RU2116206C1 - Method for determining equalizing current through section of ac traction network with double-ended power supply - Google Patents

Abstract

FIELD: electrified railway transport; electrical design of ac traction networks. SUBSTANCE: traction circuit is checked for no-load condition by relative content of third current harmonic and unknown current is calculated using known values of power and voltage. Analytical relations for mean values of equalizing current and its phase are given in description of invention. Method is implemented without limiting traffic conditions. Desired measurements can be entrusted to operating personnel. EFFECT: facilitated procedure; improved accuracy of determining equalizing current. 2 cl, 1 dwg

Description

 The invention relates to electric rail transport, in particular to methods for determining surge current in a traction AC network.

 There is a method of determining equalizing currents in a section of an alternating current traction network with two-way power supply, based on measuring supply voltages both modulo and phase. Knowing these values with the known electrical parameters of the traction network allows you to determine the surge current. However, the task is complicated by the significant distance between traction substations (35-60 km) and the inability to measure the phase difference of the voltage of the substations supplying this feeder zone. This necessitates the use of radio signals, for example, accurate time signals transmitted by the Mayak program. The radio signal through the radio signal receiving unit is recorded by loop oscilloscopes installed in substations supplying the inter-substation zone. Simultaneously with the recording of radio signals are recorded voltage. The oscillograms determine the effective voltage values and their phase shifts relative to the radio signal. From the phase shifts relative to the radio signal, the phase shift between the voltages is calculated. Using the found values, the surge current is calculated.

 The method is time-consuming and its implementation requires the use of expensive equipment and the involvement of qualified personnel. The method relates to indirect measurement methods, since the voltage differences in absolute value and phase, found by direct measurements, allow one to calculate only a single observation of the equalizing current (see, for example, Issues of increasing the efficiency of electric rolling stock and traction power supply devices in the Far East and BAM: Interuniversity collection of scientific papers. Khabarovsk Institute of Railway Engineers. - Khabarovsk, 1986 - pp. 11-14).

 The closest technical solution to the proposed method for measuring surge current is a method for determining surge current, which requires a preliminary determination of the harmonic composition of the traction current and voltage of the traction substation in two modes: with two-way power supply and the second traction substation disconnected (see AS USSR N 1643228 A1 , 1991, B 60 M 3/02). Equalizing current is determined by an analytical expression containing the effective values of the higher harmonic components of the traction current with two-way power and with the second substation switched off, as well as the values of the phase shift between the first harmonics of the current and voltage in both modes. The expression is obtained under the condition that the harmonics coefficients of the traction current on the buses of the first substation are equal for two-sided and cantilever power. The method simplifies the determination of surge current, compared with the above, due to measurements at only one of the traction substations.

 However, the applied method has several disadvantages.

 To determine each observation of the surge current, each time a violation of the specified mode of operation of the traction power supply system is required, which consists in the forced switching from two-way to one-way power supply of the traction network section.

The accepted condition for the practical equality of the coefficient of non-sinusoidality with two-way power and a disconnected second traction substation is confirmed by numerous experimental studies
The volume of statistics is limited.

 The purpose of the present invention is to simplify and improve the accuracy of determining surge current.

где
W $\genfrac{}{}{0ex}{}{\text{(пр)}}{\text{a}}$ ,W $\genfrac{}{}{0ex}{}{\text{(пр)}}{\text{p}}$ - принятые в тяговую сеть активная и реактивная энергии за период отсутствия тяговой нагрузки;
W $\genfrac{}{}{0ex}{}{\text{(отд)}}{\text{a}}$ ,W $\genfrac{}{}{0ex}{}{\text{(отд)}}{\text{p}}$ - отданные из тяговой сети во внешнюю систему электроснабжения активная и реактивная энергии;
T - суммарное время протекания уравнительного тока в межподстанционной зоне за периоды отсутствия тяговой нагрузки;
U_кс - действующее значение напряжения в контактной сети.The proposed method for determining the surge current is to determine the total time of the surge current in the inter-substation zone by the coefficient of the third harmonic of the current. The instantaneous values of the current and voltage of the first traction substation determine the active W _a and reactive W _p energy during the total flow time of the surge current in the inter-substation zone for periods of no traction load during the set time interval for determining the surge current. The values of W _a and W _p can be both positive and negative. Positive values of active and reactive energy (reception) denote respectively W $\genfrac{}{}{0ex}{}{\text{(depart)}}{\text{a}}$ , W $\genfrac{}{}{0ex}{}{\text{(depart)}}{\text{p}}$ , negative (return) - W $\genfrac{}{}{0ex}{}{\text{(depart)}}{\text{a}}$ , W $\genfrac{}{}{0ex}{}{\text{(depart)}}{\text{p}}$ . Then the mean square value of the surge current and its phase in the steady state operation of the external and traction power supply systems are determined by the expressions:

Where
W $\genfrac{}{}{0ex}{}{\text{(etc)}}{\text{a}}$ , W $\genfrac{}{}{0ex}{}{\text{(etc)}}{\text{p}}$ - active and reactive energy taken into the traction network for the period of absence of traction load;
W $\genfrac{}{}{0ex}{}{\text{(depart)}}{\text{a}}$ , W $\genfrac{}{}{0ex}{}{\text{(depart)}}{\text{p}}$ - active and reactive energy given from the traction network to the external power supply system;
T is the total time flow of equalizing current in the inter-substation zone for periods of absence of traction load;
U _x - the effective value of the voltage in the contact network.

 The set time interval of the equalizing current limits the bottom of the finished cycle of the load curve (usually one day) of the electric power system. The total flow time of equalizing current T in the inter-substation zone depends on the size of train traffic in the area under study. At low sizes of motion, T is commensurate with the established time interval for determining the equalizing current. At high traffic sizes, the value of T consists of time intervals for the absence of trains on the site, provided for repair work.

 The solution to the technical problem is illustrated in the drawing. The drawing shows a structural diagram of a measuring equalization current installation containing an electric energy meter - 1, an equalizing current control unit - 2 and a timer - 3. At the first traction substation in two-way power mode, current and voltage from current and voltage measuring transformers are supplied to the electric energy meter - 1, allowing to take into account the reception and return of active and reactive energy. The moment of the beginning of the absence of traction load in the substation zone between the first and second traction substations is determined by the equalizing current control unit - 2, which is designed to detect the absence of traction load in the substation zone by analyzing the value of the third harmonic coefficient of the traction current. Taking into account that the surge current, unlike the traction current, is almost sinusoidal, the coefficient of the third harmonic of the current serves as an informative parameter about the absence of traction in the inter-substation zone and the presence of only the surge current. In the absence or insignificant content of the third harmonic current curve, the analyzed current is taken equalizing. Experimentally establish the maximum possible value of the current coefficient of the third harmonic in the surge current. This value is significantly lower than the minimum value of the third harmonic coefficient in the presence of traction load. Two signals are generated in the equalizing current control unit - 2: the first one prohibits the operation of the electric energy meter - 1 in the presence of an electric traction load in the substation zone, the second starts a timer - 3 in the absence of an electric traction load. Upon completion of the set time interval for determining the surge current, for example, one day, the difference between the final and initial readings of the electric energy meters, the consumption of active and reactive energy are calculated, the timer is taken corresponding to the total flow time of the surge current in the inter-substation zone during periods of no traction load. Equalizing current is determined by the above formulas.

 The proposed method for determining equalizing currents allows measurements to be made without restricting the size of train movements, does not require the involvement of highly qualified personnel, since measurements can be performed by operational personnel. In addition, the proposed method does not require the use of expensive measuring and processing tools.

Claims (2)

1. A method for determining the surge current in a portion of an alternating current traction network with double-sided power supply, namely, that the current and voltage as a function of time are recorded at the first traction substation and based on them, a surge current is determined, characterized in that the start moment of absence of traction is established loads in the inter-substation feeder zone between the first and second traction substations by analyzing the relative value of the third harmonic of the current, starting from which the time intervals of the of the traction load, and from the values of current, voltage and total time, the active and reactive energy received into the traction network and supplied from the network are determined before the end of the set time interval and, with a known voltage in the contact network, the average value of the equalizing current and its phase in the steady state are determined external and traction power supply systems according to the formulas

where w $\genfrac{}{}{0ex}{}{\text{(etc)}}{\text{a}}$ , W $\genfrac{}{}{0ex}{}{\text{(etc)}}{\text{p}}$ - active and reactive energy taken into the traction network for the period of absence of traction load;
W $\genfrac{}{}{0ex}{}{\text{(etc)}}{\text{a}}$ , W $\genfrac{}{}{0ex}{}{\text{(depart)}}{\text{p}}$ - active and reactive energy given from the traction network to the external power supply system;
T is the total time flow of equalizing current in the inter-substation zone for periods of absence of traction load;
U _x - the effective value of the voltage in the contact network.  2. The method according to claim 1, characterized in that the set time interval for determining the equalizing current is limited from below to the end of the load curve in the power system, for example, for one day, and from above to the beginning of the change in the power system parameters, for example, by disconnecting one of the supply lines for revision, the total time T of the equalizing current flow in the inter-substation zone is determined from below, with intensive train sizes, the total time of absence of trains in the traction network section with planned preventive works, for example, repair of a railway track, and from above - by low sizes of train movements, commensurate with the agreed time interval for determining equalizing current.