Fully automatic transformer tester

LYFA-5000Fully automatic transformer tester?Characteristics and Parameters

It is a new generation of innovative CT and PT testing instruments developed on the basis of traditional transformer volt ampere characteristic transformation ratio polarity comprehensive testing instruments based on voltage regulators, boosters, and current boosters, extensively listening to user opinions, conducting extensive market research, and conducting in-depth theoretical research. The device adopts high-performance DSP and FPGA, * manufacturing technology, ensuring stable and reliable product performance, complete functions, high degree of automation, high testing efficiency, and is at the forefront in China. It is a professional testing instrument for transformers in the power industry.

1.1 LYFA-5000Fully automatic transformer testerMain technical features

Fully functional, it not only meets the testing requirements for excitation characteristics (i.e. volt ampere characteristics), transformation ratio, polarity, secondary winding resistance, secondary load, ratio difference, and angle difference of various CTs (such as protection, metering, TP), but also can be used for testing excitation characteristics, transformation ratio, polarity, secondary winding resistance, ratio difference, etc. of various PT electromagnetic units.

On site calibration of current transformers does not require standard current transformers, current transformers, load boxes, voltage regulation control boxes, or high current wires. It uses extremely simple testing wiring and operation to achieve the calibration of current transformers, reducing work intensity and improving work efficiency, making it convenient to carry out on-site transformer calibration work.

It can measure the ratio difference and angle difference, with an allowable error of ± 0.05% for large ratio differences and ± 2 minutes for large angle differences. It can measure 0.2S-level current transformers with a ratio measurement range of 1-40000.

Based on the frequency conversion method to test the CT/PT volt ampere characteristic curve and 10% error curve, it can output an AC voltage of only 180V and an AC current of 12Anms (peak value of 36A), but can handle CT tests with inflection points as high as 60KV.

Automatically provide CT and PT parameters such as inflection point voltage/current, 10% (5%) error curve, accuracy limit factor (ALF), instrument safety factor (FS), quadratic time constant (Ts), remanence coefficient (Kr), saturated and unsaturated inductance.

The test meets various transformer standards such as GB1208 (IEC60044-1), GB16847 (IEC60044-6), GB1207, etc., and automatically selects which standard to test according to the type and level of transformer.

The testing is simple and convenient, with one click completion of CT direct resistance, excitation, transformation ratio, and polarity testing. In addition to load testing, all other CT tests use the same wiring method.

Full Chinese dynamic graphical interface, wiring and parameter setting can be completed without referring to the manual: dynamic display of parameter settings, automatically displaying relevant parameters based on the currently selected test project; Dynamically display the help wiring diagram, and display the corresponding wiring diagram based on the currently selected test project.

5.7-inch graphic transparent LCD, clear and visible under sunlight.

Using a rotating optical mouse for operation, it is simple, fast, convenient, and easy to master.

The panel comes with a printer that can automatically print the generated test report.

The test results can be exported using a USB flash drive, and the program can be upgraded using a USB flash drive, which is convenient and fast.

The device can store 1000 sets of test data without loss in case of power failure.

Equipped with backend analysis software, it facilitates the saving, conversion, and analysis of test reports, and can be used for comparing, judging, and evaluating experimental data.

Easy to carry, device weight<9Kg.

1.2 LYFA-5000Fully automatic transformer testerDevice panel description

The structure of the device panel is shown in the diagram on the right, with wiring terminals from left to right:

·Red black S1 and S2 terminals: Test power output

·Red black S1 and S2 terminals: output voltage backtesting

·Red black P1 and P2 terminals: Inductive voltage measurement terminals

·LCD screen: Chinese display interface

·Micro printer: printing test data and curves

·Rotate mouse: Enter numerical values and operation commands

1.3 LYFA-5000Fully automatic transformer testerMain technical parameters

Chapter 2LYFA-5000Fully automatic transformer testerUser interface and operating methods

2.1 Current Transformer Test

In the parameter interface, use the rotating mouse to switch the cursor to the type bar and select the transformer type as CT.

2.1.1 Test wiring

The experimental wiring steps are as follows:

*Step: According to the CT test item description in Table 2.1, follow Figure 2.1 or Figure 2.2 for wiring (for various structures of CT, refer to the actual wiring method described in Appendix D).

Table 2.1 CT Test Item Description

Step 2: If other windings of the same CT are open circuited, one end of the CT's primary side should be grounded, and the equipment should also be grounded.

Step 3: Connect the power and prepare the parameter settings.

2.1.2 Parameter Settings

The interface for setting experimental parameters is shown in Figure 2.3.

The parameter setting steps are as follows:

Use the rotating mouse to switch the cursor and select the experimental project to be carried out. When the cursor stays on a certain experimental project, the screen displays the parameter settings related to that experimental project; When the cursor moves away from the test item, the screen displays the wiring diagram corresponding to the selected test item.

The parameters that can be set are as follows:

(1) Number: Enter the number of this experiment for easy management and retrieval of printing and saving.

(2) Rated secondary currentThe rated current of the secondary side of the current transformer is generally 1A and 5A.

(3) Level: The level of the tested winding, for CT, there are 8 options including P, TPY, metering, PR, PX, TPS, TPX, TPZ, etc.

(4) Current temperature: The temperature of the winding during testing, which can generally be input as the temperature during testing.

(5) Rated frequency: Optional values are 50Hz or 60Hz.

(6) Large test current: Generally, it can be set as the rated secondary current value. For TPY level CT, it can generally be set as twice the rated secondary current value. For P-level CT, assuming it is 5P40 and the rated secondary current is 1A, the large test current should be set at 5% * 40 * 1A=2A; Assuming it is 10P15 and the rated secondary current is 5A, the large test current should be set at 10% * 15 * 5A=7.5A.

If users want to see the following results, they need to accurately set the basic parameters (recommended for users to set).

(1) Turn ratio error, ratio difference, and phase difference

(2) Accurately calculated ultimate electromotive force and its corresponding composite error

(3) Actual measured accurate limit factor, instrument safety factor, and symmetrical short-circuit current multiple

(4) Measured transient area coefficient, peak instantaneous error, and quadratic time constant

For different levels of CT, the parameter settings are also different, as shown in Table 2.2.

Table 2.2 CT Parameter Description

Step 5: Select the start button on the right to conduct the experiment.

2.1.3 Test results

The experimental results page and interface are shown in Figure 2.4.

The test results vary for different levels of CT and selected test items, as shown in Table 2.3.

Table 2.3 CT Test Results Description

2.2 Voltage Transformer Test

In the parameter interface, use the rotating mouse to switch the cursor to the type bar and select the transformer type as PT.

2.2.1 Test wiring

The experimental wiring steps are as follows:

*Step: According to the PT test item description in Table 2.4, wire according to Figure 2.7 or Figure 2.8.

Table 2.4 Description of PT Test Items

Step 2: Open circuit in other windings of the same PT.

Step 3: Connect the power and prepare the parameter settings.

2.2.2 Parameter Settings

The interface for setting PT test parameters is shown in Figure 2.5.

The parameter setting steps are as follows:

Use the rotating mouse to switch the cursor and select the experimental project to be carried out. When the cursor stays on a certain experimental project, the screen displays the parameter settings related to that experimental project; When the cursor moves away from the test item, the screen displays the wiring diagram corresponding to the selected test item.

The parameters that can be set are as follows:

(1) Number: Enter the experimental test number.

(2) Rated secondary voltageRated voltage of the secondary side of the voltage transformer.

(3) Level: The level of the tested winding, with two options: P and measurement.

(4) Current temperature: The temperature of the winding during testing can generally be inputted as the current temperature.

(5) Rated frequency: Optional values are 50Hz or 60Hz.

(6) Large test voltage: The high power frequency equivalent voltage output by the equipment during the test.

(7) High test current: The large AC current output by the equipment during the test.

Step 4: Select the start button on the right to conduct the experiment.

2.2.3 Test results

The test result page is shown in Figure 2.6.

The test results vary for different levels of PT and selected test items, as shown in Table 2.5.

Table 2.5 Description of PT Test Results

2.3 Self check page

The self-test interface is shown in Figure 2.8. With the help of a multimeter, the self-test function can be used to check whether the device is damaged and whether the measurement circuit is normal.

2.3.1 Parameter Settings

The parameters required for self-test testing are shown in the following table:

Table 2.6 Self check Test Parameters

After setting the test current or test voltage, set the test frequency, and the device will output the voltage or current corresponding to the frequency, and display the actual voltage or current detected. After selecting the voltage, if the load is too small and the actual effective current value is greater than 5A, an overload message will be displayed. After selecting the current, if the load is too large and the actual test voltage effective value is greater than 100V, overload information will also be displayed.

2.3.2 Wiring method

·When selecting a voltage test, short-circuit S1 to another S1 and S2 to another S2. Use a multimeter to measure the voltage between S1 and S2 in the voltage range. If it matches the actual voltage, it indicates that the device can output voltage and the voltage measurement process is normal.

·During current testing, short-circuit the S1 and S2 terminals of the power output. S1 and S2 for voltage backtesting are not connected. A multimeter current range can be connected in series between S1 and S2 outputs. If the current measured by the multimeter matches the actual current, it indicates that the device can output current normally and the current measurement process is functioning properly.

2.4 Function buttons

2.4.1 Parameter page function buttons

(1) System Tools

The system tool interface is shown in Figure 2.11. In this interface, operations such as time verification and system upgrade can be performed. Among them, debugging is used for factory debugging, and upgrading is used for upgrading the software interface.

(2) . Help

(3) Print

Users can print the current test results, and this report can be used as the original record of on-site testing.

2.4.2 Results page function buttons

(1) Excitation curve

On the measurement result page of Figure 2.4 or Figure 2.6, select the excitation result, and the excitation curve interface will appear, as shown in Figure 2.13:

(2) Excitation data

On the excitation curve page in Figure 2.13, selecting excitation data will display the excitation data interface, as shown in Figure 2.14:

Three forms of excitation data can be displayed in the above figure:

Actual measurement: The voltage and current sequences captured during the instrument's voltage boosting process;

Rounding: The results of rounding the measured excitation data according to the current show that for values below 10mA, it increases by 1mA; for values between 10mA and 100mA, it increases by 5mA; and for values above 100mA, it increases by 0.1A. The rounding results are convenient for data recording and comparison;

Can display excitation data for any current point;

(3) 5% and 10% error curves

Only transformers with protection level (including transient protection level) have 5% and 10% error curves and error data; Select the P/PR/PX/TPx transformer in the CT settings. In the test result interface of Figure 2.4, selecting the error result will display a 5% error curve, as shown in Figure 2.15:

In Figure 2.15, you can also choose to display a 10% error curve. The 10% error curve of the protective transformer is a graphical display of the 10% error data, which has the same meaning. Its meaning is the relationship curve between the secondary load and the overcurrent multiple when the composite error of the transformer is not greater than 10%. The 5% error curve is the relationship curve between secondary load and overcurrent multiple when the composite error of the transformer is not greater than 5%.

(4) 5% and 10% error data

In Figure 2.15, selecting error data will display error data of 5% and 10%, as shown in Figure 2.16:

(5) Comparison and angle difference table

Only measuring grade transformers have comparison and angle difference result tables; Only transformers with winding level "metering" selected in CT settings and testing item "error" selected will have differential and angle meters. In the CT test result interface of Figure 2.4, select the error result, and the comparison and angle difference tables will appear, as shown in Figure 2.17:

The above figure shows the ratio and angle difference tables of the transformer at rated load and lower limit load, respectively. The rated load is specified on the CT settings page, and the lower limit load is set at 25% of the rated load.

Appendix

A. Principle of low-frequency method testing

The IEC60044-6 standard (corresponding to the national standard GB16847-1977) claims that CT testing can be conducted at frequencies lower than the rated frequency to avoid unacceptable voltages on the windings and secondary terminals.

The principle circuit of CT volt ampere characteristic measurement is as follows: the CT primary side is open circuit, voltage is applied from the secondary side, and the relationship curve between the applied voltage V and the input current I is measured. This curve approximates the relationship between the excitation potential E and excitation current I of CT.

If the excitation inductance of the CT excitation winding is L and the excitation impedance is Z at a certain excitation current I, then V=I · Z

The relationship between inductance L and impedance Z is as follows: Z=ω · L=2 π f L, then V=I · 2 π f L

From the formula, it can be seen that the voltage V applied to a certain excitation inductance L is proportional to the frequency f.

Assuming that when f=50Hz, the required voltage Vx to achieve the excitation current Ix is 2000V

Vx = Ix·2 π f L = 2000V，

If different frequencies are applied:

f = 50Hz，Vx ＝ 2000V

f = 5Hz， Vx ≌ 200V

f = 0.5Hz，Vx ≌ 20V

It can be seen that the CT needs to enter the same saturation level, and applying a lower frequency signal can significantly reduce the voltage required. This is the basic principle of the frequency conversion method.

It must be strictly noted that the required voltage is not linearly proportional to frequency, nor does it decrease proportionally with frequency. It is necessary to strictly follow the mathematical model of the transformer for complete theoretical calculations.

B. 10% Error Curve Calculation and Application Method

The error of current transformers is mainly due to the excitation currentThe existence of it causes secondary currentThe primary current converted to the secondary sideNot only are they not equal in numerical values, but also in phase, which causes errors in current transformers.

The ratio difference of current transformers is defined as:

Relay protection requires the primary current of the current transformerWhen equal to the large short-circuit current, the ratio difference is less than or equal to 10%. When the ratio difference is equal to 10%, the secondary currentThe primary current converted to the secondary sideAnd excitation currentThe following relationship is satisfied between them:

If M is defined as the multiple of the primary side short-circuit current and K is the transformation ratio of the current transformer, then there is

among whichFor a large short-circuit current on the primary side

Rated current on the primary side

Rated current on the secondary side

Allowable high load impedance when the ratio difference is 10%The calculation formula is:

Where:Impedance of the secondary winding of the current transformer

To induce electromotive force in the secondary winding of the current transformer,The relationship is described by the excitation characteristic curve.

According to the above formula, the multiple of the large short-circuit current can be obtainedAnd the allowable high load impedanceThe 10% error curve described (see Figure 2.29).

Application method of 10% error curve:

After obtaining the 10% error curve of a certain CT, it is also necessary to check the large short-circuit current flowing through the CTImpedance of the circuit carried by the CT secondary sideThe large short-circuit current is often obtained during the setting calculation, which is the short-circuit current when the CT is severely short circuited under the large operating mode of the line, and is a multiple of the large current(Rated current). Secondary circuit impedanceIt can be measured using CTA device.

getAfter checking the 10% error curve, if the point is（）Below the curve, it meets the requirement, indicating that the current transformation error of CT is less than 10% under severe short circuit conditions. Otherwise, it will exceed 10%.

C. The actual wiring method of CTA used for various CTs

The basic wiring steps for CTA used in CT testing (see Figure C. 1) are as follows:

(1) Connect the grounding terminal on the left side of the tester to the protective ground using a 4mm2 wire.

(2) Connect one terminal on the primary side and one terminal on the secondary side of the CT to the protective ground.

(3) Ensure that all other terminals of the CT are disconnected from the power transmission line and all other windings are open circuited.

(4) Connect the secondary side of the CT to the S1 and S2 sockets of the tester "Output" using a 2.5mm2 red and black wire, and connect the secondary side of the CT to the S1 and S2 sockets of the tester "Sec" using a 1.2mm2 yellow and black wire. Note that the two black wires are connected to the same terminal on the CT secondary side that has been grounded for protection.

(5) Connect the primary side of the CT to the P1 and P2 terminals of the "Prim" tester using a 1.2mm2 green and black wire. Connect P2 to the protective ground terminal of the CT primary side through the black wire.

(6) Check the wiring for accuracy and start testing.

The wiring method for CT testing of the tester on a delta connected transformer is shown in Figure C-2.

The wiring method for CT testing of transformer bushing using the tester is shown in Figure C.3.

Attention: Terminal H1 should not be grounded, otherwise if both sides are grounded, the tester will not be able to obtain the correct result.

The wiring method of the tester for CT testing on GIS (SF6) switches is shown in Figure C.4.

Attention: Disconnect all switches connected to the busbar and close the grounding knife switch.

D. Measurement principle of four terminal wiring

Applying a voltage source signal Vs to an impedance R will generate a current I, as shown in Figure D.1.

If the impedance value needs to be measured, the voltage V on the impedance needs to be measured:

Due to the presence of a wire from the voltage source to the measured impedance, which has a resistance r, resulting in V=Vs, measuring impedance R cannot simply replace V with the power supply voltage Vs.

The measurement circuit for impedance R should use the wiring method shown in Figure D.2. The voltmeter used to measure voltage must be connected separately with wires from both ends of R in order to measure the voltage value V. Since R is connected with 4 wires at both ends, it is called the 4-terminal wiring method. The wiring method in Figure D.3 is incorrect.

When using CTA to measure the resistance, transformation ratio, and excitation of a transformer, a four terminal wiring method is required, as shown in Figure D.4.

Attention must be paid to the terminal connection of the tested winding when using the four terminal method for wiring. The connection in Figure D.5 is the correct connection, while Figures D.6 and 7 are both incorrect connections.