RU2073876C1 - Method for detecting ground fault in power transmission line - Google Patents

Abstract

FIELD: remote protection, faulty phase selectors, ground detectors, networks with any neutral design (dead-grounded, insulated, compensated). SUBSTANCE: phase voltage and currents are measured at starting end of line, first and second reference values are shaped from them and by their conversion, mutual active power is determined as parameter at ground fault point under check. EFFECT: enlarged functional capabilities. 18 dwg

Description

 The invention relates to electrical engineering, namely to relay protection and automation of power systems, and can be used in distance protection, selectors for damaged phases, fault locators (WMDs), while it is fundamentally important, in networks with any neutral mode (solidly grounded, isolated compensated).

 The well-known (traditional) distance method is based on measuring the complexes of voltages and currents at the beginning of the line and converting them into complex resistances [1] It is characterized by a methodological error associated with the inability to accurately determine the distance at various transition resistances and various parameters and modes of the receiving part of the system.

 Known remote method, free from this drawback [2] It also includes the operation of measuring complexes of voltages and currents at the beginning of the line, but is not limited to determining the input complex resistances. Higher accuracy and wider functionality of this method are due to the fact that it relies on a different type of information parameters. The new information parameter was named the parameter of the controlled fault location, since it is determined under the assumption that the fault occurred at some arbitrary point on the line, and is a function of the distance from the beginning of the line. The controlled closure parameter has a remarkable property: it changes its sign only at the place of the actual closure. If the place of the controlled circuit is located to the left of the place of the real circuit, then the parameter has one sign, and if to the right, then the other. To determine the parameters of the controlled circuit, the measured voltages and currents are converted to voltages at the controlled circuit, determine the parameters of the controlled circuit and compare their signs. If the signs of the parameter of the fault location, controlled at the beginning of the line, and the parameter of the fault location, controlled at the end of the line, are opposite, then the circuit in the line is detected. The position of the circuit is determined by changing the sign of the parameter of the controlled circuit.

 The mentioned parameters are determined by the complexes of voltages and currents in the place of controlled faults.

 When implementing this method, the reactive parameters of the controlled faults are used: the reactive power consumed in the place of the controlled fault, or in the particular case the reactive component of the voltage. To determine the reactive parameters, two reference values are formed: the first voltage in the place of the controlled circuit, and the second - the current inside the circuit, i.e. in the transverse branch. Unlike the voltages generated quite simply, the currents in the place of the controlled circuit require for their formation more operations and more information. The fact is that these currents represent the superposition of currents to the left and right of the controlled circuit location. The current to the left of this place is generated as easily as the voltage, but the right current cannot be generated without knowing the parameters of the receiving system. In addition, the parameter type of reactive power is not sufficiently sharp depending on the coordinates of the monitored circuit, which reduces the sensitivity of the method. And finally, the parameter, which includes the fault current or its component as the second reference value, is unsuitable for networks with isolated neutral, in which the earth fault current is incomparably less than the currents in the line wires.

 The essence of the invention is expressed in simplifying the remote method while increasing its sensitivity and expanding functionality. The latter is manifested in applicability not only to networks with a dullly grounded neutral, but also to networks with an isolated neutral, and is achieved by introducing a different type of parameters of monitored fault locations and, accordingly, new operations necessary for the formation of these parameters. From the remote method, there remains the measurement of voltages and currents at the beginning of the line, converting them to first reference values, forming second reference values, converting the first and second reference values to a parameter of the controlled circuit, and as a first reference value, the voltage of the damaged phases is selected, comparison of signs parameters of fault locations, controlled at the beginning and at the end of the line, a statement of damage, if the signs are opposite, determining the location of a true fault by changing ka parameter of the monitored circuit. Distinctive features are that as the second reference values, the components of the first reference values are selected, and the parameter of the monitored circuit is defined as the mutual active power of the first and second reference values.

 The formation of the second reference values is carried out either on the basis of information about the pre-emergency mode, or using the relationships between the symmetrical components specified by the boundary conditions at the fault location.

 Thus, a distinctive feature of this method is the formation of parameters of controlled fault locations by a peculiar combination of full (main) and emergency voltages. Emergency values have been used in relay protection before [3,4]. However, in well-known technical solutions, they participated in other operations, for example, in comparing the phases of two complexes. Here, the combination of full and emergency voltages solves the problem of forming new parameters of controlled fault locations.

 In Fig.1 shows a circuit in a two-wire line, in Fig.2 a schematic model of a line and damage, in Fig.3 a line in a pre-emergency mode, in Fig.4 a line in a purely emergency mode, in Fig.5 a circuit model for this mode, in Fig.6 is a schematic model reduced to a fault location, in Fig.7 is a schematic model of a line with a prospective fault, in Fig.8 is a schematic model of a line in single-phase short circuit mode, in Fig.9 a line in pure emergency mode with a single-phase fault, in figure 10, 11 two-phase circuit and the corresponding purely emergency mode, figure 12,13 then same, but with a two-phase earth fault. The structural implementation of the method is presented in Fig.14. 15-18 serve as illustrations of the application of the proposed method to determine the location of damage in a network with isolated neutral. Fig. 15 shows damaged and undamaged feeders and voltage and current measuring instruments, in Fig. 16 sources creating a zero-sequence mode in the network, in Fig. 17 a hodograph of the earth potential at various transition resistance values and in Fig. 18 a voltage and current diagram damage to the phase of the affected feeder.

 The illustrations show a power line 1 connecting the transmitting and receiving parts of the power system 2 and 3, circuit 4 and their circuit models indicated by the same numbers.

 To implement the method, filters of orthogonal components 5-10, forming blocks 11, 12, multipliers 13-18, ejection block of damaged phases 19, controlled keys 20-25, adder 26 and output comparison unit 27 with two outputs are required: high-speed 28, which solves the problem relay protection, and the second 29, solving the problem of automation.

 In a network with isolated neutral, the damaged feeder 1 and the undamaged 30 are distinguished. It is assumed that a three-winding voltage transformer 31 with a grounded neutral is installed on the substation tires (a compensation coil can be included in the neutral). The transformer serves as a sensor of phase voltage and zero sequence voltage. Each feeder must also have 32-33 phase current transformers installed.

измеряемые комплексы напряжения и тока в начале линии, x_f истинная, но неизвестная координата короткого замыкания,

напряжение в месте контролируемого замыкания,

истинное напряжение замыкания,

ток в месте контролируемого замыкания (поперечный),

истинный ток короткого замыкания,

величины доаварийного режима,

аварийное напряжение и ток (чисто аварийные), представляющие собой разность величины наблюдаемого и предшествующего режима, R_f - переходное сопротивление.The following notation is used below: x is the coordinate of an arbitrary point on the line and the place of the controlled circuit points,

measured voltage and current complexes at the beginning of the line, x _f true but unknown coordinate of the short circuit,

voltage at the point of controlled fault,

true circuit voltage

current in place of controlled circuit (transverse),

true short circuit current,

values of pre-emergency mode,

emergency voltage and current (purely emergency), which are the difference between the magnitude of the observed and previous modes, R _f is the transition resistance.

2. В схеме чисто аварийного режима источники действуют только в месте замыкания (фиг. 4). В ней преобладают реактивные параметры (фиг.5). Следовательно, входное сопротивление относительно места замыкания близко к индуктивному

(3)
Из выражений (1) и (3) следует, что в месте замыкания напряжение нового режима (полное напряжение) и аварийное напряжение практически ортогональны

3. Напряжение контролируемого места замыкания и напряжение истинного места замыкания связаны зависимостью, определяемой параметрами линии электропередачи. Проиллюстрируем это положение на примере того случая, когда распределенную емкость линии допустимо не учитывать Тогда в схеме фиг.2

где

удельное комплексное сопротивление, а в схеме фиг.7

Из выражений (5) и (6)

Соответственно для аварийных напряжений

4. Условие ортогональности (4) может быть представлено в формуле

где U сопряженный комплекс.The proposed method is based on the following theoretical provisions:
1. The main harmonics of voltage and current at the point of fault coincide in phase:

2. In the pure emergency mode circuit, the sources operate only at the fault location (Fig. 4). It is dominated by reactive parameters (figure 5). Therefore, the input impedance relative to the circuit is close to inductive

(3)
From the expressions (1) and (3) it follows that at the point of closure the voltage of the new mode (full voltage) and the emergency voltage are almost orthogonal

3. The voltage of the controlled circuit and the voltage of the true circuit are connected by a relationship determined by the parameters of the power line. We illustrate this position by the example of the case when the distributed line capacity is acceptable not to be taken into account. Then, in the diagram of FIG. 2

Where

specific resistivity, and in the diagram of Fig.7

From expressions (5) and (6)

Respectively for emergency voltage

4. The orthogonality condition (4) can be represented in the formula

where U is the conjugate complex.

Из выражений (6) и (7)

а

комплекс, не зависящий от координаты контролируемого места замыкания х

Подстановка выражения (11) в выражение (10) дает с учетом выражения (8) следующую зависимость параметра контролируемого места замыкания от координаты х:

Данная зависимость, равно как и подобные ей, которые получаются для более сложных систем (учет распределенной емкости, отпаек на линии и т.д.), проходит через нулевое значение в единственной точке х х_f, изменяя при этом свой знак. В результате обнаруживается следующий критерий определения места повреждения:

6. Если не требуется искать место повреждения, а необходимо лишь определить зону, в которой произошло короткое замыкание (задача релейной защиты), то выражение (13) дает для этого случая более простую возможность:
signσ(O)≠signσ(l), (14)
где l координата конца защищаемой зоны.5. We introduce the parameter of the controlled circuit

From expressions (6) and (7)

a

complex independent of the coordinate of the controlled circuit point x

Substitution of expression (11) into expression (10) gives, taking into account expression (8), the following dependence of the parameter of the controlled circuit location on the x coordinate:

This dependence, as well as similar ones, which are obtained for more complex systems (taking into account the distributed capacitance, solders on the line, etc.) passes through a zero value at a single point x x _f , changing its sign. As a result, the following criteria for determining the location of damage is found:

6. If it is not necessary to look for the place of damage, but only need to determine the zone in which the short circuit occurred (relay protection task), then expression (13) gives for this case a simpler possibility:
signσ (O) ≠ signσ (l), (14)
where l is the coordinate of the end of the protected zone.

где σ_уст параметр установки.7. If the circuit occurs outside the protected zone, then, as follows from expression (12), for all controlled circuit locations 0 <x <l 1 we will have
signσ (x) = const.
8. In order to avoid the influence of interference, the level of the parameter of the monitored circuit should be checked. For example, as follows:

where σ _{mouth is} the installation parameter.

Condition (15) assumes that the emergency voltage in at least one controlled circuit location will be sufficiently large. If the level of both U _p (0) and U _p (l) is small, then it turns out that Δσ <σ _mouth and the protection action will be blocked. This measure not only prevents false operation under the influence of interference, but also serves as a means of blocking during swings and asynchronous operation - stationary modes in which emergency voltages are at the level of interference.

 9. In a three-phase line, the parameter of the monitored fault location is determined differently depending on the type of fault.

 With a single-phase circuit with a special phase g (Fig. 8).

причем ортогональность комплексов

иллюстрируется схемой фиг.9.

moreover, the orthogonality of the complexes

illustrated by the diagram of Fig.9.

где g-1 и g-2 обозначения отстающей и опережающей фаз. В соответствии с этим параметр контролируемого места замыкания можно определить выражением

От линейного напряжения в критерии (17) можно перейти к фазным напряжениям

В симметричной линии (фиг.11)

с учетом (20)

а с учетом (17) и (21)

после чего из (17) и (19)

Последнее выражение свидетельствует о том, что в симметричной линии допустимо пофазное суммирование произведений вида

но, разумеется, только на поврежденных фазах. Наряду с параметром (18) при двухфазном замыкании может быть введен еще и такой

11. При двухфазном замыкании на землю с симметричной моделью повреждения по фиг.12 в месте замыкания имеют место следующие соотношения между фазными напряжениями и токами:

где R_в и R_д переходные сопротивления, связывающие основные гармоники напряжений и токов.10. With a two-phase circuit with a special phase g (Fig. 10), the relation illustrated in Fig. 11

where g-1 and g-2 are the designations of the lagging and leading phases. In accordance with this, the parameter of the monitored circuit can be determined by the expression

From line voltage in criterion (17), we can go to phase voltages

In a symmetrical line (11)

subject to (20)

and taking into account (17) and (21)

after which from (17) and (19)

The last expression indicates that phase-wise summation of products of the form

but, of course, only on the damaged phases. Along with parameter (18), in the case of a two-phase circuit, such

11. In the case of a two-phase earth fault with the symmetrical damage model of FIG. 12, the following relationships between phase voltages and currents occur at the fault location:

where R _in and R _d transition resistance, connecting the main harmonics of voltages and currents.

где Х и Х' собственные и взаимные сопротивления относительно зажимов источников тока замыкания.The same currents will create in the symmetric system (Fig.13) the following emergency voltages recorded taking into account the fact that the reactive parameters prevail:

where X and X 'are intrinsic and mutual resistances relative to the terminals of the fault current sources.

где R R_в + R_д.We determine the sum of the products of stresses taking into account (24), (25)

where RR _at + R _d .

является вещественным числом, то правая часть равенства (26) представляет собой мнимое число, так что и при данном виде короткого замыкания выполняется равенство (22) и, следовательно, может быть принят параметр контролируемого места замыкания (23).Since the amount

is a real number, then the right-hand side of equality (26) is an imaginary number, so that with this type of short circuit, equality (22) is fulfilled and, therefore, the parameter of the controlled circuit location (23) can be adopted.

при определении параметров контролируемых мест замыканий могут быть использованы симметричные составляющие

, а также безнулевые аварийные

где индексы 1, 2 и 0 относятся к прямой, обратной и нулевой последовательности.Instead of emergency voltage

when determining the parameters of controlled places of faults, symmetrical components can be used

as well as non-zero emergency

where the indices 1, 2 and 0 refer to the forward, reverse and zero sequence.

Напряжение

представляет собой реакции на ток

, а напряжения

соответственно реакции на токи

. Отсюда следует, что наряду с параметром (16) возможно применение и таких его вариантов

Граничные условия при двухфазных замыканиях также дают дополнительные модификации параметров.With a single-phase circuit, the boundary conditions

Voltage

is a reaction to current

, and voltage

accordingly, reactions to currents

. It follows that along with parameter (16) it is possible to use such variants of it

The boundary conditions for two-phase faults also give additional parameter modifications.

(на фиг.14 не показаны), которые далее преобразуют в ортогональные составляющие комплексов

Эту операцию осуществляют фильтры ортогональных составляющих 5-10, представляющие собой, например, фильтры Фурье. Полученные комплексные сигналы преобразуют в комплексные напряжения места контролируемого замыкания. Для этого определяют сначала фазные напряжения контролируемого места замыкания. Например, в простейшем случае, когда можно не учитывать распределенную емкость линии, эта операция имеет вид

где

падение напряжения от тока нулевой последовательности.The method for determining the zone and place of closure of the power line is implemented by the sequence of operations illustrated by the diagram of Fig. 14 and justified by the above theoretical positions. Eight quantities are measured: phase voltages and currents U _v (o, t), i _v (o, t), ν = A, B, C voltage and zero sequence current U _o (O, t),

(not shown in FIG. 14), which are further converted into orthogonal components of the complexes

This operation is carried out by filters of orthogonal components 5-10, which are, for example, Fourier filters. The resulting complex signals are converted into complex voltages of the controlled circuit. To do this, first determine the phase voltage of the controlled circuit. For example, in the simplest case, when you can not take into account the distributed line capacity, this operation has the form

Where

voltage drop from the zero sequence current.

 The forming unit 11 performing this operation performs a linear conversion of its input values.

принимают напряжение поврежденной фазы

, а при междуфазном замыкании и двухфазном замыкании на землю соответственно разность и сумму напряжений поврежденных фаз

.Damaged phases and the type of fault are determined by comparing the values of the emergency components of the currents of the individual phases (block 19). After establishing the type of closure and the damaged phases, the block 19 sends signals to the closure of the corresponding controlled keys 20-25, which supply only the voltage products to the inputs of the adder 26, which corresponds to a specific type of parameter of the controlled closure location. With a single-phase circuit, as the complex voltage of the monitored circuit

take the voltage of the damaged phase

, and with interphase fault and two-phase earth fault, respectively, the difference and the sum of the voltages of the damaged phases

.

, то она формируется аналогично напряжению

, для чего предназначается формирующий блок 12, идентичный блоку 11.In parallel with this, the orthogonal components of the complex reference signal are formed. If the emergency voltage component is used as such

, then it is formed similar to voltage

what is the purpose of the forming block 12, identical to the block 11.

преобразуют в опорный сигнал контролируемого места замыкания путем перемножения одноименных ортогональных составляющих и суммирования произведений (элементы 13-18).The complex voltage of the monitored fault location U (x) and the complex reference signal

transform into a reference signal of a controlled circuit location by multiplying the orthogonal components of the same name and summing the pieces (elements 13-18).

Чтобы проверить, произошло ли замыкание в зоне защиты, фиксируют контролируемый сигнал σ(O) замыкания, предполагаемого в начале линии, и сигнал σ(l) замыкания, предполагаемого в конце линии, а затем сравнивают их знаки. Эти операции совершаются в блоке сравнения 27. Согласно алгоритму (14), решение о повреждении в зоне x O-l выносится при несовпадении знаков сигналов σ(O) и σ(l). Далее переходят к определению координаты места повреждения x_f, для чего теми же операциями (блоки 11-26) формируют сигналы других контролируемых мест замыкания σ(x), где значения х могут, например, соответствовать опорам линии электропередачи, а затем из ряда сигналов σ(x) выбирают согласно алгоритму (13) сигнал наименьшего уровня σ(x_i) и его соседние сигналы σ(x_i-1) и σ(x_i+1). Сравнивают знак сигнала σ(x_i) со знаками двух других сигналов. Если sign[σ(x_i)]≠sign[σ(x_i-1)], то идентифицируют замыкание между местами x_i и x_i-1, а если

, то между x_i и x_i+1. Определяя координату места замыкания или номер опоры, где произошло замыкание, блок сравнения 27 выставляет соответствующую информацию на своем втором выходе 29. Кроме того, в задачу блока 27 входит контроль разности Δσ согласно условию (15). Если это условие не выполняется, то замыкание не идентифицируется.

To check if a fault has occurred in the protection zone, a controlled fault signal σ (O), assumed at the beginning of the line, and a fault signal σ (l), supposed at the end of the line, are recorded, and then their signs are compared. These operations are performed in comparison block 27. According to algorithm (14), the decision on damage in the x Ol zone is made if the signs of the signals σ (O) and σ (l) do not coincide. Next, we go on to determining the coordinates of the fault location x _f , for which the same operations (blocks 11-26) generate signals of other controlled fault locations σ (x), where the values of x can, for example, correspond to the supports of the power line, and then from a series of signals σ (x) according to algorithm (13), the signal of the lowest level σ (x _i ) and its neighboring signals σ (x _i-1 ) and σ (x _{i + 1} ) are selected. The sign of the signal σ (x _i ) is compared with the signs of two other signals. If sign [σ (x _i )] ≠ sign [σ (x _i-1 )], then the closure between the places x _i and x _{i-1 is} identified, and if

, then between x _i and x _{i + 1} . Determining the coordinate of the fault location or the number of the support where the fault occurred, the comparison unit 27 sets the corresponding information on its second output 29. In addition, the task of block 27 includes monitoring the difference Δσ according to condition (15). If this condition is not met, then the closure is not identified.

(фиг.15). Фазные напряжения U_v(O,t) и напряжение нулевой последовательности U_o(O, t) измеряются на шинах подстанции. Измеренные величины подвергаются фильтрации. Из них выделяются комплексы основной гармоники

.Consider the features of the application of the method for determining the zone and location of a circuit in a network with isolated neutral. At the beginning of each feeder, phase currents are measured.

(Fig.15). Phase voltages U _v (O, t) and zero sequence voltage U _o (O, t) are measured on substation buses. Measured values are filtered. The main harmonic complexes stand out from them

.

 Instead, complexes of higher harmonics can be used.

Возникающее в сети напряжение нулевой последовательности можно представить как реакцию на воздействие источников тока

действующих в месте замыкания (фиг. 16). Связь между

определяется исключительно емкостью сети относительно земли, так как емкостное сопротивление несравненно выше активного сопротивления току в земле и индуктивного сопротивления линии. Отсюда, с учетом положительных направлений напряжения и тока (фиг.16)

Падения напряжения и фидерах от токов нулевой последовательности пренебрежимо малы, поэтому правомерно считать, что

в соответствии с чем условие (29) предстает в следующем наиболее удобном для практического применения виде

Условие (30) может служить критерием определения места повреждения, разумеется, с той оговоркой, что поврежденный фидер нагружен и зависимость

ощутима.Suppose that the damaged feeder is installed (this is an independent task) and now it is necessary to determine the location of the damage x _f . The boundary condition at the point of earth fault (27) states that when phase A is closed

The zero sequence voltage appearing in the network can be represented as a reaction to the influence of current sources

acting in the circuit (Fig. 16). Connection between

It is determined solely by the capacity of the network relative to the ground, since the capacitance is incomparably higher than the resistance to current in the ground and the inductive resistance of the line. Hence, taking into account the positive directions of voltage and current (Fig.16)

Voltage drops and feeders from zero sequence currents are negligible, therefore, it is legitimate to assume that

in accordance with which condition (29) appears in the following form most convenient for practical application

Condition (30) can serve as a criterion for determining the location of damage, of course, with the proviso that the damaged feeder is loaded and the dependence

palpable.

проявляется тем резче, чем меньше переходное сопротивление замыкания в сравнении с емкостью на землю. При изменении параметра R потенциал земли Φ₃ описывает на комплексной плоскости годограф в форме полуокружности (фиг.17). Чем меньше R, тем значительнее повернут вектор U_А(x_f) относительно своего нормального вертикального положения. В пределе при R _→ O бесконечно малый вектор

занимает горизонтальное положение.Dependence

manifests itself more sharply, the lower the transient resistance of the circuit in comparison with the capacitance to earth. When changing the parameter R, the earth potential Φ ₃ describes a hodograph in the form of a semicircle on a complex plane (Fig. 17). The smaller R, the more significant the vector U _A (x _f ) is rotated relative to its normal vertical position. In the limit as R _ → O, an infinitesimal vector

occupies a horizontal position.

При R 0 она максимальна и равна 180^o, а при R>0 тем значительнее, чем меньше R и чем больше разностный вектор

Для поиска координаты x_f используется параметр

Как следует из (30), в месте замыкания
σ(x=x)=0. (32)
Если влияние соседних линий и распределенной емкости допустимо не учитывать, то

Из (31)-(33) искомая координата определяется выражением

а для определения зоны 0<x_f < l достаточно условия (14).The dependence of the potential of the wire on the x coordinate is almost linear (Fig. 18). The vector diagram shows that the sensitivity of criterion (4) will be the higher, the greater the phase difference

At R 0 it is maximum and equal to 180 ^o , and at R> 0 the more significant, the smaller R and the larger the difference vector

To find the x _f coordinate, use the parameter

As follows from (30), at the point of closure
σ (x = x) = 0. (32)
If the influence of adjacent lines and distributed capacitance is permissible not to be taken into account, then

From (31) - (33), the desired coordinate is determined by the expression

and to determine the zone 0 <x _f <l, condition (14) is sufficient.

 As follows from the foregoing, the proposed method for determining the zone and location of the circuit is universal and equally suitable for implementing both as remote protection of power lines and a determinant of the location of damage. Of the number of possible parameters of the monitored circuit, that parameter that is used in this method is most simple, since it relies only on the voltage at the monitored circuit.

Claims (1)

 A method for determining the zone and place of closure of a power line, based on measuring voltages and phase currents at the beginning of the line, voltage and zero sequence current, converting the measured values to the orthogonal components of the complex voltage of the monitored circuit and the orthogonal components of the complex reference signal, determining the type of circuit and damaged phases, the conversion of the complex voltage of the controlled circuit, and with a single-phase circuit as a complex voltage voltages of the monitored fault location take the voltage of the damaged phase, and in case of interphase fault and two-phase earth faults, respectively, the difference and the sum of the phase voltages, the fault in the zone is judged by the signs of the controlled fault at the beginning and at the end of the zone, and the fault location is judged by the transition a signal of a controlled circuit through a zero value, characterized in that the complex reference signal is formed as a component of the complex voltage of the line, the first and second intermediate signals are formed ak product of like orthogonal components of the complex voltage controlled fault location and integrated reference signal and a signal-controlled circuit space is formed as the sum of the first and second intermediate signals.

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