CN111398695A

CN111398695A - Transformer power supply phase failure detection method

Info

Publication number: CN111398695A
Application number: CN202010250928.0A
Authority: CN
Inventors: 谢金平; 洪源平; 彭雄伟; 王声学; 冯欣; 潘永成; 司超; 万玉晶; 王金建; 杨锡宏; 徐龙; 高瑞君; 朱伟; 许亮; 肖建新; 王东阳; 胡洪涛; 彭越; 陈义东; 魏佳楠
Original assignee: Jiangsu Nuclear Power Corp
Current assignee: Jiangsu Nuclear Power Corp
Priority date: 2020-04-01
Filing date: 2020-04-01
Publication date: 2020-07-10
Anticipated expiration: 2040-04-01
Also published as: CN111398695B

Abstract

The invention belongs to the technical field of phase failure detection of transformer power supplies, in particular to a phase failure detection method of a transformer power supply, the method can solve the worldwide problem that the phase failure of the no-load power supply of the transformer cannot be accurately and reliably detected, firstly summarizes the frequency spectrum characteristics of the power supply loop of the transformer when the phase failure occurs at different positions, firstly provides a whole set of frequency domain criterion for detecting the phase failure of the power supply of the transformer, firstly provides the locking criterion for alarming the phase failure of the power supply of the transformer, solves the influence of various disturbances and the idle-rush closing of the transformer in the system on the detection result, can solve the problems of unbalanced voltage of the power supply, phase failure at different positions and misjudgment of the phase failure detection result caused by two or more adjacent transformers powered by the same line in a cluster nuclear power plant, and can sensitively and reliably detect the phase failure fault of the power supply under various conditions of the transformer and realize the positioning of fault points.

Description

Transformer power supply phase failure detection method

Technical Field

The invention belongs to the technical field of phase failure detection of transformer power supplies, and particularly relates to a phase failure detection method of a transformer power supply.

Background

In 2005, tens of nuclear power plants have been in phase failure events outside the plant, which causes tripping of motors in the plant, failure of self-starting of emergency diesel engines, shutdown and shutdown, even short-term loss of cooling of reactor cores, and brings a serious challenge to safe operation of the nuclear power plants.

Theories and practices prove that the traditional electric relay protection device is difficult to detect the power supply open-phase fault when the transformer is in no-load or light-load. For an auxiliary transformer (or a standby transformer) of a nuclear power plant, because the auxiliary transformer (or the standby transformer) is in a no-load operation state for a long time, if reliable detection of power supply phase failure of the transformer during no-load can be realized, threat of phase failure to nuclear safety is eliminated in time, and the method has important significance for the nuclear power plant.

The current device for detecting the power supply phase failure of the transformer when the transformer is in no load mainly comprises one or the combination of the following three methods:

1. detecting three-phase current at the power supply side of the transformer, and judging whether open phase exists according to the phase angle and amplitude characteristics when the no-load exciting current of the transformer meets the open phase;

2. and detecting the neutral point current of the power supply side when the transformer is in no-load operation, and determining that the phase is open when the neutral point current is detected to be larger than a certain preset value. When the transformer operates with load, the open-phase detection device automatically exits;

3. and injecting harmonic current into a neutral point of the transformer and measuring the zero-sequence impedance of the power supply side of the transformer, wherein the zero-sequence impedance is very small when the system normally operates, and the zero-sequence impedance is greatly increased when the system has an open phase. Whether or not there is an open-phase failure in the system is determined based on the phenomenon.

These detection methods are all analyzed in the time domain. Through research, the following problems are found to exist in the method: (1) the detection methods 1 and 2 do not consider the influence of the unbalanced power supply voltage on the detection result, but the three-phase voltage of the actual power supply system is unbalanced and the magnitude of the unbalance degree can be changed randomly;

(2) the conclusions obtained by the three detection methods are all based on the analysis result of the simple transformer-power system, and the influence of phase failure at different positions on the line on the detection result is not considered; (3) the method 3 does not consider the influence of a plurality of transformers supplied with power by the same circuit in the nuclear power plant of the group reactor on the detection result. These problems can lead to false positives or false negatives of phase failure. In addition, literature research shows that the three methods are also influenced by factors such as switch operation, system faults, loading conditions, time-varying changes of system impedance and the like in practical application, and some phase failure situations may occur due to false alarm or missing alarm.

Therefore, a brand-new open-phase detection method for analyzing and judging by detecting transient and steady-state frequency spectrum characteristics of the neutral line current on the power supply side of the transformer is provided, so as to solve the defects of the prior art.

Disclosure of Invention

The invention aims to provide a method for detecting the power supply open-phase of the transformer, which can sensitively and reliably detect the power supply open-phase fault of the transformer at any position during no-load and on-load operation and realize fault point positioning.

The technical scheme of the invention is as follows:

a transformer power supply phase failure detection method specifically comprises the following steps:

establishing a circuit simulation model for analyzing the phase failure of a transformer power supply;

analyzing and obtaining the frequency spectrum characteristics of the neutral line current of the transformer in normal operation by using the simulation model in the step (1);

analyzing and obtaining the frequency spectrum characteristics of the neutral line current of the transformer power supply when the phase is disconnected by using the simulation model in the step (1);

analyzing and obtaining the frequency spectrum characteristics of the neutral line current of the transformer power supply when various disturbances exist by using the simulation model in the step (1);

step (5) giving out a criterion of normal operation of the transformer by using the frequency spectrum characteristics in the step (2);

step (6) giving out a criterion of phase failure of the transformer power supply by using the frequency spectrum characteristics in the step (3);

step (7) giving a locking criterion of the phase failure of the transformer power supply by using the frequency spectrum characteristics in the step (4);

step (8) according to the step (6) and the step (7), providing a positioning method of the phase failure position of the transformer power supply;

the step (1) comprises the following steps:

step (1.1) selecting a typical transformer power supply system;

and (1.2) establishing a non-simplified circuit simulation model which is consistent with the actual transformer power system according to the step (1.1), so that the result of simulation analysis can correctly reflect the actual condition when the phase failure occurs in the power system.

The step (2) specifically comprises the following small steps:

analyzing and obtaining current spectrum characteristics of a return wire with a transformer in normal operation;

analyzing and obtaining current spectrum characteristics of a return wire with two transformers in normal operation;

and (2.3) analyzing to obtain the current spectrum characteristics of a return line with three transformers in normal operation.

In the step (2), when the system normally operates, the common frequency spectrum characteristic of a loop with different numbers of transformers is as follows, in the frequency spectrum diagram of the neutral current on the power supply side when the transformer normally operates, the harmonic frequency is mainly 3+6 × Nth harmonic (N is a natural number which is more than or equal to 0), the characteristic 2 has 3+6 × Nth harmonic frequency, the amplitude of the harmonic frequency enters the first few names of the whole frequency domain, the harmonic frequency is resonated to a certain degree by inductance and capacitance parameters of a zero sequence loop when the system normally operates, so that the amplitude of the harmonic frequency is amplified and is obviously higher than the adjacent harmonic frequency, the frequency is defined as the normal operation resonance frequency, and the amplitude of the characteristic 3-third harmonic frequency is larger than fifth harmonic and seventh harmonic.

The step (3) comprises the following steps:

step (3.1) analyzing the phase failure conditions at different positions of the power supply side of the transformer to obtain the common spectrum characteristics of the transient current of the neutral line;

analyzing the phase failure condition between a power bus of the transformer and the opposite side of the power transmission line to obtain the frequency spectrum characteristic of the transient current of the neutral line;

step (3.3) analyzing the phase failure condition between a certain transformer and a bus to obtain the frequency spectrum characteristic of the transient current of the neutral line;

step (3.4) analyzing the phase failure condition between a certain transformer and a bus to obtain the frequency spectrum characteristic of the steady-state current of the neutral line;

and (3.5) analyzing the phase failure condition between the bus and the opposite side of the power transmission line to obtain the frequency spectrum characteristic of the steady-state current of the neutral line.

The transient current of the neutral line in the step (3.1) has the following common spectrum characteristics: characteristic 1 at the instant after the phase failure of the transformer power supply, the neutral current has significant inductance-capacitance resonance frequency spectrum characteristics: the harmonic frequency with extremely small amplitude in normal operation suddenly increases at a certain moment after phase failure, the maximum value of the harmonic frequency is ranked in the first few names in the amplitude of a spectrogram, the maximum value is taken as the center, the amplitudes of adjacent spectral lines are smaller than the maximum value, and the harmonic frequency is defined as phase failure resonance frequency; characteristic 2 because there is resistance which consumes the resonance energy in the circuit, therefore the amplitude of the resonant frequency of phase failure is attenuated with time in the short time after phase failure, the higher the resonant frequency, the faster the attenuation; characteristic 3 the following two processes must occur after the phase failure of the transformer power supply, namely: the amplitude of the resonance frequency rises and reaches a maximum value within a very short time, which is the starting process, and then decays with the passage of time until the phase-failure resonance phenomenon disappears, which is the decay process.

The transient current of the neutral line in the step (3.2) has the following frequency spectrum characteristics: characteristic 1 is that in a short time after phase failure, the resonant frequency of the neutral line current of each transformer is the same, and the deviation between the amplitude percentage (the amplitude of the fundamental wave is 100%) and the average value is small; characteristic 2, in a period of time from the moment when the maximum value appears, the ranking in the frequency domain is the first two, the closer the phase-failure point is to the bus, the higher the resonant frequency is, and when the phase-failure point is at the opposite side of the line, the lowest the resonant frequency is; the characteristic 3 is that the normal operation resonant frequency is no longer the resonant frequency after phase failure because of sudden change of the zero sequence inductance and zero sequence capacitance parameters of the system, so the ranking of the amplitude of the frequency in the frequency domain is greatly reduced; the amplitude of the characteristic 4 third harmonic may be greater than the fifth and seventh harmonics, and may also be less than the fifth or seventh harmonic.

The transient current of the neutral line in the step (3.3) has the following frequency spectrum characteristics: characteristic 1 the maximum amplitude of the resonant frequency of the transformer neutral current is ranked between the second name and the fifth name in the frequency domain, and the resonant frequency is higher when the phase-cut point is closer to the transformer; conversely, when the phase-off point is closer to the bus, the lower the resonant frequency is; characteristic 2, when the resonant frequency of the neutral line current of each transformer is different, the phase failure point is always on the power circuit of the transformer with the highest resonant frequency; when the resonant frequencies are the same but the amplitude percentage difference is larger, the phase failure point is always on the power supply loop of the transformer with the largest amplitude; feature 3, the third harmonic amplitude of the transformer neutral current is changed from more than five and seven harmonics before phase failure to less than five and seven harmonics after phase failure, while the third harmonic amplitude of other transformer neutral current is still more than five and seven harmonics; characteristic 4 the ranking of the amplitude of the normal operation resonance frequency in the neutral line current of the transformer in the frequency domain will be greatly reduced, and the same conclusion cannot be drawn for the transformers with intact power supply loops.

The steady-state current of the neutral line in the step (3.4) has the following frequency spectrum characteristics: characteristic 1 the ranking of the amplitude of the normal operation resonance frequency in the neutral line current of the transformer in the frequency domain will be greatly reduced, and the same conclusion can not be obtained for the transformers with intact power supply loops; feature 2 the third harmonic amplitude of the transformer neutral current is necessarily lower than the fifth and seventh harmonics, while the third harmonic amplitude in the neutral current of other transformers must be larger than the fifth and seventh harmonics.

The steady-state current of the neutral line in the step (3.5) has the following frequency spectrum characteristics: the ranking of the amplitude of the normal operation resonant frequency in the neutral current of each transformer in the frequency domain is greatly reduced in the characteristic 1; feature 2 the magnitude of the third harmonic in each transformer neutral current is either greater than the fifth and seventh harmonics or less than the fifth or seventh harmonics.

The step (4) specifically comprises the following small steps:

step (4.1) analyzing the conditions of the change of the voltage unbalance degree of the three-phase power supply, the change of the load of the transformer, the starting or cutting of the loaded power supply and the like, and knowing that the phase failure frequency spectrum characteristic does not occur in the neutral current;

step (4.2) analyzing the condition of three-phase short circuit and three-phase short circuit grounding fault in the power supply system, knowing that the neutral line current of the transformer has phase failure resonance characteristics, but the amplitude of the fundamental component is very small and the amplitude of the direct current component is larger than the fundamental component, when the fault disappears, the resonance frequency is equal to the normal operation resonance frequency, and the amplitude of the direct current component is larger than the fundamental component;

step (4.3) analyzing the two-phase short circuit fault and fault disappearance condition in the power supply system, and knowing that the resonant frequency in the neutral current is equal to the normal operation resonant frequency;

step (4.4) analyzing the condition of two-phase short circuit grounding and single-phase grounding faults in the power supply system, knowing that phase failure frequency spectrum characteristics can not occur in the neutral line current of the transformer, when the faults disappear, the resonance frequency is equal to the normal operation resonance frequency, and simultaneously the amplitude of the direct current component is larger than the fundamental wave component;

step (4.5) analyzing the condition that three phases of a power switch of the transformer are simultaneously disconnected, knowing that phase failure frequency spectrum characteristics can appear in the neutral line current of the transformer, the amplitude of the resonant frequency is far larger than that of the fundamental wave, but the amplitude of the fundamental wave is extremely small to be ignored, and the neutral line current of other transformers has no phase failure frequency spectrum characteristics;

step (4.6) analyzing the condition of no-load impact closing of the transformer, and knowing that no phase-failure frequency spectrum characteristic occurs in the neutral line current of the transformer; if the power supply circuit is open-phase before the transformer is closed by no-load impact, the open-phase frequency spectrum characteristic can appear, and the open-phase frequency spectrum characteristic can appear in the neutral current of other transformers, but the resonant frequency is equal to the normal operation resonant frequency.

The criterion for normal operation of the transformer power supply system in the step (5) comprises the frequency of the first five ranked amplitude values in the frequency domain of the criterion 1, except that the fundamental wave is arranged at the first position, the other four frequencies are all 3+6 × N times of harmonic frequency (N is a natural number which is more than or equal to 0), the amplitude of the third harmonic wave of the criterion 2 is simultaneously more than the fifth and seventh harmonic waves, and the ranking of the amplitude of the normal operation resonant frequency of the criterion 3 in the frequency domain enters the first five frequencies.

The step (6) comprises the following steps:

step 6.1, a steady-state frequency spectrum criterion of the phase failure of the transformer power supply is given, and when the frequency spectrum characteristic of the neutral line current of the transformer does not accord with the normal operation criterion and the following two criteria are detected to simultaneously accord with each other, the phase failure in the system is judged: the ranking of the amplitude of the resonance frequency in normal operation of the criterion 1 in a frequency domain is greatly reduced, and the amplitude of the third harmonic of the criterion 2 is simultaneously lower than the fifth harmonic and the seventh harmonic;

step 6.2 provides a transient state frequency spectrum criterion of the phase failure of the transformer power supply, when the frequency spectrum characteristics in the transformer neutral line current do not accord with the normal operation criterion and the following criteria are detected to simultaneously accord with the phase failure, the phase failure is judged in the system, wherein the amplitude percentage of a certain 3+6 × N-th harmonic frequency in the criterion 1 is suddenly increased by ten times or more, or the amplitude percentage of a certain harmonic frequency which is not 3+6 × N times is suddenly increased by hundred times or more, the amplitude of the frequency reaches the maximum value in a short time after the criterion 2 meets the criterion 1, the maximum amplitude of the frequency in the criterion 3 enters the first five times of an amplitude ranking list in a frequency domain and can only be one to four of fundamental wave, direct current component, fifth time and seventh harmonic wave, and the amplitude of the frequency in the criterion 4 shows an attenuation trend along with the time after the maximum value is reached, and the amplitude of the frequency has an obvious attenuation phenomenon in a half cycle time.

The locking criterion of the phase failure of the power supply of the transformer in the step (7) comprises the following steps: the method comprises the following steps that when the current of a neutral line or the fundamental component of the current of a transformer is detected to be larger than a certain set value M, the phase failure detection is locked immediately, and locking is automatically released after a delay t, wherein the value M is far larger than the maximum current which can appear in the neutral line during normal operation and switching operation, no-load impact switch-on of the transformer and unbalanced voltage of a power grid, and a sufficient reliability coefficient is provided so as to ensure that the phase failure detection device cannot malfunction when the system has no asymmetric short circuit grounding fault; when detecting that the direct current component of the neutral line current of the transformer is larger than the fundamental component, locking and phase loss detection are carried out according to a locking criterion 2; when detecting that the resonant frequency of the neutral current is equal to the resonant frequency of normal operation of the system, the locking criterion 3 locks phase loss detection; and (4) locking and phase loss detection are carried out when the amplitude of the fundamental component of the neutral line current is detected to be less than or equal to the value m, the value m must be less than the current value of the neutral line of the transformer when the phase loss occurs at any position, and the reliability coefficient is enough.

The step (8) is specifically divided into the following small steps:

step (8.1) a graph or table of the corresponding relation between the open-phase resonant frequency and amplitude and the open-phase position is preset for each system operation mode in the open-phase detection device;

step (8.2) when the device detects that the neutral line current accords with the phase failure frequency spectrum characteristic, recording the wave immediately, and automatically storing waveform data of each period of time before and after the phase failure;

step (8.3) provides a manual positioning method of the phase-off position;

step (8.4) provides a phase failure position partition automatic positioning method, and when an automatic positioning mode is selected in advance and the neutral line current accords with the phase failure transient state frequency spectrum criterion, the automatic positioning method can be started;

step (8.5) further provides a method for automatically positioning the phase-cut position in a segmented manner on the basis of the step (8.4);

and (8.6) further providing a method for manually or automatically accurately positioning the phase-cut position on the basis that the step (8.5) is completed by the sectional positioning.

The specific method of the step (8.3) comprises the steps of manually selecting the waveform stored by the detection device, carrying out FFT (fast Fourier transform) on the waveform, increasing the data length of the FFT to improve the resolution of the frequency if necessary, and then inquiring and analyzing a graph or a table of the corresponding relation between the phase failure resonance frequency and the phase failure position of the current operation mode so as to determine the specific position of the phase failure.

The positioning method in the step (8.4) is as follows:

judging the operation condition of each transformer according to the transformer operation sign words or the switching-on/off state signals of the power circuit breaker sent by other phase failure detection devices to obtain the current operation mode of the system;

the phase-failure point partition positioning criterion is as follows: determining that the open-phase position is between the transformer and the bus when the following criteria 1 and 2 are met or the following criteria 1 and 3 are met: the amplitude of the third harmonic of the positioning criterion 1 is lower than the fifth harmonic and the seventh harmonic; when the resonant frequencies of the neutral line currents of the transformers are different, the open-phase fault point is located on a power circuit of the transformer with the highest resonant frequency; when the resonant frequencies of the neutral line currents of the transformers are the same but the amplitude percentages are different greatly, the open-phase fault point is located on a power circuit of the transformer with the largest resonant frequency amplitude;

and phase-break point partition positioning criterion II: when the resonant frequency of the neutral current of each transformer is the same and the amplitude percentage is the same or differs less, the open-phase position is determined to be on the common part of the power supply circuit of each transformer.

The method for automatically positioning in the step (8.5) comprises the step of sectionally positioning the fault point between the transformer and the power bus, wherein the relation between the resonant frequency of the transformer and the bus in the discontinuous phase and the system operation mode is not large, so that the sectionally positioning of the fault point is carried out by presetting a set of fixed values, when the transformer supplies power through a section of closed gas-insulated bus, two set values (A & gtB) are set for the section of loop, when the resonant frequency of the current is between A and B, the phase-cut point is judged to be on the section of loop, the higher the resonant frequency is, the closer the phase-cut point is to the transformer, and when the resonant frequency is equal to or greater than A, the phase-cut point is judged to be at the sleeve of the transformer or in the transformer; when a closed gas insulation bus and a high-voltage cable or an overhead transmission line are arranged between the transformer and the power bus, a method of setting three fixed values (A > B > C) can be adopted for judging the positions of open-phase fault points section by section; when the closed gas insulated bus, the high-voltage cable and the overhead transmission line are all provided, the method of setting four fixed values (A > B > C > D) can be adopted to carry out the positioning of the phase failure fault point section by section, and in the same way, when the number of the sections is n, the method of setting n +1 fixed values is adopted.

The automatic positioning method in the step (8.5) comprises the step of sectionally positioning fault points on the line, wherein a group of fixed values needs to be set for each operation mode in advance because the phase failure resonant frequency of the line has a large relation with the operation modes of the system; the number of the fixed values depends on the number of sections of the line, and when the number of sections is n, n +1 fixed values of the resonant frequency need to be set.

The manual or automatic precise positioning method for the interrupted phase position in the step (8.6) is to precisely position the interrupted phase position by adopting an interpolation method, and precisely obtain the interrupted phase position corresponding to any frequency value by applying the interpolation method according to a pre-established relation graph or table of the limited resonance frequency and the interrupted phase position of each operation mode; and secondly, the resolution of the resonant frequency is improved for accurate positioning, and the resolution of the resonant frequency is improved by increasing the data length of FFT conversion, so that the positioning precision is improved.

The invention has the following beneficial effects:

(1) the phase failure detection method based on the resonance spectrum characteristics of the neutral current of the transformer is firstly provided. Compared with a time domain analysis method, the method has incomparable advantages and can solve the worldwide problem that the phase failure of the no-load power supply of the transformer cannot be correctly and reliably detected;

(2) summarizing the frequency spectrum characteristics of the transformer power supply loop at different positions when the phase is broken for the first time;

(3) firstly, a whole set of frequency domain criterion for detecting the phase failure of the transformer power supply is provided;

(4) firstly, a set of criteria and a method for positioning the phase-failure position of the transformer power supply (partitioned positioning, segmented positioning and accurate positioning) are provided;

(5) the locking criterion of the phase failure of the transformer power supply is provided for the first time, and the problem of false alarm of the phase failure caused by various disturbances in a system and the transformer idle-rush switch-on is solved;

(6) the method can solve the problems of unbalanced power supply voltage, phase failure at different positions and misjudgment of phase failure detection results caused by two or more adjacent transformers powered by the same circuit line in the group reactor nuclear power plant;

(7) the method can sensitively and reliably detect the power phase failure fault of the transformer under various conditions and realize the positioning of fault points.

Drawings

FIG. 1 is a schematic diagram of a 220kV electrical main wiring of a nuclear power plant;

Detailed Description

The present technology is further described below:

the invention provides a transformer power supply phase failure detection method, which specifically comprises the following steps:

step (1.1) selecting a typical transformer power supply system;

and (1.2) establishing a non-simplified circuit simulation model which is consistent with the actual transformer power system according to the step (1.1), so that the simulation analysis result can correctly reflect the actual condition when the phase failure occurs in the power system.

and (2) obtaining the frequency spectrum characteristic of the neutral line current of the transformer in normal operation. Simulation analysis is respectively carried out according to the condition that one, two, three or even more transformers are arranged in a return line, the measured neutral line current waveform is transformed from a time domain to a frequency domain by adopting a Fast Fourier Transform (FFT) method, and therefore the frequency spectrum characteristic information contained in the current is obtained, and the method specifically comprises the following steps:

analyzing and obtaining current spectrum characteristics of a return line with three transformers in normal operation;

according to the steps (2.1) to (2.3), the common frequency spectrum characteristics of the loop with different numbers of transformers when the system operates normally can be obtained as follows:

characteristic 1 when the transformer normally operates, in a frequency spectrogram of neutral line current on a power supply side, harmonic frequency is mainly 3+6 × N subharmonics (N is a natural number which is more than or equal to 0);

feature 2 has a 3+6 × N harmonic frequency, and its amplitude enters the first five times of the whole frequency domain, because the inductance and capacitance parameters of the zero sequence loop resonate the harmonic frequency to a certain extent when the system is in normal operation, so that its amplitude is amplified and is obviously higher than its adjacent harmonic frequency (including its adjacent 3+6 × N harmonic frequency), and we define this frequency as the normal operation resonant frequency;

the amplitude of the characteristic 3 third harmonic frequency is greater than the fifth and seventh harmonics.

and (3) by utilizing the simulation model in the step (1), neutral line current waveform and frequency spectrum characteristics of the transformer power supply during phase failure can be obtained by simulating the phase failure condition of the one-line three-variable system at different positions. Comprises the following steps:

and (3.1) analyzing the phase failure conditions at different positions of the power supply side of the transformer to obtain that the transient current of the neutral line has the following common spectrum characteristics:

characteristic 1 at the instant after the phase failure of the transformer power supply, the neutral current has significant inductance-capacitance resonance frequency spectrum characteristics: the harmonic frequency with extremely small amplitude in normal operation suddenly increases at a certain moment after phase failure, the maximum value of the harmonic frequency is ranked in the top five names in the amplitude of a spectrogram, the harmonic frequency is taken as the center, the amplitudes of adjacent spectral lines are smaller than the maximum value, and the harmonic frequency is defined as the phase failure resonance frequency;

characteristic 2 because there is resistance which consumes the resonance energy in the circuit, therefore the amplitude of the resonant frequency of phase failure is attenuated with time in the short time after phase failure, the higher the resonant frequency, the faster the attenuation;

characteristic 3 the following two processes must occur after the phase failure of the transformer power supply, namely: the amplitude of the resonance frequency rises and reaches a maximum value within a very short time (usually within 0 to 10 ms), which is the start-up process, and then decays with time until the phase-failure resonance phenomenon disappears, which is the decay process.

And (3.2) analyzing the phase failure condition between the power bus of the transformer and the opposite side of the power transmission line to obtain the transient current of the neutral line with the following frequency spectrum characteristics:

characteristic 1 is that in a short time after phase failure, the resonant frequency of the neutral line current of each transformer is the same, and the deviation between the amplitude percentage (taking the amplitude of the fundamental wave as 100%) and the average value is small (the embodiment does not exceed 15%);

characteristic 2, in a period of time from the moment when the maximum value appears, the ranking in the frequency domain is the first two, and the closer the phase failure point is to the bus, the higher the resonance frequency is; when the phase failure point is on the opposite side of the line, the resonant frequency is lowest;

characteristic 3, because the zero sequence inductance and zero sequence capacitance parameter of the system after the phase failure are suddenly changed, the normal operation resonant frequency is no longer the resonant frequency after the phase failure, so the ranking of the amplitude of the frequency in the frequency domain is greatly reduced (at least three times of ranking is reduced);

the amplitude of the characteristic 4 third harmonic is either greater than the fifth and seventh harmonics (for a star/star wired transformer with balanced windings) or less than the fifth or seventh harmonic (for a star/delta or star/delta-delta wired transformer).

And (3.3) analyzing the condition of phase failure between a certain transformer and a bus to obtain the following frequency spectrum characteristics of the transient current of the neutral line:

feature 1 the maximum amplitude of the resonant frequency of the transformer neutral current is ranked in the frequency domain between the second name and the fifth name. When the phase-off point is closer to the transformer, the resonant frequency of the neutral current is higher; conversely, when the phase-off point is closer to the bus, the resonant frequency of the transformer neutral current is lower;

characteristic 2 when the resonant frequencies of the transformer neutral currents are different, the phase failure point must be on the power supply loop of the transformer with the highest resonant frequency. When the resonant frequency is the same but the amplitude percentage is different greatly (the deviation from the average value is more than 25%), the phase failure point is necessarily on the power supply loop of the transformer with the largest amplitude (note that the amplitude percentage is not the amplitude percentage);

feature 3 the third harmonic amplitude of the transformer neutral current is changed from certain more than five and seven harmonics before phase failure to certain less than five and seven harmonics after phase failure. The third harmonic amplitudes of the other transformer neutral currents are still larger than the fifth and seventh harmonics;

feature 4 the ranking in the frequency domain of the amplitude of the normal operating resonant frequency in the neutral current of the transformer will be greatly reduced by at least three. However, the same conclusion cannot be drawn for transformers with otherwise intact power supply circuits.

And (3.4) analyzing the condition of phase failure between a certain transformer and a bus to obtain the following frequency spectrum characteristics of the steady-state current of the neutral line:

feature 1 the ranking in the frequency domain of the amplitude of the normal operating resonant frequency in the neutral current of this transformer will be greatly reduced by at least three. However, the same conclusion cannot be drawn for transformers with intact power supply loops;

feature 2 the third harmonic amplitude of the transformer neutral current is necessarily lower than the fifth and seventh harmonics, while the third harmonic amplitude in the neutral current of other transformers must be larger than the fifth and seventh harmonics.

And (3.5) analyzing the condition of phase loss between the bus and the opposite side of the power transmission line to obtain the following frequency spectrum characteristics of the steady-state current of the neutral line:

the ranking of the amplitude of the normal operation resonant frequency in the neutral current of each transformer in the frequency domain is greatly reduced by at least three times;

feature 2 the third harmonic in the transformer neutral currents has a magnitude either greater than the fifth and seventh harmonics (for star/star wired transformers with balanced windings) or less than the fifth or seventh harmonic (for star/delta-delta wired transformers).

analyzing the condition of the transformer power supply system when various disturbances occur to obtain the transient current frequency spectrum characteristics of the neutral line, and specifically comprising the following steps of:

and (4.2) analyzing the conditions of three-phase short circuit and three-phase short circuit grounding faults in the power supply system, and knowing that the neutral line current of the transformer has open-phase resonance characteristics, but the amplitude of the fundamental wave component is very small and the amplitude of the direct current component is larger than the fundamental wave component. When the fault disappears, the resonant frequency is equal to the normal operation resonant frequency, and the amplitude of the direct current component is larger than the fundamental component;

and (4.4) analyzing the conditions of two-phase short circuit grounding and single-phase grounding faults in the power supply system, and knowing that the phase failure frequency spectrum characteristic does not occur in the neutral line current of the transformer. When the fault disappears, the resonant frequency is equal to the normal operation resonant frequency, and the amplitude of the direct current component is larger than the fundamental component;

and (5) giving a criterion for normal operation of the transformer power supply system according to the frequency spectrum characteristics in the step (2). When any one of the following criteria is met, the open-phase detection device judges that the system is in a normal operation state:

the frequency of the first five bits of amplitude ranking in the frequency domain of the criterion 1, except that the fundamental wave is arranged at the first bit, the other four frequencies are all 3+6 × N harmonic frequencies (N is a natural number which is more than or equal to 0);

the amplitude of the third harmonic wave is larger than the fifth harmonic wave and the seventh harmonic wave at the same time according to the criterion 2;

criterion 3 ranks the amplitude of the normal operation resonant frequency in the frequency domain into the first five, and the method for determining the normal operation resonant frequency comprises the following steps: the product of the amplitude and the frequency is arranged in the frequency of the first three bits of the frequency domain, and after the fundamental wave and the third harmonic frequency are eliminated, the remaining frequency is the normal operation resonant frequency.

The normal operation resonant frequency is a certain 3+6 × N-th harmonic frequency, when a loop is provided with a plurality of transformers and has a plurality of operation modes, at most three normal operation resonant frequencies are not exceeded, the N values of the frequencies are adjacent natural numbers (only one normal operation resonant frequency of 2250Hz in the embodiment), any one operation mode can only correspond to one normal operation resonant frequency, but any one normal operation resonant frequency can correspond to a plurality of operation modes.

and (6) giving a criterion of the phase failure of the transformer power supply according to the frequency spectrum characteristics in the step (3). The method specifically comprises the following steps:

and 6.1, giving a steady-state frequency spectrum criterion of the phase failure of the transformer power supply. When the frequency spectrum characteristic of the transformer neutral current does not accord with the normal operation criterion and the following two criteria are detected to simultaneously accord with each other, the phase failure in the system is judged:

the ranking of the amplitude of the normal operation resonant frequency in the frequency domain is greatly reduced (compared with the stable ranking value in the normal operation of the system, the ranking is reduced by at least three times in the embodiment);

criterion 2 the third harmonic amplitude is lower than both the fifth and seventh harmonics.

Step 6.2, giving a transient spectrum criterion of phase failure of the transformer power supply, and judging that the system has phase failure when the spectrum characteristics in the transformer neutral current do not accord with the normal operation criterion and the following criteria are simultaneously met:

the criterion 1 is that the amplitude percentage of certain 3+6 × N harmonic frequency is suddenly increased by ten times or more (compared with the previous steady state value), or the amplitude percentage of certain harmonic frequency which is not 3+6 × N harmonic frequency is suddenly increased by hundred times or more (compared with the previous steady state value);

after criterion 2 is met, the amplitude of the frequency reaches the maximum value within the time of not more than 10 ms;

criterion 3, the maximum value of the amplitude of the frequency enters the first five names of an amplitude ranking list in a frequency domain, and the maximum value of the amplitude ranked in the front of the frequency can only be one to four of fundamental waves, direct-current components, fifth harmonics and seventh harmonics;

criterion 4 shows that the amplitude of the frequency is in an attenuation trend along with time after reaching the maximum value, and the amplitude of the frequency has an obvious attenuation phenomenon (the amplitude of the frequency can be reduced to 90% or below of the maximum value in the embodiment) within half power frequency period time.

and (7) giving a locking criterion of the phase failure of the transformer power supply (locking can be realized when any one of the following criteria is met) according to the frequency spectrum characteristics in the step (4). The method specifically comprises the following steps:

when detecting that the fundamental component of the neutral line current or current of the transformer is larger than a certain set value M (indicating that a single-phase grounding or two-phase short-circuit grounding fault exists in the system), the locking criterion 1 immediately locks phase-failure detection, and automatically unlocks after a delay t (2 s in the embodiment); the M value is far larger than the maximum current which can appear on a neutral line when the system is in normal operation and switching operation, a transformer is in no-load impact closing, and the voltage of a power grid is unbalanced, and a sufficient reliable coefficient is provided so as to ensure that the phase failure detection device cannot malfunction when the system has no asymmetric short circuit and ground fault;

when detecting that the direct current component of the neutral line current is larger than the fundamental component, the locking criterion 2 indicates that the power supply system is in a recovery process after a symmetrical or asymmetrical short circuit or a short circuit grounding fault is eliminated, and the locking phase failure detection is carried out;

when detecting that the resonant frequency of the neutral current is equal to the normal running resonant frequency of the system, the locking criterion 3 indicates that the system is in a recovery process after various faults are eliminated, and the locking phase failure detection is carried out;

when the amplitude of the fundamental component of the neutral current is detected to be less than or equal to the value m, the locking criterion 4 indicates that the three-phase power supply of the transformer is disconnected or stopped, and the phase loss detection is locked; the value of m must be smaller than the current value of the neutral line of the transformer when the phase is lost at any position, and has enough reliability coefficient, and m is 0.1A in the embodiment;

and (8) positioning the phase failure position under the condition that the phase failure of the transformer power supply is judged according to the step (6) and the step (7). The method comprises the following steps:

step (8.1) a graph or table of the corresponding relation between the open-phase resonant frequency and the open-phase position is preset for each system operation mode in the open-phase detection device;

step (8.2) when the device detects that the neutral line current of the transformer accords with the phase failure frequency spectrum characteristic, recording the wave immediately, and automatically storing waveform data of each period of time before and after the phase failure;

and (8.3) providing a manual positioning method of the phase-off position. The specific method comprises the following steps:

manually selecting the waveform stored by the detection device, carrying out FFT (fast Fourier transform) on the waveform, and increasing the data length (power frequency cycle number) of the FFT if necessary to improve the resolution of frequency;

and inquiring a graph or a table of the corresponding relation between the phase failure resonant frequency and amplitude of the current operation mode and the phase failure position so as to determine the specific position of the phase failure.

And (8.4) providing a method for automatically positioning the phase-cutting position partition. When the automatic positioning mode is selected in advance and the neutral point current of the transformer accords with the criterion of phase-failure transient spectrum, the automatic positioning method can be started. The positioning method comprises the following steps:

according to transformer operation flag words (0 represents outage and 1 represents operation) sent by other open-phase detection devices or switching-on/off state signals of a power circuit breaker, judging the operation working conditions of the transformers to obtain the current operation mode of the system;

the phase-failure point partition positioning criterion is as follows: determining that the open-phase position is between the transformer and the bus (including the bus disconnecting switch) when the following criteria 1 and 2 are met or the following criteria 1 and 3 are met:

the amplitude of the third harmonic of the positioning criterion 1 is lower than the fifth harmonic and the seventh harmonic;

when the resonant frequencies of the neutral line currents of the transformers are different, the open-phase fault point is located on a power circuit of the transformer with the highest resonant frequency;

when the resonant frequencies of the neutral line currents of the transformers are the same and the amplitude percentages are different greatly (in the embodiment, the maximum deviation absolute value deviating from the average value of the amplitude percentages is more than or equal to 25% of the average value), the phase failure fault point is positioned on the power circuit of the transformer with the maximum amplitude (non-amplitude percentage) of the resonant frequency;

and phase-break point partition positioning criterion II: when the resonant frequency of the neutral line current of each transformer is the same, and the amplitude percentages are the same or have smaller difference (in the embodiment, the absolute value of the maximum deviation from the average value of the amplitude percentages is not more than 15% of the average value), it is determined that the phase failure position is on the common part of the power supply circuit of each transformer, namely, between the bus and the opposite side of the power transmission line.

And (8.5) further providing a method for automatically positioning the phase-off position in a segmented manner on the basis of the step (8.4).

The method for sectionally positioning the fault point between the transformer and the power bus is as follows (when the phase failure point partition positioning criterion is met):

because the relation between the resonant frequency of the transformer and the bus in the discontinuous phase and the system operation mode is not large, the discontinuous phase point is positioned in sections by presetting a group of fixed values;

when the transformer supplies power through a section of closed gas insulated bus (or a section of high-voltage cable or an overhead line), two set values (A & gtB) are set for the section of loop, when the resonance frequency of the current is between A and B, the phase-cut point is judged to be on the section of loop, and the higher the resonance frequency is, the closer the phase-cut point is to the transformer; when the resonant frequency is equal to or greater than A, determining that the phase-cut point is at the bushing of the transformer or in the transformer;

when a closed gas insulation bus and a high-voltage cable or an overhead transmission line are arranged between the transformer and the power bus, a method of setting three fixed values (A > B > C) can be adopted for judging the positions of open-phase fault points section by section;

when the closed gas insulated bus, the high-voltage cable and the overhead transmission line are all provided, the method of setting four fixed values (A > B > C > D) can be adopted to carry out the positioning of the phase failure fault point section by section, and in the same way, when the number of the sections is n, the method of setting n +1 fixed values is adopted.

The method for sectionally positioning the fault point on the line is as follows (when meeting the phase failure point partition positioning criterion two):

because the line phase failure resonant frequency has a large relationship with the system operation mode, a set of fixed values needs to be set for each operation mode in advance; the number of the fixed values depends on the number of the sections of the line, and when the number of the sections is n, n +1 fixed values of the resonant frequency are required to be set;

in this embodiment, when a line section location is performed in a one-line three-variable system operation mode, a line is located every 50Hz, for example, when an open-phase resonant frequency at a head end of the line is 750Hz, and an open-phase resonant frequency at a tail end of the line is 600Hz, the line is divided into 3 sections, and for this purpose, 3+ 1-4 fixed values of resonant frequency (E-750, F-700, G-650, H-600, Hz) need to be set; for other modes of operation, the number of segments and frequency settings may be determined in the manner described above.

Step (8.6) further provides a method for manually or automatically accurately positioning the phase-cut position on the basis that the step (8.5) is completed by subsection positioning, which comprises the following steps:

(1) and (4) accurately positioning by adopting an interpolation method. And accurately obtaining the open-phase position corresponding to any frequency value by applying an interpolation method according to a pre-established relation graph or table of the finite resonant frequency and the open-phase position of each operation mode. The method is used for realizing accurate positioning of the phase failure between the transformer and the power bus, because the duration of the phase failure frequency spectrum characteristic is short, but the resonant frequency is high, and when the data length (periodicity) of FFT (fast Fourier transform) is equal to 1 power frequency cycle, the positioning accuracy is higher;

(2) and the resolution of the resonant frequency is improved for accurate positioning. By increasing the data length (number of cycles) of the FFT, the resolution of the resonance frequency is improved, and thus the accuracy of positioning can be improved. The method is suitable for accurate positioning of the phase failure of the power transmission line, because the phase failure resonant frequency is relatively low, but the duration time of the resonant frequency spectrum characteristic is relatively long, and the increase of the data length of the FFT cannot cause the steady-state current waveform after the phase failure to enter a data window of the FFT.

Taking a 220kV power supply system of a certain nuclear power station as an example, the nuclear power station currently has six auxiliary transformers (star/star connection with balanced windings) or high-voltage standby transformers (star/angle-angle connection), and the 220kV side neutral points of the transformers are directly grounded. Six transformers share one 220kVGIS switch station, the switch station has 2 overhead incoming lines in total, and a double-bus split operation mode is adopted. When the bus coupler is in normal operation, the bus coupler switch is disconnected, the auxiliary switches 1, 3 and 5 are normally connected with the bus I, and the auxiliary switches 2, 4 and 6 are normally connected with the bus II. The electrical main wiring diagram is shown in fig. 1.

According to the invention, by taking the example that No. 1, 3 and 5 transformers are normally connected with the I bus as an example, corresponding simulation models are established according to the figure 1, actual parameters of a 220kV power supply system, a power transmission line and equipment in a switching station are directly or after calculation and are input into the simulation models, and simulation research for simulating phase failure at different positions is carried out.

The method comprises the steps of performing fast Fourier transform on neutral line current on the 220kV side of each transformer after phase failure, completing the transform from a time domain to a frequency domain, and obtaining resonance spectrum data of each neutral line transient current at different moments, wherein tables 1 to 3 only list data when the amplitude of resonance frequency reaches the maximum value after phase failure, numbers in brackets in the tables are the ranking of the amplitude in the frequency domain, phase failure position T in each table represents a transformer, L represents a circuit, and numbers behind letters represent the number of each phase failure position.

TABLE 1 line-to-line (No. 5) change, neutral current resonance frequency and amplitude after phase loss at different positions

TABLE 2 lines two changes (No. 1 and No. 5 changes), neutral current resonance frequency and amplitude after phase failure at different positions

TABLE 3 line-three times, neutral line current resonance frequency and amplitude after phase loss at different positions

The detection of the no-load phase failure of the transformer is a worldwide problem, and the three existing detection methods (including the methods of different combinations) which claim to detect the no-load phase failure of the transformer have defects, so that the false alarm or the false-alarm phase failure of the transformer is caused under the condition of no-load operation. The phase failure detection method based on the transformer neutral line steady-state and transient current spectrum characteristic analysis does not have the defects of the analysis method, can solve the problems that the phase failure detection accuracy is influenced by unbalanced power supply voltage, a loop with a plurality of transformers, phase failure at different positions on a line, various disturbances in a system and the like, and effectively positions the phase failure at different positions of the transformer, the nearby part of the transformer, the switch station and the power transmission line.

The present invention has been described in detail with reference to the embodiments, but the present invention is not limited to the embodiments, and various changes can be made without departing from the gist of the present invention within the knowledge of those skilled in the art. The present invention is not described in detail in the prior art.

Claims

1. A transformer power supply phase failure detection method is characterized by comprising the following steps:

and (8) providing a positioning method of the phase failure position of the transformer power supply according to the step (6) and the step (7).

2. The method for detecting the phase failure of the power supply of the transformer as claimed in claim 1, wherein the step (1) comprises the following steps:

step (1.1) selecting a typical transformer power supply system;

3. The method for detecting the phase failure of the power supply of the transformer as claimed in claim 2, wherein the step (2) comprises the following steps:

4. The method for detecting the phase failure of the power supply of the transformer as claimed in claim 3, wherein in the step (2), when the system normally operates, the common frequency spectrum of a loop with different numbers of transformers is characterized in that in a frequency spectrum diagram of neutral current on the power supply side when the transformer of the characteristic 1 normally operates, the harmonic frequency is mainly 3+6 × Nth harmonic (N is a natural number larger than or equal to 0), the characteristic 2 has 3+6 × Nth harmonic frequency, the amplitude of the harmonic frequency enters the first few names of the whole frequency domain, because the harmonic frequency is resonated to a certain degree by inductance and capacitance parameters of a zero-sequence loop when the system normally operates, the amplitude of the harmonic frequency is amplified and is obviously higher than the adjacent harmonic frequency, the frequency is defined as the normal operation resonance frequency, and the amplitude of the characteristic 3-third harmonic frequency is larger than fifth harmonic and seventh harmonic.

5. The method for detecting the phase failure of the power supply of the transformer as claimed in claim 4, wherein the step (3) comprises the following steps:

6. The method for detecting the phase failure of the transformer power supply according to claim 5, wherein: the transient current of the neutral line in the step (3.1) has the following common spectrum characteristics: characteristic 1 at the instant after the phase failure of the transformer power supply, the neutral current has significant inductance-capacitance resonance frequency spectrum characteristics: the harmonic frequency with extremely small amplitude in normal operation suddenly increases at a certain moment after phase failure, the maximum value of the harmonic frequency is ranked in the first few names in the amplitude of a spectrogram, the maximum value is taken as the center, the amplitudes of adjacent spectral lines are smaller than the maximum value, and the harmonic frequency is defined as phase failure resonance frequency; characteristic 2 because there is resistance which consumes the resonance energy in the circuit, therefore the amplitude of the resonant frequency of phase failure is attenuated with time in the short time after phase failure, the higher the resonant frequency, the faster the attenuation; characteristic 3 the following two processes must occur after the phase failure of the transformer power supply, namely: the amplitude of the resonance frequency rises and reaches a maximum value within a very short time, which is the starting process, and then decays with the passage of time until the phase-failure resonance phenomenon disappears, which is the decay process.

7. The method for detecting the phase failure of the transformer power supply according to claim 6, wherein: the transient current of the neutral line in the step (3.2) has the following frequency spectrum characteristics: characteristic 1 is that in a short time after phase failure, the resonant frequency of the neutral line current of each transformer is the same, and the deviation between the amplitude percentage (the amplitude of the fundamental wave is 100%) and the average value is small; characteristic 2, in a period of time from the moment when the maximum value appears, the ranking in the frequency domain is the first two, the closer the phase-failure point is to the bus, the higher the resonant frequency is, and when the phase-failure point is at the opposite side of the line, the lowest the resonant frequency is; characteristic 3, because the zero sequence inductance and zero sequence capacitance parameter of the system are suddenly changed, the normal operation resonant frequency is no longer the resonant frequency after the phase failure, therefore the ranking of the amplitude of the frequency in the neutral current of each transformer in the frequency domain will be greatly reduced; the amplitude of the characteristic 4 third harmonic is either greater than the fifth and seventh harmonics (for a star/star wired transformer with balanced windings) or less than the fifth or seventh harmonic (for a star/delta or star/delta-delta wired transformer).

8. The method for detecting the phase failure of the transformer power supply according to claim 7, wherein: the transient current of the neutral line in the step (3.3) has the following frequency spectrum characteristics: characteristic 1 the maximum amplitude of the resonant frequency of the transformer neutral current is ranked between the second name and the fifth name in the frequency domain, and the resonant frequency is higher when the phase-cut point is closer to the transformer; conversely, when the phase-off point is closer to the bus, the lower the resonant frequency is; characteristic 2, when the resonant frequency of the neutral line current of each transformer is different, the phase failure point is always on the power supply loop of the transformer with the maximum amplitude; when the resonant frequencies are the same but the amplitude percentage difference is larger, the phase failure point is always on the power supply loop of the transformer with the highest resonant frequency; feature 3, the third harmonic amplitude of the transformer neutral current is changed from more than five and seven harmonics before phase failure to less than five and seven harmonics after phase failure, while the third harmonic amplitude of other transformer neutral current is still more than five and seven harmonics; characteristic 4 the ranking of the amplitude of the normal operation resonance frequency in the neutral line current of the transformer in the frequency domain will be greatly reduced, and the same conclusion cannot be drawn for the transformers with intact power supply loops.

9. The method for detecting the phase failure of the transformer power supply according to claim 8, wherein: the steady-state current of the neutral line in the step (3.4) has the following frequency spectrum characteristics: the method is characterized in that 1, the ranking of the amplitude of the normal operation resonant frequency in the neutral line current of the transformer in the frequency domain is greatly reduced, and the same conclusion cannot be obtained for the transformers with good power supply loops; feature 2 the third harmonic amplitude of the transformer neutral current is necessarily lower than the fifth and seventh harmonics, while the third harmonic amplitude in the neutral current of other transformers must be larger than the fifth and seventh harmonics.

10. The method for detecting the phase failure of the transformer power supply according to claim 9, wherein: the steady-state current of the neutral line in the step (3.5) has the following frequency spectrum characteristics: the ranking of the amplitude of the normal operation resonant frequency in the neutral current of each transformer in the frequency domain is greatly reduced in the characteristic 1; feature 2 the third harmonic in the transformer neutral currents has a magnitude either greater than the fifth and seventh harmonics (for star/star wired transformers with balanced windings) or less than the fifth or seventh harmonic (for star/delta or star/delta-delta wired transformers).

11. The method for detecting the phase failure of the transformer power supply according to claim 10, wherein: the step (4) specifically comprises the following small steps:

12. The method for detecting the phase failure of the power supply of the transformer as claimed in claim 11, wherein the criteria for the normal operation of the power supply system of the transformer in the step (5) include that the frequency of the first five ranked amplitude values in the frequency domain of criterion 1, the four other frequencies except the first ranked fundamental wave are all 3+6 × N harmonic frequencies (N is a natural number greater than or equal to 0), the amplitude of the third harmonic value in criterion 2 is greater than the fifth harmonic value and the seventh harmonic value simultaneously, the ranking of the amplitude of the normal operation resonance frequency in the frequency domain of criterion 3 is carried out to the first five, and the method for determining the normal operation resonance frequency is that the product of the amplitude and the frequency is ranked in the first three ranked frequency domains, and the remaining frequency is the normal operation resonance frequency after the fundamental wave and the third harmonic frequency are excluded.

13. The method for detecting the phase failure of the transformer power supply according to claim 12, wherein: the step (6) comprises the following steps:

14. The method for detecting the phase failure of the transformer power supply according to claim 13, wherein: the locking criterion of the phase failure of the power supply of the transformer in the step (7) comprises the following steps: the method comprises the following steps that when the current of a neutral line or the fundamental component of the current of a transformer is detected to be larger than a certain set value M, the phase failure detection is locked immediately, and locking is automatically released after a delay t, wherein the value M is far larger than the maximum current which can appear in the neutral line during normal operation and switching operation, no-load impact switch-on of the transformer and unbalanced voltage of a power grid, and a sufficient reliability coefficient is provided so as to ensure that the phase failure detection device cannot malfunction when the system has no asymmetric short circuit grounding fault; when detecting that the direct current component of the neutral line current of the transformer is larger than the fundamental component, locking and phase loss detection are carried out according to a locking criterion 2; when detecting that the resonant frequency of the neutral current is equal to the resonant frequency of normal operation of the system, the locking criterion 3 locks phase loss detection; and (4) locking and phase loss detection are carried out when the amplitude of the fundamental component of the neutral line current is detected to be less than or equal to the value m, the value m must be less than the current value of the neutral line of the transformer when the phase loss occurs at any position, and the reliability coefficient is enough.

15. The method for detecting the phase failure of the power supply of the transformer as claimed in claim 14, wherein the step (8) is specifically divided into the following sub-steps:

step (8.3) provides a manual positioning method of the phase-off position;

step (8.4) provides a phase failure position partition automatic positioning method, and when an automatic positioning mode is selected in advance and the current of a neutral point accords with the phase failure transient state frequency spectrum criterion, the automatic positioning method can be started;

16. The method for detecting the phase failure of the transformer power supply according to claim 15, wherein: the specific method of the step (8.3) comprises the steps of manually selecting the waveform stored by the detection device, carrying out FFT (fast Fourier transform) on the waveform, increasing the data length of the FFT to improve the resolution of the frequency if necessary, and then inquiring and analyzing a graph or a table of the corresponding relation between the phase failure resonance frequency and the phase failure position of the current operation mode so as to determine the specific position of the phase failure.

17. The method for detecting the phase failure of the power supply of the transformer as claimed in claim 16, wherein the positioning method in the step (8.4) is as follows:

18. The method for detecting the phase failure of the transformer power supply according to claim 17, wherein: the method for automatically positioning in the step (8.5) comprises the step of sectionally positioning the fault point between the transformer and the power bus, wherein the relation between the resonant frequency of the transformer and the bus in the discontinuous phase and the system operation mode is not large, so that the sectionally positioning of the fault point is carried out by presetting a set of fixed values, when the transformer supplies power through a section of closed gas-insulated bus, two set values (A & gtB) are set for the section of loop, when the resonant frequency of the current is between A and B, the phase-cut point is judged to be on the section of loop, the higher the resonant frequency is, the closer the phase-cut point is to the transformer, and when the resonant frequency is equal to or greater than A, the phase-cut point is judged to be at the sleeve of the transformer or in the transformer; when a closed gas insulation bus and a high-voltage cable or an overhead transmission line are arranged between the transformer and the power bus, a method of setting three fixed values (A > B > C) can be adopted for judging the positions of open-phase fault points section by section; when the closed gas insulated bus, the high-voltage cable and the overhead transmission line are all provided, the method of setting four fixed values (A > B > C > D) can be adopted to carry out the positioning of the phase failure fault point section by section, and in the same way, when the number of the sections is n, the method of setting n +1 fixed values is adopted.

19. The method for detecting the phase failure of the transformer power supply as claimed in claim 18, wherein: the automatic positioning method in the step (8.5) comprises the step of sectionally positioning fault points on the line, wherein a group of fixed values needs to be set for each operation mode in advance because the phase failure resonant frequency of the line has a large relation with the operation modes of the system; the number of the fixed values depends on the number of sections of the line, and when the number of sections is n, n +1 fixed values of the resonant frequency need to be set.

20. The method for detecting the phase failure of the transformer power supply as claimed in claim 19, wherein: the manual or automatic precise positioning method for the interrupted phase position in the step (8.6) is to precisely position the interrupted phase position by adopting an interpolation method, and precisely obtain the interrupted phase position corresponding to any frequency value by applying the interpolation method according to a pre-established relation graph or table of the limited resonance frequency and the interrupted phase position of each operation mode; and secondly, the resolution of the resonant frequency is improved for accurate positioning, and the resolution of the resonant frequency is improved by increasing the data length of FFT conversion, so that the positioning precision is improved.