RU91182U1 - VOLTAGE FILTER OF SYMMETRIC COMPONENTS BASED ON A TRANSFORMER WITH A ROTATING MAGNETIC FIELD - Google Patents

Abstract

A voltage filter of symmetrical components based on a transformer with a rotating magnetic field, containing a toroidal core, on which primary windings are located, consisting of two windings for each of the three phases, located relative to each other with a 90 ° shift to produce a rotating magnetic field, the number of turns the first winding is twice as much as the second, the ballast resistor and capacitor, and the beginning of the first winding is connected to the end of the second winding, thus forming the first input of the filter, the end the first winding with a capacitor, then the capacitor is connected to a resistor, which, in turn, is connected to the beginning of the second winding, forming a second filter input, as well as multiphase secondary windings connected to the input of the multiphase rectifier.

Description

The utility model relates to measuring equipment, and more specifically to devices designed to isolate the symmetrical components of an electrical signal, and can be used as part of devices for measuring, protecting and signaling three-phase AC systems.

Known single-phase transformer with a rotating magnetic field (patent No. 2333562, class. IPC H01F 30/14), closest to the claimed utility model in design, which contains four primary windings located on the toroidal core, ballast resistor and inductance, multiphase secondary windings, with the beginning of the first winding connected to the end of the second winding, forming the first input of the device, the end of the first winding with the end of the third winding, the end of the second winding with the end of the fourth winding, end third th winding with ballast inductance, and the beginning of the fourth winding with a ballast, the other ends of which form a second input of the device when connected, and to obtain a rotating magnetic field, the first, second, third and fourth windings are located relative to each other on a toroidal magnetic core with a shift of 90 ° with the number of turns of the first and fourth windings twice as large as the second and third.

A single-phase transformer with a rotating magnetic field is close to the claimed voltage filter of the symmetrical components by the largest number of design features, but cannot be used as a filter of symmetrical components.

Also known is a filter of symmetrical components of an electric signal (patent No. 2209441, class IPC G01R 29/16), which is closest to the claimed utility model in its technical essence and the achieved result, in which the phase A clamp of the controlled signal is connected to the first input of the first adder, the clamp phase B is connected through the inverting input of the first differentiation unit to the second input of the first adder, and through the inverting input of the first proportional unit to the third input of the first adder, the clamp of phase C is connected through non-inv the rotary input of the second differentiation block with the fourth input of the first adder, and through the inverting input of the second proportional block, with the fifth input of the first adder, the output of which is connected through the non-inverting input of the third proportional block to the first output of the device, additionally contains the third and fourth differentiation blocks, the second and third adders and the fourth and fifth proportional blocks, and the phase A clamp is additionally connected to the first input of the second adder and to the first input of the third sum ator, phase B clamp is additionally connected to the second input of the second adder, connected to the second input of the third adder through the non-inverting input of the third differentiation unit, and to the third input of the third adder through the inverting input of the first proportional unit, and the output of the second adder through the non-inverting input of the fourth proportional unit connected to the second output of the device, the phase C clamp is additionally connected to the third input of the second adder, connected to the fourth input of the third adder without the inverting input of the fourth differentiation block, and with the fifth input of the third adder through the inverting input of the second proportional block, and the output of the third adder through the non-inverting input of the fifth proportional block is connected to the third output of the device.

To implement a filter of symmetrical components of an electric signal, a complex electronic base of semiconductor elements is required, which, compared with the proposed utility model, reduces the overall reliability of the device and increases its cost.

The objective of the utility model is to improve the protection of elements of power supply systems in case of asymmetric short circuits.

The technical result is to increase the reliability of power supply systems by improving the accuracy of relay protection and emergency automation in asymmetric emergency conditions.

The specified technical result is achieved in that the voltage filter of the symmetrical components based on a transformer with a rotating magnetic field includes a toroidal core on which primary windings are located, consisting of two windings for each of the three phases, located relative to each other with a 90 ° shift for obtaining a rotating magnetic field, and the number of turns of the first winding is twice as large as the second, ballast resistor and capacitor, and the beginning of the first winding is connected to the end in In this case, forming the first input of the device, the end of the first winding with a capacitor, then the capacitor is connected to a resistor, which, in turn, is connected to the beginning of the second winding, forming the second input of the device, as well as multiphase secondary windings connected to the input of the multiphase rectifier .

The developed voltage filter of symmetrical components based on a transformer with a rotating magnetic field is implemented for each of the three phases as follows: terminals 2 and 3 of the filter of each phase are connected to the input voltages. Further, the clamp 2 is connected to the beginning of the coil 4 and to the end 5 of the first winding, and the number of turns of the first of them is two times more than in the second. Thus, the magnetomotive forces of the two coils of each of the windings are mutually subtracted. In series with the coil 4, a capacitor 6 and a resistance 7 are included to provide the necessary phase shift angle between the currents of both branches of the circuit. Secondary windings 8 are made in the form of two systems, each of which consists of three phases located relative to each other at an angle of 120 °. In turn, these two winding systems are spatially shifted at an angle of 30 ° relative to each other. The ends of the unwindings are connected to the inputs of a multiphase rectifier 9, the output of which forms a rectified voltage signal of direct or reverse sequence.

The novelty of the claimed technical solution lies in the fact that this device can be implemented using a combination of windings located relative to each other at certain angles.

According to the scientific, technical and patent literature, the authors are not aware of the claimed combination of features aimed at achieving the claimed technical result, and this solution does not follow clearly from the prior art, which allows us to conclude that the solution corresponds to the inventive step.

The operation of the device is based on the use of the method of symmetrical components. Let there be a system of phase stresses A, B and C, the values of which can be determined by the expressions:

where U _a , U _b , U _c are the amplitude values of the signals of phases A, B, C;

ω is the angular frequency of the signal, ω = 2πƒ,

ƒ - signal frequency;

φ ₁ - the angle at which the signal u _{b is} ahead of the signal ;

φ ₂ is the angle by which the signal u _{c is} ahead of the signal u _a .

In accordance with the specified method, the expression for the direct sequence component u _{a1 of the} electrical signal of phase A has the form:

where a is the operator of a three-phase system;

a = e ^{j · 120 °} ; a ² = e ^{j · 240 °} ; e = 2.71828 ...

The expression for the reverse sequence component u _{a2 of the} electrical signal of phase A has the form:

These voltages determine the presence of currents that create magnetomotive forces, which ensure the transformation of signals into secondary windings of the filter and are described by the following expressions reflecting the angles of phase shifts of magnetomotive forces:

Where , , and - amplitude values of the magnetomotive forces of the phases

In normal operation, when considering the windings in phases with the indicated spatial shifts, we obtain:

With equality we have:

This is a direct sequence, which forms a direct sequence voltage in the secondary windings in the form of a multiphase system. When rectifying this signal, the amplitude value of the voltage of the direct sequence U _1m is extracted.

If a system of negative sequence current vectors is supplied, then

In accordance with the expression (5):

Therefore, the above device with the indicated arrangement of the windings forms a direct sequence filter.

To obtain a reverse sequence voltage filter, it is necessary to connect a three-phase voltage system so that phases B and C have a shift of 240 ° and 120 ° relative to phase A, respectively, that is, without changing the design of the filter device, swap the connected phase B and C signals at the filter input. Then the angles of spatial phase shifts can be reflected by the expressions:

If you apply a system of direct sequence vectors to the input of the voltage filter of the negative sequence, we obtain the following values of magnetomotive forces:

If a negative sequence vector system is fed to the filter input, we obtain the following values of magnetomotive forces:

Thus, in the secondary windings of the filter due to the magnetomotive forces f _{Σ of the} rotating magnetic field, a negative sequence voltage is generated. Therefore, the above device with the specified location of the windings forms a voltage filter of the negative sequence.

In emergency operation during a two-phase short circuit of phases B and C, the magnetomotive forces, taking into account the angles of spatial phase shifts, will have the following values for calculating a component of the direct sequence:

Direct sequence magnetomotive forces:

.

When calculating the component of the reverse sequence, the magnetomotive forces, taking into account the angles of spatial phase shifts, will have the following values:

Inverse sequence magnetomotive forces:

Equality of magnetomotive forces modulo | f _1Σ | = | f _2Σ | and the phase indicates the correspondence of the direct and reverse sequences to theoretical results [S. Ulyanov Electromagnetic transients in electrical systems. Textbook for electrical and energy universities and faculties. M., "Energy", 1970].

The figure 1 presents a circuit diagram of the primary windings of the voltage filter of the symmetrical components. The figure 2 shows a circuit diagram of the secondary windings of the voltage filter of the symmetrical components. In the figure, the primary windings of the filter are located on the toroidal core 1. Clips 2 and 3 are input terminals of the device of each of the three phases. The voltage filter for each phase contains two primary counter-connected windings (4 and 5) having a spatial shift of 90 °, as well as a ballast capacitor 6 and resistor 7. In the grooves of the toroidal core 1, a multiphase secondary winding 8 is also laid in the form of two systems, each of which consists of three phases located relative to each other at an angle of 120 °. In turn, these two winding systems are spatially shifted at an angle of 30 ° relative to each other. The ends of the windings are connected to the inputs of a multiphase rectifier 9, the output of which forms a rectified voltage signal of direct or reverse sequence.

The developed voltage filter of symmetrical components is implemented for each of the three phases as follows: terminals 2 and 3 of the filter of each phase are included in the current circuits. Further, the clamp 2 is connected to the beginning of the coil 4 and to the end 5 of the first winding, and the number of turns of the first of them is two times more than in the second. Thus, the magnetomotive forces of the two coils of each of the windings are mutually subtracted. In series with the coil 4, a capacitor 6 and a resistance 7 are included to provide the necessary phase shift angle between the currents of both branches of the circuit. Secondary windings 8 are made in the form of two systems, each of which consists of three phases located relative to each other at an angle of 120 °. In turn, these two winding systems are spatially shifted at an angle of 30 ° relative to each other. The ends of the unwindings are connected to the inputs of a multiphase rectifier 9, the output of which forms a rectified voltage signal of direct or reverse sequence.

Each phase of the voltage filter of the symmetrical components contains two identical windings with inductors 4 (L ₁ ) and 5 (L ₂ ), identical in design, located on the toroidal core at an angle of 90 ° through which currents flow and , equal in magnitude and having a phase shift of 90 ° with each other. This creates a rotating magnetic field with two magnetomotive forces formed by these currents in these windings.

Define the relationship between the parameters of the branches of the unwinding phases provided that the currents are equal and and the presence of a phase shift between them of 90 °. If the natural active resistances of coils 4 and 5 are much less than their inductive resistances, then the resistance of the branches of the primary windings of a single-phase transformer with a rotating field will be equal to:

where R ₁ - active ballast resistance 7;

C ₁ is the capacitance of the capacitor 6.

Let the following relations be true:

L ₁ = L ₂ ;

R ₁ = ωL ₂ .

Then we get:

Therefore, the ratio for the magnetomotive forces of the two coils will be:

Thus, magnetomotive forces and are equal in absolute value and are shifted relative to each other by an angle of 90 °, forming a rotating magnetic field. In this case, electromotive forces are induced in the secondary windings corresponding to their spatial arrangement for a multiphase system.

The inventive voltage filter of the symmetrical components works as follows: a voltage of 50 Hz and a phase shift of 120 ° relative to each other is applied to terminals 2 and 3 of each phase. The primary winding of the phase (4-7) by means of counter-connected sections creates a system of two perpendicular and equal in magnitude magnetomotive forces ( ) in the magnetic system 1. The described magnetomotive forces of each phase in turn create a rotating magnetic field, which induces in the secondary windings 8, forming two three-phase winding systems spatially offset from each other by an angle of 30 °, electromotive forces also have a pair phase shift 30 °, as a result, we obtained a system of voltages with the number of phases equal to 7, which, as a result of connecting to a multiphase rectifier 9, allows to obtain a constant signal at the filter output equal to the current amplitude of one of the following lnostey.

To obtain a direct sequence voltage filter, it is necessary to connect a three-phase voltage system to the input terminals of the filter, while the primary windings, according to formula (2), must be located at an angle of 120 ° relative to each other so that phases B and C have a shift relative to phase A at 120 ° and 240 ° respectively.

To obtain a negative sequence voltage filter, it is necessary to connect a three-phase voltage system to the input terminals of the filter, while the primary windings, according to formula (3), must be located at an angle of 120 ° relative to each other so that phases B and C have a shift relative to phase A in 240 ° and 120 ° respectively, that is, in comparison with a direct sequence voltage filter, it is necessary to interchange the connected phase B and C signals at the input of the filter without changing the design of the device.

The use of a filter of symmetrical components based on a multiphase transformer with a rotating field allows you to receive the signal of the corresponding sequence at the output of this filter, and also extends the capabilities of the proposed device. The multiphase of the output windings of the voltage filter of the symmetrical components allows to reduce the ripple of the resulting output voltage and to select the amplitude values of the voltages of the direct sequence U _1m and the reverse sequence U _2m, respectively.

Claims (1)

A voltage filter of symmetrical components based on a transformer with a rotating magnetic field, containing a toroidal core, on which primary windings are located, consisting of two windings for each of the three phases, located relative to each other with a shift of 90 ° to obtain a rotating magnetic field, the number of turns the first winding is twice as much as the second, the ballast resistor and capacitor, and the beginning of the first winding is connected to the end of the second winding, forming the first input of the filter, the end the first winding with a capacitor, then the capacitor is connected to a resistor, which, in turn, is connected to the beginning of the second winding, forming a second filter input, as well as multiphase secondary windings connected to the input of the multiphase rectifier.