CN115173373B - Bus protection CT (computed tomography) broken line judgment method and device - Google Patents

Bus protection CT (computed tomography) broken line judgment method and device Download PDF

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CN115173373B
CN115173373B CN202211095339.5A CN202211095339A CN115173373B CN 115173373 B CN115173373 B CN 115173373B CN 202211095339 A CN202211095339 A CN 202211095339A CN 115173373 B CN115173373 B CN 115173373B
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current
voltage
judging
branch
disconnection
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CN115173373A (en
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黄圣凯
高亮
陈洪利
王勇博
韩同刚
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Wiscom System Co ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/22—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for distribution gear, e.g. bus-bar systems; for switching devices
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H1/00—Details of emergency protective circuit arrangements
    • H02H1/0007—Details of emergency protective circuit arrangements concerning the detecting means
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured

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Abstract

Disclosure of the inventionA CT disconnection judging method and device for bus protection are provided. The judgment of the split phase of the criterion is carried out, and the stable operation of the system exceedsT 1 Time, no abnormal voltage access (if no default of voltage access is met), no sudden change of differential current and braking current, large differential current greater than CT disconnection locking constant value, and time delayT 2 And judging that the branch CT is broken after time, and carrying out differential protection according to phase locking. The method fully considers the operating conditions of the power system and the secondary circuit, can effectively judge the CT disconnection condition, and can prevent misjudgment particularly when high-resistance faults occur.

Description

Bus protection CT (computed tomography) broken line judgment method and device
Technical Field
The invention relates to a CT disconnection judging method and device for bus protection, and belongs to the technical field of relay protection of power systems.
Background
The bus differential protection is based on kirchhoff current principle, processes and calculates the collected current of each branch, and can quickly and reliably judge faults in the power system, so that the bus differential protection is widely applied as main protection in bus protection. When the branch current cannot be normally collected due to the fault of the secondary circuit, the bus protection device can quickly and correctly identify the abnormal condition and lock the differential protection, so that the bus differential protection misoperation caused by the fault current generated by the broken line is prevented, the safe operation of a power system is prevented from being influenced, and meanwhile, the phenomenon that the fault cannot be removed, the override trip is caused and the accident is enlarged due to the fact that the bus differential protection is mistakenly locked due to the fact that the fault current is misjudged when the fault such as high-resistance grounding is caused is also avoided.
The current CT disconnection judging method mainly uses the comparison of differential current and CT disconnection threshold value, and judges the CT disconnection and locks the differential protection after fixed time delay. When the method is in a high-resistance fault, the situation that the differential current is larger than the CT disconnection fixed value but smaller than the differential starting fixed value can occur, so that the CT disconnection is judged by mistake, and finally the differential protection is locked by mistake.
Disclosure of Invention
The invention aims to provide a CT disconnection judging method and device for bus protection, which can effectively deal with abnormal conditions such as high-resistance grounding, system disturbance and the like, and quickly and accurately judge and lock bus differential protection.
In order to achieve the above purpose, the invention comprises the following steps:
a bus protection CT disconnection judging method comprises the following steps:
a. obtaining branch current variation, judging branch current mutation when the branch current variation is larger than a preset current mutation threshold, circularly judging each branch, counting the number of current branches with mutation, and if the number of current branches with mutation is larger than 1, counting the number of current branches with mutationT 1 CT disconnection discrimination is not carried out within time, otherwiseT 1 B, entering after time;
b. for the connection mode with voltage, judging whether the system voltage has abnormal change or not, and if not, entering step c; for a voltage-free wiring mode, directly entering c;
c. judging whether the differential current and the braking current are mutated or not, and entering d if the differential current and the braking current are not mutated;
d. judging whether the large difference current is larger than the CT disconnection constant value, if so, delayingT 2 And then judging the disconnection of the branch CT and carrying out differential protection according to phase locking.
As a preferred embodiment, theT 1 The time is taken to be 28 to 32s; the describedT 2 And (5) time is 8 to 12s. The two time limits are introduced mainly to prevent misjudgment in case of high-resistance earth fault and possibly for longer duration in consideration of more complicated and severe faults that may occurT 1 And (4) judging time (representing the stable running time of the system) so as to avoid high-resistance grounding. Through a processT 1 After the system stability judgment of the time, the operation is carried outT 2 Time delay, auxiliary extension of judgment time, prevention of misjudgment, and two-time cooperationAnd (6) judging by new logic.
In a preferred embodiment, the branch current variation is a difference between a current cycle sample value and a previous cycle sample value of the branch.
In a preferred embodiment, the current jump threshold is determined based on a CT secondary current value.
In a preferred embodiment, the current mutation threshold is 0.03 to 0.05 I n ，I n The value is the CT secondary current value.
In a preferred embodiment, the differential current and the sudden braking current are determined by: the absolute value of the variation of the differential current/braking current and the previous 2 cycles is larger than a preset current variation threshold.
In a preferred embodiment, the current variation threshold is 0.03 to 0.05 I n ，I n The value is the CT secondary current value.
As a preferred embodiment, the method for determining whether there is a malfunction in the system voltage is as follows:
obtaining minimum phase voltageU min Zero sequence voltage 3U 0 Zero sequence voltage variation
Figure 144138DEST_PATH_IMAGE001
3U 0 Negative sequence voltageU 2 Negative sequence voltage variation
Figure 900742DEST_PATH_IMAGE001
U 2 (ii) a If any one of the following formulas is satisfied, judging that the system voltage has abnormal motion;
Figure 83461DEST_PATH_IMAGE002
Figure 145089DEST_PATH_IMAGE003
~
Figure 868195DEST_PATH_IMAGE004
respectively, are preset voltage thresholds. Preferably, the first and second liquid crystal materials are,
Figure 151409DEST_PATH_IMAGE003
~
Figure 816614DEST_PATH_IMAGE004
the values are respectively:
Figure 614806DEST_PATH_IMAGE003
=50V，
Figure 344864DEST_PATH_IMAGE005
=0.5V，
Figure 13743DEST_PATH_IMAGE006
=0.5V，
Figure 554577DEST_PATH_IMAGE007
=6V，
Figure 840065DEST_PATH_IMAGE004
=4V。
another object of the present invention is to provide a bus protection CT disconnection determining apparatus, which includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the functions implemented by the above method when executing the computer program.
The CT disconnection criterion provided by the invention is simple and clear in logic and easy to realize, can realize timely and effective discrimination when a system is subjected to simple CT disconnection (the condition that faults are simultaneously generated or the system is continuously in a larger disturbance change state when the CT disconnection is not considered) under the condition of voltage access, can cope with the simultaneous disconnection of multi-phase CT, can effectively cope with various developmental faults, can not need to consider the change relation and trend change of differential current and brake current under various complex working conditions, and effectively avoids the false locking under the special working conditions which are not considered by the complex logic. Compared with the prior time delay CT disconnection criterion which is only carried out by a differential current threshold, the criterion has more reliable performance.
Drawings
FIG. 1 is a flowchart of CT disconnection determination according to the embodiment of FIG. 1.
Detailed Description
The technical solution of the present invention is further explained by referring to the description of the drawings and the specific embodiments.
Example 1
The invention relates to a CT disconnection judging method for bus protection, which comprises the following steps:
(1) The current of each branch circuit is collected, voltage basis (such as double-bus connection) can be introduced into the connection mode with voltage, and the connection mode without voltage is judged by means of judging modes except voltage.
(2) Calculating differential current and brake current of each phase, calculating phase voltage amplitude UA/UB/UC of each bus, and calculating zero sequence voltage 3U 0 Negative sequence voltageU 2 And calculating the current amplitude of each branch.
(3) Calculating a minimum phase voltageU min Calculating the variation delta 3 of the zero sequence voltage and the previous cycleU 0 Calculating the variation delta between the negative sequence voltage and the previous cycleU 2 Calculating the variation delta between the differential current and the first 2 cyclesI d Calculating the variation delta between the braking current and the first 2 cyclesI r Calculating the variation delta between each branch current and the previous cycleI N （NNumbered branch).
Current and a cycle front variation delta
Figure 108235DEST_PATH_IMAGE008
The calculation formula is as follows:
Figure 208784DEST_PATH_IMAGE009
Figure 169787DEST_PATH_IMAGE008
is a branchNWhen the current cycle sampling value is sampled,
Figure 411412DEST_PATH_IMAGE010
is a branchNAnd sampling the previous cycle.
(4) The judgment of the criterion split-phase is that the stable operation of the system exceeds 30s, the voltage access is not abnormal (if no voltage access is satisfied by default), the differential current and the braking current are not sudden change, and the large difference currentI d Greater than the CT line break lockout constant value
Figure 483274DEST_PATH_IMAGE011
And after delaying for 10s, judging that the branch circuit CT is disconnected, and carrying out phase locking differential protection.
The determination process is executed in an interrupted manner, and the whole determination process is executed again at regular intervals (in the embodiment, the determination process is executed once in 0.833 ms), and the specific determination process is as follows (as shown in fig. 1, taking phase a as an example, and phase B/C is the same):
a. when a branch satisfies
Figure 205373DEST_PATH_IMAGE012
If so, the current of the branch circuit is judged to have sudden change,
Figure 806119DEST_PATH_IMAGE013
taking 0.03 to 0.05 as a current mutation thresholdI n ，I n Is the CT secondary current value; circularly judging each branch, and counting the number of current branches with sudden change
Figure 112204DEST_PATH_IMAGE014
When is coming into contact with
Figure 253335DEST_PATH_IMAGE015
In the meantime, the CT disconnection determination is not performed for 30s (the system steady operation timer Tdly is assigned for 30 s).
Figure 282471DEST_PATH_IMAGE016
And after 30s, the system is considered to be stable, and b is entered.
b. The voltage is judged as follows: (for a form of connection without voltage access, this condition is satisfied by default)
Figure 804850DEST_PATH_IMAGE017
In the above-mentioned formula, the compound has the following structure,
Figure 348964DEST_PATH_IMAGE018
is the minimum phase voltage;
Figure 762628DEST_PATH_IMAGE019
is the zero sequence voltage variation;
Figure 629959DEST_PATH_IMAGE020
is a zero sequence voltage;
Figure 103665DEST_PATH_IMAGE021
is the negative sequence voltage variation;
Figure 72758DEST_PATH_IMAGE022
is a negative sequence voltage. If any condition in the above formula is satisfied, judging that the system voltage is abnormal, at the moment, not judging CT disconnection, otherwise, entering c.
c. The criterion of the sudden change of the differential current and the braking current is as follows:
Figure 572004DEST_PATH_IMAGE024
Figure 575732DEST_PATH_IMAGE025
the variation of the differential current and the first 2 cycles;
Figure 954761DEST_PATH_IMAGE026
the variation of the braking current and the first 2 cycles;
Figure 411150DEST_PATH_IMAGE027
in order for the threshold to be varied in current,taking 0.03 to 0.05I n ，I n The value is the CT secondary current value. If any condition in the above formula is satisfied, judging the current disturbance of the system, at this time, not judging the CT disconnection, otherwise, judging that the differential current and the braking current are stable and have no mutation, and entering d.
d. And (4) judging that the large difference current is larger than the CT disconnection fixed value, judging the branch CT disconnection after delaying for 10s (a delayed CT disconnection timer Tctdx times for 10 s), and performing phase locking differential protection.

Claims (7)

1. A CT disconnection judging method for bus protection is characterized by comprising the following steps:
a. obtaining branch current variation, judging branch current mutation when the branch current variation is larger than a preset current mutation threshold, circularly judging each branch, counting the number of current branches with mutation, and if the number of current branches with mutation is larger than 1, counting the number of current branches with mutationT 1 The CT line breakage is not judged within the time, otherwiseT 1 B, entering after time;T 1 the time is taken to be 28 to 32s;
b. for the connection mode with voltage, judging whether the system voltage has abnormal operation or not, and entering into step c if the system voltage has no abnormal operation; for a voltage-free wiring mode, directly entering c;
c. judging whether the differential current and the braking current are mutated or not, and entering d if the differential current and the braking current are not mutated;
the differential current and the brake current sudden change are judged in the following mode: the absolute value of the variation of the differential current/braking current and the previous 2 cycles is larger than a preset current variation threshold; the current change threshold is 0.03 to 0.05 I n ，I n Is the CT secondary current value;
d. judging whether the large difference current is larger than the CT disconnection constant value, if so, delayingT 2 Then judging the disconnection of the branch CT, and locking differential protection according to the phase;T 2 and (5) time is 8 to 12s.
2. The method of claim 1, wherein the branch current variation is a difference between a current cycle sample and a previous cycle sample of the branch.
3. The method of claim 1, wherein the current break threshold is determined based on a CT secondary current value.
4. The method of claim 1, wherein the current mutation threshold is 0.03 to 0.05 I n ，I n The value is the CT secondary current value.
5. The method according to claim 1, wherein the system voltage is determined whether there is an anomaly by:
obtaining minimum phase voltageU min Zero sequence voltage 3U 0 Zero sequence voltage variation
Figure DEST_PATH_IMAGE002
3U 0 Negative sequence voltageU 2 Negative sequence voltage variation
Figure 856686DEST_PATH_IMAGE002
U 2 (ii) a If any one of the following formulas is satisfied, judging that the system voltage has abnormal motion;
Figure DEST_PATH_IMAGE004
Figure DEST_PATH_IMAGE006
~
Figure DEST_PATH_IMAGE008
respectively, a predetermined voltage threshold.
6. The method of claim 5, wherein the step of removing the metal oxide layer comprises removing the metal oxide layer from the metal oxide layerThus, the temperature of the molten steel is controlled,
Figure 540870DEST_PATH_IMAGE006
~
Figure 992711DEST_PATH_IMAGE008
the values are respectively:
Figure 292980DEST_PATH_IMAGE006
=50V，
Figure DEST_PATH_IMAGE010
=0.5V，
Figure DEST_PATH_IMAGE012
=0.5V，
Figure DEST_PATH_IMAGE014
=6V，
Figure 969337DEST_PATH_IMAGE008
=4V。
7. a bus bar protection CT disconnection determination apparatus, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the functions implemented by the method of any one of claims 1 to 6 when executing the computer program.
CN202211095339.5A 2022-09-08 2022-09-08 Bus protection CT (computed tomography) broken line judgment method and device Active CN115173373B (en)

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Denomination of invention: A Method and Device for CT Broken Line Identification of Bus Protection

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