CN108333540B - Method and system for evaluating residual magnetism of current transformer for metering - Google Patents
Method and system for evaluating residual magnetism of current transformer for metering Download PDFInfo
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Abstract
The invention discloses a method for evaluating residual magnetism of a current transformer for metering, which comprises the following steps: acquiring a current ending angle and an effective value of a short-circuit current when a short-circuit fault occurs according to a secondary recording chart of the power transmission line; acquiring a magnetic flux value of a saturation magnetic flux point and a voltage value of a saturation voltage point by using a basic magnetization curve; acquiring a residual magnetic coefficient of the current transformer and impedance of a secondary load in advance; respectively calculating the residual magnetism of the current transformer of each phase in the three phases according to the current end angle, the effective value of the short-circuit current, the magnetic flux value of the saturated magnetic flux point, the voltage value of the saturated voltage point, the residual magnetism coefficient of the current transformer and the impedance of the secondary load; respectively calculating the residual magnetism weight coefficients of the three-phase current transformer; and calculating the residual magnetism of the current transformer according to the residual magnetism of the three-phase current transformer and the residual magnetism weight coefficient of the three-phase current transformer.
Description
Technical Field
The invention relates to the technical field of electric power metering, in particular to a method and a system for evaluating residual magnetism of a current transformer for metering.
Background
The current transformer is an important primary device in a power system, can convert a large-current and high-voltage electrical signal on a primary side into a small-current and low-voltage signal and transmit the small-current and low-voltage signal to a secondary side, and plays an important role in stable operation of the power system. The current transformers can be divided into protection current transformers and metering current transformers according to purposes, and the metering circuit transformers have the main functions of monitoring a power grid and metering electric quantity. When a short-circuit fault occurs in a power grid line, strong short-circuit current can pass through the line in a transient state, the instantaneous value of the short-circuit current can reach tens of times of the rated current of the current transformer, and huge induction magnetic flux is generated in the iron core of the current transformer, so that the saturation phenomenon of the current transformer can be caused. After the fault is eliminated, due to the hysteresis characteristic of the material of the iron core of the current transformer, the magnetic flux generated by the short-circuit current cannot disappear along with the short-circuit current, but a certain residual magnetism is formed in the iron core.
Due to the existence of residual magnetism, when the current transformer operates in a stable state, the residual magnetism can improve the magnetic flux working point of the current transformer and improve the exciting current of the circuit transformer, so that the secondary side current of the circuit transformer is distorted. Therefore, the residual magnetism may cause the measurement characteristics of the current transformer for measurement to be poor, the electric quantity cannot be accurately measured, the system current cannot be monitored, and the stable operation of the power system is adversely affected.
At present, an effective remanence evaluation method for a current transformer for metering does not exist, and the traditional current transformer overhauling work can carry out demagnetization work one by one, so that overhauling personnel face huge workload. Before the overhaul work, the remanence of the current transformer is evaluated by using a remanence evaluation method, so that a more reasonable overhaul scheme can be provided for the current transformer, the work efficiency is greatly improved, the labor and material cost is saved, and the operation stability of a power system is improved.
Therefore, a technique is needed for implementing an evaluation of the remanence of a current transformer for metering. .
Disclosure of Invention
The technical scheme of the invention provides a method and a system for evaluating residual magnetism of a current transformer for metering, which aim to solve the problem of how to evaluate the residual magnetism of the current transformer for metering.
In order to solve the above problems, the present invention provides a method for evaluating residual magnetism of a current transformer for metering, the method comprising:
acquiring a current ending angle and an effective value of a short-circuit current when a short-circuit fault occurs according to a secondary recording chart of the power transmission line;
acquiring a magnetic flux value of a saturation magnetic flux point and a voltage value of a saturation voltage point by using a basic magnetization curve;
acquiring a residual magnetic coefficient of the current transformer and impedance of a secondary load in advance;
respectively calculating the residual magnetism of the current transformer of each phase in the three phases according to the current ending angle, the effective value of the short-circuit current, the magnetic flux value of the saturation magnetic flux point, the voltage value of the saturation voltage point, the residual magnetism coefficient of the current transformer and the impedance of the secondary load;
respectively calculating the residual magnetism weight coefficients of the three-phase current transformer;
and calculating the residual magnetism of the current transformer according to the residual magnetism of the three-phase current transformer and the residual magnetism weight coefficient of the three-phase current transformer.
Preferably, the obtaining a magnetic flux value of a saturation magnetic flux point and a voltage value of a saturation voltage point by using the basic magnetization curve includes:
from voltage points measured in the current-voltage characteristic curve corresponding to flux points in the magnetisation curve, i.e.
Wherein: u is any voltage point of volt-ampere characteristic, UmIs the saturation voltage point of the current-voltage characteristic curve, BmThe value of the magnetic flux at the saturation point of the basic magnetization curve is B, and the value of the magnetic flux at the corresponding point of the voltage U is B.
Preferably, the calculating the residual magnetism of the current transformer of each of the three phases separately according to the current ending angle, the effective value of the short-circuit current, the magnetic flux value of the saturation magnetic flux point, the voltage value of the saturation voltage point, the residual magnetism coefficient of the current transformer, and the impedance of the secondary load includes:
wherein, I is the effective value of the short-circuit current, Z is the load of the secondary side of the current transformer, KrwThe steady-state remanence coefficient of the current transformer is a short-circuit current ending angle theta, BrResidual magnetism of the current transformer after short-circuit fault;
wherein B isr_phase1～Br_phase3Representing the remanence of the current transformer for the first phase to the third phase.
Preferably, the respectively calculating the remanence weight coefficients of the three-phase current transformers includes:
Preferably, the calculating the residual magnetism of the current transformer according to the residual magnetism of the three-phase current transformer and the residual magnetism weight coefficient of the three-phase current transformer includes:
preferably, the current transformer comprises a current transformer made of silicon steel, an ultra-crystalline alloy and a permalloy material.
Based on another aspect of the invention, the invention provides a system for evaluating remanence of a current transformer for metering, the system comprising:
the first acquisition unit is used for acquiring a current ending angle and an effective value of a short-circuit current when the short-circuit fault occurs according to a secondary oscillogram of the power transmission line;
a second acquisition unit that acquires a magnetic flux value of a saturation magnetic flux point and a voltage value of a saturation voltage point using the basic magnetization curve;
the third acquisition unit is used for acquiring the residual magnetism coefficient of the current transformer and the impedance of a secondary load in advance;
a first calculating unit, configured to calculate, according to the current end angle, the effective value of the short-circuit current, the magnetic flux value of the saturation magnetic flux point, the voltage value of the saturation voltage point, the residual magnetism coefficient of the current transformer, and the impedance of the secondary load, the residual magnetism of the current transformer of each of the three phases respectively;
the second calculating unit is used for calculating the residual magnetism weight coefficients of the three-phase current transformer respectively;
and the third calculating unit is used for calculating the residual magnetism of the current transformer according to the residual magnetism of the three-phase current transformer and the residual magnetism weight coefficient of the three-phase current transformer.
Preferably, the second obtaining unit is further configured to:
from voltage points measured in the current-voltage characteristic curve corresponding to flux points in the magnetisation curve, i.e.
Wherein: u is any voltage point of volt-ampere characteristic, UmIs the saturation voltage point of the current-voltage characteristic curve, BmThe value of the magnetic flux at the saturation point of the basic magnetization curve is B, and the value of the magnetic flux at the corresponding point of the voltage U is B.
Preferably, the first computing unit is further configured to:
wherein, I is the effective value of the short-circuit current, Z is the load of the secondary side of the current transformer, KrwThe steady-state remanence coefficient of the current transformer is a short-circuit current ending angle theta, BrResidual magnetism of the current transformer after short-circuit fault;
wherein B isr_phase1～Br_phase3Representing the remanence of the current transformer for the first phase to the third phase.
Preferably, the second computing unit is further configured to:
Preferably, the third computing unit is further configured to:
preferably, the current transformer comprises a current transformer made of silicon steel, an ultra-crystalline alloy and a permalloy material.
The technical scheme of the invention provides a method and a system for evaluating residual magnetism of a current transformer for metering, wherein the residual magnetism of an iron core is calculated and evaluated by utilizing fault current information recorded by secondary equipment. The residual magnetism assessment method provided by the technical scheme of the invention is based on the principle that the volt-ampere characteristic of the current transformer corresponds to the magnetization characteristic. And providing a concept of integral residual magnetism evaluation according to the practical application of the current transformer for metering, and carrying out integral evaluation on the residual magnetism of the current transformer at a metering point. The technical scheme of the invention provides a concept of the weight coefficient of the remanence of each phase of the current transformer, and improves the scientificity of the remanence evaluation result. The residual magnetism evaluation method for the current transformer for metering, which is provided by the technical scheme of the invention, can effectively evaluate the residual magnetism in the iron core after the short-circuit fault, and provides powerful technical support for the daily operation and maintenance work of the current transformer. The method for evaluating the residual magnetism of the current transformer for metering is an important guarantee for the accuracy of electric energy metering and has higher economic benefit.
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A more complete understanding of exemplary embodiments of the present invention may be had by reference to the following drawings in which:
FIG. 1 is a flow chart of a method for estimating remanence of a current transformer for metering according to an embodiment of the present invention;
fig. 2 is a system configuration diagram for evaluating residual magnetism of a current transformer for metering according to an embodiment of the present invention.
Detailed Description
The exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, however, the present invention may be embodied in many different forms and is not limited to the embodiments described herein, which are provided for complete and complete disclosure of the present invention and to fully convey the scope of the present invention to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, the same units/elements are denoted by the same reference numerals.
Unless otherwise defined, terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Further, it will be understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense.
FIG. 1 is a flow chart of a method for estimating remanence of a current transformer for metering according to an embodiment of the invention. The embodiment of the invention provides a method for evaluating residual magnetism of a current transformer for metering, which is used for calculating and evaluating the residual magnetism of an iron core by utilizing fault current information recorded by secondary equipment. The remanence evaluation method provided by the application is based on the principle that the volt-ampere characteristic of the current transformer corresponds to the magnetization characteristic, and provides a concept of remanence overall evaluation according to the actual application of the current transformer for metering, so that the remanence of the current transformer at a metering point is evaluated integrally. The application provides the concept of the weight coefficient of the remanence of each phase of the current transformer, and the scientificity of the remanence evaluation result is improved. The residual magnetism evaluation method for the metering current transformer can effectively evaluate the residual magnetism in the iron core after the short-circuit fault, and provides powerful technical support for daily operation and maintenance work of the current transformer. As shown in fig. 1, a method 100 for evaluating residual magnetism of a current transformer for metering begins with step 101:
preferably, in step 101: and acquiring a current ending angle and an effective value of the short-circuit current when the short-circuit fault occurs according to the secondary oscillogram of the power transmission line.
Preferably, at step 102: and acquiring a magnetic flux value of a saturation magnetic flux point and a voltage value of a saturation voltage point by using the basic magnetization curve.
Preferably, obtaining the magnetic flux value at the saturation magnetic flux point and the voltage value at the saturation voltage point using the basic magnetization curve includes:
from voltage points measured in the current-voltage characteristic curve corresponding to flux points in the magnetisation curve, i.e.
Wherein: u is any voltage point of volt-ampere characteristic, UmIs the saturation voltage point of the current-voltage characteristic curve, BmThe value of the magnetic flux at the saturation point of the basic magnetization curve is shown, and B is the value of the magnetic flux at the saturation point of the voltage U.
Preferably, the current transformer comprises a current transformer of silicon steel, ultra-crystalline alloy, permalloy material.
Preferably, in step 103: and acquiring the residual magnetic coefficient of the current transformer and the impedance of a secondary load in advance.
Preferably, at step 104: and respectively calculating the residual magnetism of the current transformer of each phase in the three phases according to the current end angle, the effective value of the short-circuit current, the magnetic flux value of the saturated magnetic flux point, the voltage value of the saturated voltage point, the residual magnetism coefficient of the current transformer and the impedance of the secondary load.
Preferably, the calculating the residual magnetism of the current transformer of each of the three phases separately according to the current ending angle, the effective value of the short-circuit current, the magnetic flux value of the saturation magnetic flux point, the voltage value of the saturation voltage point, the residual magnetism coefficient of the current transformer, and the impedance of the secondary load includes:
wherein, I is the effective value of the short-circuit current, Z is the load of the secondary side of the current transformer, KrwThe steady-state remanence coefficient of the current transformer is a short-circuit current ending angle theta, BrResidual magnetism of the current transformer after short-circuit fault;
wherein B isr_phase1～Br_phase3Representing the remanence of the first to third phase current transformers.
Preferably, at step 105: and respectively calculating the residual magnetism weight coefficients of the three-phase current transformer.
Preferably, the residual magnetism weight coefficients of the three-phase current transformer are respectively calculated, and the method comprises the following steps:
Preferably, at step 106: and calculating the residual magnetism of the current transformer according to the residual magnetism of the three-phase current transformer and the residual magnetism weight coefficient of the three-phase current transformer.
Preferably, the calculating of the residual magnetism of the current transformer according to the residual magnetism of the three-phase current transformer and the residual magnetism weight coefficient of the three-phase current transformer includes:
when the current transformer runs on line, the current transformer cannot be flexibly operated, so that the current transformer is used as a device for transmitting the electric quantity of a primary system, and the residual magnetism in an iron core of the current transformer is evaluated according to a secondary side oscillogram of the current transformer. The variable quantity of the magnetic flux in the iron core can be obtained by using a voltage integration method according to the relation between the induced voltage and the magnetic flux of the current transformer, and in a certain range, the higher the induced voltage is, the larger the magnetic flux value obtained by integration is. The volt-ampere characteristic measurement principle is the same as the measurement principle of a hysteresis loop of a current transformer, so that a voltage point measured in a volt-ampere characteristic curve corresponds to a peak point in the hysteresis loop, or the voltage point measured in the volt-ampere characteristic curve corresponds to a magnetic flux point in a magnetization curve, as shown in formula (1):
wherein: u is any voltage point of volt-ampere characteristic, UmIs the saturation voltage point of the current-voltage characteristic curve, BmThe saturation flux point of the magnetization curve is shown, and B is the flux point corresponding to the voltage U.
When the system has short-circuit fault, the secondary wave recording equipment can record the information of short-circuit fault current. The periodic component value and the ending angle of the short-circuit current can be obtained from the short-circuit current oscillogram. Considering the condition that the residual magnetism of the current transformer is the most serious condition, namely the condition that the short-circuit current is cut off when passing zero, the magnetic flux lags the voltage by 90 degrees, and therefore the instantaneous magnetic flux value in the iron core of the current transformer is the largest. When the short-circuit current disappears, residual magnetism can be formed in the iron core of the current transformer, and according to the research of the state of the residual magnetism, the residual magnetism of the iron core can have a descending process, and finally the residual magnetism can reach a stable residual magnetism state. The calculation of the core remanence after a short-circuit fault is shown in equation (2):
wherein: i is the effective value of the short-circuit current, Z is the load of the secondary side of the current transformer, KrwIs the steady state remanence coefficient of the current transformer, BrThe residual magnetism of the iron core after short-circuit fault.
Assuming that the primary system short-circuit current can be expressed by a sine function, and the angle of the breaker for breaking the short-circuit fault is theta, because the power factor range of the secondary load of the current transformer is 0.8-1, when the short-circuit current ending angle is theta, the calculation of the residual magnetism of the iron core of the current transformer is shown as formula (3):
although the remanence has directionality, the remanence in the positive and negative directions has consistent influence on the metering characteristics of the current transformer, so the transformer remanence evaluation in the formula (3) takes the absolute value thereof, and the remanence shown in the formula (3) is the evaluation result of the remanence of the single-phase current transformer core.
According to the regulation of power transmission and transformation engineering design of national grid company, the electric quantity calculation process of the electric quantity metering device of the electric power system is completed by matching a current transformer and a voltage transformer. Generally, the wiring method of the current transformer is a three-phase four-wire system, and the like, so that the current metering error of the current transformer is comprehensively formed by the errors of the three-phase current transformer. Therefore, the evaluation of the metering characteristics in the electric energy metering device needs to take the overall remanence evaluation of the three-phase current transformer into consideration.
Because of the influence of the phase difference of three-phase current and the action of the circuit breaker in non-synchronization, the ending angle of each phase of short-circuit current is different, the residual magnetism generated in the iron core of the current transformer is also different, and the calculation of the residual magnetism of the current transformer on each phase of circuit is shown as a formula (4):
the remanence expression for the i-th phase is shown in formula (4), wherein Br_phase1～Br_phase3Representing the remanence of the first to third phases.
Since the residual magnetism of the three-phase current transformers is integrally evaluated, the evaluation result needs to include the residual magnetism of all the three-phase current transformers. However, the residual magnetism of each phase current transformer is different, and the influence weight on the electric quantity metering error of the electric energy metering device is also different. Because the residual magnetism of the current transformer is small, when the current transformer operates in a linear region in a steady state, the metering error is small. But when the remanence of the current transformer is increased and the current transformer is operated in a nonlinear area in a steady state, the metering error is increased rapidly. Therefore, when the remanence of the current transformer is evaluated, the larger the remanence is, the larger the weight coefficient of the current transformer is. The weighting factor of the remanence of each phase of the current transformer can be defined as shown in equation (5):
known from the evaluation method of the residual magnetism of the current transformer, the famous value of the residual magnetism which can be obtained at the end of the evaluation is shown in a formula (6):
this application uses silicon steel current transformer as an example, assumes after taking place three-phase short circuit fault, aassessment three-phase current transformer iron core remanence of metering point behind the short circuit fault:
(1) reading short-circuit current information of secondary wave recording equipment on a power transmission line to obtain that the effective value of the short-circuit current is 10A, and the end angles of the short-circuit current of the three-phase current transformer are respectively 0 degree, 120 degrees and 240 degrees;
(2) calling the basic magnetization curve of the current transformer at the metering point to obtain a saturation flux point B of the current transformer to be evaluatedm＝0.22T；
(3) Calling the volt-ampere characteristic curve of the current transformer at the metering point to obtain a saturation voltage point U of the current transformer to be evaluatedm＝30V；
(4) Calling other data of delivery, debugging and the like of the current transformer to obtain that the remanence coefficient of the current transformer is 0.6, and the load impedance of the secondary side of the on-site current transformer is 2.5 omega;
(5) calculating the residual magnetism of the iron core of the current transformer of each phase by using a formula (4) to obtain
(6) Calculating the weight coefficient of the remanence of each phase current transformer by using a formula (5) to obtain
(7) The integral remanence evaluation is carried out by using the formula (6) to obtain
Br＝0.11×0.5+0.055×0.25+0.055×0.25＝0.0825T。
According to the embodiment of the invention, the calculation method of the internal remanence of the current transformer made of different iron core materials after the short-circuit fault is effectively evaluated. The method can be used as a transmission mode, connects the remanence with the error, provides technical support for accurately evaluating the accuracy of the current transformer for metering, and effectively evaluates the remanence of the current transformer after short circuit fault. The residual magnetism assessment method is used for assessing residual magnetism based on the principle that the volt-ampere characteristic of the current transformer corresponds to the magnetization characteristic, when the residual magnetism assessment is conducted, firstly, an induced voltage value of a secondary side load of the current transformer at the end moment of a short-circuit fault is obtained, then, a flux value of an iron core is obtained by utilizing the volt-ampere characteristic curve and a basic magnetization curve, and finally, the residual magnetism value of the iron core is obtained by combining the residual magnetism coefficient of the current transformer. The residual magnetism method focuses on a current transformer for metering, is suitable for current transformers made of different materials such as silicon steel, ultra-microcrystalline alloy and permalloy, and carries out overall evaluation on three-phase current transformers at metering points in an electric power system. The method for evaluating the residual magnetism of the current transformer has simple operation steps, can effectively evaluate the residual magnetism of the iron core, can carry out online operation, has no adverse effect on the original structure and the normal work of the current transformer, and has important significance on the accurate measurement of the current transformer.
The method for evaluating the residual magnetism of the current transformer has high applicability, can be applied to lines with different voltage levels, and can evaluate the current transformers for metering of different iron core materials (silicon steel, ultra-microcrystalline alloy and permalloy). The residual magnetism evaluation method for the current transformer for metering can effectively evaluate the residual magnetism in the iron core after the short circuit fault, provides powerful technical support for daily operation and maintenance work of the current transformer, is an important guarantee for the accuracy of electric energy metering, and has high economic benefit.
Fig. 2 is a system configuration diagram for evaluating residual magnetism of a current transformer for metering according to an embodiment of the present invention. As shown in fig. 2, a system for evaluating remanence of a current transformer for metrology, the system comprising:
the first obtaining unit 201 is configured to obtain a current ending angle and an effective value of a short-circuit current when a short-circuit fault occurs according to a secondary oscillogram of the power transmission line.
The second acquisition unit 202 acquires a magnetic flux value at a saturation magnetic flux point and a voltage value at a saturation voltage point using the basic magnetization curve.
Preferably, the second obtaining unit 202 is further configured to:
from voltage points measured in the current-voltage characteristic curve corresponding to flux points in the magnetisation curve, i.e.
Wherein: u is any voltage point of volt-ampere characteristic, UmIs the saturation voltage point of the current-voltage characteristic curve, BmThe value of the magnetic flux at the saturation point of the basic magnetization curve is shown, and B is the value of the magnetic flux at the saturation point of the voltage U.
And a third obtaining unit 203, configured to obtain the residual magnetic coefficient of the current transformer and the impedance of the secondary load in advance.
The first calculating unit 204 is configured to calculate, according to the current end angle, the effective value of the short-circuit current, the magnetic flux value of the saturation magnetic flux point, the voltage value of the saturation voltage point, the residual magnetism coefficient of the current transformer, and the impedance of the secondary load, the residual magnetism of the current transformer of each of the three phases.
Preferably, the first computing unit 204 is further configured to:
wherein, I is the effective value of the short-circuit current, Z is the load of the secondary side of the current transformer, KrwThe steady-state remanence coefficient of the current transformer is a short-circuit current ending angle theta, BrResidual magnetism of the current transformer after short-circuit fault;
wherein B isr_phase1～Br_phase3Representing the remanence of the first to third phase current transformers.
And the second calculating unit 205 is used for calculating the residual magnetism weight coefficients of the three-phase current transformer respectively.
Preferably, the second calculation unit 205 is further configured to:
And a third calculating unit 206, configured to calculate the remanence of the current transformer according to the remanence of the three-phase current transformer and the remanence weight coefficient of the three-phase current transformer.
Preferably, the third computing unit 206 is further configured to:
preferably, the current transformer comprises a current transformer of silicon steel, ultra-crystalline alloy, permalloy material.
The system 200 for evaluating residual magnetism of a current transformer for metering according to an embodiment of the present invention corresponds to the method 100 for evaluating residual magnetism of a current transformer for metering according to another embodiment of the present invention, and will not be described herein again.
The invention has been described with reference to a few embodiments. However, other embodiments of the invention than the one disclosed above are equally possible within the scope of the invention, as would be apparent to a person skilled in the art from the appended patent claims.
Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the [ device, component, etc ]" are to be interpreted openly as referring to at least one instance of said device, component, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.
Claims (12)
1. A method for evaluating remanence of a current transformer for metering, the method comprising:
acquiring a current ending angle and an effective value of a short-circuit current when a short-circuit fault occurs according to a secondary recording chart of the power transmission line;
acquiring a magnetic flux value of a saturation magnetic flux point and a voltage value of a saturation voltage point by using a basic magnetization curve;
acquiring a residual magnetic coefficient of the current transformer and impedance of a secondary load in advance;
respectively calculating the residual magnetism of the current transformer of each phase in the three phases according to the current ending angle, the effective value of the short-circuit current, the magnetic flux value of the saturation magnetic flux point, the voltage value of the saturation voltage point, the residual magnetism coefficient of the current transformer and the impedance of the secondary load;
respectively calculating the residual magnetism weight coefficients of the three phases of the current transformer;
and calculating the residual magnetism of the current transformer according to the residual magnetism of the current transformer of each phase and the residual magnetism weight coefficient of the three phases of the current transformer.
2. The method of claim 1, wherein obtaining the magnetic flux value at the saturation flux point and the voltage value at the saturation voltage point using the basic magnetization curve comprises:
from voltage points measured in the current-voltage characteristic curve corresponding to flux points in the magnetisation curve, i.e.
Wherein: u is any voltage point of volt-ampere characteristic, UmIs the saturation voltage point of the current-voltage characteristic curve, BmThe value of the magnetic flux at the saturation flux point of the basic magnetization curve is B, and the value of the magnetic flux at the flux point corresponding to the voltage U is B.
3. The method of claim 2, said calculating the residual magnetism of the current transformer for each of the three phases separately from the current end angle, the effective value of the short circuit current, the flux value of the saturation flux point, the voltage value of the saturation voltage point, the residual magnetism coefficient of the current transformer, and the impedance of the secondary load, comprising:
wherein, I is the effective value of the short-circuit current, Z is the load of the secondary side of the current transformer, KrwThe steady-state remanence coefficient of the current transformer is a short-circuit current ending angle theta, BrResidual magnetism of the current transformer after short-circuit fault;
wherein B isr_phase1～Br_phase3Representing the remanence of the current transformer for the first phase to the third phase.
4. The method of claim 3, the separately calculating remanence weighting coefficients for a three-phase current transformer, comprising:
5. The method of claim 4, the calculating the remanence of the current transformer from the remanence of the current transformer for each phase and remanence weight coefficients of the current transformer three phases, comprising:
6. the method of claim 1, the current transformer comprising silicon steel, ultra-crystalline alloy, or permalloy material.
7. A system for assessing residual magnetism of a current transformer for metering, the system comprising:
the first acquisition unit is used for acquiring a current ending angle and an effective value of a short-circuit current when the short-circuit fault occurs according to a secondary oscillogram of the power transmission line;
a second acquisition unit that acquires a magnetic flux value of a saturation magnetic flux point and a voltage value of a saturation voltage point using the basic magnetization curve;
the third acquisition unit is used for acquiring the residual magnetism coefficient of the current transformer and the impedance of a secondary load in advance;
a first calculating unit, configured to calculate, according to the current end angle, the effective value of the short-circuit current, the magnetic flux value of the saturation magnetic flux point, the voltage value of the saturation voltage point, the residual magnetism coefficient of the current transformer, and the impedance of the secondary load, the residual magnetism of the current transformer of each of the three phases respectively;
the second calculating unit is used for calculating the residual magnetism weight coefficients of the three phases of the current transformer respectively;
and the third calculating unit is used for calculating the residual magnetism of the current transformer according to the residual magnetism of the current transformer of each phase and the residual magnetism weight coefficient of the three phases of the current transformer.
8. The system of claim 7, the second acquisition unit further to:
from voltage points measured in the current-voltage characteristic curve corresponding to flux points in the magnetisation curve, i.e.
Wherein: u is any voltage point of volt-ampere characteristic, UmIs a voltammetric curveLine saturation voltage point, BmThe value of the magnetic flux at the saturation flux point of the basic magnetization curve is B, and the value of the magnetic flux at the flux point corresponding to the voltage U is B.
9. The system of claim 8, the first computing unit to further:
wherein, I is the effective value of the short-circuit current, Z is the load of the secondary side of the current transformer, KrwThe steady-state remanence coefficient of the current transformer is a short-circuit current ending angle theta, BrResidual magnetism of the current transformer after short-circuit fault;
wherein B isr_phase1～Br_phase3Representing the remanence of the current transformer for the first phase to the third phase.
10. The system of claim 9, the second computing unit to further:
11. The system of claim 10, the third computing unit further to:
12. the system of claim 7, the current transformer comprising silicon steel, ultra-crystalline alloy, or permalloy material.
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