WO2002093183A1 - Method for detecting current transformer saturation - Google Patents
Method for detecting current transformer saturation Download PDFInfo
- Publication number
- WO2002093183A1 WO2002093183A1 PCT/KR2001/000809 KR0100809W WO02093183A1 WO 2002093183 A1 WO2002093183 A1 WO 2002093183A1 KR 0100809 W KR0100809 W KR 0100809W WO 02093183 A1 WO02093183 A1 WO 02093183A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- saturation
- current transformer
- decision function
- order difference
- value
- Prior art date
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Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H1/00—Details of emergency protective circuit arrangements
- H02H1/04—Arrangements for preventing response to transient abnormal conditions, e.g. to lightning or to short duration over voltage or oscillations; Damping the influence of dc component by short circuits in ac networks
- H02H1/046—Arrangements for preventing response to transient abnormal conditions, e.g. to lightning or to short duration over voltage or oscillations; Damping the influence of dc component by short circuits in ac networks upon detecting saturation of current transformers
Definitions
- the present invention relates to a method for detecting saturation in a current transformer, and more particularly, to a method for determining whether or not the change of a secondary current generated in the current transformer is due to saturation of the current transformer.
- a current transformer is a device that measures a current running in a current line and inputs the measured current to a protective relay in a power system. To maximize the flux linkage of the primary and secondary windings, iron-core current transformers are widely used.
- the current transformer as shown in FIG. 1, comprises an iron-core body (34), which concentrates magnetizing flux induced by a primary current running in a line (32), and a secondary coil (36), which coils the iron-core body in order to generate a secondary current from the flux induced in the iron-core body (34).
- FIG. 2 shows the equivalent circuit of a normal current transformer, in which L is a magnetizing inductance of the current transformer; i m is a magnetizing current; i 2 ' is a secondary current in accordance with the current transformation rate; and i 2 is an actual measured secondary current.
- the magnetizing inductance L is not a constant value and varies depending on the amount of the current. When the flux increases and exceeds a predetermined value, the magnetizing inductance changes significantly. When there is inner change of the current transformer, the current transformer is considered to be saturated.
- the magnetizing current i m is low, and the actual measured secondary current value is proportional to the primary current.
- the secondary current value also changes significantly. This can be explained in the equivalent circuit of FIG. 2. As the value L reduces significantly, the magnetizing current i m increases, resulting in the difference between i 2 and i ' currents. Accordingly, in cases where the current transformer is saturated, the relationship between the finally measured secondary current i 2 and the primary current is different from that of normal operation. In addition, the saturation of the current transformer may cause malfunction or time delay of relays.
- an object of the present invention to provide a method for determining saturation of a current transformer based on a predetermined decision function relating to the differences of secondary current values, regardless of remanent flux.
- the present invention provides a method for determining saturation of a current transformer, comprising the steps of: deciding a decision function which utilizes a secondary current value of the current transformer; deciding a decision function value at each point of time by measuring the secondary current value at predetermined time intervals, and determining whether the decision function value is greater than a predetermined threshold value at each point of time; and when the decision function value is determined to be greater than the predetermined threshold value, determining the beginning or end of the saturation, wherein the saturation of the current transformer is determined to end if the saturation of the current transformer begins before the point that the decision function value is greater than the predetermined threshold value, and the saturation of the current transformer is determined to begin if the saturation of the current transformer ends or does not begin before the point that the decision function value is greater than the predetermined threshold value.
- the decision function is preferably one of a second-order difference, an adjusted second-order difference, an energy function of the second-order difference and an energy function of the adjusted second-order difference.
- the decision function is preferably one of a third-order difference, an adjusted third-order difference, an energy function of the third- order difference and an energy function of the adjusted third-order difference.
- the decision function is preferably one of a fourth order difference, an adjusted fourth order difference, an energy function of the fourth order difference and an energy function of the adjusted fourth order difference.
- the step of determining the saturation includes a preventative malfunction step of determining one of the tiem points as an effective detection point and neglecting the other time points, wherein the decision function values are detected as being greater than a predetermined threshold value at a plurality of time points in series.
- FIG. 1 is a view illustrating a general construction of a current transformer.
- FIG. 2 is an equivalent circuit diagram of a general current transformer.
- FIG. 3 is a flowchart illustrating a method for determining saturation of a current transformer, according to one embodiment of the present invention.
- FIG. 4 is a graph illustrating the change of a general secondary current when the current transformer is saturated, and the first-order derivative of the secondary current.
- FIGs. 5A to 5E are graphs illustrating results of application for detecting the saturation of the current transformer according to one embodiment of the present invention, where the remanent magnetizing flux is +80%, wherein
- FIG. 5A shows a secondary current of a current transformer, where the remanent magnetizing flux is +80%
- FIG. 5B shows a first-order difference of a secondary current of a current transformer, where the remanent magnetizing flux is +80%
- FIG. 5C shows a second-order difference of a secondary current of a current transformer, where the remanent magnetizing flux is +80%
- FIG. 5D shows a third-order difference of a secondary current of a current transformer, where the remanent magnetizing flux is +80%
- FIG. 5E shows saturation sections detected by using one embodiment of the present invention, where the remanent magnetizing flux is +80%. Best Mode for Carrying Out the Invention With reference to the accompanying drawings, preferred embodiments of the present invention will be described below.
- FIG. 3 is a flowchart illustrating a method for determining saturation of a current transformer according to one embodiment of the present invention.
- the method for determining the saturation of the current transformer repeats the same procedure at a discrete calculation point of time which is represented by an index n, and increases according to a predetermined time interval.
- the procedure includes a step of deciding a decision function (S10) utilizing the secondary current value of the current transformer.
- the procedure also includes a step of determination (S20), which comprises the steps of: measuring the secondary current according to the predetermined time interval (S20-1) in order to obtain the secondary current value; deciding the decision function value (S20-2) using the obtained secondary current value at each point of time; and determining whether the decision function value is greater than a predetermined threshold value (S20-3) at each point of time.
- the procedure also includes a step of detection (S30), if the decision function value is determined to be greater than a predetermined threshold value at any point of time, referring to the status of the current transformer prior to the point of time whether an end of saturation was detected prior to the point of time (S30-1). Determining whether the detection is a new detection after the prior end of saturation (S30-2). Determining a beginning of saturation if the detection is after the end of saturation (S30-3) and determining an end of saturation if the detection is after the prior beginning of saturation (S30-4).
- One of the critical characteristics of the invention is to employ a decision function, which is related to the difference of the secondary current with time.
- the second-order difference functions of a secondary current can be used.
- One example of such a function is - cfe/l[n-l].
- t 2 [n] - t 2 [n-l] and / 2 [n] is a discretized secondary current value; and n is an index of the discretized value.
- a function proportional to can be used, since mathematical modifications are just a matter of design change.
- the following equation is expressed by z ' 2 [n] function. [Equation 1]
- FIG. 4 shows the change of a general secondary current when the current transformer is saturated, and the first-order derivative of the secondary current.
- the change to the waveform of the secondary current depends on the inner change of the iron-core.
- a first- order derivative of the secondary current shows discontinuities.
- a second-order derivative of the secondary current shows peaks at the discontinuities of the first-order derivative.
- FIGs. 5 A to 5E show the results of application for determining the saturation of the current transformer, where the remanent magnetizing flux is +80%.
- a secondary current of the current transformer deviates from a sine wave as the current transformer is saturated.
- the first derivative (di 2 /dt) or difference (del/[n] i 2 [n]-i 2 [n-l]) of the secondary current, which is discretized, exhibits discontinuities, as shown in the waveform of FIG. 5B.
- the discontinuities of the waveform indicate that significant changes to the secondary current appear at the points of time due to the beginning or end of current transformer saturation.
- the second-order difference value of the secondary current was shown in FIG. 5C.
- pulses appear at the points of time where the discontinuities are located. These points are apparently distinguished from the other points on the graph. If a predetermined threshold value is set to distinguish the beginning or end point of saturation from other points based on a decision function value of a second-order derivative or a difference of the secondary current, the beginning or end point of saturation can be easily detected by comparing the decision function value with a predetermined threshold value.
- the method for determining saturation by comparing a second-order derivative or a difference value with a predetermined threshold value may incorrectly operate the determining algorithm. In other words, if there is not a big difference in the second-order difference value between the beginning/end point of saturation and the other points, the beginning/end of saturation is possibly determined at the beginning/end point of non- saturation. This may significantly deteriorate the operation stability of a relaying system.
- the beginning and end points of saturation clearly indicated as shown in FIG. 5D.
- Use of the third-order difference further distinguishes the peak points from the other points.
- the order of differentiation or difference is higher, the distinction between the peak points and the other points is further clarified, resulting in a broad range of threshold values. This produces the effect of accurate saturation determination. Therefore, as a decision function, use of a third or higher order difference constitutes one of the critical characteristics of the present invention.
- a fourth order difference del 3[n] - del[n-l] can naturally be used to further improve the peak detection performance.
- the beginning/end point of saturation can be correctly determined by the second or higher order derivative or difference, or their mathematically modified functions.
- FIGs. 5B to 5D show examples of a first to third-order differences. However, it is obvious that the beginning/end of saturation can be determined by using a decision function of a higher order derivative or difference, or their mathematically modified functions.
- saturation beginning/end point can be determined regardless of the existence of a remanent magnetizing flux.
- FIGs. 5 A to 5E show examples of an embodiment of the present invention, wherein the remanent magnetizing flux is +80%. +80% of remanent magnetizing flux means that +80% of the magnetizing flux exists at the beginning of the detection procedure with respect to the amount of flux of which saturation begins.
- saturation beginning is determined if a new point where the decision function exceeding a threshold value is detected after the prior saturation end.
- saturation ending is determined after the prior saturation beginning.
- saturation ending and saturation beginning can be distinguished from each other by the following: a first detection after the algorithm operation beginning is determined as saturation beginning; the next detection is determined as saturation ending and the next detection is determined as saturation beginning.
- a modification is available, which counts the number of detections where a decision function exceeds a threshold value from the beginning of the algorithm operation and determining that odd numbered detections as the beginning of saturation and even numbered detections as the ending of saturation end.
- the method for detecting saturation of a current transformer of the present invention can be widely modified and applied within the technical concept of the present invention.
- the present invention is not limited by its preferred embodiments. It is obvious that saturation detection of a current transformer is available with a decision function having a secondary or higher order difference, such as a decision function having a fourth or a fifth order difference. Therefore, such a decision function is also within the technical concept of the present invention.
- the graph of the discretized decision function has broadened peaks, which extend over points of time in series around the exact point of the beginning and ending of saturation.
- general peaks in series extend over four points of time.
- the values of decision function exceed a threshold value at all points of time within the broadened peak.
- the first point of time may possibly be determined as the beginning of saturation and the next point of time in series may possibly be determined as the ending of saturation.
- a mathematical modification to a derivative or difference disclosed in the embodiments is a minor modification of the present invention, and therefore does not exceed the technical concept of the present invention.
- the decision function - del2[n-l] can be used. This can also be modified by comparing del3[n]-A to O or comparing del3[n]/a to 1 instead of comparing the decision function del3[n] to a threshold value A.
- a more complicated modification is nothing more than a minor change of the present invention, as long as it is merely a mathematically modification.
- the objective of the embodiments and drawings is to clearly explain the present invention and does not limit the technical concept of the invention.
- saturation detection is based on the difference of a secondary current value, regardless of remanent magnetizing flux.
- the present invention prevents a malfunction of the system caused by saturation of a current transformer, which results in a correct protection of a power system.
- a third or higher-order difference which is used as a decision function, clearly distinguishes the beginning and end points of saturation from other points, and thus provides a saturation decision securing a stable operation.
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Abstract
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Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
PCT/KR2001/000809 WO2002093183A1 (en) | 2001-05-17 | 2001-05-17 | Method for detecting current transformer saturation |
US10/204,769 US6617839B2 (en) | 2000-07-12 | 2001-05-17 | Method for detecting current transformer saturation |
JP2002589809A JP4097529B2 (en) | 2001-05-17 | 2001-05-17 | Judgment method of current transformer saturation |
Applications Claiming Priority (1)
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PCT/KR2001/000809 WO2002093183A1 (en) | 2001-05-17 | 2001-05-17 | Method for detecting current transformer saturation |
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WO2002093183A1 true WO2002093183A1 (en) | 2002-11-21 |
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PCT/KR2001/000809 WO2002093183A1 (en) | 2000-07-12 | 2001-05-17 | Method for detecting current transformer saturation |
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WO (1) | WO2002093183A1 (en) |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2006523942A (en) * | 2003-04-17 | 2006-10-19 | ミョンギ ユニバーシティ | Secondary current compensation method for current transformer |
US7127364B2 (en) | 2004-10-11 | 2006-10-24 | Myongji University | Method of compensating for distorted secondary current of current transformer |
CN1295833C (en) * | 2003-07-16 | 2007-01-17 | 国电南京自动化股份有限公司 | Anti-current mutual-inductor saturated suddenly-changed quantity difference current dynamic recollecting discrimination method |
CN106842099A (en) * | 2017-04-10 | 2017-06-13 | 国家电网公司 | A kind of CT saturation recognition methods and device |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP7378273B2 (en) * | 2019-11-06 | 2023-11-13 | 三菱電機株式会社 | protection relay device |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0326237A2 (en) * | 1988-01-25 | 1989-08-02 | S & C ELECTRIC COMPANY | Control circuit with validity-determining arrangement |
EP0506035A1 (en) * | 1991-03-27 | 1992-09-30 | Asea Brown Boveri Ab | Method and device for detecting saturation in current transformers |
JPH10221382A (en) * | 1997-01-24 | 1998-08-21 | Eaton Corp | Measuring device of ac current and method therefor |
US6072310A (en) * | 1997-06-04 | 2000-06-06 | Siemens Aktiengesellschaft | Method and device for detecting and correcting a saturated current profile of a current transformer |
-
2001
- 2001-05-17 WO PCT/KR2001/000809 patent/WO2002093183A1/en active IP Right Grant
- 2001-05-17 JP JP2002589809A patent/JP4097529B2/en not_active Expired - Fee Related
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0326237A2 (en) * | 1988-01-25 | 1989-08-02 | S & C ELECTRIC COMPANY | Control circuit with validity-determining arrangement |
EP0506035A1 (en) * | 1991-03-27 | 1992-09-30 | Asea Brown Boveri Ab | Method and device for detecting saturation in current transformers |
JPH10221382A (en) * | 1997-01-24 | 1998-08-21 | Eaton Corp | Measuring device of ac current and method therefor |
US6072310A (en) * | 1997-06-04 | 2000-06-06 | Siemens Aktiengesellschaft | Method and device for detecting and correcting a saturated current profile of a current transformer |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2006523942A (en) * | 2003-04-17 | 2006-10-19 | ミョンギ ユニバーシティ | Secondary current compensation method for current transformer |
CN1295833C (en) * | 2003-07-16 | 2007-01-17 | 国电南京自动化股份有限公司 | Anti-current mutual-inductor saturated suddenly-changed quantity difference current dynamic recollecting discrimination method |
US7127364B2 (en) | 2004-10-11 | 2006-10-24 | Myongji University | Method of compensating for distorted secondary current of current transformer |
CN106842099A (en) * | 2017-04-10 | 2017-06-13 | 国家电网公司 | A kind of CT saturation recognition methods and device |
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Publication number | Publication date |
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JP4097529B2 (en) | 2008-06-11 |
JP2004520601A (en) | 2004-07-08 |
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