RU2050660C1 - Method for detecting defective phases in power transmission line or feeder - Google Patents

Abstract

FIELD: relay protection of distribution systems and high-voltage power transmission lines. SUBSTANCE: method depends on mechanisms characteristic of relationships between energies of emergency addends of their no-zero components and zero-sequence components. In faulty phases, difference between energies of emergency addends and energy of zero-sequence component exceeds energy of no-zero component. In case of phase-to-phase fault, when zero sequence is negligible, levels of emergency energies of separate phases are checked. EFFECT: improved selectivity of method due to using energy of emergency addends of electric quantities as information parameters. 4 dwg

Description

 The invention relates to relay protection and automation of electrical systems and can be used in the remote protection of power lines and in a single-phase automatic reconnection device for selecting damaged phases, as well as in distribution networks (with insulated neutral) for selecting a damaged feeder and indicating its damaged phases.

 Known methods are intended for use on a network with any one neutral mode. The proposed method is built based on any mode.

 A known method for determining a damaged feeder by analyzing the angular relationships between voltage and current complexes [1] It is focused on the allocation of the established terms of the input quantities, usually voltage and zero-sequence current. But the steady-state zero-sequence current in networks with isolated neutral is insignificant, it is at the level of unbalance current, which results in a reduced sensitivity of the method.

 More sensitive are the methods that operate during transients in the electric network [2]. These methods require fixing the moment of short circuit, the formation of emergency components of voltages and currents and determining the sign of their instantaneous power. If the feeder is damaged, its emergency power at the first moment should have a negative sign. However, such a condition is not absolute, i.e. over time, emergency power may change sign. Therefore, these methods do not have absolute selectivity.

 It is further shown that, unlike instantaneous emergency power, absolute selectivity is guaranteed by instantaneous emergency energy. The energy mark of emergency components is used as a parameter of damage. However, we are talking about emergency terms of interphase quantities, i.e. line voltages and currents, and single-phase short circuits are identified by a slight change in the value associated with intact phases. Therefore, emergency energy is used as a parameter only to identify line damage, but not to select damaged phases. If line damage is identified by the operation of determining the sign of energy, which guarantees absolute selectivity, then the damaged phases are determined by the operation of comparing the value with the set point. The choice of the setpoint is a statistical task, therefore, absolute selectivity is not guaranteed here.

 The purpose of the invention is to increase the selectivity of the method of selecting damaged phases using information parameters such as energy transmitted in a purely emergency mode.

 The goal is achieved in that the method for determining the damaged phases of a power line (feeder) by unilaterally measuring the voltages and currents of each line, fixing the moment of damage, generating emergency components of voltages and currents, determining the sign of their energy and reporting damage, if the sign is negative, supplemented by operations, clearly revealing damaged phases, namely the formation of non-zero emergency components of voltages and currents by eliminating the zero sequence (centering), determining three types of phase energies and also zero-sequence energies, the first phase energies for the emergency terms of voltages and currents, the second for non-zero (centered) emergency terms, and the third as the difference of the first energies and zero sequence energies, identifying energies of an adequate level, determining their signs and, if all the signs are negative, stating damage to the feeder, comparing the absolute values of the second and third energies of each phase and stating damage to those phases in which the third energy exceeds the second.

 There are patterns that establish certain relationships between different types of energies when individual phases of a power line are damaged. Previously, these ratios were not known. They are the basis of the proposed method.

 FIG. 1 and 2 illustrate damage to one phase of a distribution network feeder: in FIG. 1 is a network diagram; FIG. 2 its model for non-zero components of phase ν in FIG. 3 is a vector diagram of various components of three feeder currents in a two-phase earth fault; in FIG. 4 functional diagram of the method.

The monitored network includes damaged and undamaged feeders 1 and 2 with their loads 3 and 4. The feeders are connected to the buses 5 powered by a transformer 6 connected to the source 7. Coil 8 is connected to the buses. FIG. 2 C _s1 and C _r2 capacitance of the left and right parts of the damaged feeder, R _r1 , R _r2 , L _r1 , L _r2 resistance and load inductance of feeders, L _t and L _{to the} inductance of the transformer and coil.

 The block diagram consists of multipliers 9-15, playing the role of instantaneous power sensors, integrators 16-22, performing the function of energy sensors, calculators 23-25, threshold elements 26-28, designed to determine the level and sign of energy, a logical element And 29, fixing damage to the feeder, a comparison circuit 30-32 comparing the energy levels of different types, and a trigger 33, fixing the moment of damage. The integrators 16-25 are equipped with installation inputs to zero 34-40 and only start after removing the signal from these inputs.

и

. Если доаварийный процесс был периодическим, то экстраполяция заключается в повторении периодов. Ааварийные слагаемые входных величин определяются как разности двух сигналов: наблюдаемого и генерируемого по памяти:
i_νp(t)= i_ν(t)-

(t); u_νp(t)= u_ν(t)

(t). (1)
Дополнительно определяются безнулевые токи и напряжения путем устранения из аварийных слагаемых (1) нулевой последовательности:
i_νp'(t) i_νp(t) i_o(t);
U_νp'(t) U_νp(t) U_o(t). (2)
C помощью фиг. 1 и 2 иллюстрируются теоретические основы предлагаемого способа. Схема замещения сети для аварийных слагаемых электрических величин содержит только те источники, которые действуют в самом месте повреждения. Так, при однофазном замыкании (фиг. 1) все аварийные слагаемые (1) представляют собой реакцию сети (при нулевых начальных условиях) на включение в момент t= 0 источника тока i_f. С аварийными слагаемыми связаны мгновенная аварийная мощность и мгновенная аварийная энергия, передаваемые по каждой фазе сети напряжением U_νp и током i_νp:
P_νp(t) U_νp(t) i_νp(t); (3)
ω_νp(t)

p_νp(τ)dτ. (4)
Очевидно, что в начальной стадии аварийного процесса мощность передается во все стороны от источника i_f. В резистивных элементах сети эта мощность рассеивается, и потребляемая ими энергия монотонно возрастает, а в индуктивностях и емкостях процессы протекают сложнее. В начальной стадии мощность идет на накопление энергии, т.е. потребляется, но вскоре эти элементы могут приступить к обмену энергией с сетью, после чего их мощность изменяет свой знак. Энергия же (в отличие от мощности) пассивных участков сети отрицательной стать не может: энергия индуктивности и емкости в любой момент времени определяется как L i_L ²/2 и Cu_C ²/2, где i_L и U_C ток и соответственно напряжение этих элементов. Следовательно, знак переданной аварийной энергии безошибочно свидетельствует о взаимном расположении единственного источника и остальной части сети. Данное положение справедливо как для полных аварийных величин, так и для их отдельных составляющих. Так, очевидно, что энергия нулевой последовательности
ω₀₁=

u₀₁(τ) i₀₁(τ)dτ (5) зарегистрирована в начале поврежденного фидера 1 как отрицательная величина, поскольку источники этой энергии действуют в месте повреждения, а приемники подключены к шинам. В частности, таким приемником является и неповрежденный фидер 2, внутри которого источников нет, и его энергия ω₀₂ зафиксирована как положительная величина. Электрическая связь нагрузок 3 и 4 двух фидеров может заметно снизить уровень энергии ω₀₂, но не должна повлиять на ее знак, так как поврежденный фидер остается кратчайшим путем, связывающим источник аварийной энергии с общими шинами подстанции.The input quantities are the voltages and currents at the beginning of each feeder (power line) U _ν and i _ν , where ν A, B, C is the designation of an arbitrary phase. In addition, in the same places measured voltages and currents of the zero sequence U _o and i _o . Suppose that at time t = 0, a network damage was detected, which manifested itself, for example, in a sharp increase in the current level i _o . From this moment, the observed mode is interpreted as emergency, and the preceding one as pre-emergency. The currents and voltages of the pre-emergency mode are stored as values i _νn and U _νn , and then extrapolated to the time after t _o as values

and

. If the pre-accident process was periodic, then extrapolation consists in repeating periods. The accidental terms of the input quantities are defined as the differences of two signals: the observed and the generated from memory:
i _νp (t) = i _ν (t) -

(t); u _νp (t) = u _ν (t)

(t). (1)
In addition, non-zero currents and voltages are determined by eliminating from the emergency terms (1) the zero sequence:
i _νp '(t) i _νp (t) i _o (t);
U _νp '(t) U _νp (t) U _o (t). (2)
Using FIG. 1 and 2 illustrate the theoretical foundations of the proposed method. The network equivalent circuit for the emergency components of electrical quantities contains only those sources that act in the place of damage. So, with a single-phase closure (Fig. 1), all the alarm terms (1) represent the network response (at zero initial conditions) to the inclusion of the current source i _f at time t = 0. The emergency components are associated with instantaneous emergency power and instantaneous emergency energy transmitted over each phase of the network with voltage U _νp and current i _νp :
P _{νp (} t) U _νp (t) i _νp (t); (3)
ω _νp (t)

p _νp (τ) dτ. (4)
It is obvious that at the initial stage of the emergency process, power is transmitted in all directions from the source i _f . In the resistive elements of the network, this power is dissipated, and the energy consumed by them monotonically increases, and in inductors and capacitors, the processes proceed more complicated. In the initial stage, the power goes to the accumulation of energy, i.e. consumed, but soon these elements can begin to exchange energy with the network, after which their power changes its sign. The energy (as opposed to power) coasting network negative can not become: inductance energy and capacity at any given time is defined as _L i L ^2/2 and Cu _C ^2/2 where i _L and U _C current and accordingly the tension of these elements. Consequently, the sign of the transmitted emergency energy accurately indicates the relative position of the single source and the rest of the network. This provision is valid both for full emergency values, and for their individual components. So, obviously, the zero sequence energy
ω ₀₁ =

u ₀₁ (τ) i ₀₁ (τ) dτ (5) is registered at the beginning of damaged feeder 1 as a negative value, since the sources of this energy act at the place of damage and the receivers are connected to the buses. In particular, such a receiver is also an intact feeder 2, inside which there are no sources, and its energy ω _{02 is} fixed as a positive value. The electrical connection of the loads 3 and 4 of the two feeders can significantly reduce the energy level ω ₀₂ , but should not affect its sign, since the damaged feeder remains the shortest path connecting the emergency power source with the common substation buses.

=

u

(τ) i

(τ) dτ<0 передается из поврежденного фидера в индуктивности катушки 8 и трансформатора 6. В нее также входит аварийная энергия, поступающая в фидер 2 и фиксируемая его напряжением и током как положительная величина

=

u

(τ) i

(τ) dτ>0
Таким образом, поврежденный фидер распознается четырьмя условиям: знаками трех энергий безнулевых аварийных составляющих и энергии нулевой последовательности:
ω_Ap' < 0; ω_Bp'< 0; ω_Cp'< 0; (6)
ω_o < 0 (7)
Теоретической основой выявления поврежденных фаз служит различие структур аварийных мощностей, распространяющихся по здоровым и поврежденным фазам. Посмотрим, в какой комбинации входят в аварийную мощность, а следовательно, и в аварийную энергию мощности безнулевых аварийных составляющих P_νp' U_νp' i_νp' и нулевой последовательности P_o=U_o i_o:
P_νp U_νp i_νp (U_νp' + U_o)(i_νp' + i_o)
P_νp' + P_o + U_νp' i_o + U_o i_νp'. (8)
Введем понятие о взаимной аварийной мощности безнулевой и нулевой последовательности
P_νb3 U_νp' i_o + U_o i_νp' (9)
и о соответствующей энергии

=

P_νb3(τ) dτ. (10)
Согласно выражению (8) аварийная мощность, а следовательно, и аварийная энергия каждой фазы состоит из трех слагаемых:
P_νp P_νp' + P_o + P_νb3;
ω_νp=ω_νp'+ω_o+ω_νb3. (11)
Внося равный вклад в аварийные энергии всех фаз фидера, энергия нулевой последовательности ничего не добавляет к информации о поврежденных фазах. Целесообразно поэтому ввести понятие о разностной аварийной энергии
Δω_νp= ω_νp-ω_o= ω (12) и при выявления поврежденных фаз ориентироваться на соотношения между энергиями Δω_νp и ω_νp'. Таким образом, в общем случае в рассмотрение вводятся четыре типа энергий: первые аварийные ω_νp, вторые энергии безнулевых аварийных слагаемых ω_νp', третьи разностные Δω_νp и четвертая нулевой последовательности.Non-zero voltages and currents act in separate phases (Fig. 2), for each of which the provision on the sign of emergency energy is valid. So, in the specific circuit of FIG. 2 emergency energy

=

u

(τ) i

(τ) dτ <0 is transferred from the damaged feeder to the inductance of coil 8 and transformer 6. It also includes emergency energy supplied to feeder 2 and recorded by its voltage and current as a positive value

=

u

(τ) i

(τ) dτ> 0
Thus, a damaged feeder is recognized by four conditions: signs of three energies of non-zero emergency components and zero sequence energy:
ω _Ap '<0; ω _Bp '<0; ω _Cp '<0; (6)
ω _o <0 (7)
The theoretical basis for identifying damaged phases is the difference in the structures of emergency capacities propagating through healthy and damaged phases. Let us see in which combination the emergency power, and therefore the emergency energy, of the power of non-zero emergency components P _νp 'U _νp ' i _νp 'and the zero sequence P _o = U _o i _o :
P _νp U _νp i _νp (U _νp '+ U _o ) (i _νp ' + i _o )
P _νp '+ P _o + U _νp ' i _o + U _o i _νp '. (8)
We introduce the concept of mutual emergency power of non-zero and zero sequence
P _νb3 U _νp 'i _o + U _o i _νp ' (9)
and about the corresponding energy

=

P _νb3 (τ) dτ. (10)
According to expression (8), the emergency power, and therefore the emergency energy of each phase, consists of three components:
P _νp P _νp '+ P _o + P _νb3 ;
ω _νp = ω _νp '+ ω _o + ω _νb3 . (eleven)
Making an equal contribution to the emergency energies of all phases of the feeder, zero sequence energy adds nothing to the information about the damaged phases. It is therefore advisable to introduce the concept of differential emergency energy
Δω _νp = ω _{νp -ω o} = ω (12) and when revealing damaged phases, focus on the relationship between the energies Δω _νp and ω _νp '. Thus, in the general case, four types of energies are introduced into consideration: the first emergency ω _νp , the second _nonzero energy of the emergency terms ω _νp ', the third difference Δω _νp and the fourth zero sequence.

Between the values of the zero sequence and emergency non-zero components there are interconnections established primarily by the boundary conditions that develop in the place of damage. So, with a single-phase fault, the non-zero current of the damaged phase A at the fault location coincides in direction with the zero sequence current and doubles it:
i _fA '2 i _fo , (13) and the currents of undamaged phases are opposite to the current i _fo and one level with it:
i _fB 'i _fC ' if _o . (fourteen)
In other words
i _fA '2 i _fB ' 2 i _fC '. (fifteen)
At the beginning of the line, the following equalities follow the relations (15):
i _Ap '2 i _Bp ' 2 i _Cp '; (sixteen)
U _Ap '2 U _Bp ' 2 U _Cp ', whence it follows that
ω _Ap '= 4ω _Bp ' = 4ω _Cp '. (17)
The conditions for the passage of components of zero and non-zero sequences in the electric network differ, but not qualitatively, but only quantitatively, in the sense that the nature of each element of the electric network for these sequences is the same: inductive for coils, capacitive for feeders, resistive for loads. Considering relations (6), (7), (9), (10), (13), (14) in their relationship, we are convinced that the mutual energy of the damaged phase has the same sign as its two other energies:
signω _Ab3 = signω _Ap '= signω _o , i.e.

sign

= sign ω_o;
sign

sign

= sign ω_o, т.е.ω _Ab3 <0, and in the undamaged phases the situation is opposite:
sign

sign

= sign ω _o ;
sign

sign

= sign ω _o , i.e.

;

4

;

4

+ 2

;

=

-

, сводящиеся к информационным признакам поврежденной фазы Δω_Ap|>|ω_Ap'| (19) и неповрежденных фазΔω_Bp|<|ω_Bp'|Δω_Cp|<|ω_Cp'| (20)
Дополнительный признак ω_Ap'|>|ω_Bp|ω_Ap'|>|ω_Cp'|
При междуфазном замыкании (фазы B и C) в отсутствие тока нулевой последовательности граничные условия в месте повреждения предельно просты:
i_fA' 0; i_fB' i_fC',
вследствие чего в месте наблюдения
i_Ap' 0; i_Bp' i_Cp'.ω _Bb3 >0; ω _Cb3 > 0,
and from expression (16) it is clear that
ω _Ab3 = -2ω _Bb3 = -2ω _Cb3 . (eighteen)
As a result, from the expressions (12), (17), (18) the following relations between the modules of different energies follow:

;

4

;

4

+ 2

;

=

-

reducible to information signs of the damaged phase Δω _Ap |> | ω _Ap '| (19) and intact phases Δω _Bp | <| ω _Bp '| Δω _Cp | <| ω _Cp ' | (twenty)
An additional feature is ω _Ap '|> | ω _Bp | ω _Ap '|> | ω _Cp '|
With an interphase fault (phases B and C) in the absence of a zero sequence current, the boundary conditions at the fault location are extremely simple:
i _fA '0; i _fB 'i _fC ',
as a result, at the observation site
i _Ap '0; i _Bp 'i _Cp '.

In this situation
ω _o 0; (21)
ω _Ap '0; (22)
ω _Bp '= ω _Cp '<0. (23)
Conditions (21) (23) carry the necessary information about the damaged phases. It is enough to make sure that in one phase the energy level of non-zero components is imperceptible, while in others it is quite large.

= sign

;
sign

sign

;

<0;

<0

>

;

>

Итоговый результат заключается в том, что энергии аварийного режима несут необходимую информацию о поврежденных фазах: при междуфазных замыканиях об этом свидетельствуют условия (22), (23), а при замыканиях на землю условия (19), (20) (однофазное замыкание) и (27), (34) (двухфазное).When two phases B and C are shorted to ground, the boundary condition
i _fA 'i _fo (24)
or
i _fB '+ i _fC ' i _fo (25)
From the expression (24) it follows that at the point of observation the signs of the currents i _Ap 'and i _о are basically opposite, which applies equally to the voltages U _Ap ' and U _o . But then from the expressions (9), (10), the opposite of the signs of the energies appears:
sign ω _Ab3 ≠ signω _Ap ', (26)
those. in intact feeder phase
ω _Ab3 >0; (27) Δω _Ap | <| ω _Ap '|
The situation in the damaged phases is more complicated, since relation (25) only indicates the proximity of the current i _о to the sum of non-zero currents at the site of damage, and in order to evaluate the energy ratios, it is necessary to use the interdependencies between the voltages. Most clearly, they appear with a metal short circuit, when in the circuit
U _Bf 0 U _Cf 0;
U _o = U _Af / 3, (28)
U _Bf 'U _o ; U _Cf 'U _o ; (29)
U _Af '2 U _o (30)
If we denote by U _{νfn the} voltage of the previous (pre-emergency) mode in the place of future damage, then considering that
U _νf U _νfn + U _νfp U _νf '+ U _o U _νfn +
+ U _νfp '+ U _o , (31)
we find from expressions (29), (30) for the emergency components of stresses at the damage site
U _Afp '2U _o U _Afn ; (32)
U _Bfp 'U _o U _Bfn ;
U _Cfp '- U _o U _Cfn . (33)
The vector diagram of FIG. 3 illustrates relations (28) - (33) in the proposition that all quantities are sinusoidal. The starting voltage is the phase voltage U _A at the fault location. The zero sequence voltage Uo is determined by relation (28), and the nonzero term U _A '= U _A U _o as a consequence. The opposite of the signs of the voltages U _o and U _Ap 'follows from the relationship between currents (24). The stresses U _Ap U _Ap '+ U _o and U _An U _A U _Ap are also determined as a consequence. If the pre-emergency mode is symmetric, the quantity U _An determines the voltages of two other phases: U _Bn and U _C n, after which their non-zero emergency terms are determined from expression (33). The result confirms that the non-zero emergency terms of the damaged phase voltages U _Bp 'and U _Cp ' are shifted relative to the zero sequence voltage by angles less than 90 ^° , i.e. the intervals of coincidence of the values of U _Bp 'and U _o , like U _Сp ' and U _o1 , are longer _{than the} intervals of mismatch. This implies the relationship between the energies related to the damaged phases:
sign

= sign

;
sign

sign

;

<0;

<0

>

;

>

The final result is that the emergency mode energies carry the necessary information about the damaged phases: in case of interphase faults, conditions (22), (23) indicate this, and in case of earth faults, conditions (19), (20) (single-phase fault) and (27), (34) (two-phase).

The discovered patterns constitute the content of the method implemented by the operations, the most significant of which are reflected in the structural diagram of FIG. 4. The scheme does not include blocks that pre-process the input quantities: filters of emergency terms _{extracting the} components U _νp and i _νp , and subtractors to determine the non-zero components U _νp 'and i _νp '. It is assumed that these values are determined and fed to the inputs of multipliers 9-14. The output signals of the multipliers 9–11 are proportional to the instantaneous powers of the nonzero emergency terms P _νp 'U _νp ' i _νp ', and the output signals of the multipliers 12-14 are the powers of the emergency terms P _νp . Thus, blocks 12-14 implement operations (3). The multiplier 15 determines the power of the zero sequence P _o U _o i _o . Signals proportional to the power are fed to the inputs of the integrators 16-22, converting them into energy. Integrators 16-18 form energy ω _νp ', integrators 19-21 energy ω _νp and integrator 22 energy ω _o .

The starting element 33 is launched in the initial stage of a short circuit, fixing the moment t = 0. The launch is carried out according to the level of emergency terms and (or) terms of the zero sequence. Integrators 16-22 are turned on only by the signal of the launching body, thereby realizing integration operations from the initial moment of time. So, integrators 19-21 implement operation (4). The third difference energies Δω _ν are allocated by subtractors 23-25, acting in accordance with definition (12).

The remaining operations are associated with the control of signs and signal levels proportional to the energies ω _νp 'and the comparison of energy levels ω _νp ' and Δω _νp . It is assumed that the threshold elements 26-28 not only determine the signs of the energies, but also fix their correspondence to the set thresholds of low positive ω _min , low negative ω _min and high negative ω _max . The following three conditions are checked.
ω _νp '<ω _min (35)
ω _νp '<-ω _min (36)
ω _νp '<-ω _max . (37)
A single threshold element is triggered when condition (35) is met, but the relationships between elements 26-28 are such that they can block each other's work, allowing simultaneous operation only when condition (36) and even more so (37) is satisfied in all three phases, or condition (36) in one phase is not satisfied, but condition (35) is satisfied, and in the other two phases the most stringent condition (37) is satisfied. At the same time, all three signals were sent to the inputs of the And 29 element, which, when triggered, creates a signal about damage to this feeder for all types of faults, including phase-to-phase, when one of the signals ω _νp 'is low, but the other two are high. Thus, with interphase faults, information on damaged phases is detected by threshold elements 26-28 and can be obtained directly from those elements that have found that condition (37) is satisfied.

Blocks 30-32 comparison are related to the identification of damaged phases during earth faults. According to relations (19), (20), (27), (34), the signals ω _{νp of the} damaged phases exceed the signals ω _νp 'in level, and in the undamaged phases the opposite pattern is observed. The triggering condition for each of the three circuits 30-32 has the form Δω _νp |> | ω _νp '| therefore, the operation of any block indicates damage to the corresponding phase of the feeder under the condition of the simultaneous operation of the And 29 element, since the operation of circuits 30-32 does not in itself mean that the controlled feeder is damaged.

 The set of operations that make up the proposed method, provides a selective choice of the damaged feeder and its damaged phases for all types of short circuits in networks with any neutral mode.

Claims (1)

 METHOD FOR DETERMINING DAMAGED PHASES OF A ELECTRIC TRANSMISSION LINE (FEEDER) by unilaterally measuring the voltages and currents of each line, fixing the moment of damage, generating emergency components of voltage and currents, determining the sign of their energy and reporting damage to the line with a negative sign, characterized in that they additionally form non-zero emergency terms voltages and currents by eliminating from the emergency terms the corresponding values of the zero sequence, determine the first three, three second and three third basic energies, as well as zero sequence energy, the first phase energies are determined by converting the emergency components of voltages and currents, the second phase energies are determined by converting the nonzero emergency components of voltages and currents, the zero sequence energy is determined by converting the voltage and current of the zero sequence, and the third phase energies determined by subtracting zero sequence energy from the first phase energies, the absolute values of the second phase energies are compared at the given levels, they determine the signs of energies that exceed the minimum level and, if they are negative, report damage to the feeder, if the second energy of one phase is below the minimum level and the other two are higher than the maximum, then the closure of the corresponding two phases is detected, the absolute values of the second and the third energies of each phase of the damaged feeder and note the damage of three phases, in which the absolute value of the third energy is higher than the second.

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