bank will change the frequency characteristics of the harmonic impedance of the system. For power frequency, the inductive reactance X _S of the system is very small, so resonance generally does not occur, but when the system contains harmonic components, it may occur with Parallel resonance of the system. As shown in Figure 5, n is the harmonic order; I _n is the harmonic current source in the grid; U _n is the harmonic current injection point bus harmonic voltage; nX _s is the system equivalent harmonic inductance; X _C /n is the harmonic reactance of the capacitor bank; nX _L is the harmonic inductive reactance of the series reactor of the capacitor bank.

Parallel resonance is the resonance generated by the system and the parallel capacitor bank. Its resonant frequency depends on the system harmonic inductance and capacitor bank harmonic capacitance (capacitor branch). The resonance condition is: system harmonic inductance = parallel capacitor harmonic capacitance Anti-series reactor harmonic inductance, namely nX _S ＝X _C /n-nX _L From X _S ＝ωL _S 、X _L ＝ωL _L 、X _C ＝1/(ωC) nωL _S ＝1/( nωC)-nωL _L is the resonant angular frequency ω=1/n(L _S +L _L )C and ω=2∏f, so the resonant frequency: f=1/2∏n(L _S +L _L )C. When the frequency of the nth harmonic is close to the resonant frequency f, parallel resonance will occur. At this time, the voltage and current in the circuit are in phase, and its equivalent harmonic inductance X _n = nX _S (nX _L -X _C /n )/nX _S +nX _L -X _C /n, because nX _S +nX _L ≈X _C /n when parallel harmonic resonance occurs, the denominator nX _S +nX _L -X _C /n≈0, so the value of X _n is very is large, and U _n =I _n X _n , so the resonant voltage U _n on the substation bus will be very high. The harmonic current distribution I _cn ＝I _nn Xs/(nX _S +nX _L -X _C /n) entering the capacitor bank branch; the harmonic current component entering the system I _sn ＝I _n (nX _L -X _C /n )/(nX _S +nX _L -X _C /n). The distribution of harmonic current entering the system and capacitor bank branch is different due to the difference of harmonic order, system reactance and series reactor reactance, and I _sn > I _n may appear, which is called system harmonic current amplification; also I _cn > _In may occur, which is called capacitor bank harmonic current amplification; when I _sn >I _n and I _cn > _In appear at the same time, it is called severe harmonic current amplification. When parallel resonance occurs, the harmonic current amplification reaches its maximum value.

As mentioned above, the condition for parallel harmonic resonance to occur is nX _s +nX _L =X _C /n, that is, nX _S +nKX _C =X _C /n, K=1/n ² -X _s /X _c . Adding series reactors to parallel capacitor banks is an effective measure to suppress harmonic current amplification, and the rated reactance rate of capacitor bank devices should be K>1/n ² -X _s /X _c . Assume that the short-circuit capacity of the bus bar at the installation place of the parallel capacitor bank device is S _d , then S _d = U ² /Xs, and the capacity of the capacitor bank Q _C = (3U ² /X _C ) ^-2 , so K>1/n ² -X _S /X _C can be deduced that K＞1/n ² -Q _C /S _d , Q _c ＞S _d (1/n ² -K) This is the verification avoidance given by the design specification for parallel capacitor devices The capacitor bank capacity of parallel resonance should be designed according to the background harmonics of the system when determining the group capacity of the capacitor group. When the group capacitors are operated according to various capacity combinations, the resonance capacity should be avoided as far as possible for verification, and serious amplification of harmonics should not occur. Harmony.

Series harmonic resonance: The series loop composed of series reactors and parallel capacitor banks has a condition for series resonance of the nth harmonic: nX _L = X _c /n, at this time, the series loop composed of series reactors and parallel capacitor banks The total reactance is zero, the current and voltage are in phase, and the loop current reaches the maximum value. To avoid series resonance, it should satisfy nX _L >X _C /n, that is, nKX _C >X _C /n, K>1/n ² , that is, K>1/n ² must be satisfied. It can be seen from the above analysis that the rated reactance K of the capacitor bank device that avoids parallel resonance must satisfy K>1/n ² -Q _C /S _d . Since the capacity of the capacitor bank is very small relative to the short-circuit capacity of the system, that is, the ratio of Q _C /S _d is very small, it is obvious that the value of the rated reactance rate K of the capacitor bank device that avoids series resonance is very close to the value of K that avoids parallel resonance. Therefore, in order to avoid slipping into the parallel resonance state due to various reasons during operation, a certain margin must be left when the rated reactance rate K of the capacitor bank device satisfies K>1/n ² in actual engineering.

The effect achieved: the reactance rate can be adjusted according to the harmonic situation of the grid to achieve the best harmonic suppression effect, and the reactance rate K=X can be maintained automatically by adjusting the inductance value of the reactor when switching capacitors in groups according to the reactive power of the grid _L /X _C remains unchanged to achieve the function of suppressing a certain harmonic.

Claims (4)

1. the adjustable reactive power compensator of reactance is characterized in that, comprises Regulatable reactor (1) and capacitor group (2); Regulatable reactor (1) and capacitor group (2) series connection back parallel connection are on the line.

2. the adjustable reactive power compensator of reactance as claimed in claim 1 is characterized in that, capacitor group (2) comprises many group switches (2-1) and multiple unit capacitor (2-2); Parallel with one another again after each switch (2-1) and each capacitor (2-2) series connection, constitute capacitor group (2).

3. the adjustable reactive power compensator of reactance as claimed in claim 1, it is characterized in that, Regulatable reactor (1) comprises that reactor winding (1-1) and core of reactor (1-2) constitute, core of reactor (1-2) adopts variable cross-section, the cross section of iron core is reduced in the middle of the iron core a bit ofly, change the induction reactance value of reactor by the degree of saturation of change small bore magnetic circuit.

4. the adjustable reactive power compensator of reactance as claimed in claim 2 is characterized in that switch (2-1) can be A.C. contactor, controllable silicon or combination switch; If switch (2-1) is an A.C. contactor, then in ac contactor circuit, be connected in series a fuse, with protection switch.

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