CN106383328A - Excitation characteristic test method applicable to ultrahigh-voltage TPY current transformers - Google Patents

Abstract

The invention discloses an excitation characteristic test method suitable for UHV TPY-level current transformers. A certain DC voltage is applied to the secondary terminals of the current transformer, and the corresponding excitation current is measured to determine the magnetic flux of the iron core of the secondary turn chain winding. The relationship with the applied voltage; when determining the rated frequency of the current transformer, the mathematical model of the relationship between the root mean square value of the equivalent voltage and the secondary circuit current, and the relationship curve between the excitation voltage and the excitation current when constructing the excitation characteristics of the current transformer; according to the data The model is used to test the excitation characteristics of UHV TPY-level current transformers based on the DC saturation method. A DC voltage is applied to the secondary terminals of the current transformer, and the excitation current is collected on the secondary terminals at the same time. Line connection for test line connection, calculate CT ratio and knee voltage. The excitation saturation speed of the current transformer of the invention is fast, and the test efficiency is improved.

Description

A test method for excitation characteristics suitable for UHV TPY class current transformers

technical field

The invention relates to an excitation characteristic testing method suitable for an ultra-high voltage TPY level current transformer.

Background technique

The excitation characteristics of a current transformer refer to the relationship between the excitation current on the secondary side and the applied voltage when the primary side of the transformer is open circuited. Through the excitation characteristic test, it is possible to check the quality of the iron core of the newly put into operation current transformer and find out the current mutual inductance. The inflection point voltage and current when the transformer is saturated are used to judge whether there are defects such as inter-turn short circuit in the secondary winding of the transformer.

The traditional current transformer excitation characteristic test method is mainly the manual voltage regulation measurement method, using the manually adjusted output voltage of the auto-coupling step-up voltage regulator, adding it to the secondary side of the current transformer, reading with the voltage and ammeter, and then manually drawing Excitation characteristic curve. The test equipment used in this method has a large volume and weight, complex wiring, poor safety, low test efficiency, and it is impossible to measure the TPY-level current transformer with a high inflection point.

In recent years, the AC frequency conversion method has been widely used at home and abroad to test the excitation characteristics of current transformers. The test equipment based on this principle is small in size and light in weight, and has been widely used in the test of excitation characteristics of current transformers with voltage levels of 500 kV and below. However, with the continuous improvement of the grid voltage level, the capacity and transformation ratio of the current transformers used are also increasing, and the saturation inflection point voltage has increased from several thousand volts to tens of thousands of volts. The AC frequency conversion method is used to test this type of current mutual inductance When the device is used, the added test frequency is very low, resulting in a longer test cycle and affecting the test efficiency. Therefore, it is necessary to find a new method for testing the excitation characteristics of high-inflection point TPY-level current transformers in UHV substations.

Contents of the invention

In order to solve the above problems, the present invention proposes a method for testing the excitation characteristics of UHV TPY-level current transformers. This method can effectively shorten the time for testing the excitation characteristics of UHV TPY-level current transformers without affecting the accuracy of the test. It solves the problem of slow test speed of the excitation characteristics of the existing UHV TPY-level current transformer.

In order to achieve the above object, the present invention adopts the following technical solutions:

A method for testing excitation characteristics applicable to UHV TPY-level current transformers, comprising the following steps:

(1) Apply a certain DC voltage on the secondary terminal of the current transformer, measure the corresponding excitation current, and determine the relationship between the magnetic flux of the secondary turn chain winding core and the applied voltage;

(2) When determining the rated frequency of the current transformer, the mathematical model of the relationship between the root mean square value of the equivalent voltage and the secondary circuit current, and constructing the relationship curve between the excitation voltage and the excitation current when the excitation characteristics of the current transformer are constructed;

(3) According to the data model, test the excitation characteristics of UHV TPY-level current transformer based on the DC saturation method, apply DC voltage on the secondary terminal of the current transformer, and collect the excitation current on the secondary terminal at the same time. The secondary side terminal adopts four-wire connection for test line connection, and calculates CT transformation ratio and inflection point voltage.

In the step (1), the excitation current corresponds to the peak value of the magnetic flux, and the excitation voltage corresponds to the root mean square value.

In the step (1), the applied DC voltage can keep the magnetic flux in the current transformer at a certain value, and at time t, the relationship between the secondary turn-link winding core magnetic flux φ(t) and this voltage is as follows: :

$\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; t</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}$

Among them, R _ct is the secondary winding resistance of the current transformer, and _im is the excitation current of the secondary circuit.

In the step (2), the relationship between the root mean square value U of the equivalent voltage under the rated frequency f of the current transformer and the magnetic flux φ of the secondary turn chain winding core is:

$\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; f</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; f</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}}{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; t</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; .</span>$

In the step (3), when testing, the connection between the current transformer and its secondary circuit needs to be disconnected, and when the excitation characteristics of a certain winding are tested, other windings need to be opened.

In the described step (3), the secondary terminal of the current transformer is the signal input terminal and the signal acquisition terminal, and the secondary side terminal of the transformer is connected with a test line by clamps, and each test clamp of the test lead should be directly connected to the test line. Connect to the secondary terminals of the current transformer.

In the step (3), the capacity, accuracy class, rated symmetrical short-circuit current multiple, rated transient area coefficient, primary time constant or/and secondary time constant parameters of the current transformer need to be set during the test.

In the step (3), the standard used to calculate the inflection point is IEC 60044-6.

The beneficial effects of the present invention are:

(1) The DC saturation method is used to test the excitation characteristics of the UHV TPY-level current transformer. By applying a DC voltage, the excitation saturation speed of the current transformer is fast, which improves the test efficiency. When using the AC frequency conversion method to test the excitation characteristics of UHV TPY-level current transformers, the higher the inflection point voltage, the lower the test frequency, and the longer the test time required for each test cycle. Because the TPY-level current transformer used in UHV stations The inflection point voltage is as high as tens of thousands of volts, so the working efficiency of the AC method is much lower than that of the DC method;

(2) Adopting the DC test principle greatly improves the test efficiency of the excitation characteristics of the UHV TPY level current transformer.

Description of drawings

Figure 1 is a schematic diagram of testing the excitation characteristics of a current transformer;

Figure 2 is the excitation characteristic curve of the TPY-level current transformer using the DC method;

Figure 3 is the excitation characteristic curve of the TPY-level current transformer using the AC method.

detailed description:

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

The invention provides a method for measuring the excitation characteristics of an UHV TPY-level current transformer using a DC saturation method, including:

(1) Apply a certain DC voltage on the secondary terminal of the current transformer, and measure the corresponding excitation current. The excitation current corresponds to the peak value of the magnetic flux, and the excitation voltage corresponds to the root mean square value.

(2) The applied DC voltage can keep the magnetic flux in the current transformer at a certain value continuously. At time t, the relationship between the magnetic flux φ(t) of the secondary turn chain winding core and this voltage is:

$\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; t</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}$

(3) The relationship between the root-mean-square value U of the equivalent voltage at the rated frequency f of the current transformer and the core flux φ of the secondary turn chain winding is:

$\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; f</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; f</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}}{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; t</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}$

This is the mathematical model of the relationship between the root mean square value of the equivalent voltage and the secondary circuit current, that is, the relationship curve between the excitation voltage and the excitation current when the DC method is used to test the excitation characteristics of the current transformer. In the formula, R _ct is the secondary winding resistance of the current transformer, and _im is the excitation current of the secondary circuit.

(4) Using the mathematical model described in step (3), construct a test scheme for the excitation characteristics of UHV TPY-level current transformers based on the DC saturation method, and its test schematic diagram is shown in Figure 1. During the test, the connection between the current transformer and its secondary circuit should be disconnected. When testing the excitation characteristics of a certain winding, other windings should be open.

(5) According to the current transformer excitation characteristic test schematic diagram described in step (4), the method adopts applying a DC voltage on the secondary terminal of the current transformer, and simultaneously collecting the excitation current on the secondary terminal, and the secondary terminal of the current transformer The terminal is both the signal input end and the signal acquisition end. The test method of the present invention uses clamps to connect the test line to the secondary side terminals of the transformer. In order to eliminate the impact of the voltage drop caused by the contact resistance of the clamp, four-wire connection Technology, that is, each test clamp of the test lead should be directly connected to the secondary terminal of the current transformer, as shown in Figure 1.

(6) When testing the UHV TPY level current transformer by the method, it is necessary to set parameters such as the capacity, accuracy level, rated symmetrical short-circuit current multiple, rated transient area coefficient, primary time constant, and secondary time constant of the current transformer , the standard used to calculate the inflection point is IEC 60044-6, using other standards will lead to incorrect test results.

(7) The test method has obvious rapidity when testing UHV TPY level current transformers, and is not much different from the AC test method when testing current transformers of other voltage levels.

The invention adopts a DC saturation method to test the excitation characteristics of the UHV TPY-level current transformer. By applying the DC voltage, the excitation saturation speed of the current transformer is fast, and the test efficiency is improved. When using the AC frequency conversion method to test the excitation characteristics of UHV TPY-level current transformers, the higher the inflection point voltage, the lower the test frequency, and the longer the test time required for each test cycle. Because the TPY-level current transformer used in UHV stations The inflection point voltage is as high as tens of thousands of volts, so the working efficiency of the AC method is much lower than that of the DC method.

The data listed in the table below are the comparative data of the same winding of the UHV TPY class current transformer tested by the AC method and the DC method.

Table 1 Comparison of test data between DC method and AC method

From the comparison of the test data in the above table, it can be seen that for the TPY class current transformer with the same winding, the saturation inflection point voltage measured by the DC saturation method and the AC frequency conversion method is basically the same, which proves that the test accuracy of the two principles is basically the same, but the DC saturation method is used. The test efficiency of the saturation method is 6-7 times higher than that of the AC frequency conversion method. The invention adopts the direct current test principle to greatly improve the test efficiency of the excitation characteristic of the UHV TPY level current transformer.

In order to verify the validity of the test method of the present invention, the AC method and the DC method are selected to test the excitation characteristics of the TPY-level current transformer of the 1000 kilovolt UHV Quancheng Station respectively, and the measured TPY-level current transformers all include two transformation ratios of 3000/1 and 6000/1 winding taps. Two methods are used to test the 3000/1 winding respectively, and the specific implementation steps are as follows.

The schematic diagram of the test is shown in Figure 1 of the technical scheme. Before starting the test, first ensure that the primary side of the current transformer is in the disconnected position, and all secondary windings are open except the test winding. For the test winding, the wiring should be carried out from the root of the current transformer winding. The wiring technology adopts the four-wire wiring technology mentioned in the technical plan. In order to ensure the accuracy and speed of the test, it is necessary to pre-set the relevant parameters of the current transformer to be tested, including Accuracy level, transformation ratio, capacity, rated symmetrical short-circuit current multiple, rated transient area coefficient, primary time constant, secondary time constant and test standard IEC60044-6. In order to ensure the safety of the test process, the equipment used in the test needs to be reliably grounded. After the test starts, first demagnetize the current transformer, and then complete the test according to the specified duty cycle.

The present invention uses the DC saturation method to test the excitation characteristic curve of the TPY-level current transformer of the 1000 kV UHV Quancheng Station. The test data are shown in Table 2, and the test data of the same winding using the AC frequency conversion method are shown in Table 3. By comparing the data in Table 2 and Table 3, the accuracy of testing the excitation characteristics of UHV TPY-level current transformers using the DC saturation method and AC frequency conversion method is basically the same. Considering that UHV TPY-level current transformers mainly provide secondary current, and the designed load capacity of the transformer is much larger than its secondary load. Therefore, in the case of little difference in test accuracy, priority should be given to the rapidity of the transformer excitation characteristic test. According to the beneficial effects provided by the present invention, the comparison of the test time of the two principles can be seen that the test efficiency of the DC saturation method is much higher. Compared with the AC frequency conversion method, this can save a lot of time for the test of the excitation characteristics of UHV TPY-level current transformers. Taking the 1000 kV UHV Quancheng Station as an example, there are 14 bays in this station, and each bay has 6 current transformers, and each current transformer has 2 3000/1 TPY windings and 2 6000/1 TPY windings , the test time of the TPY level current transformer in the whole station by AC frequency conversion method is 14*6*2*7+14*6*2*12=3192min, and the test time by DC saturation method is 14*6*2*1+ 14*6*2*2=504min, using the direct current method saves 2688min of time and increases the work efficiency by 6.3 times.

Table 2 Test data of excitation characteristics of TPY class current transformer (DC method)

Numbering U(V) I(A) Numbering U(V) I(A) 1 18201.28 5.85381 11 3696.362 0.442124 2 17993.31 5.088904 12 2069.686 0.248664 3 17668.72 4.417188 13 1161.077 0.139965 4 17220.92 3.313553 14 634.2334 0.07871 5 16553.49 2.484919 15 263.264 0.033221 6 14982.63 1.862991 16 109.505 0.014022 7 11938.7 1.397603 17 81.3475 0.010503 8 9164.643 1.048259 18 59.4879 0.007886 9 6578.39 0.786278 19 32.7876 0.004435 10 4934.236 0.589614 20 7.3406 0.001055

Table 3 Test data of excitation characteristics of TPY class current transformer (AC method)

According to the test data, the excitation characteristic curve of the test current transformer is drawn as shown in Figure 2 and Figure 3. The excitation characteristic curve presents a linear characteristic before the current transformer is saturated, which is in line with the characteristics of the excitation characteristic curve of the current transformer, indicating that the DC method is used. The excitation characteristic curve can accurately reflect the excitation characteristics of the current transformer.

Although the specific implementation of the present invention has been described above in conjunction with the accompanying drawings, it does not limit the protection scope of the present invention. Those skilled in the art should understand that on the basis of the technical solution of the present invention, those skilled in the art do not need to pay creative work Various modifications or variations that can be made are still within the protection scope of the present invention.

Claims (7)

1. a kind of excitation characteristic test method being applied to extra-high voltage TPY level current transformer, is characterized in that：Walk including following Suddenly：

(1) a certain DC voltage is applied on Current Transformer Secondary terminal, measures corresponding exciting current, determine secondary linkage Winding iron core magnetic flux and the alive relation of institute；

(2) when determining current transformer rated frequency, the mathematics of relation between equivalent voltage root-mean-square valve and secondary loop current Model, the relation curve of excitation voltage and exciting current when building current transformer excitation property；

(3) according to data model, carry out the extra-high voltage TPY level current transformer excitation characteristic test based on direct current saturation, DC voltage is applied on Current Transformer Secondary terminal, gathers exciting current on secondary terminals, to transformer secondary side simultaneously Terminal carries out p-wire connection using four lines connections, calculates CT no-load voltage ratio and knee voltage.

2. a kind of excitation characteristic test method being applied to extra-high voltage TPY level current transformer as claimed in claim 1, it is special Levying is：In described step (1), exciting current is corresponding with peak flux value, and excitation voltage is corresponding with root-mean-square valve.

3. a kind of excitation characteristic test method being applied to extra-high voltage TPY level current transformer as claimed in claim 1, it is special Levying is：In described step (1), the DC voltage being applied can make magnetic flux in current transformer persistently maintain a certain value, During time t, secondary linkage winding iron core magnetic flux φ (t) and the relation of this voltage are：

$\mathrm{\&phi;}\left(t\right)={\&Integral;}_0^t(U-R_{ct}{i}_m)dt$

Wherein, R_ctFor secondary winding in current transformer resistance, i_mFor secondary circuit exciting current.

4. a kind of excitation characteristic test method being applied to extra-high voltage TPY level current transformer as claimed in claim 1, it is special Levying is：In described step (2), equivalent voltage root-mean-square valve U under current transformer rated frequency f is unshakable in one's determination with secondary linkage winding The relation of magnetic flux φ is：

$U=\frac{2\mathrm{\&pi;}f}{\sqrt{2}}\&CenterDot;\mathrm{\&phi;}=\frac{2\mathrm{\&pi;}f}{\sqrt{2}}{\&Integral;}_0^t(U-R_{ct}{i}_m)dt$

Wherein, R_ctFor secondary winding in current transformer resistance, i_mFor secondary circuit exciting current.

5. a kind of excitation characteristic test method being applied to extra-high voltage TPY level current transformer as claimed in claim 1, it is special Levying is：In described step (3), when being tested, need the connection of turn-off current transformer and its secondary circuit, test a certain winding Excitation property when, other windings need open a way.

6. a kind of excitation characteristic test method being applied to extra-high voltage TPY level current transformer as claimed in claim 1, it is special Levying is：In described step (3), Current Transformer Secondary terminal is signal input part is signal acquisition terminal again, and transformer is secondary Side terminal carries out p-wire connection using clamp, and each test clamp of test lead all should be connected directly to current transformer On secondary terminals.

7. a kind of excitation characteristic test method being applied to extra-high voltage TPY level current transformer as claimed in claim 1, it is special Levying is：In described step (3), need during test the capacity of setting electric current transformer, class of accuracy, specified symmetrical short-circuit electric current multiple, Specified transient dimension factor, a time constant or/and secondary time constant parameter.