The reactive power compensator

 

(57) Abstract:

Area of use: for the three-phase voltage substations (industrial, traction and forming part of the power systems for compensation and reactive power control. The inventive compensator contains a three-phase bridge with lockable gates included in the reactor, two Converter block and capacitors for surge suppression. Each Converter unit contains two groups of three lockable valves and the reactor between them in the branch DC. One group of valves has an angle regulation2=1+ and the other3=1- where1- the angle of the control valve three-phase bridge, the angle value and the ratio between the constant currents of the three-phase bridge Converter blocks are selected so as to reduce the content of higher harmonics in the input current compensator. 3 Il, 1 table.

The invention relates to power engineering and can be used on three-phase voltage substations (industrial, traction and forming part of the power systems for compensation and reactive power control.

Famous new reactive power compensator before the district thyristor compensator [2] is they give reactive power due to the forced commutation of the current in the negative angles regulation. As a result, for issuance to the power grid reactive power is not required structures capacitor Bank corresponding capacity.

In a known compensators to improve the quality of the input current (to reduce the content of higher harmonics) are used converters high pasnosti 12,18 and 24-phase [1].

Their lack of need to use one winding or several two-winding transformers, the impossibility of a direct connection of the Converter to the tires of three-phase voltage.

Closest to the invention is the compensator with one two-winding transformer, three-phase bridge with lockable gates and capacitors to limit surges that occur when forced, almost instantaneous switching current lockable gates [3].

The disadvantage of this compensator in the quality of its input current, which contains higher harmonics of order n = 6k 1, where k = 1,2,3..., has a high THD (about 30%).

TSE is of the compensator directly to the tires without the use of a transformer.

The essence of the invention lies in the fact that the proposed compensator to its entrance in addition to the three-phase bridge connected two Converter unit with multi-directional lockable gates. Each block contains two groups of valves and the reactor between them in the branch DC. One group of three valves has an angle regulation2=1+ and another group3=1- where1- the angle of the control valve three-phase bridge.

The angle value and the ratio between the constant current Id1three-phase bridge and a constant current Idthe first and second unit are selected so as to reduce the content of higher harmonics in the input current compensator. Good results are obtained when = 24aboutand Id1= Idor = 30aboutand Id1= Id.

Adding these two Converter blocks improves the quality of the input current compensator due to the formation of the three input phase currents of the bridge and both blocks and produce a three-stage current, similar in its shape to a sine wave. Note that adding two Converter blocks leads to a corresponding increase in power compensator and therefore obiecana diagram of the proposed compensator; in Fig.2 and 3 are graphs showing the form of the compensator currents.

Three-phase input of the compensator 1 (Fig.1) is connected capacitors 2, three-phase bridge 3 with lockable gates 4 and reactor 5, the first converting unit 6 with lockable valves 7 and 8 and the reactor 9, and the second Converter unit 10, which differs from block 6 only reverse the direction of the gates.

Capacitors 2 provide limitation of overvoltage arising from virtually instantaneous switching current lockable gates. Power capacitor 2 does not exceed 15% of the nominal power of the compensator. Capacitors 2 can be connected in a "star" (Fig.1) or on a "triangle".

When the compensator with the consumption of reactive power valves 4 three-phase bridge 3 are angle regulation1= 90about- where the angle depends on the power losses in the compensator, its value lies in the range 1about. When the compensator with the issuance of reactive power angle1= -90about+ .

Groups of three lockable valves 7 Converter blocks 6 and 10 have the angle regulation2=1and groups of three lockable valves 8 of these blocks - angle mode is constant current Idthe first and second Converter block are selected so as to reduce the content of higher harmonics in the total current of the bridge and both blocks and, as a consequence, in the input current compensator.

Good results in reducing the higher harmonics in the input current are obtained in two variants: = 24about, Id1= Id; = 30about, Id1= Id.

Graphics currents compensator for the first variant built on Fig.2 assuming constant currents of the bridge 3 and blocks 6 and 10 fully smoothed reactors 5 and 9. Relative to the time axis 11 shows the phase current i1at the entrance of the bridge 3, relative to the time axis 12 and 13, respectively phase currents i2and i3valves 7 and 8 two Converter blocks 6 and 10. Built timelines phase current i1, i2and i3belong to the same phase. In accordance with the angle regulation2current i2ahead of the current i1angle = 24about.

Similarly, in accordance with the angle regulation3current i3lags the current i1on the same angle = 24about. Relative to the time axis 14, we plot the phase current i, which is a sum of phase currents of the bridge and three-phase bridge.

Input current compensator consists of two components: current converters i and a relatively low current of the capacitor 2, therefore, the quality of the input current can be judged by the quality of the current transformers i.

Current converters i contains the first harmonic of i(1)and higher harmonics i(n). The first harmonic of i(1)it is shown in Fig.2, its effective value

I(1)= (1+2cos24)Id= 2,20 Id.

When the compensator angle regulation of three-phase bridge -90aboutthe first harmonic of i(1)current converters ahead of the corresponding phase voltage U on the 90aboutas shown in Fig.2. The compensator thus shows the electrical network to which it is attached, reactive power. When190aboutthe first harmonic of i1current transducers behind at the same angle from the voltage compensator consumes reactive power value (issued and consumed) is subject to a small change of angle control valves, which leads to a change of the currents Id1and Id.

The relative importance of each of the higher harmonics of order n in the current transducers i of the version under consideration to/P> The results of the calculation of I(n)*for the first eight harmonics contained in the currents i1, i2and i3shown in the table. For comparison it also lists the known values of I(n)*for the current i1three-phase bridge.

These tables describe the reduction in the content of higher harmonics in the input current of the proposed compensator. When Id1= Idand = 24aboutin the input current of the proposed compensator is missing 5-th and 25-th harmonic, the other harmonics are reduced. To improve the quality of the input current is especially important exception of the 5th harmonic and a significant decrease in the magnitude of the 7th and 11th harmonics. The THD of the current i of about 10%, about 3 times less than for the current i1.

Schedule DC converters i, for the second variant of its formation, when Id1= Idand = 30aboutbuilt on Fig.3. Was a well-known classical form of the input current 12-phase Converter. This current i contains the first harmonic and higher harmonics of order n = 12k 1, where k = 1,2,3, . .. There are no harmonics, for which n = 5, 7,17, 19... the Relative values of the remaining harmonics (n =11,13,23,25...) are the same as in

Thus, both options give good results in the decrease in the input current compensator higher harmonics and, as a consequence, to improve its quality.

Can be applied to other variants of the formation of the three-current transformers i. So, for example, to exclude it 7th harmonics should Id1= Idset angle = 17,1about. In this embodiment, the relative values of the 5th and 11th harmonics, respectively, of 7.9% and 3.1%, the THD of the current is about 13%.

The choice of one or another variant of formation of the three-step current (ratio between the Id1and Idand the value of the angle ) depends on the specific parameters of the electric network, which connects the compensator (primarily from the frequency characteristics of its reactance) and from the requirements to the quality of the input current compensator.

The REACTIVE POWER COMPENSATOR containing a three-phase bridge with lockable valves, reactor, included between the poles of the bridge, and capacitors connected to the three phase input of the compensator on a "star" or "triangle", wherein the input of the compensator additionally attached two preobrazuemyh valves and the reactor between them in the branch DC the first and second groups of gates are angles regulation

2=1+ and3=1- ,

where

1- the angle of the control valve three-phase bridge,

and the angle is selected within 17,1o30oprovided that the ratio

1 ,

where I is the constant current three-phase bridge;

Id- DC Converter units.

 

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