1) Chromatographic analysis of dissolved gases in oil;     2) measuring the DC resistance of the winding;     3) measuring the winding insulation resistance, absorption ratio or polarization index;     4) testing of tan δ of windings and capacitor bushings;     5) AC withstand voltage test;     6) measuring the winding leakage current;     7) Measuring the insulation resistance of the piercing bolt, the iron jaw clamp, the iron core and the pressure ring;     8) Check the voltage ratio of all taps of the winding;     9) Check the polarity of the three-phase transformer group or single-phase transformer;     10) measuring no-load current and no-load loss;     11) Measure short-circuit impedance and load loss;     12) partial discharge measurement ;     13) Check the operation of the on-load tap-changer;     14) Insulating oil test;     15) Transformer winding deformation test. I. Chromatographic analysis of dissolved gases in oil     (1) Attention should be paid to the H2 and hydrocarbon gas content (volume fraction) in the operating equipment oil exceeding any of the following values ​​(total hydrocarbons include CH4, C2H6, C2H4 and C2H2):         The total hydrocarbon content is greater than 150 * 10 -6 ;         H: content is greater than 150 * 10 -6 ;         QH: The content is greater than 5 * 10 -6 (500 x V transformer is 1X10-6).     (2) The gas production rate of the sum of hydrocarbon gases is greater than. 0.25 mL/h (open) and 0.5 (closed), or relative gas production rate greater than 10% / month, the device is considered abnormal. Note that equipment with a low total hydrocarbon content should not be judged by the relative gas production rate.     (3) When the content of dissolved gas components has an increasing trend, it can be judged in combination with the gas production rate, and if necessary, shorten the cycle for tracking analysis. Second, the measurement of winding DC resistance     Measuring the DC resistance of a transformer winding is an important means of finding defects in the conductive loop. It can check whether the conductive circuit inside the transformer is in good contact, whether the welding quality inside the winding and the lead is reliable, whether the tap changer and the bushing lead screw are tightened.     1. Measurement method     There are many methods for measuring DC resistance , and the bridge method is often used for measurement. The mechanism and method of the bridge method can be found in the first section of Chapter 2. Here are three more practical ways to speed up the measurement.     (1) Direct method. An additional resistor can be connected to the power supply side of the double-arm bridge. The principle wiring is shown in Figure 3-1. This method is called a resistance mutation method.     In Figure 3-1, an additional resistor R is inserted in the current loop. The value is 4-6 times of the measured resistance. The closed switch S2 shorts the resistance. When S1 is turned on, all the voltage is applied to the measured resistance. The charging current has a large rising speed, and S2 is turned off until a predetermined charging current. The current quickly reaches a steady state and the DC resistance is measured.     The method is generally used on transformers of 110-220 kV and 120 MVA; for 10-35 kV transformers; direct measurement by bridge.     (2) Magnetic assist method. Due to the large charging time constant of the large capacity and low resistance transformers, in order to shorten the measurement time, the magnetic assist method can be used for measurement. When measuring the low-voltage winding resistance, the high-voltage side and low-voltage side current loops are strung together, and the current is kept in the same direction, so that the iron core is saturated as soon as possible, the inductance is reduced (ie, the time constant is reduced), and rapid measurement is performed. Figure 3-2 shows the wiring diagram for this method.     In Figure 3-2, the external power supply with the double-arm bridge is used to measure the magnetic flux through the high-voltage winding. At this time, the requirements are as follows: 1 The wiring is correct; 2 It is not suitable for long-time charging measurement to prevent the measurement error caused by the zero drift of the bridge; Power supply voltage, its value should be satisfied 2 I 0 (R x +R 1 )         Where I 0 - transformer no-load current;             R x - the resistance of the entire circuit, including the high voltage winding and the low voltage winding power pack;             R 1 - internal resistance of the instrument;             I m - steady state current.     The wiring diagram of the bridge assisted magnetic method is listed in Table 3-1 for on-site comparison.     (3) Degaussing method. The degaussing method is opposite to the magnetically assisted method. The method strives to make the core flux zero, and the opposite current is used to cancel the magnetic flux in the two windings of the same core column, so that the measuring circuit reaches a linear circuit which is basically a pure resistance. . The charging process is very short, eliminating the adverse factors affecting the measurement, making the measurement accurate and stable, simple and rapid. Figure 3-3 shows the wiring of this method.     2. Test requirements     In accordance with the requirements of the "pre-regulation":     (1) For transformers above 1.6MVA, the difference between the winding resistances of each phase should not be greater than 2% of the average value of the three phases. The windings with no neutral point should not differ by more than 1% of the average value of the three phases.     (2) For transformers of 1.6 MVA and below, the phase difference is generally not more than 4% of the average value of the three phases, and the difference between the lines is generally not more than 2% of the average value of the three phases.     (3) Compared with the measured values ​​of the same parts in the past, the change should not exceed 2%.     (4) Resistance values ​​at different temperatures are converted according to equation (3-2) R2=R1[(T+t1)/(T+t2)]     Where R1, R2 are the resistance values ​​at temperatures t1 and t2, respectively;         The constant for T-one calculation is 235 for copper wire and 225 for aluminum wire. Third, the winding insulation resistance, absorption ratio or polarization index measurement     1. Measurement method     In addition to the commonality of the insulation resistance of other equipment, the measurement of the insulation resistance of the transformer winding has its particularity. The first is that the measurement method is different. In the measurement, the insulation resistance between each winding and the other windings should be measured in turn. The lead ends of the tested windings should be short-circuited, and the other sub-side windings should be short-circuited to ground. In this way, the insulation between the grounded part and the different voltage parts of the tested winding can be measured, and the measurement error caused by the residual charge in each winding can be avoided. The measurement locations and sequence are as shown in Table 3-2.     When measuring the insulation resistance , the oil-filled cycle should be allowed to stand for a while before measuring. For small transformers to stand for 6h, large transformers are allowed to stand for 24h.     The measurement is carried out using a 2500V or 5000V megohmmeter. The test windings should be fully discharged before and after the measurement. The large transformer discharges for more than 5 minutes, and the small transformer discharges for more than 2 minutes. It should be measured as much as possible when the oil temperature is below 50 °C.     2. Judgment and analysis of test results     According to the requirements of the "pre-regulation" and according to the actual situation, the test results should be judged and analyzed according to the following requirements:     (1) The insulation resistance should be converted to the same temperature and should not change significantly compared with the previous test result, generally not lower than 70% of the previous value. The temperature conversion formula is: R2=R1*15 (t1-t2)/10         Wherein R1 and R2 are insulation resistance values ​​at t1 and t2, respectively.     (2) The absorption ratio (in the range of 10 to 30 ° C) is not less than 1.3 or the polarization index is not less than 1.5, and neither of them is subjected to temperature conversion. Since the absorption ratio is uncertain in determining the insulation condition, especially for large transformers, the polarization index (PI) is used to judge the insulation condition, as shown in Table 3-3.     (3) When the insulation resistance is 10000 MΩ, the absorption ratio should be not less than 1.1, or the polarization index should not be less than 1.3.     (4) When the insulation resistance of the site is lower than 70% of the factory value, it should be considered whether the transformer oil is the same as the factory. If they are different, the effects of different insulating oils on the measurement results should be considered. Fourth, the leakage current test of the winding     The leakage current test of the winding is similar to the measurement of the insulation resistance. Due to the high DC voltage applied, it is usually found that some insulation resistance tests cannot find defects. The sequence and location of the test are the same as the measured insulation resistance (see Table 3-2). The test voltage standards are shown in Table 3-4.     During the measurement, the negative voltage power supply is used to pressurize the test voltage, and the current value read after 1 minute is the measured leakage current value. In order to make the readings accurate, the micro-ampere should be connected to a high potential; the test should be fully discharged at the end of the test, and the oil temperature should be recorded at the same time. For transformers that are not oiled, the voltage applied to the transformer should be half of the values ​​in Table 3-4 when measuring the leakage current.     The test results should be unchanged from the previous test results. Five, winding tanδ test     1. Measurement method     The tan δ of the winding can be measured with the QS1 type Xilin bridge, or with the M type medium tester. Here is mainly the sequence, location and method of measurement with Xilin Bridge. Since the fuel tank of the transformer is directly grounded, the anti-wiring method of the Xilin Bridge is often used for measurement, and the measurement parts are performed according to Table 3-5.     According to Table 3-5, the tans and capacitance value C of the double-winding transformer are measured as shown in Figure 3-4. In the figure, A is connected to the QS1 type bridge A point.     It can be seen from Figure 3-4 that the two ends of the winding to be tested are short-circuited during measurement, and the non-measured windings are short-circuited to avoid the winding inductance to bring errors to the measurement.     Wherein, under each physical quantity, the angle mark H represents a high pressure; L represents a low pressure; H+L represents a high pressure and a low pressure.     Solving the above equations in series, the capacitance value and dielectric loss tangent of each part are obtained. C 1 =(C 1 -C H -G L+H )/2; C 2 =C L -C 1 ;C 3 =C H -C 2 Sixth, AC withstand voltage test     AC withstand voltage test transformer includes the applied frequency voltage withstand test, pressure test and the operation frequency wave induction voltage test. For fully insulated transformers of 66kV and below, when the site conditions are not available, only the external construction frequency withstand voltage test can be performed. The explanations are given below.     (1) External construction frequency sealing test face     The external construction frequency withstand voltage test plays a decisive role in assessing the main insulation of the transformer and inspecting local defects. It can effectively find that the main insulation is damp, cracked, or loosened, displaced, and attached to the winding insulation due to vibration during transportation.     (1) The wiring method of the test must be correct. The correct wiring method should be short-circuit connection of all the bushings of the tested transformer, and the non-tested windings should also be short-circuited and reliably grounded. Figure 3-5 to Figure 3-7 show the correct and incorrect wiring. Figure 3-6 shows the wrong wiring with neither of the two windings shorted. Figure 3-7 shows the wrong wiring where both windings are shorted and the low voltage winding is not grounded.     It can be seen from Fig. 3-6 that due to the influence of the distributed capacitance, there will be a capacitor current flowing through each winding, and the current flowing through the entire tested winding is not equal. The higher the potential near the X terminal due to the capacitance rise effect, the ratio is higher. The applied voltage is also high; and because the untested winding is open, the reactance of the tested winding is large, resulting in an increase in the potential of the X terminal, which may damage the insulation in severe cases. It can be seen from Fig. 3-7 that since the non-tested winding is not grounded and is in a suspended state, it is likely that the low-voltage side insulation is broken when the high-voltage side is under voltage. The floating voltage on the low voltage side is determined by the inter-winding capacitance and the capacitance to ground.     (2) Measurement method of test voltage. Due to the effect of the capacitance rise of the capacitive load of the transformer, the test voltage must be measured on the high voltage side and subject to the peak value; if measured on the low voltage side or calculated by the capacitance rise, it is difficult to ensure accurate measurement.     (3) Pay attention to the following items during the test: 1 Confirm that the tested transformer shell and the non-test winding have been reliably grounded; 2 After the oil-immersed transformer is filled with oil or after re-pressurization after the test breakdown, it should be allowed to stand for a while. 3) When correcting the ball gap or withstand voltage, the measured voltage should be divided by the peak value by A; 4 avoid cutting off the power supply under the test voltage to prevent overvoltage and damage the product. If there is discharge or breakdown, The power should be turned off immediately.     (2) Frequency doubled induction withstand voltage test     The frequency doubled induction withstand voltage test is to increase the power supply frequency and reduce the excitation current to achieve the purpose of increasing the applied voltage, and is suitable for the voltage withstand test of the graded insulated transformer. For the main insulation test of the graded insulated transformer, the general external high voltage method cannot be used. Only the induction withstand voltage test can be used. For example, if the tested transformer is properly wired, the main and vertical insulation can be tested at the same time. For fully insulated transformers, it can be used to check its longitudinal insulation (between winding layers, turns and inter-segments). Due to the increase of frequency, the test time is t=60 x100/f(s) (t is the pressurization time; f is the test power frequency) to determine, but not less than 15s.     Test method     (1) Induction withstand voltage test of fully insulated transformers. It can be tested by applying 2 times the rated voltage of 2 times and above according to the wiring shown in Figure 3-8. This type of wiring can only achieve the test voltage between the lines, and the external high voltage main insulation withstand voltage test is required for the neutral point and the winding. Whether the longitudinal insulation withstands the inductive withstand voltage needs to be judged based on the comparison of the no-load loss test values ​​before and after the test.     (2) Induction withstand voltage test of graded insulation transformer. For the main insulation of the graded insulation transformer, neither the external voltage test nor the three-phase induction withstand voltage can be used. The reason is: for graded insulation transformers, the phase and relative insulation levels are the same, such as 220kV grade products, the ground and phase test voltage is 400kV. It is impossible for both to meet the test voltage requirements at the same time, so it is only possible to test with single-phase induction withstand voltage. The various connections shown in Figure 3-9 can avoid excessive voltage between the ends of the wires. According to the structure of the transformer, the corresponding connection method is adopted to make the voltage between the ends of the winding wires and the ground reach the test requirements as much as possible. The scope of application is as follows:     1) When the neutral point insulation level of the high voltage winding can withstand at least 1/3u, the three connections of Figure 3-9 (a1), (a2), (a3) ​​can be used, and the output of the double frequency generator is connected to the Test the transformer on the low voltage winding. If the three-phase transformer is a five-column or shell type, only the connection of Figure 3-9 (a1) can be used.     2) For three-phase five-column or shell-type transformers, the connection method of Figure 3-9(b) can also be used. If the transformer under test has a delta connection, it should be turned on.     3) The induction withstand voltage test of the autotransformer can use the connection method of Figure 3-9(c) to boost the neutral point voltage u1 of the transformer from the test with an auxiliary transformer.     The rated voltages of the two self-disconnection windings are UN1 and UN2, and the corresponding test voltages are UN1 and UN2. The following relationship is available.     This connection method can also be applied to a three-phase three-column graded insulation transformer, and the neutral point insulation level is less than 1/3 ut.     2. Test power supply     The frequency of the transformer induction withstand voltage test power supply is generally 100~250Hz. The intermediate frequency synchronous generator can be used as the test power source, or the 100 Hz test power supply can be obtained by the wire-wound asynchronous motor reverse drag method, or the three-phase single-phase transformer can be used to form the primary winding star connection, and the secondary winding is composed of the open triangle. 150Hz test power supply. The FM test power supply unit is the safest test power source, and it can be used for partial discharge test at the same time.     (3) Operational wave withstand test     The operating wave withstand voltage test is a test to assess the ability of the transformer to withstand overvoltage. The test has been listed in the "pre-regulation", and the large-voltage transformers of 20kV and below are allowed to use the operating wave withstand voltage instead of the double-frequency withstand voltage test. Seven, partial discharge measurement     The partial discharge of the transformer can damage the oil-paper insulation in a short period of time, and eventually cause insulation breakdown. Conventional withstand voltage tests cannot detect partial discharges in insulation, and partial discharge tests have become an important safety measure.     1. Procedures and standards for transformer partial discharge test     Figure 3-16 shows the pressurization procedure and duration of the transformer partial discharge test.     Turn on the power and boost to U2, and perform partial discharge measurement at this voltage for 5 min, then rise to U1, hold for 5 s, and finally drop to recognize, then carry out measurement and hold for 30 min. According to the "pre-regulation": when the line voltage (ie, recognized) is 1.5Um/√3, the discharge is generally not more than 500æ²; when the line voltage is 1.3Um, the discharge is generally not more than 300pC, Um is the equipment. The highest working voltage (ie U1 in the figure).     2. Basic wiring of transformer partial discharge test     Figure 3-17 shows the basic wiring of the partial discharge test of the transformer. The test power supply uses 50Hz multiplier or other suitable frequency. The three-phase transformer can be three-phase excitation (see Figure 3-17(b)], or single phase. Excitation [see Figure 3-17 (a)]. Figure 3-17(c) shows the wiring measured and calibrated at the casing tap.     A, transformer winding deformation measurement     According to the "pre-regulation" requirements: For transformers of 110kV and above, the transformer winding deformation should be measured under the following conditions:     (1) once every 6 years;     (2) After replacing the windings;     (3) When necessary (if a short circuit occurs near the zone).     At present, there are two methods for measuring the deformation of windings used in China's power system: low-voltage pulse method (LVI) and frequency response method (FRA). The frequency response method is recommended in the Pre-Regulation as a method for judging the deformation of the winding. This section will give an explanation.     1. The basic principle of frequency response method     The frequency response method is based on a transformer distributed circuit composed of a complex resistor, capacitor and inductor. The inductance is nonlinear. Therefore, when a voltage of different frequency is applied to one line, it is obtained at each line at the other line. The response is not the same. If the frequency response curve of some line ends is recorded when the transformer is normal, and the frequency response curve of the corresponding line end is re-recorded after the exit short circuit occurs, the degree of coincidence of the two curves can be compared to know the deformation of the winding. Because the deformation of the winding inevitably leads to a change in the distribution parameters, the frequency curve also changes.     2. Measurement wiring of frequency response method     The measurement wiring of the frequency response method is shown in Figure 3-18. The frequency of the output voltage of the frequency response analyzer in the figure can be changed linearly or logarithmically within a selected range. The output voltage range is 30mV ~ 3V (the frequency can be selected from 10Hz~1MHz). At the neutral or line end of the winding. The measurement line is connected to other line ends, and the measured signal is sent back to the frequency response analyzer, and the frequency response curve is drawn by the XY recorder (the X-axis is the frequency and the Y-axis is the response).     3. Frequency response method measurement example     In recent years, power systems have been used to test many transformers with frequency response method, and have achieved certain results and experience; many defects of winding deformation have been found and processed. The following is an example.     Due to the careless construction of the 220kV transformer, the transformer outlet is short-circuited, and the C-phase short-circuit develops into a three-phase phase-to-phase short circuit. It lasts for 1.2s, short-circuit current is 11200A, and heavy gas action. Then, tests and chromatographic analysis of insulation resistance, ratio, DC resistance, etc. were performed, and no abnormality was observed. After 10 days, the winding deformation test was carried out. The test results are shown in Figure 3-19 and Figure 3-20. It can be seen from the figure that the three-phase consistency of the high-voltage winding is good, basically no obvious deformation, and the low-voltage winding is consistent at 30kH: Good performance, 30kH: There is a significant difference above, indicating that the low-voltage winding has been deformed. A, B phase moves toward the low frequency direction compared with the C-phase resonance point, the resonance amplitude increases, and there is a peak-to-valley reversal phenomenon. It is indicated that the inductance may be reduced, the capacitance to ground may increase, and the A and C phase windings may be deformed in the longitudinal direction. After inspection by the sling core, it is found that the high-voltage winding is basically free of deformation, the phase A of the low-voltage winding is protuberantly deformed from the fifth struts, and the phase B is similarly deformed from the 5th struts of the 25th to the 100th layers. Phase C has no deformation.     4. Frequency response method test considerations     (1) The tap changer position and the lead lead length of the transformer have a great influence on the frequency response curve of the winding, so the state of the transformer must have certain stability during the side test. Deformation testing should normally be carried out without any outgoing lines, and the position of the tap-changer must be recorded for comparison on the same gear.     (2) The test wiring method is different, which also directly affects the frequency response curve of the winding. It must have a relatively fixed test method when testing.     (3) The key to judge the test results of transformer winding deformation is to have the frequency response curve of the winding structure or the frequency response curve of the transformer of the same structure. The comparison of the three-phase frequency response curves is an expedient measure, which has certain limitations. Sex.     (4) Pay attention to the influence of the position of the signal source. The output of the "A" input, the "O" output and the "O", the end input, and the "A" output are different. Table 3-7 lists the FRA. Method of deformation test wiring.     (5) The frequency response method can be combined with some conventional inspection and test methods to judge the deformation of the transformer winding, such as the suspension method, the single-phase impedance method and the leakage inductance method. Nine, the polarity group and the ratio test of the transformer     1. Polarity test of transformer     First of all, the definition of "reduce polarity" and "add polarity" of the transformer should be clarified. This is because the winding direction of the winding and the direction of the current entering are different, so that there is "reduction of polarity" between the primary and secondary windings. And "add polarity" issues. The so-called "reduction of polarity" means that when the corresponding terminals of the primary and secondary windings are of the same name, after connecting X and x, UAA, = U1 - U2, that is, the voltage between A and a is the primary side and the secondary side. The difference in voltage. "Plus polarity" means that when the corresponding terminals of the primary and secondary windings are different names, after connecting X and x, UAA=U1+U2, that is, the voltage between A and a is the voltage of the primary and secondary sides. Sum. As shown in Figure 3-21, where (a), (b) is the polarity reduction, (c), (d) is the polarity.     The transformer polarity test is for single phase transformers. There are generally two methods of direct current method and alternating current method. The explanations are given below.     (1) DC method. The wiring of this method is shown in Figure 3-22 (a). Use 1.5-3v for the battery or 2-6V battery, the high voltage A terminal is connected positively, and the X terminal is connected negative. Use the DC millivoltmeter "+" to connect to the a terminal and the "-" to the x terminal. When the switch s is instantaneous, if the millivolt meter is positively biased, then A, a are the same polarity end, the transformer is the polarity reduction, and vice versa.     (2) Communication method. The wiring of this method is shown in Figure 3-22 (b). Close switch S and adjust the regulator so that the output voltage is 1/2-1/3 of the voltmeter scale. At the same time, PV1 and PV2 are read. If the PV2 reading is greater than PV1, then A and a are the same polarity terminals, and the transformer is reduced in polarity, and vice versa.     2. Transformer group test     The same group of transformers (also known as the junction group label) is one of the necessary conditions for the parallel operation of the transformer. The group test of the three-phase transformer is used to check whether the transformer group is consistent with the nameplate. It is one of the tests that should be done after the transformer is shipped, handed over and overhauled.     (1) Representation of the number of transformer junction groups. The connection group labels of three-phase double-winding transformers are commonly Yynl2, Ydll, YNd11, etc. The connection group labels of three-phase three-winding transformers are commonly YNynO, dll. Where Y, y, d are the wiring of the winding (star or delta connection), 12, 11 is the voltage phase difference between the high and low voltage windings (indicated by the clock).     (2) Test method for the joint group label. The test method generally has four methods: DC method, dual voltmeter method, phase meter method and variable ratio bridge method. This section only introduces the two voltmeter method and the variable ratio bridge method.     1) Dual voltmeter method. This is one of the commonly used methods in the field, and its wiring is shown in Figure 3-23. Connect A, a, add three-phase AC 380V on the high-voltage side of the transformer, and measure the unbalance of the voltage between the three phases should be no more than 2%. Use the 0.5-level meter to map the measurement results as a phasor diagram. 3-24), this transformer group is available as an 11-point connection.     The measurement results are as follows: U AB = 380 V, U Aa = 360 V, U Bc 380 V, U BC = 380 v, U Bb = 360 V, U CB = 380.7 V, U CA = 380 V, U Cc = 360 V.     2) Variable ratio bridge method. The measuring bridges of the various connection groups commonly used in the variable ratio bridge are attached. If the connection group of the sample is the same as the measurement group selected for the bridge, and the bridge can be balanced under the ratio of the junction group and the nameplate voltage calculation, the ratio and connection group of the sample are correct. If the bridge is unbalanced, if the ratio is correct, the connection group is not in compliance.     3. Transformer voltage ratio (ratio) measurement     The voltage ratio of the transformer refers to the ratio of the primary side voltage U1 to the secondary side voltage UZ when the transformer is running at no load, that is, the ratio K=U1/U2. According to the requirements of the "pre-regulation":     (1) The ratio of all taps of the windings should be measured.     (2) The ratio of the corresponding joints should not be significantly different from the nameplate and should be in accordance with the law.     (3) For transformers below 35kV with a ratio of less than 3, the allowable deviation is ±1%; for other transformers: the rated tap voltage is ±0.5% of the allowable deviation, and the voltage ratio of other taps should be at the impedance voltage (%) Within 1/10, but not more than ±1.     Common methods for measuring the ratio are the dual voltmeter method and the variable ratio bridge method. Because the dual voltmeter method has the disadvantages of requiring precision instruments, large errors, high test voltage, and unsafe, at present, the variable ratio bridge method is often used for the ratio test.     QT-35 type and QT-80 type ratio bridge are used in the field, which has high accuracy, high sensitivity, low test voltage, safety, variable ratio error can be directly read, and can simultaneously measure the transformer connection group. Etc.     The voltage ratio of the transformer under test can be conveniently measured by using a variable ratio bridge. The measurement principle is shown in Figure 3-25. Only need to add voltage U1 on the primary side of the transformer under test to induce voltage U2 on the secondary side of the transformer, adjust the resistance R1 to make the galvanometer zero, and then calculate the voltage ratio K by simple calculation;     Figure 3-26 shows the working diagram of the ratio bridge.     The calculation formula of the measured voltage ratio K is K=U1/U2 two (R1+R2)/R2=1+(R1/R2)     In order to read the voltage ratio error while measuring the voltage ratio, a sliding-plate resistor R 3 is strung between R 1 and R 2 , as shown in Figure 3-27. The contact point of R: is C. Assume that R MC =R CN =R 3 /2, if the test product ratio fully meets the standard ratio K, adjust R: to make the galvanometer zero, then the ratio is calculated according to the formula K=(R1+R2+R3)/R2+R3/2=1+R1/(R2+R3/2)+R3/2/(R3+R3/2)     If the ratio of the transformer under test is not the standard ratio K, but with a certain error, the voltage ratio error ΔK can be derived. â–³K≈-100â–³R/(R2+R3/2)     ΔR is the resistance value of point C deviating from the midpoint of R3. For convenience, R2+R3/2=1000Ω is taken, and if the maximum percentage error ΔK=±2%, ΔR=±20Ω. That is, when the error varies within ±2%, the slider C point needs to be changed within a range of ±20 Ω from the midpoint of R:. When point C slides on R3, the potential at point C will also change accordingly, and it can reach equilibrium with U2 within a certain range.     At present, there are automatic ratio measuring instruments at home and abroad. The principle is still the voltage measurement method and the bridge method. However, the microprocessor, the receiving panel keyboard and the switch input are used to automatically track and control the range and bridge balance. Data processing of the measurement results, and finally, the measurement results are stored and printed.     Figure 3-28 shows a basic block diagram of a voltage ratio automatic measuring instrument. After the power frequency supply voltage is selected by the test terminal selector, it is added to the high voltage side winding of the transformer under test. The voltage and power supply voltage of the low voltage side voltage selected by the test terminal selector are converted by the standard voltage transformer and sent to the AC/DC converter. The device is converted into a DC voltage, and then amplified by a filter and a programmable gain amplifier to obtain voltages Ux and Un. These two voltages simultaneously enter the AC/DC converter, and the microprocessor is based on the input voltage ratio of the input, the measured UN, rated voltage Ux and the gain of the amplifier and the standard voltage transformer or the like to calculate the data, process, store and display the measured value and the voltage ratio deviations from the voltage ratio. Ten, transformer no-load and short-circuit test     The no-load test of the transformer is to test the rated voltage of the AC rated frequency from the winding of either side of the transformer, the other windings are open, and the no-load current and loss of the transformer are tested. Through the no-load test, it can be found that the core silicon steel sheet is short-circuited, loose or poorly insulated, short-circuit between the turns of the winding, and short-circuit of the parallel branch.     The short-circuit test of the transformer is to short-circuit one side of the transformer, and the rated voltage of the AC rated frequency is added from the other side of the winding, so that the current in the winding is rated, and the applied voltage (impedance voltage) and power (short-circuit loss) are measured. . Through the short-circuit test: 1 measured the impedance voltage to determine the parallel operation of the transformer; 2 found that the structural parts of the transformer or the fuel tank wall, the partial overheating of the tank cover, the casing flange heating; 3 short-circuit or transposition between parallel wires in the winding Defects such as errors. XI. Test and inspection of on-load voltage regulator     According to the requirements of the "pre-regulation", the test and inspection items for the transformer's on-load voltage regulator are:     1 check the action sequence, action angle; 2 operation test; 3 check and switch test; 4 check operation box; 5 switch switch room insulation oil test; 6 secondary circuit insulation test.     (1) Check the action sequence and angle. This test is used to find out whether there is deformation, jam, loose bolts and excessive wear inside the switch, and also to determine whether the position of the switch components is correct. The measurement methods include an audible method, an indicator method, and a multimeter method.     Taking the listening method as an example, the steps of the measurement are as follows:     1) Use the handle to perform the tap change operation, listen to the selector and switch operation sounds, and record the number of turns of the handle;     2) When the selector sends out the first sound from the original tap position, record the number of handle swings m1;     3) When the selector turns on the new tap position and makes a second beep, record the number of handle swings m2;     4) When the switch switch operation emits a third beep, record the number of handle wobbles m3.     If m1>m2>m3, it means that the tap-changer works in the correct order; if there is no jam in the hand-operating operation, the force is even, indicating that the tap-changer is in good condition.     (2) Operation test. The main purpose of this test is to verify the correct operation of the switch and the ability to carry the load. Generally, manual operation is first performed to check the mechanical limit and the presence or absence of a click phenomenon; then, the electric operation is performed to check whether the electrical limit and the mechanical transmission are normal. During the operation of the impact closing maneuver, several cycles of no-load operation are carried out, or several tap adjustments are made within the range allowing adjustment.     (3) Check and switch tests. The test is divided into 5 small test items, namely measuring the resistance of the transition resistance; measuring the switching time; checking the contact of the inserted contact, the moving and static contact, the connection of the electrical circuit; Linear resistance test; check the discharge gap between single and double contacts.     The measurement of the transition resistance and switching time should be carried out in the transformer oil. Generally, it can be measured with a transformer winding measuring instrument. If there is any doubt, it can be measured by the oscilloscope method. The oscilloscope method wiring is shown in Figure 3-32.     Check the contact condition of the static and dynamic contacts, use the spring dynamometer and multimeter to measure. In the static and indirect contact multimeter ohmic gear, slowly pull up the contact with the dynamometer. When the ohmmeter pointer starts to move or the signal light goes out, measure The force indicated by the force gauge is the contact pressure of the contact.     For the non-linear resistance between single and double contacts, the relationship between current and voltage should be made according to the manufacturer's requirements, and compared with the manufacturer's requirements.     (4) Check the operation box. Check the various components in the operating box (including contactors, motors, drive gears, auxiliary contacts, position indicators, counters, etc.) and work properly.     (5) The switching capacitor insulation oil shall have a breakdown voltage of not less than 25kV as required by the Pre-Regulation. (6) The insulation resistance of the secondary circuit can be tested by 2500V megohmmeter, and the insulation resistance should be no less than 1MΩ. Feed Through Terminal Block Section
Feed Through Terminal Block.
In the electrotechnics, the terminal refers to the terminal and is designed to run through the terminal production. The type is divided into single hole, double hole, socket, hook, etc. from the material, copper silver plating, copper zinc plating, copper, aluminum, iron, etc. their functions are mainly to transmit electrical signals or conduct electricity. The unit of terminal block is "bit", and one wiring bit is "bit". Usually the so-called table is the serial number of the terminal, which has different definitions in different applications. "Jie" and "bit" have the same meaning, but they are called differently. Groups are made up of sections.
Feed Through Terminal Block ShenZhen Antenk Electronics Co,Ltd , https://www.antenksocket.com
 According to the requirements of the "pre-regulation", the following tests should be carried out on oil-immersed power transformers :