Method for detecting partial discharge of high-voltage and low-voltage leads of power transformer

Abstract

The invention discloses a method for detecting partial discharge of high-voltage and low-voltage leads of a power transformer. The method comprises the following steps: step 1, acquiring ultrahigh-frequency signals, ultrasonic signals and vibration signals at all wiring joints of a high-voltage side and a low-voltage side; step 2, performing judgment based on the ultrahigh frequency signals, and if the ultrahigh frequency signals are acquired at more than or equal to five wiring joints, entering step 3 for further judgment; step 3, obtaining a power spectrum of the ultrasonic signal, performing judgment based on power frequency positive and negative half-cycle energy in the power spectrum of the ultrasonic signal, and if the power frequency negative half-cycle energy in the power spectrum is greater than the power frequency positive half-cycle energy in the power spectrum, entering step 4 for further judgment; and step 4, obtaining a frequency spectrum of the vibration signals, performing judgment based on the frequency spectrum of the vibration signals, and if the vibration signals in the frequency spectrum are intensively distributed near the integral multiple power frequency signals, determining that the partial discharge phenomenon of the lead occurs. The safety and reliability of the transformer are improved.

Description

Technical Field

[0001] The present invention relates to the field of transformer partial discharge detection methods, and specifically to a method for detecting partial discharge of high-voltage and low-voltage leads of a power transformer. Background Art

[0002] Power transformers are key core equipment in the power system. The operating status of transformers directly affects the reliability of power supply. If a fault occurs, it will cause significant economic losses and even casualties. Ensuring its safe and stable operation is a prerequisite for ensuring the stable operation of the entire power system. According to statistics, a large proportion of power outages in the actual operation of the power system are caused by transformer failures, and the long-term existence of partial discharge in the leads will cause insulation aging and damage, and then trigger transformer failures.

[0003] At present, the insulation detection technology of power transformers judges the overall insulation condition of the transformer by measuring the insulation resistance of the transformer, and cannot realize the judgment of the insulation condition of the local leads of the transformer. Moreover, the insulation resistance detection method is affected by various factors, and high accuracy requires strict control of the influencing factors. It is necessary to cut off the power supply for detection, and it is impossible to monitor the insulation status of the power transformer leads in real time.

[0004] Therefore, how to effectively detect partial discharge of high-voltage and low-voltage leads is an issue studied by those skilled in the art. Summary of the Invention

[0005] The present invention provides a method for detecting partial discharge of high-voltage and low-voltage leads of a power transformer to solve the problem that the existing insulation resistance detection method cannot monitor the insulation condition of local leads in real time.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A method for detecting partial discharge of high-voltage and low-voltage leads of a power transformer, comprising the following steps:

[0008] Step 1: Collect ultra-high frequency signals, ultrasonic signals, and vibration signals from all connection points on the high-voltage side and all connection points on the low-voltage side of the power transformer respectively;

[0009] Step 2: Judge based on the ultra-high frequency signals of all connection points obtained in Step 1: If the ultra-high frequency signals are collected from less than five connection points, the judgment result is that there is no partial discharge phenomenon in the leads; if the ultra-high frequency signals are collected from greater than or equal to five connection points, then enter Step 3 for further judgment;

[0010] Step 3: Based on the ultrasonic signals of all the wiring connection points on the high-voltage side and the low-voltage side obtained in Step 1, obtain the power spectrum of the ultrasonic signals, and make a judgment based on the power of the positive and negative half-cycles of the power frequency in the power spectrum of the ultrasonic signals: If the power of the negative half-cycle of the power frequency in the power spectrum is less than or equal to the power of the positive half-cycle of the power frequency in the power spectrum, the judgment result is that there is no partial discharge phenomenon in the lead; If the power of the negative half-cycle of the power frequency in the power spectrum is greater than the power of the positive half-cycle of the power frequency in the power spectrum, go to Step 4 for further judgment;

[0011] Step 4: Based on the vibration signals of all the wiring connection points on the high-voltage side and the low-voltage side obtained in Step 1, obtain the frequency spectrum of the vibration signals, and make a judgment based on the frequency spectrum of the vibration signals: If the vibration signals in the frequency spectrum are not concentrated near the integer multiple power frequency signals, the judgment result is that there is no partial discharge phenomenon in the lead; If the vibration signals in the frequency spectrum are concentrated near the integer multiple power frequency signals, the judgment result is that there is a partial discharge phenomenon in the lead.

[0012] Further in Step 3, the power spectrum is obtained by performing a fast Fourier transform on the ultrasonic signals of all the wiring connection points.

[0013] Further in Step 3, first amplify and perform a discrete Fourier transform on the ultrasonic signals, and then perform a fast Fourier transform.

[0014] Further in Step 4, the frequency spectrum is obtained by performing a fast Fourier transform on the vibration signals of all the wiring connection points.

[0015] Further in Step 4, first filter and shape the vibration signals, and then perform a fast Fourier transform.

[0016] The present invention has the following beneficial effects:

[0017] 1. Improve the safety and reliability of the transformer. By detecting partial discharge in the lead, insulation defects and potential faults in the internal leads of the transformer can be discovered in time, thus avoiding power accidents caused by insulation failures and ensuring the safe and stable operation of the power system.

[0018] 2. The detection of partial discharge in the lead can provide early diagnosis information on the insulation status of the transformer leads, which helps to implement preventive maintenance strategies and reduce unexpected power outages and maintenance costs.

[0019] 3. The detection of partial discharge in the lead is a non-destructive test item and can be carried out without damaging the transformer, which is of great significance for evaluating the insulation performance of the transformer and extending its service life. Description of the Drawings

[0020] Figure 1 It is the flowchart of the method of the embodiment of the present invention. Detailed implementation mode

[0021] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0022] As Figure 1 shown, this embodiment discloses a method for detecting partial discharge of high-voltage and low-voltage leads of a power transformer. The power transformer is a three-winding transformer. The high-voltage side and the low-voltage side of the three-winding transformer each have at least three sets of terminal connections, that is, each has A, B, and C phase terminal connections respectively. Therefore, this voltage transformer has a total of at least six connection joints. This embodiment includes the following steps:

[0023] Step 1: Arrange UHF sensors, ultrasonic sensors, and vibration sensors at each high-voltage side connection joint of the power transformer, and arrange high-frequency sensors, ultrasonic sensors, and vibration sensors at each low-voltage side connection joint of the power transformer.

[0024] Collect UHF signals of all connection joints on the high-voltage side and low-voltage side of the power transformer through UHF sensors, collect ultrasonic signals of all connection joints on the high-voltage side and low-voltage side of the power transformer through ultrasonic sensors, and collect vibration signals of all connection joints on the high-voltage side and low-voltage side of the power transformer through vibration sensors. Since the high-voltage side and the low-voltage side of the power transformer each have at least three sets of terminal connections, this embodiment collects at least six sets of UHF signals, at least six sets of ultrasonic signals, and at least six sets of vibration signals in total.

[0025] Step 2: Judge based on the UHF signals of all connection joints including the high-voltage side and the low-voltage side obtained in Step 1: If the UHF signals are collected at less than five connection joints among all connection joints, the judgment result is that there is no partial discharge phenomenon of the lead; if the UHF signals are collected at greater than or equal to five connection joints among all connection joints, go to Step 3 for further judgment.

[0026] Step 3: Based on the ultrasonic signals of all connection joints including the high-voltage side and the low-voltage side obtained in Step 1, obtain the power spectrum of the ultrasonic signals. The power spectrum calculation process is as follows:

[0027] 3.1) Since the ultrasonic signals received by the ultrasonic sensors are usually weak, in this embodiment, the collected ultrasonic signals are first preliminarily amplified by a preamplifier and then amplified a second time to enhance the signal intensity;

[0028] 3.2) In order to convert the received discrete signals from the time domain to the frequency domain, perform a discrete Fourier transform on each amplified ultrasonic signal on the high-voltage side and the low-voltage side to convert the discrete signals from the time domain to the frequency domain. The calculation is as shown in formula (1):

[0029]

[0030] In formula (1): S(k) is the complex form of the k-th frequency component of the sequence s(n), where the sequence s(n) is a discrete signal in the time domain. The ultrasonic signals on each of the high-voltage side and the low-voltage side form a discrete signal sequence, and this discrete signal sequence becomes s(n) after amplification; N is the total number of samples of the signal s(n); j is the imaginary unit; k is the frequency index, varying from 0 to N - 1; n is the sample index of the time-domain signal.

[0031] 3.3) Calculate the power spectrum as shown in formula (2):

[0032]

[0033] In formula (3): P(k) is the power spectrum of the k-th frequency component, ∣S(k)∣ is the magnitude of the discrete Fourier transform DFT result S(k), and N is the total number of samples of the signal.

[0034] 3.4) Use a filter to obtain the power frequency component in the power spectrum.

[0035] 3.5) Calculate the energies of the positive and negative half-cycles of the power frequency in the power spectrum as shown in formula (3):

[0036]

[0037] In formula (3): E + represents the energy of the positive half-cycle of the power frequency in the power spectrum; E - represents the energy of the negative half-cycle of the power frequency in the power spectrum; t 1+ to t 2+ is the time interval of the positive half-cycle of the power frequency; t 1- to t 2- is the time interval of the negative half-cycle of the power frequency; s(t) represents the amplitude value of the power frequency component signal at time t.

[0038] After obtaining the energies of the positive and negative half-cycles of the power frequency in the power spectrum of the ultrasonic signal, make a judgment based on the energies of the positive and negative half-cycles of the power frequency in the power spectrum of the ultrasonic signal: If the energy E - of the negative half-cycle of the power frequency in the power spectrum is less than or equal to the energy E + of the positive half-cycle of the power frequency in the power spectrum, then the judgment result is that there is no lead partial discharge phenomenon; If the energy E - of the negative half-cycle of the power frequency in the power spectrum is greater than the energy E + of the positive half-cycle of the power frequency in the power spectrum, then proceed to step 4 for further judgment.

[0039] Step 4: Based on the vibration signals of all the wiring connection points on the high-voltage side and the low-voltage side obtained in step 1, obtain the frequency spectrum of the vibration signals. The calculation process is as follows:

[0040] 4.1) First, remove the low-frequency interference in the vibration signal through four high-pass filters (with cut-off frequencies of 500 Hz, 1000 Hz, 1500 Hz, and 2000 Hz respectively) to reduce the vibration signal caused by the mechanical fault itself.

[0041] 4.2) Use input shaping technology to shape the filtered vibration signal to reduce the vibration response of the system. The calculation is as shown in formula (4):

[0042]

[0043] In formula (4): A i is the amplitude of the vibration signal pulse before shaping; ζ is the damping ratio; ω n is the natural frequency; ω d is the frequency of damped vibration; t i is the time of the i-th pulse; φ i is the phase of the i-th shaping pulse; is the vibration signal after shaping.

[0044] 4.3) Perform a fast Fourier transform on the shaped vibration signal for frequency-domain analysis, convert the time-domain signal into a frequency-domain signal, and the formula used is as shown in formula (5):

[0045]

[0046] In formula (6): V[k] is the complex form of the k-th frequency component of the shaped vibration signal v[n], v[n] is the discrete signal after shaping in the time domain; N is the total number of samples of the signal v[n]; j is the imaginary unit; n is the sample index of the time-domain signal.

[0047] 4.3) Take the modulus of the result of the fast Fourier transform to obtain the amplitude spectrum, as shown in formula (6):

[0048] A[k] = V[k] (6)

[0049] In formula (7): A[k] is the amplitude of the k-th frequency component.

[0050] After obtaining the frequency spectrum of the vibration signal, make a judgment based on the frequency spectrum: Select 31 integer multiple power frequency signal points from 500 Hz to 2000 Hz in the frequency spectrum for observation. For these 31 signal points, if there is a peak in the frequency range of any integer multiple power frequency signal point frequency ±20 Hz, then mark this integer multiple power frequency signal point as a characteristic point. If the total number of characteristic points does not exceed 10, the judgment result is that there is no lead partial discharge phenomenon; if the total number of characteristic points exceeds 10, the judgment result is that a lead partial discharge phenomenon has occurred.

[0051] Thus, in this embodiment, it can be determined whether there is partial discharge in the power transformer. When it is determined that there is partial discharge, the determination result and the signals collected by each sensor are transmitted to the background monitoring device, providing a basis for partial discharge for the background monitoring device.

[0052] The preferred embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings. The embodiments described in the present invention are only descriptions of the preferred embodiments of the present invention, and do not limit the concept and scope of the present invention. Among the various specific technical features described in the above specific embodiments, they can be combined in any suitable manner without contradiction. As long as such a combination does not violate the idea of the present invention, it should also be regarded as the content disclosed in this disclosure. To avoid unnecessary repetition, the present invention does not separately describe various possible combination methods.

[0053] The present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention and without departing from the design idea of the present invention, various variations and improvements made by those skilled in the art to the technical solution of the present invention should all fall within the protection scope of the present invention. The technical content claimed by the present invention has been fully recorded in the claims.

Claims

1. A method for detecting partial discharge of high and low voltage leads of a power transformer, characterized in that: The following steps are involved: Step 1, collecting ultra-high frequency signals, ultrasonic signals, and vibration signals from all wiring connections on the high-voltage side and all wiring connections on the low-voltage side of the power transformer respectively; Step 2: Make a judgment based on the UHF signals of all the wiring connections obtained in step 1: if less than five wiring connections collect UHF signals, the judgment result is that no partial discharge of the lead occurs; if more than or equal to five wiring connections collect UHF signals, proceed to step 3 for further judgment; Step 3, based on the ultrasonic signals of all wiring connections on the high-voltage side and the low-voltage side obtained in step 1, obtain the power spectrum of the ultrasonic signal, and make a judgment based on the positive and negative half-cycle energy of the power frequency in the power spectrum of the ultrasonic signal: if the negative half-cycle energy of the power frequency in the power spectrum is less than or equal to the positive half-cycle energy of the power frequency in the power spectrum, the judgment result is that no partial discharge of the lead occurs; if the negative half-cycle energy of the power frequency in the power spectrum is greater than the positive half-cycle energy of the power frequency in the power spectrum, proceed to step 4 for further judgment; Step 4. Based on the vibration signals of all wiring connections on the high-voltage side and the low-voltage side obtained in step 1, the frequency spectrum of the vibration signal is obtained, and a judgment is made based on the frequency spectrum of the vibration signal: if the vibration signal in the frequency spectrum is not concentrated near the integer multiple of the power frequency signal, the judgment result is that no partial discharge of the lead occurs; if the vibration signal in the frequency spectrum is concentrated near the integer multiple of the power frequency signal, the judgment result is that partial discharge of the lead occurs.

2. A method for detecting partial discharge of high and low voltage leads of a power transformer according to claim 1, characterized in that: In step 3, the power spectrum is obtained by performing fast Fourier transform on the ultrasonic signals at all wiring connections.

3. A method for detecting partial discharge of high and low voltage leads of a power transformer according to claim 2, characterized in that: In step 3, the ultrasonic signal is first amplified, discrete Fourier transformed, and then fast Fourier transformed.

4. A method for detecting partial discharge of high and low voltage leads of a power transformer according to claim 1, characterized in that: In step 4, the frequency spectrum is obtained by performing fast Fourier transform on the vibration signals at all wiring connections.

5. A method for detecting partial discharge of high and low voltage leads of a power transformer according to claim 4, characterized in that: In step 4, the vibration signal is first filtered and shaped, and then fast Fourier transform is performed.

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