RU2796196C1 - Stand for identifying short-circuit currents of inter-substation zone of traction network - Google Patents

Abstract

FIELD: power supply.

SUBSTANCE: invention is related to a power supply system for a traction network and can be used to identify the short-circuit (SC) currents of an inter-substation section of an alternating current traction network with two-way power supply. The external power supply circuit is represented by three resistances Z₀₁, Z₀₂, Z₁₂ connected in a "triangle" scheme. Resistances Z₀₁ and Z₀₂ connect the inputs B_A and B_B of substations A and B with the second output of power source U_o, and resistance Z₁₂ connects the same inputs of substations A and B. Resistance Z₁₂ is calculated based on the actual cross section and length of the line. Resistances Z₀₁ and Z₀₂ are determined using the following expressions:

Z₀₁ = [(Z₁₂)²-2Z_C1Z₁₂]/[2(Z_C1-Z₁₂-Z_C2)] – √[(Z₁₂)⁴+4Z_C1Z_C2(Z₁₂)²]/[2(Z_C1-Z₁₂-Z_C2)], Z₀₂ = [(Z₁₂)²-2Z_C2Z₁₂]/[2(Z_C2-Z₁₂-Z_C1)] – [√{(Z₁₂)⁴+4Z_C1Z_C2(Z₁₂)²}]/[2(Z_C2-Z₁₂-Z_C1)], where Z_C1 and Z_C2 are SC resistances at inputs B_A and B_B of traction substations A and B. Based on the calculated resistances, the voltage of power source U_o and the readings of ammeters A_A and A_B, short-circuit currents I_A and I_B are determined for the corresponding circuits.

EFFECT: improving the accuracy of determining SC currents.

1 cl, 1 dwg

Description

The invention relates to a power supply system for a traction network, namely to the development of a stand for determining short-circuit currents of an inter-substation section of an AC traction network with two-way power supply by calculating the resistance of the short circuit.

Calculations of short-circuit currents in the traction network of railways are carried out according to regulatory documents [1]. However, in [2, 3] it was shown that in some cases an error in the calculation of the short-circuit current is possible with an incomplete scheme of the external power supply system (ESS). The danger of a large error in the calculation of short-circuit currents is manifested, first of all, by the subsequent incorrect calculation of relay protection.

At the time of design calculations, in most cases, for various reasons, there is no complete external power supply scheme for traction substations, and therefore the results of calculations in the project in some cases are given out as approximate ones. However, before the first switching on of traction substations after installation and commissioning, such an SHE scheme (even if it is temporary) already exists, but even in this case, the calculation according to the regulatory document is made with an error, since the equivalent circuit does not take into account the parallel operation of two traction substations, and the calculation practically performed by ignoring the second adjacent substation. Therefore, it is necessary to clarify the calculation of short-circuit currents for two-way power supply of the traction network.

Attempts to refine calculation methods were made in [3] and [4]. However, they were associated with additional conditions for organizing short circuit experiments [3] or with the need for additional calculations of line resistances to traction substations [4].

We accept [3] as a prototype. It considers a stand for determining short-circuit currents in a traction network, containing two traction substations A and B with resistances of traction transformers of each substation with a voltage of 110 kV / 27.5 kV (220 kV / 27.5 kV) for two-way power supply of the traction network, which, when short circuit (SC) represents a three-beam resistance star, two beams of which ZtcA and ZtcB are connected to the first terminals of the transformer resistances, the second terminals of which are connected to the first terminals of the equivalent resistances of the 110 (220) kV supply lines of traction substations, and the third beam of the three-beam star includes an equivalent resistance Z _AB of the short circuit, and connect it to the first output of the source.

The disadvantage of determining short circuit currents according to the prototype [3] is the need to organize additional experiments of real short circuits at existing traction substations. However, at the time the traction substations are put into operation, there are already data on the short circuit power (or short circuit resistance) at the inputs of traction substations from the power system, but, as indicated above, the existing calculation methods are performed with an error.

The purpose of the invention is to improve the accuracy of calculating short circuit currents in the traction network using the data obtained from the power system on the short circuit power (or short circuit resistance) of adjacent traction substations.

To realize the purpose of the invention, three resistances of the external power supply system Z ₀₁ , Z ₀₂ , Z ₁₂ connected in a "triangle" are introduced into the stand, and which connect the inputs of substations A and B (Z ₀₁ and Z ₀₂ ) with the second output of the power source, and the resistance Z ₁₂ connects the inputs of substations, while the resistance Z ₁₂ is calculated from the actual cross section and length of the line.

The power system provides short circuit power (Sc ₁ , Sc ₂ , MVA) or short circuit resistance (Zc ₁ , Zc ₂ , Ohm) at the inputs of 110 (220) kV for traction substations. The specified resistances Zc ₁ and Zc ₂ are determined as follows:

In these equations, the known values are Zc ₁ and Zc ₂ , and the unknowns are Z ₀₁ and Z ₀₂ . By transforming the system of equations (1) and (2), we obtain quadratic equations with unknowns Z ₀₁ and Z ₀₂ , which are determined by the expressions:

- then, according to the calculated resistances Z ₀₁ , Z ₀₂ , and Z ₁₂ in the corresponding circuits and according to the given voltage of the power source, the short-circuit currents I _A and I _B are determined.

To explain the proposed method for determining the short-circuit currents of the inter-substation zone, consider the block diagram (Fig. 1), where the following designations are introduced (all resistances are adjustable and reduced to a voltage of 27.5 kV):

Z _tsA and Z _tsV and - equivalent resistance of the traction network on the first (Z _tsA ) and second (Z _tsV ) sections of the inter-substation zone, at the junction point Z _tsA and Z _tsV on the diagram we show the short circuit point;

X _tA and X _tV - resistance of traction transformers at substation A (X _tA ) and substation B (X _tV );

Z _AB - resistance at the place of short circuit (Z _AB );

U ₀ - voltage (U ₀ ) of the power source, reduced to the traction winding, is taken according to the relevant requirements of regulatory documents [1];

В _А and В _В - 110 (220) kV inputs of traction substations А and В, respectively, for which the power system generates short-circuit resistances (Zc1 and Zс2);

Z ₀₁ and Z ₀₂ - resistance from the power source (RP) to the tires 110 (220) kV traction substations A (Z ₀₁ ) and B (Z ₀₂ ) respectively;

Z ₁₂ - line resistance VL-110 (220) kV between substations A and B;

A _A and A _B are ammeters.

The proposed stand with the considered resistance parameters essentially differs from the stand according to the prototype [3] by the introduced three adjustable resistances of the external power supply circuit according to the “triangle” scheme, which allow, without additional experiments, as it was in [3], to calculate the short-circuit currents for the given short-circuit powers by the power system in the traction network.

The sequence for determining short-circuit currents on the stand is as follows: first of all, the parameters of a given traction power supply system are set, then the resistances Z ₀₁ , Z ₀₂ are determined by the values Zc ₁ , Zc ₂ , Z ₀₂ according to formulas (3), (4). Due to the fact that when calculating short-circuit currents in the traction network, it is necessary to calculate two-phase short circuits of the external power supply system and traction transformers, their phase resistances are multiplied by a factor of 2 and the corresponding doubled resistances are set in the stand. According to the given voltage of the power source U ₀ and the corresponding resistances on the stand, according to the readings of the ammeters A _A and A _B , short-circuit currents I _A and I _B are determined in the corresponding circuits. Calculations are repeated for all short circuit points, which are set by changing the resistances Z _tsA and Z _tsV (Fig. 1).

The technical and economic effect is manifested in the fact that the calculations of short-circuit currents are specified and, accordingly, the calculations of relay protection are specified. This simplifies the calculation procedure in comparison with the prototype, since there is no need to perform additional short circuit experiments [3].

Literature

1. STO 07.021.4-2015. Protection of railway power supply systems from short circuits and overload. Part 4. Methodology for selecting protection settings in the AC traction power supply system. JSC Russian Railways.

2. German L.A., Subkhanverdiev K.S. Evaluation of the error in calculating short-circuit currents in an alternating current traction network. Electronics and electrical equipment of transport, 2017, No. 1, p.5-10.

3. Patent 2705517 dated 12/26/2018. Stand for calculating short-circuit currents in an AC traction network (German L.A., Subkhanverdiev K.S., Serebryakov A.S.), Publ. 11/07/2019. Bull. No. 31.

4. Figurnov E.P., Zharkov Yu.I., Popova N.A. Equivalent circuits of the external power supply system. Electricity No. 8 2020 p.30-35.

Claims (6)

Stand for determining the short circuit currents of the intersubstation zone of the AC traction network with the calculation of the resistance of the short circuit circuit, containing an external power supply system to which two traction substations A and B are connected with the resistance of transformers X _tA and X _tV with a voltage of 110 kV / 27.5 kV or 220 kV / 27.5 kV for two-way supply of the traction network, which in the event of a short circuit (short circuit) is a three-beam resistance star, two beams of which Z _tsA and Z _tsV are connected to the first terminals of the resistances of the transformers X _ta and X _tv , the second terminals of which are connected to inputs of traction substations, and the third beam of a three-beam star, including the equivalent resistance Z _AB of the short circuit, is connected to the first output of the power source U _about , characterized in that three resistances of the external power supply system Z ₀₁ , Z ₀₂ , Z ₁₂ connected in "triangle", moreover, the resistances Z ₀₁ and Z ₀₂ connect the inputs B _A and B _B of substations A and B with the second output of the power source U _o , and the resistance Z ₁₂ connects the same inputs of substations A and B, while: - resistance Z ₁₂ is calculated according to the real section and the length of the line; - resistances Z ₀₁ and Z ₀₂ are determined by the expressions:

where Z _С1 and Z _С2 are short-circuit resistances at inputs В _А and В _В of traction substations A and B, provided by the power system, - according to the calculated resistances and the given voltage of the power source U ₀ , as well as according to the readings of the ammeters A _A and A _B , short-circuit currents I _A and I _B are determined in the corresponding circuits.

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