CN109444528B - Transformer state monitoring system and method based on iron core grounding current - Google Patents
Transformer state monitoring system and method based on iron core grounding current Download PDFInfo
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- CN109444528B CN109444528B CN201811306205.7A CN201811306205A CN109444528B CN 109444528 B CN109444528 B CN 109444528B CN 201811306205 A CN201811306205 A CN 201811306205A CN 109444528 B CN109444528 B CN 109444528B
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- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical group [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 title claims abstract description 72
- 238000000034 method Methods 0.000 title claims abstract description 23
- 238000012544 monitoring process Methods 0.000 title claims abstract description 22
- 230000008859 change Effects 0.000 claims description 15
- 238000004364 calculation method Methods 0.000 claims description 3
- 230000007547 defect Effects 0.000 abstract description 6
- 238000005070 sampling Methods 0.000 abstract description 5
- 238000012423 maintenance Methods 0.000 abstract description 2
- 230000002159 abnormal effect Effects 0.000 abstract 1
- 238000004804 winding Methods 0.000 description 16
- 238000010586 diagram Methods 0.000 description 6
- 230000008878 coupling Effects 0.000 description 5
- 238000010168 coupling process Methods 0.000 description 5
- 238000005859 coupling reaction Methods 0.000 description 5
- 238000009413 insulation Methods 0.000 description 4
- 238000012806 monitoring device Methods 0.000 description 4
- 241001270131 Agaricus moelleri Species 0.000 description 3
- 230000015556 catabolic process Effects 0.000 description 3
- 230000005684 electric field Effects 0.000 description 2
- 230000004907 flux Effects 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 230000006978 adaptation Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000003990 capacitor Substances 0.000 description 1
- 230000002950 deficient Effects 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000008030 elimination Effects 0.000 description 1
- 238000003379 elimination reaction Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 230000005284 excitation Effects 0.000 description 1
- 238000009421 internal insulation Methods 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- 230000001360 synchronised effect Effects 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/25—Arrangements for measuring currents or voltages or for indicating presence or sign thereof using digital measurement techniques
- G01R19/2506—Arrangements for conditioning or analysing measured signals, e.g. for indicating peak values ; Details concerning sampling, digitizing or waveform capturing
Abstract
The invention discloses a transformer state monitoring system and method based on iron core grounding current, wherein the system comprises a transformer, a through mutual inductor, a collecting device and a collecting device alternating current power supply, the transformer and the collecting device alternating current power supply are respectively connected by adopting independent through mutual inductors, and the monitoring method identifies the operating states of the transformer, such as three-phase unbalance, overexcitation, partial discharge and the like, by measuring the fundamental wave amplitude and phase, and each harmonic amplitude and phase of the iron core grounding current. The monitoring system and the monitoring method overcome the defects of the traditional mode, adopt a precise mutual inductor and a high-speed sampling device, are matched with an exquisite algorithm, accurately obtain the fundamental wave and each subharmonic numerical value of the measured analog quantity, do not need to be externally connected with other equipment signals, accurately judge the abnormal state of the transformer, are simple and convenient to implement, provide a reliable data base for the daily operation and maintenance work of a transformer system, and discover accident potential in advance.
Description
Technical Field
The invention relates to the technical field of state monitoring of electrical equipment, in particular to a transformer state monitoring system and method based on iron core grounding current.
Background
The transformer core is an important part of insulation design, and in order to ensure the insulation performance of the transformer, the transformer core must be at the ground potential to stabilize the electric field distribution around the core. Because the iron core has power frequency magnetic flux, when the iron core is grounded at two points, a magnetic flux hinge is often arranged in the area included by a grounding loop, so that loop current can be formed, the iron core is locally overheated, and faults such as insulating oil degradation, gas alarm and the like are further caused.
At present, in order to monitor the insulation state of an iron core, an iron core grounding current monitoring device is generally arranged on a transformer with the voltage class of 110kV or above, and the fundamental wave amplitude of grounding current is collected. Under the normal operation condition, the grounding current of the iron core is generally less than 30mA, and the defect elimination treatment is needed when the grounding current is more than 100mA according to the national standard. The conventional iron core grounding current monitoring device has the resolution of about 1mA, and can meet the requirement of insulation monitoring. With the continuous progress of the technical level, the high-performance DSP chip and the high-performance AD chip are applied to the field of iron core grounding current monitoring, and the resolution of the current to be measured is greatly improved. The window function truncation technology is adopted, so that errors caused by non-whole-cycle sampling are basically eliminated, after the frequency of the iron core grounding current is accurately obtained, the accurate numerical value of the measured analog quantity can be obtained through a compensation algorithm, the measured resolution can reach 1uA level, slight changes of the iron core grounding current caused by the operation state of some typical transformers can be observed and summarized into the criterion for popularization and application.
Therefore, a need exists in the art for a method and system for monitoring the state of a transformer based on the core grounding current, which can identify the operating state of the transformer.
Disclosure of Invention
The purpose of the invention is as follows: in order to overcome the defects in the prior art, the invention provides a transformer state monitoring system and method based on iron core grounding current, which can judge the running state of a transformer by analyzing and calculating the iron core grounding current, provide a reliable data base for the daily running and maintenance work of a transformer system, and discover accident potential in advance.
The technical scheme is as follows: in order to achieve the purpose, the invention adopts the following technical scheme:
the utility model provides a transformer state monitoring system based on iron core ground current which characterized in that: the transformer comprises a transformer, a straight-through mutual inductor, a collecting device and a collecting device alternating current power supply, wherein the transformer and the collecting device alternating current power supply are connected through the straight-through mutual inductor respectively, the straight-through mutual inductor is used for collecting and detecting iron core grounding current of the transformer and the collecting device alternating current power supply, and the collecting device synchronously collects the iron core grounding current and the collecting device alternating current power supply.
A transformer state monitoring system method based on iron core grounding current is characterized in that: the transformer comprises a transformer, a straight-through mutual inductor, a collecting device and a collecting device alternating current power supply, wherein the transformer and the collecting device alternating current power supply are connected by adopting independent straight-through mutual inductors respectively, the straight-through mutual inductor is used for collecting and detecting iron core grounding current of the transformer and the collecting device alternating current power supply, the collecting device synchronously collects the iron core grounding current and the collecting device alternating current power supply, the collecting device takes the alternating current power supply as a reference vector to obtain the amplitude and the phase of the iron core grounding current relative to the fundamental wave of the alternating current and the amplitude and the phase of each subharmonic, and the running state of the transformer is judged by identifying the information of the fundamental wave and the harmonic wave of the iron.
Specifically, when the amplitude of the fundamental wave of the iron core grounding current is increased, the integral multiple harmonic amplitude of 3 is close to zero, and the amplitudes of the rest harmonics and the amplitude of the fundamental wave are increased in equal proportion, the transformer is judged to be in a three-phase unbalanced state.
Preferably, a whole harmonic change threshold of 3 is set according to the low-voltage side load property of the transformer, and when the fundamental wave and the rest of harmonics are increased, if the whole harmonic of 3 does not exceed the threshold, the transformer is judged to be in a three-phase unbalanced state.
Specifically, when the amplitude change of the fundamental wave of the iron core grounding current is not more than 10%, the amplitudes of 5 th harmonic wave and 7 th harmonic wave are increased, and the amplitudes of the rest harmonic waves are not more than 5%, the transformer is judged to be in an overdriving state.
Specifically, 5, 7 harmonic current amplitude thresholds are set according to the over-excitation multiple of the transformer, and when the 5, 7 harmonic currents increase beyond the threshold, if the phase difference of the 5, 7 harmonic currents is stable in a plurality of calculation periods, the fundamental wave change is less than 10%, and the other harmonic changes are less than 20%, the transformer is judged to be in the over-excitation state.
Specifically, when the fundamental wave amplitude of the iron core grounding current is unchanged, the amplitude of each subharmonic wave is increased in an equivalent manner, and the phase of each subharmonic wave is unchanged, the transformer is judged to be in a partial discharge state.
Preferably, a fundamental current threshold is set according to the load characteristics and the voltage level of the transformer, and when the change of the fundamental current is smaller than the threshold value, if the amplitudes of 2-20 harmonics are increased, the amplitude of higher harmonics is larger than that of lower harmonics, and the phase of the harmonic current is stable, the transformer is judged to be in a partial discharge state.
Specifically, when one acquisition device is simultaneously connected with iron core grounding current data of a plurality of transformers, the area of the transformer with partial discharge is judged by detecting the harmonic phase of the iron core grounding current.
Specifically, the acquisition device adopts a low-noise high-speed 16-bit AD sampler and adopts a frequency compensation algorithm to obtain fundamental wave and each harmonic numerical value of the measured analog quantity.
Has the advantages that: compared with the prior art, the transformer state monitoring system and method based on the iron core grounding current have the following beneficial effects:
the external connection of the measuring system related by the invention is completely the same as that of a conventional iron core grounding current monitoring system, namely, no new connection wire or equipment is added, but the evaluation of the running state of the transformer is realized. The input parameters used by the method are all from the iron core current monitoring device, and other external equipment signals are not needed, so that the system is simple and reliable, and is simple and convenient to implement.
Drawings
FIG. 1 is a schematic structural diagram of an iron core grounding current collecting device of the present invention;
FIG. 2 is a diagram illustrating core grounding current in the prior art;
FIG. 3 is a flow chart illustrating the determination of the unbalanced three-phase operating condition of the transformer according to the present invention;
FIG. 4 is a flow chart of the determination of the overexcitation operation state of the transformer according to the present invention;
FIG. 5 is a flowchart illustrating a partial discharge operation status determination process of a transformer according to the present invention;
FIG. 6 is a diagram illustrating a self-learning manner of the method and system of the present invention.
Detailed Description
The present invention will be further described with reference to the accompanying drawings.
Fig. 2 is a schematic diagram of core grounding current in the prior art:
the high-voltage winding of the transformer generates voltage in the low-voltage winding through magnetic coupling, the voltage to ground of the low-voltage winding generates leakage current through a capacitor between the low-voltage winding and an iron core, and the sum of the three-phase leakage current of the low-voltage winding is the iron core grounding current. The high-voltage winding also has capacitive leakage current to the iron core, but because the low-voltage winding is positioned at the inner side and is close to the iron core, and the low-voltage winding has a power frequency shielding function to the high-voltage winding at the outer side, the iron core grounding current is mainly generated by the capacitive coupling of the low-voltage winding. The mutual inductor of iron core grounding current is generally a straight-through mutual inductor, and the frequency band of the mutual inductor is generally lower in order to improve the acquisition precision.
Fig. 1 is a schematic diagram of an iron core grounding current collecting device provided by the invention:
the grounding current of the iron core is connected into the acquisition device through the straight-through mutual inductor, the power supply of the acquisition device is connected into another straight-through mutual inductor after passing through the current-limiting resistor, the output of the two mutual inductors is synchronously acquired by the acquisition device, and the accurate phase difference of the two analog quantities can be calculated. The power supply of the acquisition device can adopt an alternating current 220V power supply, is taken from a transformer for a substation, and has a stable phase relation with a main transformer of the transformer substation, so that the phase of the iron core grounding current is an absolute phase relative to the main transformer. When a plurality of main transformers exist, a plurality of iron core grounding current collection devices use the same alternating current power supply for power supply, and the phases of a plurality of iron core grounding currents are comparable.
The system solves the problem of measuring the grounding current phase of the iron core by adding the straight-through transformer, and provides a basis for judging the state of the transformer. Namely, the measurement system according to the present invention obtains the absolute phase of the core grounding current by measuring the ac power supply. The invention has no synchronous sampling pulse input, the current phase obtained by the conventional iron core grounding current monitoring device is generally a random value, and two modes of pulse synchronization and vector synchronization are generally adopted for obtaining the absolute phase of the iron core grounding current. The pulse synchronization needs to be accessed to the sampling pulse to control the sampling time, so that the workload of field wiring is increased, and pulse signals are easily interfered in a long distance; the invention adopts a vector synchronization mode, takes an alternating current power supply as a reference vector, obtains the reference vector of the iron core grounding current without increasing the wiring workload, and further obtains the stable phase of the iron core grounding current. The AC power supply is generally taken from a station transformer and has a stable relation with the three essential phases of the transformer.
The upper limit of the preferred frequency of the transformer used by the system of the invention reaches 1000Hz, 20 harmonics can be measured, the measurement result comprises 20 amplitudes and 20 phases, and 40 parameters are totally obtained, and different operation states of the transformer can be reflected to the 40 parameters through an iron core grounding current loop.
Fig. 3 is a flowchart for determining the three-phase unbalanced operating state of the transformer according to the present invention:
when the three phases of the voltage of the high-voltage side system of the transformer are unbalanced or the three-phase load of the low-voltage side is unbalanced, the sum of the three phases of the voltage of the high-voltage side and the voltage of the low-voltage side of the transformer is not zero, the current coupled into the iron core through the capacitance is not close to zero any more, and the current is obviously increased. Because the iron core grounding current is mainly generated by coupling of the low-voltage side winding, the low-voltage side winding is generally in angular connection, the integral harmonic of 3 forms a circulating current in the winding, the circulating current is not reflected in the ground potential of the low-voltage side winding, the integral harmonic of 3 in the iron core grounding current is not obviously increased, and the fundamental wave and the rest of harmonics are increased in equal proportion according to the three-phase unbalance.
If the integer harmonic variation threshold of 3 is set to 5% of the fundamental wave, when both the fundamental wave and the remaining harmonics are increased, if the integer harmonic of 3 does not exceed the threshold, it is considered that this type of variation is caused by the transformer three-phase imbalance. The integral multiple harmonic change threshold of 3 can be adjusted according to the load property of the low-voltage side of the transformer, and is not limited to the value.
Fig. 4 is a flow chart for determining the overexcitation operation state of the transformer provided by the present invention:
when the voltage of the high-voltage side of the transformer exceeds 20% of the rated voltage, the transformer is over-excited, a larger exciting current peak appears on the high-voltage side, the exciting current forms a voltage drop on a proper reactance of the transformer, the voltage waveform of the low-voltage side of the transformer is a flat top wave, the voltage waveform of the low-voltage side of the transformer is still positive and negative symmetrical, the third harmonic forms a circulating current in an angle joint, the odd harmonics on the low-voltage side winding are mainly harmonics 5 and 7, and the phases of the harmonics 5 and 7 are fixed, so that the flat top voltage waveform of the low-voltage side is formed together. And when the amplitude change of the fundamental wave of the grounding current of the iron core is not more than 10%, the amplitudes of 5-order harmonic waves and 7-order harmonic waves are increased, and the amplitudes of the rest harmonic waves are not more than 5%, judging that the transformer is in an overdriving state.
As shown in fig. 4, the low-voltage side winding couples the 5 th and 7 th harmonics into the core ground current through the distributed capacitance, and at this time, the 5 th and 7 th harmonics in the core ground current will be significantly increased and the relative phase is stable. The fundamental wave in the iron core grounding current is increased by only 20%, and the three phases are still balanced, so that the fundamental wave current is not obviously increased. Higher harmonics have a certain increase but have a limited effect on forming the flat-top wave, so that the amplitude is not increased significantly. Setting the amplitude thresholds of the 5 th harmonic current and the 7 th harmonic current to be 50%, checking the phase relation of the 5 th harmonic current and the 7 th harmonic current when the 5 th harmonic current and the 7 th harmonic current increase to exceed the threshold values, checking the amplitude characteristics of the fundamental wave and other harmonic currents if the phase difference is stable in a plurality of calculation periods, and judging that the type of change is caused by over excitation of the transformer when the fundamental wave changes by less than 10% and the other harmonic currents change by less than 20%. The threshold setting of each criterion needs to be actually set according to the over-excitation multiple of the transformer, and is not limited to the numerical value.
Fig. 5 is a flowchart for determining a partial discharge operation state of a transformer according to the present invention:
when the internal insulation of the transformer has early defects, the electric field at the defective parts is concentrated, and local breakdown is easy to occur. The current generated by the local breakdown will propagate outward from the defect site through capacitive coupling, the path of propagation including the core ground return path. Because the rising edge of the partial discharge current is steep, the frequency spectrum distribution is wide, and effective components exist in each frequency band. The occurrence of partial discharge has a large correlation with the voltage phase, and discharge generally occurs at a specific phase. When positive and negative half-waves are symmetrically discharged, the positive and negative half-waves are mainly odd harmonics: when the positive half wave and the negative half wave are asymmetrically discharged, even harmonic components exist in the harmonic waves. Because the capacitive coupling loop has small impedance to high-frequency signals, higher harmonics in the grounding current of the iron core are obviously increased compared with lower harmonics. Since the discharge current is caused by the defect, the fundamental current does not change.
The fundamental current threshold is set to be 10%, when the change of the fundamental current is smaller than the threshold value, if the amplitudes of 2-20 harmonics are increased, the amplitude of higher harmonics is larger than that of lower harmonics, and the phase of the harmonic current is stable, partial discharge pulses are considered to be coupled into an iron core grounding loop. When there are 3 or more transformers connected to the high-side bus, the harmonic phase in the core ground loop can be used for approximate positioning of the discharge signal. The transformer with high-frequency current phase in the iron core grounding loop and the inverse phase of other transformers is close to the discharge pulse, and the discharge point is positioned in the bus section of the transformer. The threshold setting of each criterion needs to be actually set according to the load characteristic and the voltage grade of the transformer, and is not limited to the numerical value.
Fig. 6 is a schematic diagram of a self-learning manner of the main system provided by the present invention. When the method provided by the invention is used for identifying the running state of the transformer, the method needs to rely on a verified finger library, and identification criteria in the fingerprint library are influenced by external factors such as transformer load, voltage grade and the like and need to be adjusted according to running parameters of the transformer. Under the condition of accessing external transformer operation data, the system has self-learning capability, and when the external operation data access condition is not met, typical criteria in a fingerprint library can be perfected in a manual modification mode.
The foregoing is considered as illustrative only of part of the principles of the invention and is not intended to limit the invention in any way. The method for judging the running state of the transformer by adopting the fundamental wave and harmonic wave characteristics of the iron core connected with the electric current belongs to the protection scope of the technical scheme of the invention.
The above description is only of the preferred embodiments of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the invention and these are intended to be within the scope of the invention.
Claims (6)
1. A transformer state monitoring method based on iron core grounding current is characterized in that: the transformer comprises a transformer, a straight-through mutual inductor, a collecting device and a collecting device alternating current power supply, wherein the transformer and the collecting device alternating current power supply are connected by adopting independent straight-through mutual inductors respectively;
when the fundamental wave amplitude of the iron core grounding current is increased, the integral multiple harmonic amplitude of 3 is close to zero, and the amplitudes of the rest harmonics and the fundamental wave are increased in equal proportion, the transformer is judged to be in a three-phase unbalanced state;
and setting a whole harmonic change threshold of 3 according to the low-voltage side load property of the transformer, and judging that the transformer is in a three-phase unbalanced state if the whole harmonic of 3 does not exceed the threshold when the fundamental wave and the rest of harmonics are increased.
2. The method for monitoring the state of the transformer based on the iron core grounding current according to claim 1, wherein: and when the amplitude change of the fundamental wave of the grounding current of the iron core is not more than 10%, the amplitudes of 5-order harmonic waves and 7-order harmonic waves are increased, and the amplitudes of the rest harmonic waves are not more than 5%, judging that the transformer is in an overdriving state.
3. The method for monitoring the state of the transformer based on the iron core grounding current according to claim 1, wherein: setting 5 and 7 harmonic current amplitude thresholds according to the over-excitation multiple of the transformer, and judging that the transformer is in an over-excitation state if the phase difference of the 5 and 7 harmonic currents is stable in a plurality of calculation periods, the fundamental wave change is less than 10 percent and other harmonic waves change is less than 20 percent when the 5 and 7 harmonic currents increase to exceed the threshold value.
4. The method for monitoring the state of the transformer based on the iron core grounding current according to claim 1, wherein: when the fundamental wave amplitude of the iron core grounding current is unchanged, the amplitude of each subharmonic wave is increased in an equivalent way, and the phase of each subharmonic wave is unchanged, judging that the transformer is in a partial discharge state;
and setting a fundamental current threshold according to the load characteristics and the voltage level of the transformer, and judging that the transformer is in a partial discharge state if the amplitude of 2-20 harmonics is increased, the amplitude of higher harmonics is greater than that of lower harmonics and the phase of harmonic current is stable when the change of the fundamental current is smaller than the threshold value.
5. The method for monitoring the state of the transformer based on the iron core grounding current according to claim 4, wherein the method comprises the following steps: when one acquisition device is simultaneously connected with iron core grounding current data of a plurality of transformers, the area of the transformer with partial discharge is judged by detecting the harmonic phase of the iron core grounding current.
6. The method for monitoring the state of the transformer based on the iron core grounding current according to claim 1, wherein: the acquisition device adopts a low-noise high-speed 16-bit AD sampler and adopts a frequency compensation algorithm to obtain fundamental wave and each subharmonic numerical value of the analog quantity to be measured.
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| CN107247175A (en) * | 2017-06-30 | 2017-10-13 | 国网天津市电力公司电力科学研究院 | A kind of transformer iron core grounding current live detection method for eliminating electromagnetic environmental impact |
| CN112834811A (en) * | 2021-01-04 | 2021-05-25 | 中国电力科学研究院有限公司 | Ground current state monitoring method and device applying magnetic resistance sensing and storage medium |
| CN113311359A (en) * | 2021-05-13 | 2021-08-27 | 上海远观物联网科技有限公司 | Transformer internal fault discrimination method based on vector analysis |
| CN116299048B (en) * | 2023-05-15 | 2023-08-25 | 山东海鲲数控设备有限公司 | Leakage early warning system based on roadside transformer |
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