WO2023022580A1

WO2023022580A1 - Method for protecting two parallel transmission lines

Info

Publication number: WO2023022580A1
Application number: PCT/KZ2021/000019
Authority: WO
Inventors: Бауыржан Ерболович МАШРАПОВ; Ризагуль Мегданиятовна МАШРАПОВА; Марк Яковлевич Клецель; Динара Амирбеккызы АМИРБЕК
Original assignee: Некоммерческое Акционерное Общество "Торайгыров Университет"
Priority date: 2021-08-17
Filing date: 2021-08-17
Publication date: 2023-02-23

Abstract

The invention relates to electrical engineering, and more particularly to protective relay technology, and can be used for protecting parallel transmission lines against short-circuiting. The technical result is more responsive protection. This is achieved in that a method for protecting two parallel transmission lines includes measuring the time tref2 after the instantaneous current values i1 or i2 reach the value iref1, comparing the instantaneous current values i1 and i2 with a second reference current iref2 (iref2>iref1), and registering, in each line, the number of phases in which the currents are greater than or equal to iref2; if ∆t≥tref1, then the line in which the current reached iref1 first and, during tref2, reaches iref2 is deactivated; if ∆t<tref1 and the current in one line is greater than or equal to iref2 and the current in the other line is less than iref2, then the line in which the current is greater than or equal to iref2 is deactivated; if, during the time tref2 after the currents have reached the value iref1 in the first (or second) line, said currents reach the value iref2 and the currents in the second (or first) line do not reach iref1, then the first (or second) line is deactivated.

Description

METHOD FOR PROTECTING TWO PARALLEL LINES

The invention relates to the electric power industry, namely to relay protection technology, and can be used to protect two parallel lines from short circuits.

A known method of protecting two parallel lines [Kletsel M.Ya. Principles of construction and models of differential protection of electrical installations on reed switches // Electrical engineering - 1991. - No. 10. - S. 47-50.], in which the instantaneous values of currents ii and 12 are measured in the same phases of the first and second lines with increasing currents, and ii and 12 are compared with the standard (current i _3T ).

The disadvantage of this method is the need to perform a large number of operations and the associated difficulty of implementation and low reliability.

A known method of protecting two parallel lines [RU 2631679 MIC H02H 7/22, publ. 09/26/2017], at which the instantaneous values of currents ii and 12 are measured in the same phases of the first and second lines as they increase, these values are compared with the first current standard i _3T i, the sequence of moments when the currents ii and 1g are reached when they increase, the value i _3T i, measure the time At between the moment when ii=i _3T i and the moment when i2=i ₃ Ti, and compare At with the time reference t _3Ti .

The disadvantage of this method is the limited sensitivity of the protection to short circuits on the lines.

The objective of the invention is to increase the sensitivity of protection by reducing the zone of cascade action.

This is achieved by the fact that in the method of protecting two parallel lines, as well as in the prototype, they measure the instantaneous values of currents ii and 12 in the same phases of the first and second lines as they increase, compare these values with the first current standard i _3T i, fix the sequence of moments achievement by currents ii and 1r when they increase the value i _3T i, measure the time At between the moment when ii=i _3T i, and the moment when i2=i ₃ Ti, and compare At with the time standard t _3T i.

According to the invention, the time t _3T 2 is counted after the instantaneous values of the currents ii or 12 reach the value i _3T i, the instantaneous values of the currents ii and 12 are compared with the second current standard i _3T 2 (1 ₃ t2>1 ₃ t1), the number of phases of each line is fixed , in which the currents are greater than or equal to i _3T 2, if At>t _3T i, then turn off the line in which the current reached i _3Ti first and during t _3T 2 reaches i _3T 2, if At<t _3T i, and the current in one line is greater than or equal to i _3T 2, and in the other less than i _3T 2, then turn off the line in which the current is greater than or equal to i _3T 2, if during the time t _3T 2 after the currents in the first (second) line reach the value i _3T i, they reach the value i _3T 2, and the currents in the second (first) line do not reach i _3T i, then turn off the first (second) line.

In the claimed method, in contrast to the prototype, the currents in the same phases of the lines of the second current standard are controlled, which makes it possible to increase the current amplitude at which the time standard t _3Ti will be determined. This increase, in turn, leads to a decrease in the value of t _3T i, and thus provides a higher protection sensitivity.

The figure 1 shows a device that implements a method for protecting two parallel lines.

Figure 2 shows the time At in the event of a short circuit on the busbars of the receiving substation.

Figure 3 shows the time At with a short circuit on the first line.

The method for protecting two parallel lines can be implemented using a device (Fig. 1), which contains current sensors 1 (DT1), 2 (DT2), blocks 3 (BS1) and 4 (BS2) for comparing the instantaneous values of the current as it rises with the first current standard i _3T i, connected to current sensors 1 (DT1) and 2 (DT2), blocks 5 (BSZ) and 6 (BS4) for comparing instantaneous current values when it increases with the second current standard i _3T 2, connected to current sensors 1 (DT1) and 2 (DT2), blocks 7 (BOV1) and 8 (BOV2) of the time count t _3T 2 connected to blocks 3 (BS1) and 4 (BS2), block 9 (FO1) fixing the sequence of reaching currents ii and 12 i _3Ti values with outputs 10, 11, connected to blocks 3 (BS1) and 4 (BS2), block 12 (FO2) fixing the order in which currents ii and 12 reach values i _3Ti with outputs 13, 14, connected to blocks 3 (BS1) and 4 (BS2), blocks 15 (BIV1), 16 (BIV2) for measuring the time At and comparing it with the time standard t _3T i, connected to blocks 3 (BS1) and 4 (BS2), blocks 17 (KF1) and 18 ( KF2) fixing the number of phases ne the first and second lines, in which the currents are greater than or equal to i _3T 2, connected to blocks 5 (BSZ) and 6 (BS4), blocks 19 (BL1) and 20 (BL2) of logic connected to blocks 5 (BSZ), 7 ( BOV1), 9 (FO1), 15 (BIV1), 17 (KF1) and 6 (BS4), 8 (BOV2), 12 (FO2), 16 (BIV2), 18 (KF2), elements OR 21 (OR1), 22 (OR2) connected to blocks 19 (BL1), 20 (BL2). Signals at outputs 10 and 13 of blocks 9 (FO1) and 12 (FO2) appear if the current ii reached the value i _3Ti first (block 3 (BS1) worked), and at outputs 11 and 14 - if 12 (block 4 (BS2) worked). )).

As current sensors 1 (DT1), 2 (DT2), inductors, Rogowski coils, current transformers, reed switches, etc. can be used. In the application standard current transformers are used. Blocks 3 (BS1), 4 (BS2) and 5 (BSZ), 6 (BS4) comparing currents as they rise with the first and second current standards, blocks 7 (BOV1), 8 (BOV2) of the time count t _3T 2, blocks 9 (FO1), 12 (FO2) fixing the order in which currents ii and 12 reach values i _3T i, blocks 15 (BIV1), 16 (BIV2) measuring the time At and comparing it with the time standard t _3T i, blocks 17 (KF1) and 18 (KF2) fixing the number of phases of the first and second lines, in which the currents are greater than or equal to i _3T 2, logic blocks 19 (BL1) and 20 (BL2) can be performed on a 51 series microcontroller from atmel AT89S53.

Time At allows you to determine the short circuit on the lines or not. This can be easily seen by comparing the At time shown in FIG. 2 and FIG. 3. With external short circuits, the difference in the measured currents (Fig. 2) is due only to the influence of the errors of the current sensors and the device. Therefore, the time At is insignificant and tends to zero with decreasing errors. With a short circuit on the lines, for example, on the first one (Fig. 3), q>12, therefore ii reaches the value i _3Ti earlier than 12. As a result, At increases significantly, and if it exceeds t _3T i, then the presence of damage on the lines is fixed. The time t _3Ti is determined when flowing in current lines with an amplitude equal to i _3T 2, assuming that the currents are sinusoidal, and taking into account the influence of errors si and £2 of the current sensors and the device, according to the formula:

where ti and t2 are the time from the moment the sinusoid passes through zero until the currents in the first and second lines reach the value i _3Ti ; k _ots - detuning factor, taking into account calculation errors; w is the angular frequency.

Time t _3T 2 allows you to fix that the current in the line has not reached i _3Ti or i _3T 2. In this case, t _3T 2=5 ms, since the current in each half-wave increases only during this time. Time control t _3T 2 makes it possible to actuate the protection for disconnecting a damaged line in case of a short circuit near the busbars of the supply substation and in the zone of cascade action, when the current in the undamaged line is less than i _3T i.

The current value i _3T 2 must satisfy two conditions:

1. To be greater than the amplitude value of 1 _Hmax of the maximum load current, so that the protection does not work falsely when one of the lines is disconnected from the opposite side: k ”/ 2 ~ 1 ' nagpah. ' (2)

2. Be as large as possible so that the time t _3Ti is minimal, and at the same time provide the required sensitivity coefficient (k _h \u003d 1.5) in case of short circuit at the border of the cascade action zone after disconnecting the damaged line from the receiving side, i.e. 1kd - amplitude value of the minimum current in the damaged line during a short circuit at the border of the cascade action zone after it is turned off on the receiving side (it is convenient to take the minimum short circuit current on the buses of the receiving substation when one of the lines is turned off).

The magnitude of the current i _3T i, as calculations have shown, to ensure the zone of cascade action of no more than 25% of the length of the lines must satisfy the condition: i , < 0.5i ₉ ; (4)

Taking into account (4), expression (1) will take the form: arc sin - - - - - arcsinO, 5 2- (1- g )

The value of the zone / _vd of the cascade action of protection in fractions of the length of the lines can be determined using the Mathcad program from the expression:

where I is the amplitude value of the maximum current of a three-phase short circuit on the buses of the receiving substation; x - share / _vd of the entire length of the line.

Let two parallel lines with a length of 7=45 km, made with wires with a cross section of 120 mm ² , through which the maximum load current with 1 _N ag.max=409 A can flow, are fed from a power transformer with a power of 40 MBA. Then, assuming the resistance _of _the system to _be equal _to zero, we find c=1.3, w=0.1 and £2=0.05, from (5) we obtain t _3T i=284 μs. We find from (6) x=0.18.

Note that in the protection method adopted for the prototype, there is only one current setting - i _3T i, which detunes from 1 _N ag.shah, and the time t _3Ti is selected when flowing in current lines with an amplitude equal to 1, 15i _3T i. The choice of t _3Ti at large values of the current amplitude in the line can lead to false operation of the protection when the current l,15i _3T i flows. From (5) with the specified to _ots and errors, we get t _3T i=l,l 1 ms. Then from (6) for the considered lines x=0.36, i.e. the sensitivity of the protection adopted for the prototype is lower than that of the claimed.

The device works as follows. In case of a three-phase short circuit (short circuit) on the protected lines outside the zone of cascade action, for example, at the first at a distance of 0.25 / from the busbars of the receiving substation, the amplitudes of the currents in the lines are equal to ii=l.67 kA and 12=1 kA. Since ii and 12 are greater than i _3Ti and i _3T 2, blocks 3 (BS1), 4 (BS2) and 5 (BSZ), 6 (BS4) for comparing currents with the first and second current standards are triggered. In this case, block 3 (BS1) gives a signal earlier, than block 4 (BS2), since the current of the first line reaches the value i _3Ti earlier. As a result, blocks 9 (FO1) and 12 (FO2) of fixing the order in which the currents ii and 12 reach the value i _3Ti determine that the current ii reached the value i _3Ti first, block 7 (BOV1) starts counting the time t _3T 2, block 15 (BIV1 ) measuring the time At and comparing it with the time standard t _3Ti and blocking block 16 (BIV2) measuring the time At and comparing it with the time standard t _3T i. After the current 12 reaches the value i _3Ti block 4 (BS2) issues a signal and stops block 15 (BIV1). In this case, the time At, which he measured, is equal to:

. 308 . 308 arcsin - arcsin -

Since At>t _3T i, block 15 (BIV1) outputs a signal to the input of logic block 19 (BL1). After the current ii reaches the value i _3T 2, which occurs less than after t _3T 2=5 ms, block 5 (BSZ) outputs signals to the inputs of the logic block 19 (BL1), which is triggered and delivers a signal through the OR element 21 (OR1) to the trip circuit of the first line circuit breaker.

With a three-phase short circuit in the zone of cascade action, for example, on the second line at a distance of 0.1 / currents ii=l, 15 kA and 12=1.4 kA. In this case, current 12 reaches the value i _3Ti first. Therefore, block 4 (BS2) generates a signal earlier than block 3 (BS1) and starts block 16 (BIV2). At the same time, block 8 (BOV2) is started, counting the time t _3T 2, and in block 12 (FO2) it is recorded that block 4 (BS2) was the first to work. After the current ii reaches the value i _3Ti, block 3 (BS1) is activated and block 16 (BIV2) stops. The time At=160 µs is less than t _3T i and the protection fails. After switching off the switch of the second line on the receiving side, ii<i _3T 2, and 12=1.34 kA exceeds i _3T 2. Let it turn out that ii is also less than i _3T i. Then blocks 4 (BS2) and 6 (BS4) emit signals, while blocks 3 (BS1) and 5 (BSZ) do not. As a result, after the block 8 (BOV2) completes the countdown time t _3T 2, the logic block 20 (BL2) issues a signal through the OR element 22 (OR2) to turn off the second line.

The behavior of protection in other modes is considered similarly. Note that the operational current is supplied to the protection only if the switches on the supply side of both lines are turned on.

Claims

CLAIM

A method for protecting parallel lines, in which the instantaneous values of currents ii and 12 are measured in the same phases of the first and second lines as they increase, these values are compared with the first current standard i _3T i, the sequence of moments when currents ii and 1g reach values i _3T i is fixed, time At between the moment when ii=i ₃ Ti and the moment when i2=i ₃ Ti , and compare At with the time standard t _3T i, characterized in that the time t _3T 2 is counted after the instantaneous values of the currents ii or 12 reach the value i _3T i, compare the instantaneous values of currents ii and 12 with the second current standard i _3T 2 (i ₃ T2>i ₃ -ri), fix the number of phases of each line in which the currents are greater than or equal to i _3T 2, if At>t _3T i, then turn off that line, the current in which reached 1 _E t1 first and during t _3T 2 reaches i _3T 2, if At<t _3T i, and the current in one line is greater than or equal to i _3T 2, and in the other is less than i _3T 2, then the line is switched off, the current in which is greater than or equal to i _3T 2, if during the time t _3T 2 after it is reached If the currents in the first (second) line of the value i _3T i, they reach the value i _3T 2, and the currents in the second (first) line do not reach i _3T i, then the first (second) line is switched off.

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