CN112260224B - Overcurrent protection device and method suitable for integrated CT (computed tomography) protection - Google Patents
Overcurrent protection device and method suitable for integrated CT (computed tomography) protection Download PDFInfo
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- CN112260224B CN112260224B CN202010815908.3A CN202010815908A CN112260224B CN 112260224 B CN112260224 B CN 112260224B CN 202010815908 A CN202010815908 A CN 202010815908A CN 112260224 B CN112260224 B CN 112260224B
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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
- H02H7/04—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 transformers
- H02H7/042—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 transformers for current transformers
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Abstract
The invention discloses an overcurrent protection device and method suitable for integrated CT (computed tomography) protection, which solve the defects in the prior art, and the method comprises the following steps: step 1, starting and detecting a circuit phase current by the overcurrent protection device, if the circuit phase current is larger than a set fixed value, jumping to step 2, and if the circuit phase current is smaller than or equal to the set fixed value, continuing to keep detection; step 2, the overcurrent protection device calculates the current amplitude by adopting a two-point method, carries out overcurrent judgment, jumps to step 3 if the current amplitude exceeds a set fixed value, and jumps to step 1 if the current amplitude does not exceed the set fixed value; and 3, outputting an overcurrent alarm by the overcurrent protection device, and simultaneously carrying out corresponding operation on the protection circuit by the overcurrent protection device.
Description
Technical Field
The invention relates to the technical field of power system distribution network protection, in particular to an overcurrent protection device and method suitable for integrated CT (computed tomography) protection.
Background
At present, under abnormal operation and fault conditions of a power system, current transformation of a corresponding circuit is supplied to a relay protection device and other similar electric appliances, such as overcurrent protection, distance protection, differential protection and the like. The measurement accuracy is required to be 10P10, 10P20, 5P10, 5P20, etc. Taking 10P10 as an example, when the current flowing through the primary side is within 10 times of the rated current, the secondary output error is less than 10%. For the Current Transformer (CT) for protection, exciting current is a main cause of error. The larger the dynamic range of the CT for protection is, the larger the fault current at the two sides can be accurately; however, the larger the dynamic range is, the larger the iron core volume is, the volume of the ring main unit can be correspondingly increased, and the manufacturing cost is increased.
In the actual conditions of medium-low voltage distribution networks in China, 10kV distribution networks in most areas at present mainly adopt 10P10 ferromagnetic current transformers integrating protection and measurement.
The P-level current transformer is a ferromagnetic current transformer with an iron core, and has low manufacturing cost and stable performance, but the saturation problem of the P-level current transformer is more and more prominent at present that the power grid structure is more and more complex and the short circuit capacity is more and more large due to the magnetic saturation effect of the iron core. Analysis of field accidents shows that CT saturation is one of the main fault causes causing power distribution network faults. The current distribution network is often provided with a protection CT, the dynamic range of 10 times rated current is usually taken, when a fault or a transformer is empty and charged, the protection CT easily causes deep saturation, current cannot be transmitted correctly, distribution network protection refusal or misoperation is easily caused, further override trip accidents occur, and serious harm is formed to the safety of equipment and the stable operation of a system.
Disclosure of Invention
The invention aims to overcome the defects that in the prior art, when a fault or a transformer is empty and charged, a protection CT is easy to cause deep saturation, current cannot be transmitted correctly, network distribution protection refusal or misoperation are easy to cause, further an override trip accident occurs, and serious harm is formed to the safety of equipment and the stable operation of a system, and provides an overcurrent protection device and method suitable for protecting and measuring an integrated CT.
The invention aims at realizing the following technical scheme:
an overcurrent protection method suitable for integrated CT (computed tomography) protection comprises the following steps:
step 1, starting and detecting a circuit phase current by the overcurrent protection device, if the circuit phase current is larger than a set fixed value, jumping to step 2, and if the circuit phase current is smaller than or equal to the set fixed value, continuing to keep detection;
step 2, the overcurrent protection device calculates the current amplitude by adopting a two-point method, carries out overcurrent judgment, jumps to step 3 if the current amplitude exceeds a set fixed value, and jumps to step 1 if the current amplitude does not exceed the set fixed value;
and 3, outputting an overcurrent alarm by the overcurrent protection device, and simultaneously carrying out corresponding operation on the protection circuit by the overcurrent protection device.
As a preferable scheme, the two-point method for calculating the current amplitude is specifically as follows:
setting N sampling points in one cycle, wherein the first sampling point is a sampling point of a certain point, the second sampling point is another sampling point for abrupt criterion, and the square of the current amplitude is the sum of the squares of the current value of the first sampling point and the current value of the second sampling point.
As a preferred scheme, the second sampling point is used as a mutation criterion, if the mutation criterion of the second sampling point does not meet the condition in the set widening time, the two-point method calculated current amplitude is judged to be effective, the overcurrent protection device carries out a corresponding operation protection circuit, and if the mutation criterion of the second sampling point meets the condition, the two-point method calculated current amplitude is judged to be ineffective, and the overcurrent protection device does not operate. The two-point algorithm is easy to be affected by harmonic waves, and particularly at the moment of sudden amplification of exciting current, the current calculated by the two-point algorithm is far greater than the actual current amplitude, and the two-point algorithm overcurrent protection is needed to be locked at the moment. The scheme designs the mutation criterion, and when the mutation criterion meets the mutation criterion condition in the set widening time, the two-point algorithm overcurrent protection is locked, so that the protection misoperation is prevented.
As a preferred embodiment, the set stretching time is 1-7ms. The reason for setting this range is that the abrupt change occurs at the inflection point of the magnetic flux, and if the sampling density is high, there is a case where the abrupt change criterion does not satisfy the condition but is high, so that the locking condition is required to be widened.
As a preferable scheme, the over-current protection device also measures the amplitude of the interphase voltage, if the amplitude of the interphase voltage is larger than the set amplitude, the over-current protection device starts blocking over-current protection, and if the amplitude of the interphase voltage is smaller than or equal to the set amplitude, the over-current protection device does not start blocking over-current protection. The design prevents the misoperation of the overcurrent protection device when the two points of the criterion calculate the current amplitude caused by the inrush current of the transformer during no-load closing.
As a preferred solution, the overcurrent protection device also measures that the proportion of the second harmonic of the phase current exceeds a set proportion value, and the overcurrent protection device starts the blocking overcurrent protection, and if the proportion of the second harmonic of the phase current does not exceed the set proportion, the overcurrent protection device does not start the blocking overcurrent protection. The design prevents the misoperation of the overcurrent protection device when the two points of the criterion calculate the current amplitude caused by the inrush current of the transformer during no-load closing.
As a preferred solution, the two-point method calculates the broadening time of the current amplitude to be greater than 20ms. The design is used for ensuring that the logic judgment AND gate has continuous output when in fault, and meets the requirement of delay time constant value of the delay relay. The logic judgment AND gate is used for judging that the conditions of the two-point algorithm, the circuit phase current being larger than the set fixed value and the like are met, sending out an alarm through the delay relay and carrying out corresponding operation on the protection circuit. Since there is always a linear region per cycle, the actual stretching time is only greater than 20ms.
In the step 2, the overcurrent protection device calculates the current amplitude through fourier transform, if the current amplitude calculated by the two-point method or the current amplitude calculated by the fourier transform exceeds a set constant value, the step 1 is skipped, and if the current amplitude calculated by the two-point method or the current amplitude calculated by the fourier transform does not exceed the set constant value, the step 3 is skipped. The design further ensures the operation accuracy of the overcurrent protection device by the joint cooperation of two-point method calculation and Fourier transformation calculation.
As a preferable scheme, the overcurrent protection device starts and detects circuit phase current, and the circuit phase current comprises an overcurrent first-section phase current, an overcurrent second-section phase current and an overcurrent third-section phase current.
The overcurrent protection device suitable for the integrated CT comprises a protection device for realizing an overcurrent protection method suitable for the integrated CT.
The beneficial effects of the invention are as follows: the invention adopts a two-point algorithm, the current amplitude can be calculated only by two sampling points, the current amplitude obtained by calculating the two current sampling points of a secondary current transformation linear region has an error of not more than 30% with the actual current amplitude, and the action reliability of overcurrent protection can be effectively improved by combining the abrupt change criterion and the corresponding delay widening logic. The invention is used for a 10kV distribution network system, does not need to replace an easy-to-saturate CT, directly adopts the CT of 10P10 or 5P10 widely applied at present, is used as the current input of a distribution network protection device, can greatly improve the action reliability of the overcurrent protection device, prevents the distribution network overcurrent protection from exceeding the relay protection tripping due to CT saturation when the near region of a 10kV line fails seriously, enlarges the power failure range and improves the power supply reliability of the 10kV system.
Drawings
FIG. 1 is a logical block diagram of an overcurrent embodiment of the present invention;
FIG. 2 is an overcurrent two-stage logic block diagram of the present invention;
fig. 3 is an overcurrent three-segment logic block diagram of the present invention.
Detailed Description
The invention is further described below with reference to the drawings and examples.
Examples:
an overcurrent protection method suitable for integrated CT (computed tomography) protection comprises the following steps:
step 1, starting and detecting a circuit phase current by the overcurrent protection device, if the circuit phase current is larger than a set fixed value, jumping to step 2, and if the circuit phase current is smaller than or equal to the set fixed value, continuing to keep detection;
step 2, the overcurrent protection device calculates the current amplitude by adopting a two-point method, carries out overcurrent judgment, jumps to step 3 if the current amplitude exceeds a set fixed value, and jumps to step 1 if the current amplitude does not exceed the set fixed value;
and 3, outputting an overcurrent alarm by the overcurrent protection device, and simultaneously carrying out corresponding operation on the protection circuit by the overcurrent protection device.
The two-point method for calculating the current amplitude is specifically as follows:
setting N sampling points in one cycle, wherein the first sampling point is a sampling point of a certain point, the second sampling point is another sampling point for abrupt criterion, and the square of the current amplitude is the sum of the squares of the current value of the first sampling point and the current value of the second sampling point.
And if the mutation criterion of the second sampling point meets the conditions, judging that the calculated current amplitude of the two-point method is invalid, and the overcurrent protection device does not operate. The two-point algorithm is easy to be affected by harmonic waves, and particularly at the moment of sudden amplification of exciting current, the current calculated by the two-point algorithm is far greater than the actual current amplitude, and the two-point algorithm overcurrent protection is needed to be locked at the moment. The scheme designs the mutation criterion, and when the mutation criterion meets the mutation criterion condition in the set widening time, the two-point algorithm overcurrent protection is locked, so that the protection misoperation is prevented.
The set stretching time is 3ms. The reason for setting this range is that the abrupt change occurs at the inflection point of the magnetic flux, and if the sampling density is high, there is a case where the abrupt change criterion does not satisfy the condition but is high, so that the locking condition is required to be widened.
The over-current protection device also measures the amplitude of the interphase voltage, if the amplitude of the interphase voltage is larger than the set amplitude, the over-current protection device starts blocking over-current protection, and if the amplitude of the interphase voltage is smaller than or equal to the set amplitude, the over-current protection device does not start blocking over-current protection. The design prevents the misoperation of the overcurrent protection device when the two points of the criterion calculate the current amplitude caused by the inrush current of the transformer during no-load closing.
The overcurrent protection device also measures that the proportion of the second harmonic of the phase current exceeds a set proportion value, and the overcurrent protection device starts the blocking overcurrent protection, and if the proportion of the second harmonic of the phase current does not exceed the set proportion, the overcurrent protection device does not start the blocking overcurrent protection. The design prevents the misoperation of the overcurrent protection device when the two points of the criterion calculate the current amplitude caused by the inrush current of the transformer during no-load closing.
The widening time of the current amplitude calculated by the two-point method is more than 25ms. The design is used for ensuring that the logic judgment AND gate has continuous output when in fault, and meets the requirement of delay time constant value of the delay relay. The logic judgment AND gate is used for judging that the conditions of the two-point algorithm, the circuit phase current being larger than the set fixed value and the like are met, sending out an alarm through the delay relay and carrying out corresponding operation on the protection circuit. Since there is always a linear region per cycle, the actual stretching time is only greater than 20ms.
In the step 2, the overcurrent protection device calculates the current amplitude through fourier transform, if the current amplitude calculated by the two-point method or the current amplitude calculated by the fourier transform exceeds a set fixed value, the step 3 is skipped, and if the current amplitude calculated by the two-point method or the current amplitude calculated by the fourier transform does not exceed the set fixed value, the step 1 is skipped. The design further ensures the operation accuracy of the overcurrent protection device by the joint cooperation of two-point method calculation and Fourier transformation calculation.
The overcurrent protection device starts and detects circuit phase current including overcurrent first-section phase current, overcurrent second-section phase current and overcurrent third-section phase current.
The overcurrent protection device suitable for the integrated CT comprises a protection device for realizing an overcurrent protection method suitable for the integrated CT.
Fig. 1 is a logic block diagram of an overcurrent section, and numerals 1 to 11 are inputs of the logic block diagram. Wherein 2 and 4-8 are criteria obtained by calculation according to current or voltage; 1. 3 and 9 are set control words; 10 can be a control word or an outlet pressing plate of an actual device; 11 is an outlet soft pressing plate set by an actual device; the delay/stretching relays are 12-14, namely a first delay stretching relay, a second delay stretching relay and a third delay stretching relay.
Criterion 5 adopts two-point algorithm to calculate and obtain current amplitudeAnd is used for overcurrent discrimination. The specific criteria are as follows:
the two-point algorithm is as follows:
wherein:
iS k ＝i k 。
i k i is the current sampling value of the kth point k-1 For the current sample at point k-1, N is the number of samples taken per cycle for the fundamental, but may be, but is not limited to, 80 samples taken per cycle. I is
Criterion 6 is iC k The mutation criterion is specifically as follows:
(diC k ＞m*AiC k )&&(diC k ＞diCth)
wherein:
diC k ＝|iC k -iC k-1 |。
the dic th is a fixed value, and takes half of the overcurrent fixed value. AiC k Taking the maximum value of the absolute value of the sampling value of the current including k point and the previous cycle, m is a coefficient not greater than 1 but greater than or equal to 0.5.
The first delay widening relay is used for widening the result of the criterion 6 for 3ms, so that overcurrent protection is ensured not to cause overcurrent protection misoperation due to calculation errors of a two-point algorithm. A second delay spread relay for satisfying iC k The two-point algorithm overcurrent criterion (output by the AND gate) after the abrupt criterion is subjected to the widening and locking is widened for 25ms so as to ensure that the AND gate 7 has continuous output when in fault and meet the requirement of a third delay widening relay, namely a relay delay fixed value. Because each cycle always has a section of linear region, the actual stretching time is only longer than 20ms, and is not recommended to be longer than 20ms, so the scheme takes 25ms.
The criterion 2 is to prevent the false operation of the criteria 5 and 7 caused by the inrush current of the transformer during no-load closing, and the specific criteria are as follows:
wherein the method comprises the steps ofIs the magnitude of the interphase voltage. I.e. when the inter-phase voltage is greater than 6kV, the overcurrent protection is blocked.
The criterion 4 is to prevent the false operation of the criteria 5 and 7 caused by the inrush current of the transformer during no-load closing, and to lock and protect the overcurrent protection when the second harmonic of the phase current is larger than a certain proportion.
The criterion 7 is an overcurrent I section starting criterion. The maximum phase current is greater than 0.95 times of the 'overcurrent one-section constant value', and the overcurrent one-section alarm or outlet control word is input, the phase overcurrent starting element acts and widens for 10s.
Tgl1 in the third delay spread relay is the user setting value.
Fig. 2 is a logic block diagram of one segment of the overcurrent, except that the specific setting values of the constant value and the control word are different, and the logic meaning is identical to that of two segments of the overcurrent.
Fig. 3 is a logic block diagram of three sections of overcurrent, compared with fig. 1 and 2, the harmonic blocking is removed, and other meanings are the same as the first section of overcurrent and the second section of overcurrent.
The above-described embodiment is only a preferred embodiment of the present invention, and is not limited in any way, and other variations and modifications may be made without departing from the technical aspects set forth in the claims.
Claims (8)
1. The overcurrent protection method suitable for the integrated CT is characterized by comprising the following steps of:
step 1, starting and detecting a circuit phase current by the overcurrent protection device, if the circuit phase current is larger than a set fixed value, jumping to step 2, and if the circuit phase current is smaller than or equal to the set fixed value, continuing to keep detection;
step 2, the overcurrent protection device calculates the current amplitude by adopting a two-point method, carries out overcurrent judgment, jumps to step 3 if the current amplitude exceeds a set fixed value, and jumps to step 1 if the current amplitude does not exceed the set fixed value;
step 3, the overcurrent protection device outputs an overcurrent alarm, and meanwhile, the overcurrent protection device carries out corresponding operation protection circuits;
the two-point method for calculating the current amplitude is specifically as follows:
setting N sampling points in a cycle, wherein the first sampling point is a sampling point of a certain point, the second sampling point is another sampling point for abrupt change criterion, and the square of the current amplitude is the sum of the squares of the current value of the first sampling point and the current value of the second sampling point;
the second sampling point is used as a mutation criterion, if the mutation criterion of the second sampling point does not meet the condition in the set widening time, the two-point method calculated current amplitude is judged to be effective, the overcurrent protection device carries out a corresponding operation protection circuit, and if the mutation criterion of the second sampling point meets the condition, the two-point method calculated current amplitude is judged to be ineffective, and the overcurrent protection device does not operate; calculating to obtain current amplitude by adopting two-point algorithmThe specific criteria used for overcurrent judgment are as follows:
>overcurrent a section of fixed value;
the two-point algorithm is as follows:
wherein:
iS k ＝i k ；
i k i is the current sampling value of the kth point k-1 The sampling value of the current at the k-1 th point is N, namely the sampling point number of the weekly wave aiming at the fundamental wave, I is
iC k The specific criteria are mutation criteria:
(diC k ＞m*AiC k )&&(diC k ＞diCth)
wherein:
diC k ＝|iC k -iC k-1 |；
the dic point is a fixed value, and half of the overcurrent fixed value is taken out, aiC k Taking the maximum value of the absolute value of the sampling value of the current including k point and the previous cycle, m is a coefficient not greater than 1 but greater than or equal to 0.5.
2. The overcurrent protection method for the integral CT of claim 1, wherein the set dwell time is 1-7ms.
3. The overcurrent protection method for the integrated CT as set forth in claim 1 or 2, wherein the overcurrent protection device further measures the amplitude of the inter-phase voltage, and if the amplitude of the inter-phase voltage is greater than the set amplitude, the overcurrent protection device starts the blocking overcurrent protection, and if the amplitude of the inter-phase voltage is less than or equal to the set amplitude, the overcurrent protection device does not start the blocking overcurrent protection.
4. The overcurrent protection method for the integrated CT as set forth in claim 1 or 2, wherein the overcurrent protection device further measures that the proportion of the second harmonic of the phase current exceeds a set proportion value, and the overcurrent protection device activates the blocking overcurrent protection, and does not activate the blocking overcurrent protection if the proportion of the second harmonic of the phase current does not exceed the set proportion.
5. An overcurrent protection method suitable for integrated CT as claimed in claim 1 or 2, wherein the two-point method calculates the spread time of the current amplitude to be greater than 20ms.
6. The overcurrent protection method for the integrated CT as set forth in claim 1, wherein in the step 2, the overcurrent protection device further calculates the current amplitude through fourier transform, and jumps to the step 3 if the current amplitude calculated by two-point method or the current amplitude calculated by fourier transform exceeds a set constant value, and jumps to the step 1 if neither the current amplitude calculated by two-point method nor the current amplitude calculated by fourier transform exceeds the set constant value.
7. The overcurrent protection method for the integrated CT of claim 1 wherein the overcurrent protection device is configured to start and detect a circuit phase current comprising an overcurrent one-phase current, an overcurrent two-phase current, and an overcurrent three-phase current.
8. An over-current protection device suitable for a protection integrated CT, comprising a protection device for implementing the over-current protection method suitable for a protection integrated CT according to any one of claims 1 to 7.
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Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0577339A1 (en) * | 1992-06-30 | 1994-01-05 | Eaton Corporation | Overcurrent protection device |
| CN101969292A (en) * | 2010-09-10 | 2011-02-09 | 中冶南方（武汉）自动化有限公司 | Method for identifying stator resistance parameters |
| CN102280854A (en) * | 2011-07-18 | 2011-12-14 | 重庆电力高等专科学校 | Excitation current quick-breaking protection method in unsaturated zone during no-load closing of transformer |
| CN102916402A (en) * | 2012-10-17 | 2013-02-06 | 南京国电南自美卓控制系统有限公司 | Criterion suitable for overcurrent protection of high-voltage motor |
| CN111030054A (en) * | 2019-11-19 | 2020-04-17 | 积成电子股份有限公司 | Amplitude abrupt change starting method based on two-point product construction method |
-
2020
- 2020-08-14 CN CN202010815908.3A patent/CN112260224B/en active Active
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0577339A1 (en) * | 1992-06-30 | 1994-01-05 | Eaton Corporation | Overcurrent protection device |
| CN101969292A (en) * | 2010-09-10 | 2011-02-09 | 中冶南方（武汉）自动化有限公司 | Method for identifying stator resistance parameters |
| CN102280854A (en) * | 2011-07-18 | 2011-12-14 | 重庆电力高等专科学校 | Excitation current quick-breaking protection method in unsaturated zone during no-load closing of transformer |
| CN102916402A (en) * | 2012-10-17 | 2013-02-06 | 南京国电南自美卓控制系统有限公司 | Criterion suitable for overcurrent protection of high-voltage motor |
| CN111030054A (en) * | 2019-11-19 | 2020-04-17 | 积成电子股份有限公司 | Amplitude abrupt change starting method based on two-point product construction method |
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Effective date of registration: 20240703 Address after: 310008 room 1711, building 2, Shuicheng building, Shangcheng District, Hangzhou City, Zhejiang Province Patentee after: ZHEJIANG HUAYUN CLEAN ENERGY CO.,LTD. Country or region after: China Address before: 310008 Building 2, No.16, Xiyuan 1st Road, Xihu District, Hangzhou City, Zhejiang Province Patentee before: ZHEJIANG HUAYUN INFORMATION TECHNOLOGY Co.,Ltd. Country or region before: China Patentee before: Zhejiang Huayun Information Technology Co.,Ltd. smart energy service branch |