CN112526412A - Method and system for testing polarity of current transformer of transformer lifting seat - Google Patents
Method and system for testing polarity of current transformer of transformer lifting seat Download PDFInfo
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Abstract
The invention discloses a method and a system for testing the polarity of a current transformer of a transformer lifting seat, which belong to the technical field of transformers and are used for solving the technical problems of high difficulty, low efficiency and the like of the polarity test after the current transformer lifting seat current transformer is installed, and the method specifically comprises the following steps: 1) applying a unidirectional-change direct current at two ends of a transformer winding to serve as a primary current for raising a base current transformer; 2) collecting induced voltage in a secondary winding of the elevated current transformer; 3) and judging the polarity of the lifting seat current transformer according to the induced voltage. The invention has the advantages of simple and rapid operation, high test precision, high test efficiency, low cost and the like.
Description
Technical Field
The invention mainly relates to the technical field of power transformers, in particular to a method and a system for testing the polarity of a current transformer of a transformer lifting seat.
Background
A lifting seat of the power transformer is arranged on a transformer body, a core-through current transformer (TA for short) is arranged in the lifting seat, a high-voltage bushing is arranged on the lifting seat, a high-voltage lead passes through an inner hole of the TA of the lifting seat to connect a bushing lead with a transformer winding, and the internal structure of the high-voltage bushing is shown in figure 1.
The ascending seat TA is also called as a sleeve TA, and the secondary current of the ascending seat TA is often used as a signal source of a transformer substation protection and measurement and control system to realize the functions of monitoring and protecting the operation of the power system. If the polarity of the TA is wrong, the correct metering of a metering loop can be influenced or the misoperation of a protection device can be caused, so that the polarity of the internal transformer is checked again after the lifting seat which is overhauled is installed again, and the important is that. However, after the transformer is installed, it is difficult to accurately and rapidly measure the polarity of the internal TA by the existing means.
Protection of the transformer against overcurrent, short circuit, overload, differential, etc., as well as measurement of the transformer load, current, wattmeter, etc., require a current signal from the TA. The TA is an important item in TA test because if the polarity is wrong, it will affect the correct metering of the metering loop or cause the protection device to malfunction.
However, in view of the particularity of the elevated seat structure, after the transformer is integrally installed, to measure the polarity of the elevated seat TA, the high-voltage winding of the transformer must be used as the primary winding of TA. This has a series of effects on the polarity test of the elevated seat TA: the transformer has the advantages that the number of turns of winding coils of the transformer is large, the inductance is large, the transformer has the effects of direct resistance alternating current and low frequency resistance high frequency, the transformer with larger capacity has stronger effects of direct resistance alternating current and low frequency resistance high frequency, and the polarity is difficult to measure by using a traditional test method. At present, polarity measurement of a TA of a lifting seat of a transformer is carried out before installation, and relevant tests are not carried out together with the transformer after installation, so that a TA current loop of the lifting seat cannot be thoroughly checked, and hidden danger exists.
At present, two more common methods are used for measuring the TA polarity of the lifting seat after installation: the "direct current induction method" and the "primary pressure rising method".
As shown in fig. 2, in the conventional measurement method, "dc induction method", 3V dc is applied between the bushing lead of the transformer and the neutral point lead, and a tester uses milliampere gear of a multimeter to measure the secondary side of TA, and observes the deflection of the pointer to perform polarity judgment. The 'direct current induction method' adopts the method of applying direct current voltage and judging the polarity of the rising seat TA by using the change of current in the transient process of an RL circuit, but the method is limited by large impedance of a primary side, the primary side of the transformer rising seat TA is connected in series with large primary impedance of the transformer, the abrupt current generated by the primary side in the transient process is small, the primary side current of the TA is made to be I1, the secondary side current of the TA is I2, the number of turns of a primary winding is N1, the number of turns of a secondary winding is N2, according to the magnetic potential balance principle, I1N 1I 2N 2 (magnetic potential generated by exciting current is ignored), the secondary side current I2 is I1/N2(N1 is the number of turns of a primary coil of the rising seat TA, N2 is the number of secondary coils, actually, one N1 is 1 turn, and the secondary N2> 1 turn), the secondary current I2 is reduced by N2, even if the change of the I2 of the minimum direct current can not be detected by a multimeter, however, with precision instrumentation, the cost of the corresponding instrument would be prohibitive. And because the transformation ratios of the current transformers on all sides are inconsistent, the induced current of the secondary winding is small and inconsistent, the ammeter is difficult to select in series connection, the deflection of the pointer with low sensitivity is not obvious, and the pointer with high sensitivity can exceed the measuring range of the pointer or even burn the ammeter due to the fact that the induced current of the secondary winding on one side is large. Therefore, the method is difficult to measure the polarity of the elevated base current transformer.
In addition, the 'primary pressurization and current rise method' is that 380V alternating current voltage is directly added to three phases on one side of the transformer, other sides are in short circuit to form short circuit current, and the polarity of the short circuit current is verified through a hexagonal diagram of a secondary winding load test. The method is generally used for transformers below 110kV, and the capacity is low. The value of the secondary short-circuit current measured by pressurization is small, the meter level is required to be high, the investment is large (ten thousand yuan meter), along with the high-speed development of the construction of China, the load and the short-circuit current of a system are continuously increased, the capacity and the transformation ratio of a transformer are increased, the induced current of a secondary winding of the test method is smaller and smaller, and the precision requirement of a common volt-ampere characteristic meter cannot be met. And the method has high danger of one-time pressurization, high wiring difficulty and low test efficiency, so the test method is difficult to popularize.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: aiming at the problems in the prior art, the invention provides the method and the system for testing the polarity of the current transformer of the transformer lifting seat, which are simple and quick to operate, high in testing precision and high in efficiency.
In order to solve the technical problems, the technical scheme provided by the invention is as follows:
a polarity test method for a current transformer of a transformer lifting seat comprises the following steps:
1) applying a unidirectional-change direct current at two ends of a transformer winding to serve as a primary current for raising a base current transformer;
2) collecting induced voltage in a secondary winding of the elevated current transformer;
3) and judging the polarity of the lifting seat current transformer according to the induced voltage.
As a further improvement of the above technical solution:
the specific judgment process of the step 3) is as follows: if the input direct current is positive and the measured induced voltage is greater than zero, the polarity is judged to be minus polarity, namely homopolar, and if not, the polarity is judged to be plus polarity, namely heteropolar.
In step 1), the unidirectionally varying direct current is a gradually increasing direct current or a gradually decreasing direct current.
In step 1), the direct current i satisfies the relationship: i ═ I0(1-e-t/τ) Or I ═ I0e-t/τ(ii) a In the formula: i is0And the constant is a fixed value, e is a natural constant, t is a time variable, L/R is a time constant, L is the inductance of the primary winding of the transformer, and R is the resistance of the primary winding of the transformer.
In the step 3), the induction voltage is firstly filtered and amplified, and then is judged.
The invention also discloses a polarity test system for the current transformer of the transformer lifting seat, which comprises
The direct current generating unit is used for applying a unidirectional-change direct current at two ends of a transformer winding and serving as a primary current for raising the base current transformer;
the voltage sampling unit is used for collecting the induced voltage in the secondary winding of the lifting seat current transformer;
and the judging unit is used for judging the polarity of the current transformer of the lifting seat according to the induced voltage.
As a further improvement of the above technical solution:
the direct current generating unit comprises a direct current generator, and current output interfaces I + and I-are respectively connected to the head end and the tail end of the transformer winding.
The voltage sampling unit comprises a voltage sampler, and input interfaces V + and V-of the voltage sampler are respectively connected to the head end and the tail end corresponding to the secondary winding of the current transformer.
The input end of the signal amplification and filtering processing circuit is connected with the output end of the voltage sampling unit, and the output end of the signal amplification and filtering processing circuit is connected with the input end of the judging unit; and the signal amplification and filtering processing circuit is used for filtering and amplifying the induced voltage collected by the voltage sampling unit.
The judging unit is a control unit, and the control unit is connected with a display unit and a human-computer interaction module.
Compared with the prior art, the invention has the advantages that:
the invention adopts a direct current rising (falling) method to replace the traditional direct current induction method, the direct current at the primary side is slightly influenced by the impedance of a transformer winding, and larger voltage can be induced at the secondary side of a rising base current transformer, thereby facilitating measurement and simultaneously improving the detection precision; the acquired secondary voltage is amplified through the signal amplification and filtering processing circuit, so that the test can be more accurate, and meanwhile, the time required by signal judgment in the step 3) is shortened; the whole testing process is simple and convenient to operate and quick in response, and the field measuring efficiency is greatly improved; in addition, for a large-capacity transformer, the capacity of acquiring secondary voltage can be improved by increasing the input direct current, so that the test method is simplified, and the blind area that the traditional method is not suitable for TA polarity measurement of a lifting seat of the large-capacity transformer is made up; meanwhile, the polarity of the current transformer is obtained under the condition that the transformer bushing is not disassembled, the hoisting cost is reduced, and the hidden danger of equipment is eliminated.
The polarity test system of the transformer elevated seat current transformer is used for executing the test method, and has the advantages of the method. And the field wiring is simple and quick, the carrying is convenient, the time for measuring the TA polarity of the lifting seat is short, and the field testing efficiency can be greatly improved.
Drawings
Fig. 1 is a schematic structural diagram of a transformer lifting base in the prior art.
Fig. 2 is a schematic diagram of a dc induction method in the prior art.
FIG. 3 is a block diagram of a test system according to an embodiment of the present invention.
FIG. 4 is a schematic diagram of the testing system of the present invention in a specific application.
Fig. 5 is a schematic diagram of a magnetic field calculation model of the elevated seat current transformer of the present invention.
Fig. 6 is a schematic diagram of the secondary side induced voltage of the step-up base current transformer according to the present invention.
FIG. 7 is a flow chart of a method of the present invention in an embodiment.
Detailed Description
The invention is further described below with reference to the figures and the specific embodiments of the description.
As shown in fig. 7, the method for testing the polarity of the current transformer on the transformer riser according to the embodiment includes the steps of:
1) applying a unidirectional-change direct current at two ends of a transformer winding to serve as a primary current for raising a base current transformer;
2) collecting induced voltage in a secondary winding of the elevated current transformer;
3) and judging the polarity of the lifting seat current transformer according to the induced voltage.
Specifically, a direct current which rapidly rises from zero is applied to two ends of a transformer winding to serve as a primary current of the lifting seat current transformer, the current flows through the core-through type current transformer in the lifting seat and is increased from zero to stable, the magnetic field intensity generated by the primary current is larger and larger, the magnetic flux in an iron core of the lifting seat current transformer can be gradually increased under the same condition, an induced voltage which obstructs the increase of the magnetic flux in the iron core can be generated in a secondary winding of the lifting seat current transformer according to the Lenz law, and the polarity of the lifting seat current transformer can be measured by collecting the signal through a voltage sampling unit, processing and judging.
The invention adopts the direct current rising method to replace the traditional direct current induction method, the direct current at the primary side is slightly influenced by the impedance of the transformer winding, and larger voltage can be induced at the secondary side of the rising base current transformer, thereby facilitating the measurement and simultaneously improving the detection precision; the whole testing process is simple and convenient to operate and quick in response, and the field measuring efficiency is greatly improved; in addition, for a large-capacity transformer, the capacity of acquiring secondary voltage can be improved by increasing the input direct current, so that the test method is simplified, and the blind area that the traditional method is not suitable for TA polarity measurement of a lifting seat of the large-capacity transformer is made up; meanwhile, the polarity of the current transformer is obtained under the condition that the transformer bushing is not disassembled, the hoisting cost is reduced, and the hidden danger of equipment is eliminated.
In an embodiment, the specific determination process in step 3) is: if the input direct current is positive and the measured induced voltage is greater than zero, the polarity is judged to be minus polarity, namely homopolar, and if not, the polarity is judged to be plus polarity, namely heteropolar.
In a specific embodiment, in step 1), the unidirectional dc current is a gradually increasing dc current. Wherein the direct current i satisfies the relationship: i ═ I0(1-e-t/τ) (ii) a In the formula: i is0And the constant is a fixed value, e is a natural constant, t is a time variable, L/R is a time constant, L is the inductance of the primary winding of the transformer, and R is the resistance of the primary winding of the transformer. Of course, in other embodiments, other gradually increasing or gradually decreasing dc currents may be used.
In an embodiment, in step 3), the induced voltage is filtered and amplified before being determined, so as to improve the accuracy of the determination and shorten the measurement time.
As shown in FIG. 3, the invention also discloses a polarity test system for the current transformer of the transformer lifting seat, which comprises
The direct current generating unit is used for applying a unidirectional-change direct current at two ends of a transformer winding and serving as a primary current for raising the base current transformer;
the voltage sampling unit is used for collecting the induced voltage in the secondary winding of the lifting seat current transformer;
and the judging unit is used for judging the polarity of the current transformer of the lifting seat according to the induced voltage.
In one embodiment, the dc current generating unit comprises a dc current generator, and the current output interfaces I + and I-are respectively connected to the head end and the tail end of the transformer winding. The voltage sampling unit comprises a voltage sampler, and input interfaces V + and V-of the voltage sampler are respectively connected to the head end and the tail end corresponding to the secondary winding of the current transformer.
In a specific embodiment, the device further comprises a signal amplification and filtering processing circuit, wherein the input end of the signal amplification and filtering processing circuit is connected with the output end of the voltage sampling unit, and the output end of the signal amplification and filtering processing circuit is connected with the input end of the judging unit; and the signal amplification and filtering processing circuit is used for filtering and amplifying the induced voltage collected by the voltage sampling unit.
In one embodiment, the determining unit is a control unit (e.g., a computer system), and the control unit is connected to a display unit (e.g., a display) and a human-computer interaction module.
The polarity test system of the transformer elevated seat current transformer is used for executing the test method, and has the advantages of the method. And the field wiring is simple and quick, the carrying is convenient, the time for measuring the TA polarity of the lifting seat is short, and the field testing efficiency can be greatly improved.
The following is a complete description of the test method and system of the present invention by way of a complete embodiment:
as shown in fig. 3, the whole test system structure includes a dc current generator, a current output interface, a voltage sampling interface, a signal amplifying and filtering processing circuit, an analog-to-digital conversion circuit, a computer system, a data storage circuit, and a human-computer interaction module.
Specifically, the dc current generator is a current output circuit composed of a digital potentiometer and an operational amplifier. The single chip microcomputer changes the amplitude of the voltage at the output end of the digital potentiometer, adjusts the output voltage of the operational amplifier by utilizing the virtual short principle of the input end of the operational amplifier, and changes the grid voltage of the field effect transistor, thereby achieving the purpose of outputting the required direct current. The signal amplifying and filtering processing circuit takes the operational amplifier TS462CD as a core device, filters stray interference voltage, amplifies the amplitude of an input signal, and enables the analog-to-digital conversion of the later stage to be more stable and accurate. The analog-to-digital conversion circuit adopts a high-speed analog-to-digital converter chip AD7606, the sampling rate reaches 3.125KHZ, the voltage value of an analog input end can reach plus or minus 10V, and the measurement range is large. The data storage circuit uses a serial port data storage chip, the data storage capacity reaches more than 2M, and the data storage circuit has the function of not losing data when power is down. The computer system uses STM32 single chip microcomputer as core device, has up to 96 IO ports, and operating frequency 72MHZ, has richer interface circuit compared with 8-bit single chip microcomputer, has faster data processing ability.
The direct current generator is connected to two ends of a tested transformer winding through a test current output interface and outputs direct current which is rapidly increased from 0 to be stable, wherein the current can be selected through the man-machine interaction module. A secondary winding of the step-up base current transformer is connected with a voltage sampling input interface, and in the transient process of the direct current step-up, a voltage signal of the secondary winding of the current transformer is collected; processing the acquired voltage signal by a signal amplification and filtering processing circuit, filtering stray interference voltage, and amplifying the amplitude of the input signal; then inputting the amplified signal into an analog-to-digital converter, converting the analog signal into a digital signal, and storing the data in a buffer area for processing by a computer system; the computer performs polarity determination by measuring the numerical range of the voltage: if the input current is positive and the measured secondary voltage is a voltage greater than zero, the polarity is judged to be minus polarity (minus polarity is homopolar), otherwise the polarity is judged to be plus polarity (plus polarity is heteropolar), and the measurement result is sent to the display for displaying.
As shown in fig. 4, during the specific test, the current output interface I + (current positive electrode) and I- (current negative electrode) of the dc current generator are connected to the head end and the tail end of the transformer winding. The voltage sampling input interface V + (voltage anode) and V- (voltage cathode) are respectively connected to the corresponding head end and tail end of the secondary winding of the current transformer (I + is connected with the head end of the transformer winding, then V + is connected with the head end of the secondary winding of the current transformer, or I-is connected with the head end of the transformer winding, then V-is connected with the head end of the secondary winding of the current transformer).
After wiring is finished, firstly, the measuring device is opened to set parameters, the direct current is set according to test requirements, and then, the test is started by clicking. After the test is selected, the program-controlled power switch is automatically turned on, and the measured voltage signal is amplified; and starting analog-to-digital conversion, carrying out digital measurement on the voltage V, storing the result in a cache, judging the polarity according to the numerical range of the measurement result, and displaying the measurement result.
The direct current applied to the head end of the transformer winding and the secondary winding of the lifting seat current transformer have the corresponding relation that:
according to the magnetic field calculation method of the current-carrying straight conductor, a magnetic field model in the transformer lifting base current transformer can be equivalent to that shown in fig. 5.
Assuming that the current flowing through the straight conductor is i and the tiny line element of the current is dl, the straight current is considered as a set of current elements, the magnitude of any current element on the straight conductor is idl, the distance from the current element to the field point P is r, and alpha is the current element
And vector
The included angle therebetween. According to the Biao-Saval law, the magnetic induction dB excited by the current element at the point P is
And magnetic induction intensity
In the direction of
Determination of magnetic induction
Current element
Distance between two adjacent plates
The directions of the three vectors conform to the right hand rule. Obviously, the magnetic induction intensity direction excited by each current element at the point P is consistent. Therefore, the total magnetic induction intensity can be directly obtained by the integral of the above formula
The following geometrical relationships can be seen in fig. 5: sin α ═ cos β, r ═ r0 secβ，l＝r0tan β. The magnetic induction intensity relation can be deduced
Considering that the length of the lead at the upper end of the lifting seat is far larger than the diameter of the lifting seat current transformer, the lead can be approximately equivalent to a semi-infinite-length lead, and the magnetic induction intensity of the point P can be simplified as follows:
and the direction of the magnetic induction B is always along the tangential direction of the iron core of the current transformer of the lifting seat.
The flux flowing through is:
the induced voltage generated by the secondary winding is:
in the above formula: i is the current of the straight wire, r is the distance from the current element to the field point P, l is the vertical distance from the current element to the horizontal plane of the point P, r0Is the vertical distance from point P to the straight conductor, and alpha is the current element
The included angle between the P point and the vector r, beta is the included angle between the connecting line from the P point to the current element and the horizontal line, and beta is the included angle between the connecting line from the P point to the current element and the horizontal line1Is the angle between the line from the point P to the uppermost end of the wire and the horizontal line, beta2Is the included angle between the line from the point P to the lowest end of the wire and the horizontal line, B is the magnetic induction intensity, mu0For the vacuum permeability, L is the integral path, Φ is the magnetic flux, S is the core cross-sectional area, E is the secondary side induced voltage, and N is the number of induction coil turns (here equal to the number of secondary coil turns).
Therefore, a gradually increasing direct current is applied from the head end of the transformer winding, the secondary winding of the elevated seat current transformer induces a voltage with the same polarity, the secondary voltage is in direct proportion to the input direct current, the larger the input current is, the larger the voltage on the secondary side is, and the polarity can be measured more easily.
Field verification: the system is used for testing the polarity of a medium-voltage side lifting seat current transformer of a 220kV main transformer, as mentioned above, the direct current required by the test is firstly connected to the two ends of a transformer winding, and the output current is set to be 10A; collecting a voltage signal of a secondary winding at a terminal box of the lifting seat current transformer; when the field part is connected, the positive pole of the current output is connected with a neutral point sleeve, the negative pole is connected with a high-voltage A-phase sleeve, the positive pole of the voltage test is connected with an S2 winding, and the negative pole is connected with an S1 winding. After the test line is connected, the test is started, and the polarity reduction is displayed on the instrument for about 10 seconds. The measured result is completely consistent with the actual polarity of the lifting seat current transformer.
The invention can measure the TA polarity of the lifting seat after the transformer is installed, and a voltage can be induced by the TA secondary winding of the lifting seat by applying a direct current which is gradually increased to be stable on the winding of the transformer; the magnitude of the direct current input at the primary side can be adjusted by the direct current generator, the magnitude of the secondary side induction voltage is in direct proportion to the input direct current, and for a large-capacity transformer, the capability of acquiring the secondary voltage can be improved by increasing the input direct current, so that the polarity testing method is simplified.
The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above-mentioned embodiments, and all technical solutions belonging to the idea of the present invention belong to the protection scope of the present invention. It should be noted that modifications and embellishments within the scope of the invention may be made by those skilled in the art without departing from the principle of the invention.
Claims (10)
1. A polarity testing method for a current transformer of a transformer lifting seat is characterized by comprising the following steps:
1) applying a unidirectional-change direct current at two ends of a transformer winding to serve as a primary current for raising a base current transformer;
2) collecting induced voltage in a secondary winding of the elevated current transformer;
3) and judging the polarity of the lifting seat current transformer according to the induced voltage.
2. The method for testing the polarity of the current transformer of the transformer riser according to claim 1, wherein the specific judgment process in the step 3) is as follows: if the input direct current is positive and the measured induced voltage is greater than zero, the polarity is judged to be minus polarity, namely homopolar, and if not, the polarity is judged to be plus polarity, namely heteropolar.
3. The method for testing the polarity of the current transformer of the transformer riser according to claim 1, wherein in the step 1), the unidirectional direct current is gradually increased direct current or gradually decreased direct current.
4. The method for testing the polarity of the current transformer of the transformer elevated seat according to claim 3, wherein in the step 1), the direct current i satisfies the relationship: i ═ I0(1-e-t/τ) Or I ═ I0e-t/τ(ii) a In the formula: i is0And the constant is a fixed value, e is a natural constant, t is a time variable, L/R is a time constant, L is the inductance of the primary winding of the transformer, and R is the resistance of the primary winding of the transformer.
5. The method for testing the polarity of the current transformer of the transformer riser according to any one of claims 1 to 4, wherein in the step 3), the induced voltage is filtered and amplified before being judged.
6. A polarity test system for a current transformer of a transformer lifting seat is characterized by comprising
The direct current generating unit is used for applying a unidirectional-change direct current at two ends of a transformer winding and serving as a primary current for raising the base current transformer;
the voltage sampling unit is used for collecting the induced voltage in the secondary winding of the lifting seat current transformer;
and the judging unit is used for judging the polarity of the current transformer of the lifting seat according to the induced voltage.
7. The system of claim 6, wherein the dc current generating unit comprises a dc current generator, and the current output ports I + and I-are connected to the head end and the tail end of the transformer winding, respectively.
8. The system for testing the polarity of a current transformer of a transformer riser as claimed in claim 7, wherein the voltage sampling unit comprises a voltage sampler, and input ports V + and V-of the voltage sampler are respectively connected to the head end and the tail end of the secondary winding of the current transformer.
9. The polarity test system of the transformer elevated base current transformer according to any one of claims 6 to 8, further comprising a signal amplification and filtering processing circuit, wherein an input end of the signal amplification and filtering processing circuit is connected with an output end of the voltage sampling unit, and an output end of the signal amplification and filtering processing circuit is connected with an input end of the judging unit; and the signal amplification and filtering processing circuit is used for filtering and amplifying the induced voltage collected by the voltage sampling unit.
10. The polarity testing system of the current transformer of any one of claims 6 to 8, wherein the judging unit is a control unit, and the control unit is connected with a display unit and a human-computer interaction module.
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| CN202011285484.0A CN112526412A (en) | 2020-11-17 | 2020-11-17 | Method and system for testing polarity of current transformer of transformer lifting seat |
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| CN202011285484.0A CN112526412A (en) | 2020-11-17 | 2020-11-17 | Method and system for testing polarity of current transformer of transformer lifting seat |
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| CN202011285484.0A Pending CN112526412A (en) | 2020-11-17 | 2020-11-17 | Method and system for testing polarity of current transformer of transformer lifting seat |
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| CN113376563A (en) * | 2021-06-08 | 2021-09-10 | 中国南方电网有限责任公司超高压输电公司 | Transformer lifting seat structure with current transformer test wire and test method |
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| CN113376563B (en) * | 2021-06-08 | 2022-08-12 | 中国南方电网有限责任公司超高压输电公司 | Transformer lifting seat structure with current transformer test wire and test method |
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