CN-122017386-A - Pulse injection-based broadband characteristic measurement system and method for low-frequency transformer

CN122017386ACN 122017386 ACN122017386 ACN 122017386ACN-122017386-A

Abstract

The invention relates to the technical field of power equipment testing, and discloses a low-frequency transformer broadband characteristic measurement system and method based on pulse injection, wherein the system comprises an impedance shaping pulse generator, a broadband coupling device and a broadband response analysis unit, and the impedance shaping pulse generator comprises a monostable main control switch and a frequency-varying impedance network; the system utilizes the time constant difference of the two branches, automatically completes the time domain physical switching of the output impedance from a transient low-impedance source to a steady high-impedance source in a single switching action period, matches the distributed capacitance charging requirement of a tested transformer in a high frequency band and the iron core magnetic flux establishment requirement in the low frequency band, solves the physical contradiction that the prior single excitation source cannot consider the broadband energy distribution, realizes the high signal-to-noise ratio acquisition of the impedance characteristic of the full frequency band through a passive topology, and automatically eliminates the residual magnetism of the iron core by utilizing counter electromotive force.

Inventors

LI JIANCHAO
WANG ZHITAO
WANG CHENXING
PENG LONG
LI PENGFEI
WANG SHULAI
CHEN ZHIWEI
SHAO BINGBING
CHENG HAILONG
ZHU ZHIQIAN

Assignees

国网冀北电力有限公司电力科学研究院
国家电网有限公司
合肥工业大学

Dates

Publication Date: 20260512
Application Date: 20251223

Claims (10)

1. The system for measuring the broadband characteristics of the low-frequency transformer based on pulse injection is characterized by comprising an impedance shaping pulse generator, a broadband coupling device and a broadband response analysis unit: the impedance shaping pulse generator is connected between the high-voltage direct-current source and the transformer to be tested to form a source end for injecting excitation energy into the winding of the transformer to be tested; The broadband coupling device is connected between the output end of the impedance shaping pulse generator and the high-voltage sleeve of the transformer to be tested to form a signal injection channel; The broadband response analysis unit is connected to the end screen port of the transformer to be tested to form a signal acquisition end; the impedance shaping pulse generator comprises a monostable main control switch and a frequency-varying impedance network, wherein the monostable main control switch is arranged in series between a high-voltage direct-current source and the frequency-varying impedance network to execute single closing action, the frequency-varying impedance network comprises a first passive branch and a second passive branch which are connected in parallel, the first passive branch presents capacitive impedance characteristics, a low-impedance passage is provided at the conduction moment of the monostable main control switch, the nanosecond rising edge of an excitation pulse is established and rises along with impedance of a capacitor charging process, the second passive branch presents inductive or resistive impedance characteristics, the impedance is lower than that of the first passive branch after charging in a steady-state discharging stage after the rising edge of the excitation pulse is established, a discharging loop is taken over, the millisecond-level attenuation trailing of the excitation pulse is maintained, and the system utilizes the time constant difference of the first passive branch and the second passive branch to realize automatic switching of source output impedance from low to high in a single action period of the monostable main control switch so as to match the distributed capacitor charging requirement of a tested transformer in a high frequency band and the magnetic flux building requirement in a low frequency band.
2. The pulse injection-based low frequency transformer broadband characteristic measurement system according to claim 1, wherein the first passive branch comprises a sharpening capacitor and a first damping resistor connected in series, and the capacitance value of the sharpening capacitor and the resistance value of the first damping resistor are set according to a preset rising time of an excitation pulse, so that dominant high frequency current injection is ensured to be provided within nanosecond time of monostable master switch operation.
3. The system of claim 1, wherein the second passive branch comprises an energy storage inductor or a second damping resistor connected in series, and the resistance of the second damping resistor is set to be larger than the characteristic impedance of the transformer winding to be tested, so as to form high internal resistance in the tailing stage of the excitation pulse and maintain the magnetic field energy attenuation process in the winding inductor.
4. The low-frequency transformer broadband characteristic measurement system based on pulse injection according to claim 1 is characterized in that the broadband coupling device comprises a unidirectional isolation component which is arranged in series between the output end of a frequency-dependent impedance network and a measured transformer, the unidirectional isolation component is composed of a fast recovery diode stack, the unidirectional isolation component is conducted by forward pressure difference during excitation pulse injection to establish an energy injection channel, and is cut off by the disappearance of the forward pressure difference or the occurrence of reverse pressure difference during free response after the excitation pulse is ended, the electrical connection of the frequency-dependent impedance network and the measured transformer is cut off, and the interference of residual oscillation on a source side on a measurement signal is blocked.
5. The low-frequency transformer broadband characteristic measurement system based on pulse injection according to claim 1 is characterized in that an automatic demagnetizing branch circuit is connected in parallel with a frequency-dependent impedance network, the automatic demagnetizing branch circuit comprises a demagnetizing capacitor and a damping resistor which are connected in series, after the tail of an excitation pulse is finished, the automatic demagnetizing branch circuit is conducted by utilizing inductive counter electromotive force generated by a transformer winding to be measured, absorbs reverse energy and forms an under-damped oscillation loop with the transformer winding to be measured, demagnetizing current with polarity alternately attenuated is injected into the transformer to be measured, and iron core remanence is eliminated.
6. The system for measuring the broadband characteristics of the low-frequency transformer based on pulse injection according to claim 1 is characterized in that the broadband response analysis unit comprises a first measurement channel and a second measurement channel which are arranged in parallel, wherein the first measurement channel is provided with a high-frequency voltage divider and is used for collecting excitation pulse fronts and high-frequency oscillation signals, the second measurement channel is provided with a low-frequency voltage divider and an integration circuit and is used for collecting excitation pulse tails and low-frequency response signals, and the broadband response analysis unit is used for performing time domain splicing on data of the first measurement channel and data of the second measurement channel based on a unified clock reference.
7. The system for measuring the broadband characteristics of the low-frequency transformer based on pulse injection according to claim 4, wherein the unidirectional isolation component is connected in parallel with a high-frequency compensation capacitor, and the capacitance value of the high-frequency compensation capacitor is set so that the equivalent alternating-current impedance of the unidirectional isolation component in a cut-off state is larger than the stray capacitance impedance of the transformer winding to be measured in a high frequency band.
8. The pulse injection based broadband characteristic measurement system for a low frequency transformer according to claim 5, wherein the capacity of the degaussing capacitor in the automatic degaussing branch is Equivalent main inductance with transformer to be tested A specific under-damped oscillation condition is satisfied to ensure that the resulting demagnetizing current has a sufficient number of zero crossings, the under-damped oscillation condition being defined by the relationship: , wherein, For the sum of the damping resistance and the winding DC resistance, For the main inductance value of the iron core of the transformer to be tested, The system configures damping parameters according to the relation to generate demagnetizing waveforms with decreasing amplitude and alternating polarity.
9. The system for measuring the broadband characteristics of the low-frequency transformer based on pulse injection according to claim 1 is characterized in that an impedance shaping pulse generator is packaged in a grounded metal shielding cavity, a high-voltage direct-current source, a monostable main control switch and a frequency-variable impedance network are arranged in a coaxial structure to reduce loop distributed inductance, an output end of the system is connected to a broadband coupling device through a high-voltage coaxial cable, the system further comprises a current detection transformer connected to a neutral point of the transformer to be measured, the current detection transformer is used for monitoring response current flowing through a winding of the transformer and forms an original data set for calculating a broadband transfer function of the transformer together with a voltage signal acquired by a broadband response analysis unit, and the original data set covers a frequency domain range from a Hertz level to a MHz level.
10. A method for measuring broadband characteristics of a low-frequency transformer based on pulse injection, for implementing the measurement system of claim 1, comprising the steps of: executing a single closing action by using a monostable main control switch in the impedance shaping pulse generator to trigger the energy release of the high-voltage direct current source; Performing time domain impedance shaping on the released energy through a frequency-varying impedance network, wherein a nanosecond rising edge of an excitation pulse is established by utilizing the leading action of a first passive branch with capacitive impedance characteristics at the switching-on moment, and a steady-state connection pipe action after the rising edge of a second passive branch with inductive or resistive impedance characteristics is established is utilized to maintain the millisecond-level attenuation trailing of the excitation pulse, so that the automatic switching of the source end output impedance from low to high is realized in a single pulse period; injecting the shaped excitation pulse into a high-voltage sleeve of the transformer to be tested through a broadband coupling device, conducting the excitation pulse during injection by utilizing a unidirectional isolation assembly to establish a channel, and cutting off the excitation pulse during free response to isolate source-end interference; and acquiring broadband signals comprising high-frequency distribution parameter response and low-frequency iron core magnetic flux response from the end screen port of the tested transformer by utilizing a broadband response analysis unit, and performing full-spectrum analysis to acquire broadband impedance characteristics of the transformer.

Description

Pulse injection-based broadband characteristic measurement system and method for low-frequency transformer Technical Field The invention relates to a low-frequency transformer broadband characteristic measurement system and method based on pulse injection, and belongs to the technical field of power equipment testing. Background The current power transformer is used as power grid core equipment, wherein early recognition of winding deformation, turn-to-turn short circuit and core looseness internal faults depends on measurement of broadband impedance characteristics of the equipment, an impulse frequency response analysis method utilizes excitation signals to inject into the winding and collects port response data, and the method is widely used for site census and transient characteristic analysis of large-scale inductive equipment of the converter transformer due to high test efficiency without changing the operation wiring state of the equipment, a fixed resistance-capacitance parameter impulse generator is generally used as an excitation source in a conventional impulse injection technology, and faults are diagnosed by acquiring a transfer function fingerprint representing the mechanical state of the equipment. The large-scale equipment electrical structure of the converter transformer has both a henry-level main inductance and a picofarad-distributed capacitance, when broadband characteristic measurement is carried out, mutual exclusion physical constraint exists on the output impedance of an excitation source, megahertz-level high-frequency response of a corresponding winding distribution parameter is excited, excitation pulses are required to have nanosecond-level steep rising edges, and the excitation source is required to have extremely low internal resistance to provide high-current charging capacity in a transient state; excitation pulse needs to maintain millisecond long trailing to complete magnetic flux establishment, an excitation source is required to stably present a high internal resistance maintenance voltage decay time constant, the existing fixed impedance topology-based single excitation source cannot simultaneously meet broadband energy distribution requirements in a time domain, practical engineering application is limited, for example, china patent No. CN111460605B discloses a transformer broadband hybrid model taking core nonlinearity into consideration and an establishment method, a hybrid mathematical model is constructed to carry out simulation prediction on the transformer broadband response, the defect that a traditional broadband admittance model lacks nonlinearity characterization is overcome, however, the accuracy of the post-processing method based on mathematical modeling and simulation depends on the quality of input measurement data, if an initial data acquisition link such as poor impedance matching of the excitation source, low signal-to-noise ratio and incomplete elimination of core remanence is not achieved, systematic errors of original data cannot be avoided by the follow-up model, and particularly, the measurement reliability of a low frequency range is difficult to ensure. Therefore, how to construct a magnetic state measuring system which automatically adapts to the high-low frequency energy requirement in a single injection period, isolates the source-end interference in a measuring stage and automatically resets after the test is finished becomes the technical problem to be solved by the invention. Disclosure of Invention In order to solve the problems in the background technology, the technical scheme of the invention is as follows, the low-frequency transformer broadband characteristic measurement system based on pulse injection comprises an impedance shaping pulse generator, a broadband coupling device and a broadband response analysis unit: The impedance shaping pulse generator is connected between the high-voltage direct-current source and the transformer to be tested to form a source end for injecting excitation energy into the winding of the transformer to be tested; the broadband coupling device is connected between the output end of the impedance shaping pulse generator and the high-voltage sleeve of the tested transformer to form a signal injection channel; The impedance shaping pulse generator comprises a monostable main control switch and a frequency-variable impedance network; the monostable main control switch is arranged between the high-voltage direct-current source and the frequency-variable impedance network in series, and performs a single closing action; the frequency-dependent impedance network comprises a first passive branch and a second passive branch which are connected in parallel, wherein the first passive branch is of a capacitive impedance characteristic, a low impedance path is provided at the conduction moment of a monostable main control switch, a nanosecond rising edge of an excitation pulse is established, and impedance rises