CN112698246A - Transformer excitation inrush current identification method and device based on current abrupt change - Google Patents
Transformer excitation inrush current identification method and device based on current abrupt change Download PDFInfo
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- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
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Abstract
The invention discloses a transformer magnetizing inrush current identification method and device based on a current abrupt change. The method comprises the following steps: determining a first differential current sudden change characteristic or a second differential current sudden change characteristic corresponding to the current sampling moment according to the acquired current of each phase at the Y side and the current of each phase at the delta side of the transformer; determining whether a first excitation inrush current criterion is established or not according to an accumulated value of the first differential current sudden change characteristic from a first sampling moment to a current sampling moment in the current cycle; or determining whether a first excitation inrush current criterion is established or not according to the accumulated value of the characteristics of the sudden change of the second differential current from the first sampling moment to the current sampling moment in the current cycle; when a first magnetizing inrush current criterion is met, the transformer is determined to be in a magnetizing inrush current state, and a locking instruction is generated and used for locking the differential current protection of the transformer. The method can quickly and reliably identify the magnetizing inrush current state of the transformer within one cycle, and has the advantages of simple calculation and good anti-interference performance.
Description
Technical Field
The invention belongs to the technical field of relay protection, and particularly relates to a transformer magnetizing inrush current identification method and device based on a current abrupt change.
Background
Transformers are one of the important electrical primary devices in power systems where they function to change voltage levels.
Along with the grid-connected operation of a supercritical unit, the construction of an extra-high voltage transmission network and the formation of close connection among all large-area power grids, the position of a large transformer becomes particularly important along with the construction of a large-capacity and large-power grid, and the improvement of the reliability, the sensitivity and the like of the transformer protection has great significance for ensuring the safe and stable operation of the whole system.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a transformer magnetizing inrush current identification method and device based on a current abrupt change, and aims to solve the problem that the reliability and the sensitivity of the transformer magnetizing inrush current identification method in the prior art are insufficient.
In a first aspect, the present invention provides a method for identifying a transformer inrush current based on a current break variable, including:
determining a first differential current sudden change characteristic or a second differential current sudden change characteristic corresponding to the current sampling moment according to the acquired current of each phase at the Y side and the current of each phase at the delta side of the transformer;
determining whether a first excitation inrush current criterion is established or not according to an accumulated value of the first differential current sudden change characteristic from a first sampling moment to a current sampling moment in the current cycle; or
Determining whether a first excitation inrush current criterion is established or not according to the accumulated value of the characteristics of the sudden change of the second differential current from the first sampling moment to the current sampling moment in the current cycle;
when a first magnetizing inrush current criterion is met, the transformer is determined to be in a magnetizing inrush current state, and a locking instruction is generated and used for locking the differential current protection of the transformer.
Specifically, the method further comprises the following steps:
determining whether a second excitation inrush current criterion is established according to an accumulated value of the first differential current sudden change characteristic from a first sampling moment to a current sampling moment in the current cycle; or
Determining whether a second excitation inrush current criterion is established according to an accumulated value of the characteristics of the sudden change of the second differential current from the first sampling moment to the current sampling moment in the current cycle;
and when a second magnetizing inrush current criterion is met, determining that the transformer is in a magnetizing inrush current state, and generating a locking instruction, wherein the locking instruction is used for locking the differential current protection of the transformer.
Specifically, when a first magnetizing inrush current criterion is not established and a second magnetizing inrush current criterion is established, determining that the transformer is in a magnetizing inrush current state, and generating a locking instruction, wherein the locking instruction is used for locking the differential current protection of the transformer; or
And when the first magnetizing inrush current criterion is established but the second magnetizing inrush current criterion is not established, determining that the transformer is in a magnetizing inrush current state, and generating a locking instruction, wherein the locking instruction is used for locking the differential current protection of the transformer.
Specifically, when the first magnetizing inrush current criterion is not established and the second magnetizing inrush current criterion is not established, it is determined that the transformer is not in the magnetizing inrush current state.
Specifically, determining a first differential current abrupt change characteristic corresponding to the current sampling moment comprises the following steps:
and carrying out weighted summation on the difference value of the current sudden change quantity of the current phase Y side and the zero sequence current of the Y side and the difference value of the current sudden change quantity of the current phase delta side and the current sudden change quantity of the current phase delta side adjacent to the current sudden change quantity of the current phase delta side along the clockwise direction to obtain a first differential current sudden change quantity characteristic.
Specifically, determining a second differential current abrupt change characteristic corresponding to the current sampling time includes:
and carrying out weighted summation on the sum of the current sudden change quantity of the current phase Y side and the zero sequence current of the Y side and the difference between the current sudden change quantity of the current phase delta side and the current sudden change quantity of the current phase delta side adjacent to the current sudden change quantity of the current phase delta side along the clockwise direction to obtain a second differential current sudden change quantity characteristic.
Specifically, determining whether the first magnetizing inrush current criterion is satisfied includes:
determining a first excitation inrush current judging quantity according to an accumulated value of the characteristics of the sudden change quantity of the first differential current, the total sampling time number of each cycle and the rated current of the transformer from the first sampling time to the current sampling time in the current cycle, and determining that a first excitation inrush current criterion is established when the first excitation inrush current judging quantity is not greater than a preset first threshold value; or
And determining a first excitation inrush current judging quantity according to an accumulated value of the characteristics of the sudden change quantity of the second differential current, the total sampling time quantity of each cycle and the rated current of the transformer from the first sampling time to the current sampling time in the current cycle, and determining that a first excitation inrush current criterion is established when the first excitation inrush current judging quantity is not more than a preset first threshold value.
Specifically, determining whether the second magnetizing inrush current criterion is satisfied includes:
determining a second excitation inrush current judgment quantity according to an accumulated value of first differential current sudden change quantity characteristics, the total sampling time number of each cycle and the maximum value of the first differential current sudden change quantity characteristics corresponding to the current cycle from the first sampling time to the current sampling time from the first sampling time in the current cycle, and determining that a second excitation inrush current judgment criterion is established when the second excitation inrush current judgment quantity is not greater than a second threshold value, wherein the second threshold value is determined according to the accumulated value of the first differential current sudden change quantity characteristics from the first sampling time to the current sampling time in the current cycle; or
Determining a second excitation inrush current judging quantity according to an accumulated value of second differential current abrupt change quantity characteristics, the total sampling time number of each cycle and the maximum value of the second differential current abrupt change quantity characteristics corresponding to the current cycle from the first sampling time to the current sampling time in the current cycle, and determining that a second excitation inrush current judging quantity is established when the second excitation inrush current judging quantity is not greater than a second threshold value, wherein the second threshold value is determined according to the accumulated value of the second differential current abrupt change quantity characteristics from the first sampling time to the current sampling time in the current cycle.
In a second aspect, the present invention provides a transformer magnetizing inrush current recognition apparatus based on a current transient, including:
the differential current sudden change characteristic determining unit is used for determining a first differential current sudden change characteristic or a second differential current sudden change characteristic corresponding to the current sampling moment according to the acquired phase current at the Y side and phase current at the delta side of the transformer;
the first excitation inrush current criterion determining unit is used for determining whether the first excitation inrush current criterion is satisfied according to an accumulated value of the first differential current sudden change characteristic from a first sampling time to a current sampling time in the current cycle; or
Determining whether a first excitation inrush current criterion is established or not according to the accumulated value of the characteristics of the sudden change of the second differential current from the first sampling moment to the current sampling moment in the current cycle;
and the inrush current identification response unit is used for determining that the transformer is in an inrush current state and generating a locking instruction when a first inrush current criterion is met, wherein the locking instruction is used for locking the differential current protection of the transformer.
Specifically, the method further comprises the following steps:
the second excitation inrush current criterion determining unit is used for determining whether a second excitation inrush current criterion is satisfied according to an accumulated value of the first differential current sudden change characteristic from a first sampling time to a current sampling time in the current cycle; or
Determining whether a second excitation inrush current criterion is established according to an accumulated value of the characteristics of the sudden change of the second differential current from the first sampling moment to the current sampling moment in the current cycle;
and the inrush current identification response unit is further used for determining that the transformer is in an inrush current state and generating a locking instruction when a second inrush current criterion is met, wherein the locking instruction is used for locking the differential current protection of the transformer.
In a third aspect, the present invention provides a computer storage medium for executing the method for identifying a transformer magnetizing inrush current based on a current inrush quantity according to the first aspect.
The transformer magnetizing inrush current identification method and device based on the current abrupt change eliminate the differential current abrupt change of the zero sequence current by using the current abrupt change, construct the transformer magnetizing inrush current identification criterion by using the differential current abrupt change, accurately identify the transformer magnetizing inrush current state within a cycle by using the criterion, and have the advantages of simple calculation and good anti-interference performance. According to the transformer magnetizing inrush current identification method and device based on the current abrupt change, the magnetizing inrush current identification criterion of the transformer is constructed by using the magnetizing inrush current component in the zero sequence current, so that the magnetizing inrush current identification capability is improved; the identification efficiency of the magnetizing inrush current is effectively improved by the introduced characteristic quantity of the maximum value of the sudden change of the differential current.
Drawings
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 schematic flow chart of a transformer magnetizing inrush current identification method based on a current mutation quantity according to a preferred embodiment of the present invention;
FIG. 2 is a schematic diagram of the transformer magnetizing inrush current identification device based on the current break variable according to the preferred embodiment of the present invention;
3(a), 3(b), 3(c) and 3(d) are simulation curves of the phase current of the fault phase A when a fault occurs in a certain type of transformer area and the result of the criterion;
fig. 4(a), 4(B), 4(c) and 4(d) are schematic diagrams of current waveforms of a certain type of transformer which is put into no-load operation to generate magnetizing inrush current, and the current waveforms of the certain type of transformer which is put into no-load operation are identified as the magnetizing inrush current by using a second inrush current identification criterion for a phase B with the maximum differential current;
fig. 5(a), 5(B), 5(c) and 5(d) are schematic diagrams of a current waveform of a certain type of transformer which is put into no-load operation to generate a magnetizing inrush current and a characteristic that the current waveform is identified as the magnetizing inrush current by using a first inrush current identification criterion for a phase B with the maximum differential current.
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.
The power transformer is an important device of a power plant and a transformer substation, and the safe operation of the power transformer is directly related to the continuous stable operation of the whole power system. The transformer has inherent parameters of rated capacity, rated voltage, rated current and the like.
The transformer differential current protection establishes a differential current criterion according to currents obtained from current transformers on a high-voltage side and a low-voltage side, and realizes protection of internal faults of a transformer. That is, when no internal fault occurs in the transformer, the differential current protection does not operate; when an internal fault occurs in the transformer, the differential current protection operates to remove the power transformer from the system.
Specifically, the differential current protection determines an excitation current of the transformer from a current value obtained from the current transformer, and determines whether or not an internal failure of the transformer occurs based on a criterion related to the excitation current. When no internal fault occurs in the transformer, the criterion related to the exciting current is not established, and the differential current protection does not act. When an internal fault occurs in the transformer, a criterion related to the exciting current is established, and the differential current protection acts to cut the power transformer from the system.
When the transformer normally operates, the magnetic conductivity of the transformer is very large, so that the excitation inductance of the transformer is also very large, the iron core of the transformer is unsaturated, the excitation current is relatively small, and the excitation current is approximately 2% -5% of the rated current. At this time, the exciting current does not trigger the differential current protection action, so that the differential current protection malfunction does not occur and the normal operation of the transformer is not influenced. However, when the transformer is switched into a no-load state, the electromagnetic phenomenon peculiar to the transformer is triggered, and at this time, the transformer is in a magnetizing inrush current state.
Specifically, when the transformer is switched into no-load operation, the voltage of the transformer rises to its rated voltage instantaneously, a large step occurs in the voltage, and the transformer must establish a corresponding magnetic flux to establish magnetomotive force balance. In the process of establishing the magnetic flux, the step voltage easily causes the transformer core to be seriously saturated even to the degree of complete saturation, the transformer directly works in the core saturation state, and when the core is in the saturation state, the equivalent excitation impedance is very small, and very large excitation current is generated. During the transient process of voltage step, the transient exciting current with amplitude much larger than the rated current of the transformer is generated and is generally called exciting inrush current.
According to field operation and laboratory data statistics, when the transformer is put into no-load operation, the maximum magnetizing inrush current can reach 4-8 times of the normal operation current. At present, magnetizing inrush current is a main source causing misoperation of differential current protection of a transformer.
Aiming at 2 working conditions of no-load input and internal faults of a transformer in operation, differential current protection is required to act when the internal faults occur; when the load is switched on, the differential current protection does not act.
According to the method for identifying the magnetizing inrush current of the transformer based on the current abrupt change, disclosed by the embodiment of the invention, after the magnetizing inrush current state of the transformer under the no-load operation working condition is identified, the differential current protection of the transformer is locked, the protection misoperation is avoided, and the stable operation of the transformer is ensured.
The inrush current identification device of the embodiment of the invention does not modify or replace the existing differential current protection of internal faults; in the existing transformer, a magnetizing inrush current identification software module is newly added, and the software module identifies whether the transformer is in a magnetizing inrush current state or not according to current data acquired from a current transformer; and when the transformer is in an excitation inrush current state, the existing differential current protection is actively locked.
As shown in fig. 1, a method for identifying a transformer magnetizing inrush current based on a current mutation according to an embodiment of the present invention includes:
step S100: determining a first differential current sudden change characteristic or a second differential current sudden change characteristic corresponding to the current sampling moment according to the acquired current of each phase at the Y side and the current of each phase at the delta side of the transformer;
step S210: determining whether a first excitation inrush current criterion is established or not according to an accumulated value of the first differential current sudden change characteristic from a first sampling moment to a current sampling moment in the current cycle; or
Step S220: determining whether a first excitation inrush current criterion is established or not according to the accumulated value of the characteristics of the sudden change of the second differential current from the first sampling moment to the current sampling moment in the current cycle;
step S300: when a first magnetizing inrush current criterion is met, the transformer is determined to be in a magnetizing inrush current state, and a locking instruction is generated and used for locking the differential current protection of the transformer.
The above steps S210 and S220 do not distinguish the execution sequence, and the technical effect is the same regardless of the execution sequence.
Specifically, the method further comprises the following steps:
determining whether a second excitation inrush current criterion is established according to an accumulated value of the first differential current sudden change characteristic from a first sampling moment to a current sampling moment in the current cycle; or
Determining whether a second excitation inrush current criterion is established according to an accumulated value of the characteristics of the sudden change of the second differential current from the first sampling moment to the current sampling moment in the current cycle;
and when a second magnetizing inrush current criterion is met, determining that the transformer is in a magnetizing inrush current state, and generating a locking instruction, wherein the locking instruction is used for locking the differential current protection of the transformer.
Specifically, when a first magnetizing inrush current criterion is not established and a second magnetizing inrush current criterion is established, determining that the transformer is in a magnetizing inrush current state, and generating a locking instruction, wherein the locking instruction is used for locking the differential current protection of the transformer; or
And when the first magnetizing inrush current criterion is established but the second magnetizing inrush current criterion is not established, determining that the transformer is in a magnetizing inrush current state, and generating a locking instruction, wherein the locking instruction is used for locking the differential current protection of the transformer.
Specifically, when the first magnetizing inrush current criterion is not established and the second magnetizing inrush current criterion is not established, it is determined that the transformer is not in the magnetizing inrush current state.
Specifically, determining a first differential current abrupt change characteristic corresponding to the current sampling moment comprises the following steps:
and carrying out weighted summation on the difference value of the current sudden change quantity of the current phase Y side and the zero sequence current of the Y side and the difference value of the current sudden change quantity of the current phase delta side and the current sudden change quantity of the current phase delta side adjacent to the current sudden change quantity of the current phase delta side along the clockwise direction to obtain a first differential current sudden change quantity characteristic.
Wherein the first differential current step change characteristic is calculated according to the following formula:
in the formula (1), the reaction mixture is,
calculating the zero sequence current of the Y side of the transformer at any sampling time t:
as shown in formula (1), the first differential current abrupt change is characterized by 3:
the differential current abrupt change characteristics correspond to the A, B, C three phases.
When the transformer normally operates, the A, B, C three-phase magnetic potential is balanced, and the first differential current sudden change characteristics corresponding to the A, B, C three phases are all 0.
Specifically, according to equation (2), the Y-side current transient of each phase is calculated, respectively:
in formula (2):
respectively obtaining the current of each phase Y side of the transformer at any sampling time t in the current cycle;
wherein T is a power frequency period; when the power frequency is 50, T is 20ms, and the value range of T is 1-20 ms.
In specific implementation, 24 sampling data are acquired in each cycle, that is, there are 24 sampling time instants, N = 24.
That is, for each phase on the Y side of the transformer, the difference between the current values corresponding to the same sampling time (i.e., the same phase of the cycle) in the adjacent 2 cycles is used as the Y-side current abrupt change of each phase.
That is, the Y-side current jump of each phase is defined as the change of the current amplitude of the same phase in 2 adjacent cycles.
Specifically, the amount of current variation on each phase Δ -side is calculated according to equation (3):
in formula (3):
respectively obtaining the current of each phase delta side of the transformer at any sampling time t in the current cycle;
wherein T is a power frequency period; when the power frequency is 50, T is 20ms, and the value range of T is 1-20 ms.
That is, for each phase on the delta side of the transformer, the current values corresponding to the same sampling time (i.e., the same phase of the cycle) in the adjacent 2 cycles are differentiated to be used as the delta side current abrupt change of each phase.
That is, the delta-side current jump of each phase is defined as the change amount of the current amplitude of the same phase in the adjacent 2 cycles.
Specifically, determining a second differential current abrupt change characteristic corresponding to the current sampling time includes:
and carrying out weighted summation on the sum of the current sudden change quantity of the current phase Y side and the zero sequence current of the Y side and the difference between the current sudden change quantity of the current phase delta side and the current sudden change quantity of the current phase delta side adjacent to the current sudden change quantity of the current phase delta side along the clockwise direction to obtain a second differential current sudden change quantity characteristic.
Wherein the second differential current step change characteristic is calculated according to the following formula:
as shown in equation (4), the second differential current step change is characterized by 3:
the differential current abrupt change characteristics correspond to the A, B, C three phases.
When the transformer normally operates, the characteristics of the sudden change quantities of the second differential currents respectively corresponding to the A, B, C three phases are all 0.
It is to be understood that formula (4) differs from formula (1) in that, in one formula, it is "
", 2 is in the formula"
". The reason for introducing the zero sequence current by the sum value and the difference value is that the theoretical basis that a large amount of inrush current components are contained in the zero sequence current on the Y side of the transformer is utilized, and the inrush current identification is facilitated to be fast and accurate.
In summary, there are 3 first differential current step-change characteristics, and 3 second differential current step-change characteristics; therefore, the 6 characteristics of the sudden change of the differential current are respectively applied to the first excitation inrush current criterion, and 6 identification conclusions can be obtained. Aiming at all 6 identification conclusions, the transformer can be judged to be in the magnetizing inrush current state as long as any one of the identification conclusions is in the magnetizing inrush current state; and only if all 6 recognition conclusions are not in the magnetizing inrush current state, the transformer can be judged not to be in the magnetizing inrush current state.
In summary, there are 3 first differential current step-change characteristics, and 3 second differential current step-change characteristics; and the 6 characteristics of the sudden change of the differential current are respectively applied to a second excitation inrush current criterion, so that 6 identification conclusions can be obtained. Aiming at all 12 identification conclusions, the transformer can be judged to be in the magnetizing inrush current state as long as any one identification conclusion is in the magnetizing inrush current state; and only if all 12 recognition conclusions are not in the magnetizing inrush current state, the transformer can be judged not to be in the magnetizing inrush current state.
Specifically, determining whether the first magnetizing inrush current criterion is satisfied includes:
determining a first excitation inrush current judging quantity according to an accumulated value of the characteristics of the sudden change quantity of the first differential current, the total sampling time number of each cycle and the rated current of the transformer from the first sampling time to the current sampling time in the current cycle, and determining that a first excitation inrush current criterion is established when the first excitation inrush current judging quantity is not greater than a preset first threshold value; or
And determining a first excitation inrush current judging quantity according to an accumulated value of the characteristics of the sudden change quantity of the second differential current, the total sampling time quantity of each cycle and the rated current of the transformer from the first sampling time to the current sampling time in the current cycle, and determining that a first excitation inrush current criterion is established when the first excitation inrush current judging quantity is not more than a preset first threshold value.
Specifically, the first excitation inrush current criterion is shown as equation (5),
wherein the content of the first and second substances,K set1 is a first setting coefficient (also called a first threshold value);
n is the number of sampling moments in each cycle;
the running total spans M sample times from the first sample time to the current sample time.
Specifically, from the first sampling time, equation (5) is always satisfied, and it is determined that the transformer is in the inrush current state; until a certain sampling moment is delayed after the time, the equation (5) is not satisfied any more, and the transformer is determined not to be in the magnetizing inrush current state.
Specifically, will
And respectively substituting the results into the formula (5) to obtain 6 inrush current identification results aiming at the first excitation inrush current criterion. The inrush current identification result includes: and determining that the transformer is in a magnetizing inrush current state and determining that the transformer is not in the magnetizing inrush current state.
Specifically, determining whether the second magnetizing inrush current criterion is satisfied includes:
determining a second excitation inrush current judgment quantity according to an accumulated value of first differential current sudden change quantity characteristics, the total sampling time number of each cycle and the maximum value of the first differential current sudden change quantity characteristics corresponding to the current cycle from the first sampling time to the current sampling time from the first sampling time in the current cycle, and determining that a second excitation inrush current judgment criterion is established when the second excitation inrush current judgment quantity is not greater than a second threshold value, wherein the second threshold value is determined according to the accumulated value of the first differential current sudden change quantity characteristics from the first sampling time to the current sampling time in the current cycle; or
Determining a second excitation inrush current judging quantity according to an accumulated value of second differential current abrupt change quantity characteristics, the total sampling time number of each cycle and the maximum value of the second differential current abrupt change quantity characteristics corresponding to the current cycle from the first sampling time to the current sampling time in the current cycle, and determining that a second excitation inrush current judging quantity is established when the second excitation inrush current judging quantity is not greater than a second threshold value, wherein the second threshold value is determined according to the accumulated value of the second differential current abrupt change quantity characteristics from the first sampling time to the current sampling time in the current cycle.
Specifically, the second excitation inrush current criterion is shown as equation (6),
wherein the content of the first and second substances,
；
K set2 Is a second setting coefficient (also called a second threshold value);
Specifically, from the first sampling time, equation (6) is always satisfied, and it is determined that the transformer is in the inrush current state; until a certain sampling moment is delayed after the time, the equation (6) is not satisfied any more, and the transformer is determined not to be in the magnetizing inrush current state.
Specifically, will
And respectively substituting the results into the formula (6) to obtain 6 inrush current identification results aiming at the second excitation inrush current criterion. The inrush current identification result includes: and determining that the transformer is in a magnetizing inrush current state and determining that the transformer is not in the magnetizing inrush current state.
As shown in fig. 2, the apparatus for identifying inrush current of transformer based on abrupt current variation according to an embodiment of the present invention includes:
the differential current sudden change quantity characteristic determining unit 10 is used for determining a first differential current sudden change quantity characteristic or a second differential current sudden change quantity characteristic corresponding to the current sampling moment according to the acquired phase current at the Y side and phase current at the delta side of the transformer;
a first excitation inrush current criterion determining unit 21, configured to determine whether a first excitation inrush current criterion is satisfied according to an accumulated value of first differential current abrupt change characteristics from a first sampling time to a current sampling time in a current cycle; or
Determining whether a first excitation inrush current criterion is established or not according to the accumulated value of the characteristics of the sudden change of the second differential current from the first sampling moment to the current sampling moment in the current cycle;
and the inrush current identification response unit 30 is used for determining that the transformer is in an inrush current state when a first inrush current criterion is met, and generating a locking instruction, wherein the locking instruction is used for locking the differential current protection of the transformer.
Specifically, the method further comprises the following steps:
a second excitation inrush current criterion determining unit 22, configured to determine whether a second excitation inrush current criterion is satisfied according to an accumulated value of the first differential current abrupt change characteristic from a first sampling time to a current sampling time in the current cycle; or
Determining whether a second excitation inrush current criterion is established according to an accumulated value of the characteristics of the sudden change of the second differential current from the first sampling moment to the current sampling moment in the current cycle;
the inrush current identification response unit 30 is further configured to determine that the transformer is in an inrush current state when a second inrush current criterion is met, and generate a locking instruction, where the locking instruction is used to lock the transformer differential current protection.
In specific implementation, the identification device is realized by adopting a software program and is stored in a computer storage medium; the inrush current identification method can be implemented by executing the software program by a microcomputer.
Preferably, the transformer implemented with the method for identifying magnetizing inrush current of a transformer based on a current abrupt change comprises:
the current transformers are respectively arranged on the Y side and the delta side;
a differential current protection connected to the current transformer;
the magnetizing inrush current identification device is connected with the current transformer, and is shown in FIG. 2;
when the transformer has an internal fault, differential current protection acts;
when the transformer is in a magnetizing inrush current state, the magnetizing inrush current recognition device generates a lock-out command for locking out the differential current protection.
The transformer magnetizing inrush current identification method based on the current abrupt change identifies the magnetizing inrush current state by using the current abrupt change, and is high in identification degree, reliable in criterion and quick in response.
The method identifies the magnetizing inrush current state at each sampling moment in each cycle, and is rapid and accurate, and good in reliability and anti-interference performance.
The transformer magnetizing inrush current identification method based on the current abrupt change is simple in principle, can quickly and accurately identify the transformer magnetizing inrush current state, and further achieves locking differential current protection during inrush current so as to prevent the differential current protection from being mistakenly operated to influence the stable operation of a power system.
The excitation inrush current identification method is suitable for the most widely applied delta-shaped wiring form, and is explained in a Y-delta-shaped wiring form, wherein Y represents star-shaped wiring and is a high-voltage side; Δ represents a triangular wiring, which is a low voltage side.
Each calculation formula in the inrush current identification method is specifically derived below.
1.1) respectively calculating the current break quantity of each phase Y side by using three-phase current of the transformer Y side:
in the formula (2-1):
respectively obtaining the current of each phase Y side of the transformer at any sampling time t in the current cycle;
wherein T is a power frequency period; when the power frequency is 50, T is 20ms, and the value range of T is 1-20 ms.
In specific implementation, 24 sampling data are acquired in one cycle, that is, there are 24 sampling times, N = 24.
That is, for each phase on the Y side of the transformer, the difference between the current values corresponding to the same sampling time (i.e., the same phase of the cycle) in the adjacent 2 cycles is used as the Y-side current abrupt change of each phase.
That is, the Y-side current jump of each phase is defined as the change of the current amplitude of the same phase in 2 adjacent cycles.
1.3) calculating the differential current break variable by using the Y-side current break variable of each phase, the delta-side current break variable of each phase and the Y-side zero sequence current, wherein the formula is as follows:
in the formula (2-3),
calculating the zero sequence current of the Y side of the transformer at any sampling time t:
That is, the weighted sum of the differential value between the current phase delta-side current break variable and the current zero sequence current on the Y side and the differential value between the current phase delta-side current break variable and the current break variable on the delta-side current break variable on the adjacent phase in the clockwise direction is obtained.
When the transformer normally operates, A, B, C three-phase magnetic potential is balanced, and the first differential current sudden change quantity characteristic corresponding to each of the A, B, C three phases is 0.
1.4) calculating the differential current break variable by using the Y-side current break variable of each phase, the delta-side current break variable of each phase and the Y-side zero sequence current, wherein the formula is as follows:
in the formula (2-4), the metal salt,
a, B, C three phases of corresponding second differential current sudden change characteristics.
When the transformer normally operates, the values of the formula (2-1) and the formula (2-2) are zero; the second differential current abrupt change characteristic corresponding to each of the A, B, C three phases is 0.
1.5) respectively utilizing the current mutation quantity of each phase Y side, the current mutation quantity of each phase delta side, the first differential current mutation quantity characteristic and the second differential current mutation quantity characteristic to construct the following transformer excitation inrush current identification criterion:
criterion 1:
（2-5）
in the formula (5), the reaction mixture is,K set1 is a first setting coefficient.
Specifically, from the first sampling time, equation (2-5) is always satisfied, and it is determined that the current is in the magnetizing inrush current state; until a certain sampling time is delayed after the time, the expression (2-5) is not satisfied, and the condition of excitation inrush current is determined.
Specifically, will
These 6 variables are substituted into equations (2-5), respectively, and 6 inrush current recognition results for criterion 1 can be obtained. The inrush current identification result includes: and determining that the device is in a magnetizing inrush current state and determining that the device is not in the magnetizing inrush current state.
Respectively utilizing the current break variable of each phase Y side, the current break variable of each phase delta side, the first differential current break variable characteristic and the second differential current break variable characteristic to construct the following transformer excitation inrush current identification criterion:
criterion 2:
wherein the content of the first and second substances,
；
Nthe number of sampling moments in each cycle is obtained;
K set2 setting coefficient of criterion 2;
Specifically, from the first sampling time, equation (2-6) is always satisfied, and it is determined that the current is in the magnetizing inrush current state; until a certain sampling time is reached after the time, the expression (2-6) is no longer satisfied, and it is determined that the magnetizing inrush current state is not present.
Specifically, will
These 6 variables are substituted into equations (2-6), respectively, and 6 inrush current recognition results for criterion 2 can be obtained. The inrush current identification result includes: and determining that the device is in a magnetizing inrush current state and determining that the device is not in the magnetizing inrush current state.
Preferably, the first and second electrodes are formed of a metal,K set1 setting coefficients preset in the criterion 1;K set2 setting coefficients preset in the criterion 2; value of whichThe range is 0-1.
1.6) comprehensive decision.
When the magnetizing inrush current is identified by comprehensive decision, the transformer is judged to be in the magnetizing inrush current state as long as any one of the 12 identification results is determined to be in the magnetizing inrush current.
Preferably, the left-hand equation of the calculation formula (2-5) of the criterion 1 is included in the calculation formula (2-6) of the criterion 2. As long as any one of the criterion 1 and the criterion 2 corresponding to the sudden change of the phase A, the phase B or the phase C is established, the current can be judged to be in the magnetizing inrush current; from the perspective of saving the operation amount, the specific implementation formula firstly calculates the criterion 1; only if criterion 1 is not met, criterion 2 is recalculated.
And finally, if any one of the criterion 1 and the criterion 2 corresponding to the sudden change of the phase A, the phase B or the phase C is established, the transformer is identified to be in the magnetizing inrush current state, the locking condition aiming at the existing protection is met, and a locking instruction is generated to lock the existing protection of the transformer.
In conclusion, the transformer magnetizing inrush current identification method based on the current break variable calculates the differential current break variable characteristic containing the zero sequence current by using the current break variable, and constructs the transformer magnetizing inrush current identification criterion by using the differential current break variable characteristic; the principle is simple, device hardware does not need to be changed, the transformer excitation inrush current can be rapidly and accurately identified, and then locking protection in the inrush current is realized, so that the method has important significance for guaranteeing the safe and stable operation of a power system.
Specifically, the method for identifying the magnetizing inrush current of the transformer based on the current abrupt change may be implemented by the following steps:
1) calculating a current break variable of the Y side by using a sampling current value of the Y side of the transformer;
2) calculating a delta side current abrupt change by using a delta side sampling current value of the transformer;
3) calculating a first differential current sudden change characteristic by using the sampling current values of the Y side and the delta side of the transformer and each current sudden change;
4) calculating a second differential current mutation characteristic by using the sampling current values of the Y side and the delta side of the transformer and each current mutation;
5) constructing a transformer excitation inrush current identification criterion by using the first differential current sudden change characteristic and the second differential current sudden change characteristic;
6) and if any condition of the criterion 1 and the criterion 2 of the phase A (or the phase B and the phase C) is met, identifying that the transformer is in an excitation inrush current state, and generating a locking instruction to lock the transformer differential current protection.
Taking a transformer of a certain type as an example, at this time, there are
。
And simulating the fault in a certain transformer area, and giving a simulation curve and a criterion result of the phase current of the fault phase A. In fig. 3(a) and 3(b), the first excitation inrush current criterion is shown, the threshold value is a straight line, in fig. 3(c) and 3(d), the second excitation inrush current criterion is shown, and the latching value curve changes with time. FIGS. 3(a) and 3(c) are schematic diagrams of
The simulation results after being respectively substituted into the first excitation inrush current criterion and the second excitation inrush current criterion, and fig. 3(b) and 3(d) are simulation results
And respectively substituting the simulation results into a first excitation inrush current criterion and a second excitation inrush current criterion. Simulation results show that at 15ms, the first magnetizing inrush current criterion and the second magnetizing inrush current criterion are not satisfied, so that the transformer is not in a magnetizing inrush current state, but is in an internal fault working condition, and differential current protection of the transformer needs to be reliably operated. At this time, no latch command is generated, and the transformer differential current protection is not latched.
And simulating the waveform of the magnetizing inrush current generated by the no-load input of a certain type of transformer, and giving a judgment result of the B phase with the maximum differential current. In fig. 4(a) and 4(b), the first magnetizing inrush current criterion is shown, and the threshold value is a straight line; fig. 4(c) and 4(d) show a second excitation inrush current criterion, the blocking value curve varying with time. FIGS. 4(a) and 4(c) are schematic diagrams of
Respectively introducing the simulation results into a first excitation inrush current criterion and a second excitation inrush current criterion, and FIGS. 4(b) and 4(d) are graphs of the simulation results
And respectively substituting the simulation results into a first excitation inrush current criterion and a second excitation inrush current criterion. Simulation results show that the second magnetizing inrush current criterion is continuously established, so that the transformer is in a magnetizing inrush current state, but not in an internal fault condition. At this point, a latch command is generated to latch the transformer differential current protection.
And simulating the waveform of the magnetizing inrush current generated by the no-load input of a certain type of transformer, and giving a judgment result of the B phase with the maximum differential current. In fig. 5(a) and 5(b), the first magnetizing inrush current criterion is shown, and the threshold value is a straight line; fig. 5(c) and 5(d) illustrate a second excitation inrush current criterion, the dwell curve varying with time. FIGS. 5(a) and 5(c) are schematic diagrams of
Respectively introducing the simulation results into a first excitation inrush current criterion and a second excitation inrush current criterion, and FIGS. 5(b) and 5(d) show that
And respectively substituting the simulation results into a first excitation inrush current criterion and a second excitation inrush current criterion. Simulation results show that the first magnetizing inrush current criterion is continuously established, so that the transformer is in a magnetizing inrush current state, but not in an internal fault condition. At this point, a latch command is generated to latch the transformer differential current protection.
As will be appreciated by one skilled in the art, embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, embodiments of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, embodiments of the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
Embodiments of the present invention are described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The invention has been described above by reference to a few embodiments. However, other embodiments of the invention than the above disclosed are equally possible within the scope of the invention, as would be apparent to those skilled in the art from this disclosure, as defined by the appended 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// the [ device, component, etc ]" are to be interpreted openly as at least one instance of a 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 (11)
1. A transformer magnetizing inrush current identification method based on a current abrupt change is characterized by comprising the following steps:
determining a first differential current sudden change characteristic or a second differential current sudden change characteristic corresponding to the current sampling moment according to the acquired current of each phase at the Y side and the current of each phase at the delta side of the transformer;
determining whether a first excitation inrush current criterion is established or not according to an accumulated value of the first differential current sudden change characteristic from a first sampling moment to a current sampling moment in the current cycle; or
Determining whether a first excitation inrush current criterion is established or not according to the accumulated value of the characteristics of the sudden change of the second differential current from the first sampling moment to the current sampling moment in the current cycle;
when a first magnetizing inrush current criterion is met, the transformer is determined to be in a magnetizing inrush current state, and a locking instruction is generated and used for locking the differential current protection of the transformer.
2. The identification method according to claim 1, further comprising:
determining whether a second excitation inrush current criterion is established according to an accumulated value of the first differential current sudden change characteristic from a first sampling moment to a current sampling moment in the current cycle; or
Determining whether a second excitation inrush current criterion is established according to an accumulated value of the characteristics of the sudden change of the second differential current from the first sampling moment to the current sampling moment in the current cycle;
and when a second magnetizing inrush current criterion is met, determining that the transformer is in a magnetizing inrush current state, and generating a locking instruction, wherein the locking instruction is used for locking the differential current protection of the transformer.
3. The identification method according to claim 2,
when the first magnetizing inrush current criterion is not established and the second magnetizing inrush current criterion is established, determining that the transformer is in a magnetizing inrush current state, and generating a locking instruction, wherein the locking instruction is used for locking the differential current protection of the transformer; or
And when the first magnetizing inrush current criterion is established but the second magnetizing inrush current criterion is not established, determining that the transformer is in a magnetizing inrush current state, and generating a locking instruction, wherein the locking instruction is used for locking the differential current protection of the transformer.
4. The identification method according to claim 2,
and when the first excitation inrush current criterion is not established and the second excitation inrush current criterion is not established, determining that the transformer is not in an excitation inrush current state.
5. The identification method according to claim 1,
determining a first differential current sudden change characteristic corresponding to the current sampling moment, wherein the first differential current sudden change characteristic comprises the following steps:
and carrying out weighted summation on the difference value of the current sudden change quantity of the current phase Y side and the zero sequence current of the Y side and the difference value of the current sudden change quantity of the current phase delta side and the current sudden change quantity of the current phase delta side adjacent to the current sudden change quantity of the current phase delta side along the clockwise direction to obtain a first differential current sudden change quantity characteristic.
6. The identification method according to claim 1,
determining a second differential current abrupt change characteristic corresponding to the current sampling moment, wherein the second differential current abrupt change characteristic comprises the following steps:
and carrying out weighted summation on the sum of the current sudden change quantity of the current phase Y side and the zero sequence current of the Y side and the difference between the current sudden change quantity of the current phase delta side and the current sudden change quantity of the current phase delta side adjacent to the current sudden change quantity of the current phase delta side along the clockwise direction to obtain a second differential current sudden change quantity characteristic.
7. The identification method according to claim 1,
the determining whether the first excitation inrush current criterion is satisfied includes:
determining a first excitation inrush current judging quantity according to an accumulated value of the characteristics of the sudden change quantity of the first differential current, the total sampling time number of each cycle and the rated current of the transformer from the first sampling time to the current sampling time in the current cycle, and determining that a first excitation inrush current criterion is established when the first excitation inrush current judging quantity is not greater than a preset first threshold value; or
And determining a first excitation inrush current judging quantity according to an accumulated value of the characteristics of the sudden change quantity of the second differential current, the total sampling time quantity of each cycle and the rated current of the transformer from the first sampling time to the current sampling time in the current cycle, and determining that a first excitation inrush current criterion is established when the first excitation inrush current judging quantity is not more than a preset first threshold value.
8. The identification method according to claim 2,
the determining whether the second excitation inrush current criterion is satisfied includes:
determining a second excitation inrush current judgment quantity according to an accumulated value of first differential current sudden change quantity characteristics, the total sampling time number of each cycle and the maximum value of the first differential current sudden change quantity characteristics corresponding to the current cycle from the first sampling time to the current sampling time from the first sampling time in the current cycle, and determining that a second excitation inrush current judgment criterion is established when the second excitation inrush current judgment quantity is not greater than a second threshold value, wherein the second threshold value is determined according to the accumulated value of the first differential current sudden change quantity characteristics from the first sampling time to the current sampling time in the current cycle; or
Determining a second excitation inrush current judging quantity according to an accumulated value of second differential current abrupt change quantity characteristics, the total sampling time number of each cycle and the maximum value of the second differential current abrupt change quantity characteristics corresponding to the current cycle from the first sampling time to the current sampling time in the current cycle, and determining that a second excitation inrush current judging quantity is established when the second excitation inrush current judging quantity is not greater than a second threshold value, wherein the second threshold value is determined according to the accumulated value of the second differential current abrupt change quantity characteristics from the first sampling time to the current sampling time in the current cycle.
9. A transformer magnetizing inrush current recognition device based on a current abrupt change amount is characterized by comprising:
the differential current sudden change characteristic determining unit is used for determining a first differential current sudden change characteristic or a second differential current sudden change characteristic corresponding to the current sampling moment according to the acquired phase current at the Y side and phase current at the delta side of the transformer;
the first excitation inrush current criterion determining unit is used for determining whether the first excitation inrush current criterion is satisfied according to an accumulated value of the first differential current sudden change characteristic from a first sampling time to a current sampling time in the current cycle; or
Determining whether a first excitation inrush current criterion is established or not according to the accumulated value of the characteristics of the sudden change of the second differential current from the first sampling moment to the current sampling moment in the current cycle;
and the inrush current identification response unit is used for determining that the transformer is in an inrush current state and generating a locking instruction when a first inrush current criterion is met, wherein the locking instruction is used for locking the differential current protection of the transformer.
10. The apparatus of claim 9, further comprising:
the second excitation inrush current criterion determining unit is used for determining whether a second excitation inrush current criterion is satisfied according to an accumulated value of the first differential current sudden change characteristic from a first sampling time to a current sampling time in the current cycle; or
Determining whether a second excitation inrush current criterion is established according to an accumulated value of the characteristics of the sudden change of the second differential current from the first sampling moment to the current sampling moment in the current cycle;
and the inrush current identification response unit is further used for determining that the transformer is in an inrush current state and generating a locking instruction when a second inrush current criterion is met, wherein the locking instruction is used for locking the differential current protection of the transformer.
11. A computer storage medium for performing the method of identifying inrush current in a transformer according to any one of claims 1 to 8.
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Application publication date: 20210423 |