RU2018146C1 - Method of checking operating state of smoothing filter - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: method of estimating an operating state of a smoothing filter involves comparing harmonic parameter values measured at predertmined obtained ratio of dc Voltages with harmonic voltage parameter values normalized at the same ratio. EFFECT: enhanced normalization accuracy. 3 dwg

Description

 The invention relates to measuring technique and is intended to control the technical condition of the smoothing filter. Such filters are always installed in traction substations of direct current electric railways to protect wireline communication devices and railway automatics from the interfering influence of voltage harmony generated by substation converters and penetrate into the traction network.

Analogues of the proposed technical solutions are:
- a method based on the use of non-working converters of the traction substation of the measuring voltage, which has a sinusoidal shape and a frequency equal to the frequency of the harmonics smoothed by the filter;
- a method involving the measurement of the psophometric value of the voltage of the variable component at the output of the smoothing filter during power supply by the load converter;
- a method based on determining the ratio of the psophometric voltage measured in the previous method to the nominal value of the rectified voltage of the converter;
- a method of controlling the magnitude of the ratio (smoothing coefficient) of the psophometric value of the voltage of the variable component at the input of the smoothing filter (between the poles of the rectified voltage of the power converter and the psophometric value of the voltage of the variable component at the output of the filter, at the points of its connection and the load of the converter.

 For control according to the first method, it is required to deactivate the converter, the controlled filter and stop the load supply. Fulfillment of these conditions is associated with laborious shutdown operations of power equipment. With regard to electric railways, such control is accompanied by a disconnection of the traction substation. This limits the carrying capacity of railway transport, reduces the reliability of the protection devices of the power supply system. The known method does not allow to quickly monitor the technical condition of the smoothing filter during its operation, which reduces the effectiveness of this control method.

 The remaining three known methods allow you to determine the diagnostic parameters during the operation of the smoothing filter and therefore are devoid of the above disadvantages. However, these methods do not provide a depth of control sufficient to identify defects in all filter elements.

 The closest prototype is a method involving the simultaneous measurement of the load current of the converter, the effective and psofometric values of the variable component of the voltage at the output of the controlled filter. Measurement of the effective value of the variable component and the load current make it possible to provide the necessary depth of control. At the same time, the composition of the measuring operations and the rules for processing and analyzing the measurement results prescribed by the control algorithm are complicated.

 This is due to the following reasons. A mandatory operation of the known method is the normalization of the measured parameters of the variable component at a certain value of the indicator of the intensity of the load mode of the converter, which uniquely characterizes its effect on the harmonic voltage of the variable component. The magnitude of the current, which is measured in a known method for monitoring the intensity of the load mode, does not provide the uniqueness of such a relationship. Therefore, it is necessary to additionally measure the voltage of the valve winding of the converter transformer or the voltage of its network winding and from this voltage, taking into account the real position of the switching devices of the transformer, find the voltage of its valve winding. Further, using the parameters of a specific traction substation (short-circuit voltage, rated power and the number of operating network and converter transformers, short circuit power of the supply network), which have different values, find the switching angle of the converter, which corresponds to the measured values of its load current, voltage the specified windings of the converter transformer and the parameters of the variable component of the voltage at the output of the controlled filter. With the known value of the switching angle, it is possible to ensure the normalization of the parameters of the variable component necessary for filter control, since, firstly, there is an unambiguous relationship between the voltage of its harmonics and the switching angle and, secondly, the switching angle gives a quantitative estimate of the intensity of the load mode. This standardization allows you to have the values of the measured parameters of the variable component that characterize the technical condition of the controlled filter.

 From the above data it follows that the complexity of the control algorithm by the known method is characterized by three measurement operations and one calculation operation by a complex dependence, which includes 8 parameters of the traction substation and 2 measured values.

 The aim of the invention is to improve the quality of control by improving the accuracy of standardization.

 The invention consists in the following. Simultaneously with the measurement at the terminals of the controlled filter parameters (psophometric voltage, ratio of psophometric voltage to the nominal value of the rectified converter voltage, smoothing coefficient of psophometric voltage, ratio of psophometric and effective values of the variable component of the voltage at the filter output, voltage of individual harmonics) harmonics voltage generated during operation power converter, for recording the intensity of its load mode Follow the important following additional operations. They form (receive) a constant voltage proportional to the amplitude of certain half-waves of the variable component of the rectified voltage at the output of the controlled smoothing filter, which is determined by the minimum value of this voltage. A constant voltage is also obtained, which is proportional to the amplitude of the alternating voltage of the transformer windings of the power converter. Find the ratio of the obtained constant stresses. The technical condition of the controlled smoothing filter is estimated by comparing the values of the harmonics parameters measured at a certain value of the obtained ratio with the harmonics voltage parameters normalized at the same value of this ratio.

 The ratio obtained on the basis of measurements is in direct proportion to the angle of switching of the converter. Therefore, such a relationship, on the one hand, characterizes the load mode of the converter, and on the other hand, there is an unambiguous relationship between this ratio and the harmonic voltage and the parameters measured accordingly. Therefore, the resulting ratio allows you to normalize the voltage parameters of the harmonics. In this case, two quantities can be measured (the harmonic voltage parameter and this ratio, expressed, for example, in voltage units), i.e. one value less compared to the known method. Subsequent calculations are not required, as is the case in the known method. Two measured values allow us to draw a conclusion about the technical condition of the filter. Thus, the proposed method has a simpler control algorithm, which can be classified as improving the quality of control, which is the aim of the invention.

 We establish the relationship between the angle of switching and the magnitude of the ratio measured in the control process according to the proposed method. For this, we turn to the voltage diagrams, which are shown in figure 1.

These diagrams give an idea of the nature of the change in time ωt of the instantaneous value of the rectified voltage during the six-pulse conversion, which is widely used in DC traction substations of electric railways. The upper (lower) diagram corresponds to a smaller (larger) switching angle ωt = γ. The rectified voltage has an average value (constant component) U _d and is formed from segments (shown by solid lines) of the sinusoids U ₁ and U ₂ (shown by dashed lines), which have different amplitudes and are phase-shifted by 30 degrees. email relative to each other. The variable component of the rectified voltage is the difference between its instantaneous and average values and is shown in the diagrams by the shaded area. The amplitude Δ U of the corresponding half-wave of the variable component used for control is the difference between the voltage U _d and the instantaneous value of the sinusoid U ₁ at ωt = γ. A comparison of the upper and lower diagrams shows that the shape of the variable component depends on the value of γ. If the angle γ is small and the voltage U _{d is} greater than the amplitude of the sinusoid U ₁ (large and voltage U _{d is} less than the amplitude of the sinusoid U ₁ ), then the variable component has the form shown in the upper (lower) diagram. It is important to note that for any form of the variable component the condition is met: if ω t = γ, then ΔU = U _d - U ₁ .

5

U_мsinωtd(ωt)+

U_мsinωtd(ωt)

=

(1+cosγ)U_м . При этих обозначениях среднее значение выпрямленного напряжения
ΔU=U_d-0,5

U_мsin(90+γ)=

(1+cosγ)-

cos

×
Тогда для амплитуды Δ U справедливо следующее соотношение:
× U_м=

1+

1-

cos

U_м
Разделив амплитуду Δ U на величину aU_м, которая пропорциональна амплитуде синусоиды U₂, получаем используемую при контроле величину
K_γ=

=

1+

1-

cos

.If we assume that the sinusoid U ₂ has an amplitude U _m , then the sinusoid U _{1 has an} amplitude of U _d =

5

U _m sinωtd (ωt) +

U _m sinωtd (ωt)

=

(1 + cosγ) U _m . With these designations, the average value of the rectified voltage
ΔU = U _d -0.5

U _m sin (90 + γ) =

(1 + cosγ) -

cos

×
Then for the amplitude Δ U the following relation holds:
× U _m =

1+

1-

cos

U _m
Dividing the amplitude Δ U by aU _m , which is proportional to the amplitude of the sinusoid U ₂ , we obtain the value used in the control
K _γ =

=

1+

1-

cos

.

амплитуды фазного напряжения вентильной обмотки аналогичного трансформатора). Располагая значением коэффициента трансформации трансформатора силового преобразователя, величину U_м можно выразить через напряжение его сетевой обмотки, т.е. через напряжение питающей сети.The value of a included in this formula is a scale factor that allows us to obtain K _γ values that are convenient for use and depends on the transformation coefficient of the transformers of the device that implements the method and the transformer of the power converter. Between the value of U _m and the alternating voltage of the windings of the power converter there is a certain proportionality, the quantitative nature of which depends on the rectification scheme. In a three-phase bridge circuit (two reverse stars with a surge reactor), the voltage U _m is equal to the amplitude of the linear voltage of the valve coil of the transformer of the power converter (0.5

the amplitude of the phase voltage of the valve winding of a similar transformer). Having the value of the transformation coefficient of the transformer of the power converter, the value of U _m can be expressed in terms of the voltage of its network winding, i.e. through the mains voltage.

Therefore, to measure the voltage U _m or a value proportional to it, it will be necessary to connect a voltage transformer, respectively, to the valve or network winding of the transformer of the power converter. Traction substation converters usually do not have voltage transformers. Therefore, it is easiest to have a ≠ 1 and measure the voltage proportional to U _m using a voltage transformer that is connected to the network supplying the converter and, as a rule, is available at the traction substation. In this case, a voltage proportional to U _m is introduced into the device that implements the division operation and a certain value of a is adopted. If the parameters of the converter change during the monitoring process, for example, the position of the switch regulating the transformation coefficient of the converter transformer, then coefficient a changes accordingly.

We calculate the dependence of K _γ on γ, taking a = 3/20 π. The calculation results are presented in the graph in figure 2. The graph shows that this dependence is non-linear and quite convenient for practical use.

 The proposed method can be implemented using the device, which is shown in Fig.3. The same figure shows the elements of the power circuit of the traction substation necessary to explain the principle of the device: AC bus 1, which feed the power converter, its transformer 2 and its semiconductor rectifier 3, a smoothing filter 4 with a reactor 5, an aperiodic (capacitive) circuit 6, the terminals 7, forming the input of the filter 4, and the terminals 8, forming its output, the load 9, which feeds the power Converter, and a measuring voltage transformer 10.

 A device that implements the proposed method has a harmonic voltage parameter meter 11, an isolation capacitor 12, a first measuring rectifier 13 with a transformer 14, a diode 15 and a storage capacitor 16 at the output, a functional converter 17, a DC voltage voltmeter 18, and a second measuring rectifier 19 with a transformer 20 , a diode bridge 21 and a storage capacitor 22 at the output.

 The input of the measuring rectifier 13 is formed by the winding of its transformer 14, which is connected through an isolation capacitor 12 to the input of the controlled filter 4. A prerequisite for the measuring rectifier 13 is that it has a half-wave rectification circuit.

 At the measuring rectifier 19, the input is formed by the winding of the transformer 20, which is connected to the voltage transformer 10. The voltage transformer 10 is used to connect the described device along the way. The main purpose of voltage transformer 10 is the power supply of electricity metering devices, measuring instruments, relay protection. The listed devices are not shown in the diagram. When connecting transformers 14 and 20, as shown in the diagram, one of them must have an adjustable transformation ratio. The diagram shows that the transformer 20 has an adjustable transformation ratio. Transformer 20 can be connected not only as shown in the diagram. It can be connected parallel to the valve winding of the transformer, which is connected to the semiconductor rectifier 3. In the second case, both transformers 14 and 20 can have unregulated transformation ratios. In any case, the voltage supplying the transformer 20 and the voltage supplying the transformer 2 should vary proportionally.

 The diagram shows that one meter 11 of the harmonic voltage parameters is used, which is connected to the output of the controlled filter 4. The described device can also have a second meter of a similar purpose, which is connected to the input of the controlled filter 4. As such meters, IMN devices can be used (meters interfering voltage), widely used in traction substations of direct current electric railways, psophometers used in monitoring communication lines, selective and conventional light meters.

 As a functional transducer 17, a serial measuring transducer of the E818 / 1 type can be used with the following parameters: input voltage 0-10 V, input voltage range 10-100%, input resistance 100 kOhm, load resistance 10 kOhm, error ± 0.5 % (see the Handbook of electrical measuring instruments. Edited by K.K. Ilyunin. Energoatomizdat, 1983, p. 555-597).

 Voltmeter 18 can serve as a pointer or digital device with appropriate measurement limits.

 The proposed method allows you to control not only a single-link aperiodic filter, which is shown in the diagram, but also any other filter from among those used at DC traction substations.

 The device monitors the technical condition of the smoothing filter when it smoothes the rectified voltage of the power converter supplying its load. The control is carried out as follows.

 When the power converter is operating, a rectified voltage is applied to the input of the controlled filter 4, which has constant and alternating components. A constant component is applied to the isolation capacitor 12, the variable component is fed to the input of the measuring rectifier 13. Its transformer 14 transforms the voltage of the variable component, providing, firstly, galvanic isolation between the high-voltage power converter circuits and low-voltage measuring circuits, and secondly provides a voltage (signal) that is convenient for subsequent processing. The diode 15 straightens one specific half-wave of a variable component (see figure 1). In this case, the storage capacitor 16 is charged to the amplitude value of the voltage rectified by the diode 15, and remembers the amplitude value during the time when the inverse half-wave of the variable component is applied to the diode 15. When the intensity of the load mode of the power converter changes, the amplitude of the voltage rectified by the diode 15 and, accordingly, the voltage of the storage capacitor 16 are realized. Thus, the operation of obtaining a constant voltage is implemented, the value of which monitors the amplitude of one particular half-wave of the variable component of the rectified voltage and, accordingly, the intensity of the load mode of the Converter.

Simultaneously with this operation, an operation is performed to obtain a constant voltage, which is proportional to the amplitude of the alternating voltage on the windings of the transformer 2 and, accordingly, to the voltage U _m used in the subsequent control operation. To implement the operation of obtaining a second constant voltage of a certain value, the voltage of the secondary winding of voltage transformer 10 is used. This voltage is supplied to the input of the measuring rectifier 19. Its transformer 20 with an adjustable transformation coefficient provides a certain voltage value that is rectified by the diode bridge 21. The storage capacitor 22 is charged to the amplitude values of the rectified voltage of the diode bridge 21 and remembers this value at those time intervals when m the main value is less than the amplitude value of the voltage rectified by the diode bridge 21. If there is a change in the supply voltage, the voltage of the transformer windings 2 changes. These changes are repeated by the voltage of the voltage transformer 10 and, accordingly, the voltage of the capacitor 22.

The need to adjust the transformation ratio of the transformer 20 of the measuring rectifier is caused by the following considerations. The voltages of the capacitors 16 and 22 are associated with voltages U _m and Δ U, respectively, by the following relationships:
U ₁₆ = Δ U: K _t14 ,
U _m = U _22: (K _{communication} ˙ ˙ K K _{T20 T10: m2} K), where R _T14, R _T20, R _T10, R _T2 - transformation ratio transformers 14, 20, 10, 2; To _St - the coefficient of the rectification circuit, characterizing the influence of it and the measuring circuit on the relationship between the voltages U _m and U ₂₂ .

. Если трансформатор подключен не на фазное, как показано на схеме, а на линейное напряжение трансформатора 10, то К_св = 1. Величины К_т14 и (К_св ˙K_{т20 ˙} К_т10:К_т2) характеризуют пропорциональность между U₁₆, Δ U и U₂₂, U_м и поэтому должны иметь постоянное значение, чтобы иметь возможность нормировать параметры напряжения гармоник при определенном значении K_γ . Коэффициенты К_св, К_т14, К_т10 являются постоянными величинами. Коэффициент трансформации К_т2 зависит от положения переключателя обмоток трансформатора 2 и поэтому при регулировании его напряжения изменяется. В этом случае соответствующее регулирование К_т20 обеспечивает постоянство величины (К_св ˙ К_т20 ˙ К_т10 :К_т2), которое необходимо для нормирования. Из приведенных данных следует, что при реализации предложенного способа должно выполняться равенство
K_γ=

=

. Поэтому между масштабным коэффициентом а и коэффициентами К_св, К_т20, К_т10, К_т2 имеет место следующее соотношение:
a=

.The coefficient K _St with constant rectification schemes has a constant value, for the circuit of figure 3 K _St =

. If the transformer is connected not to the phase, as shown in the diagram, but to the linear voltage of the transformer 10, then K _sv = 1. The values of K _t14 and (K _st ˙K _{t20 ˙} K _t10 : K _t2 ) characterize the proportionality between U ₁₆ , Δ U and U ₂₂ , U _m and therefore must have a constant value in order to be able to normalize the harmonics voltage parameters at a certain value of K _γ . The coefficients K _St , K _t14 , K _t10 are constant values. The transformation coefficient K _t2 depends on the position of the switch of the windings of the transformer 2 and therefore, when regulating its voltage, it changes. In this case, the corresponding regulation of K _t20 ensures the constancy of the value (K _St ˙ K _t20 ˙ K _t10 : K _t2 ), which is necessary for normalization. From the above data it follows that when implementing the proposed method should be equal
K _γ =

=

. Therefore, between the scale factor a and the coefficients K _{communication,} R _T20, R _T10, R _t2 following relation holds:
a =

.

If the transformer 20 is connected directly to the valve winding of the transformer 2 connected to the semiconductor rectifier 3, then in this case it is not necessary to adjust K _t20 , because the influence of the variable K _t2 on the quantitative character of proportionality between U _m and U _{22 is} excluded. With this embodiment of the device, the installed power of the transformer 20 increases, because with this inclusion it is not only a matching device, but also isolates the high-voltage circuits of the power converter from low-voltage measuring circuits.

 From the outputs of the measuring rectifiers 13 and 19, a constant voltage is supplied to the inputs of a functional converter 17, which implements the operation of dividing these voltages and creates a constant voltage at the output, the value of which is equal to the quotient of the division of the input voltages.

The readings of the voltmeter 18, which is connected to the output of the functional converter 17, give a quantitative idea of the value of K _γ .

Simultaneously with the determination of the value of K _γ characterizing the intensity of the load mode of the power converter, the readings of the meter 11 are recorded, which give a quantitative idea of the harmonics voltage parameters.

The operation of assessing the technical condition of the controlled filter is final and is performed as follows. The measured values of the harmonics voltage parameters are compared with the normalized values of these parameters. Comparison is made for the same values of K _γ . Based on the results of the comparison, a conclusion is drawn about what kind of technical condition the controlled filter has.

For example, if the psophometric value at the output of the smoothing filter is used as a controlled parameter of the harmonics voltage, then, when its functioning is correct (incorrect), the measured values of the psophometric voltage should be less than or equal to (more) than its normalized values. Normalized values of psophometric stress can be determined by its dependence on K _γ . It can be obtained on the basis of the dependences of the psophometric voltage on the switching angle, which are usually given in the guidelines, and the dependence of K _γ on the switching angle. The nature of the dependence of the psophometric voltage on K _γ thus obtained is determined only by the type of smoothing filter. Therefore, this dependence is universal for traction substations with the same filters. This regularity is also inherent in the dependences on K _{γ of} other harmonic voltage parameters that can be used to control smoothing filters.

Claims (1)

 METHOD FOR CONTROLING THE TECHNICAL CONDITION OF THE SMOOTHING FILTER, connected by an input to the poles of the rectified voltage of the power converter and an output to its load circuit, consisting in measuring the harmonic voltage parameters at the output of the smoothing filter and registering the load mode of the power converter, characterized in that, in order to improve the quality of monitoring by increasing the accuracy of standardization, form a constant voltage proportional to the amplitude of a certain half-wave of the variable component of the rectifier ennogo input voltage smoothing filter, and a DC voltage proportional to the amplitude of the AC voltage of the power converter transformer winding ratio are values obtained and evaluate the technical condition of the smoothing filter by comparing the measured values of the harmonics of the voltage parameters obtained at a normalized value of the ratio.

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