CN103235280B - Direct measuring method of magnetic saturation margin of current transformer based on scaling converter - Google Patents

Abstract

A method for directly measuring the magnetic saturation margin of a current transformer based on a proportional converter, in which the current proportional converter is cascaded with the current transformer TAx of the test object, and is connected with a transformer calibrator, a standard current transformer, and a load box Form a new circuit for measuring the magnetic saturation margin of the current transformer, read the error of the current transformer of the test object on the transformer calibrator, that is, the ratio difference f and the phase difference δ; complete the magnetic saturation of the current transformer of the test object margin measurement. The present invention utilizes the existing standard current transformer, transformer calibrator and other current transformer testing equipment, and can realize the direct measurement of the magnetic saturation margin of the current transformer. Make the standard current transformer and transformer calibrator work at 50% or 100% of the rated current to ensure the traceability of the value of the detection device. The method has the advantages of simple, economical, scientific, practical, strong operability and low cost. The invention is applicable to the technical field of current transformer detection.

Description

Direct Measurement Method of Current Transformer Magnetic Saturation Margin Based on Proportional Converter

technical field

The invention relates to a method for directly measuring the magnetic saturation margin of a current transformer based on a proportional converter, and belongs to the technical field of electric power metering current transformer detection.

Background technique

JJG1021-2007 "Verification Regulations for Power Transformers" §4.5 Magnetic saturation margin: "When the magnetic flux density of the core of the current transformer is equivalent to 1.5 times the rated current and rated load, the error should not be greater than the rated current and rated load. 1.5 times the error limit." Southern Power Grid requires that when the flux density of the current transformer core is equivalent to twice the rated current and rated load, the error should not be greater than 2 times the error limit under the rated current and rated load. . The current transformer verification device is mainly composed of: standard current transformer, transformer calibrator and load box, according to JJG313-2010 "Verification Regulations for Current Transformers for Measurement", JJG169-2010 "Verification Regulations for Transformer Calibrators" and JJF1264-2010 "Calibration Specification for Transformer Load Box" requires that standard current transformers, transformer calibrators and load boxes cannot meet the requirements of overloading to 1.5 times the rated current, and the existing current transformer verification devices cannot directly measure current transformers magnetic saturation margin. JJG1021-2007 "Verification Regulations for Power Transformers" §6.3.8.2 Indirect measurement: "If there is no standard device for measuring the error at 150% of the rated current point, it can be measured indirectly by adding a secondary load. The current selected during measurement Not less than 20% of the rated current. Set the selected current percentage point as m%, the rated secondary load of the current transformer is Z _B , and the leakage reactance of the secondary winding resistance is _{Z 2} . Percentage point m% and secondary load 2Z _B + Z ₂ , current percentage point 0.5 m% to measure the error of the current transformer, get f ₁ , δ ₁ and f ₂ , δ ₂ . Then in the secondary load (150/m) Z _B + (150/m-1) Z ₂ , measure the error of the current transformer at the current percentage point m%, and obtain f ₃ , δ ₃ . The error at the 150% current percentage point of the tested current transformer is calculated as follows:

…………⑴

…………⑵

The indirect measurement method needs to measure the impedance of the secondary winding of the test product and calculate Z ₂ ; configure the secondary load according to the value of Z ₂ ; however, the value of Z ₂ is a random value, and the traditional series load box can no longer meet the requirements, so a new impedance network must be developed; The secondary load box has a short board in principle, and it is difficult to deduct the resistance of the external wire. Therefore, it is of practical significance to study a scientific, accurate and operable direct detection method for the magnetic saturation margin of current transformers.

Invention content

The purpose of the present invention is, in order to solve the problem that the current detection equipment of the current transformer cannot meet the requirement of being overloaded to 1.5 times of the rated current, and the magnetic saturation margin of the current transformer cannot be carried out. The method is improved to realize the measurement of the magnetic saturation margin of the current transformer, and the invention provides a method for directly measuring the magnetic saturation margin of the current transformer.

The technical scheme of the present invention is, on the basis of the verification circuit of the existing "Current Transformer Verification Regulations", the current proportional converter is cascaded with the test current transformer TA _X , and the transformer calibrator, the standard current transformer , load box to form a new circuit for measuring the magnetic saturation margin of the current transformer, read the error of the current transformer of the test product on the transformer calibrator, that is, the ratio difference f and the phase difference δ; complete the current transformer of the test product The magnetic saturation margin measurement. f is the ratio difference, unit: (%); δ phase difference, unit: (′) points.

According to the verification circuit diagram (see Figure 1) of JJG1021-2007 "Current Transformer Verification Regulations", the present invention uses a current proportional converter with a transformation ratio of 10A/5A; an accuracy level of 0.01% and the current mutual inductance of the test product The transformer TA _X is cascaded and connected to form the direct measurement and detection wiring diagram of the magnetic saturation margin of the current transformer as shown in Figure 2.

The circuit for measuring the magnetic saturation margin of the current transformer in the present invention is: connect the secondary current terminal K2 of the standard current transformer _TA0 to the working current loop test terminal T0 of the transformer calibrator, and connect the secondary current terminal _K2 of the standard current transformer _TA0 to the secondary current terminal _K2 of the standard current transformer TA0 The secondary current polarity terminal K ₁ and the secondary current polarity terminal K ₂ of the current proportional converter are connected in parallel to the differential current loop test terminal K of the transformer calibrator, and the secondary current polarity terminal K ₁ of the current proportional converter is connected to the mutual inductance The working current loop test terminal T _X of the device calibrator; the primary current polarity terminal L ₁ of the standard current transformer TA _O is connected in series with the primary current polarity terminal L ₁ of the test current transformer TA _X , and the standard current transformer TA _O The primary current polarity terminal L ₂ of the test object current transformer TA _X is respectively connected to the output terminal of the current booster; the primary current polarity terminal _{L 1 of} the current proportional converter passes through the load box Z and the test object The secondary current polarity terminal K ₂ of the current transformer TA _X is connected, and the primary current polarity terminal L ₂ of the current proportional converter is connected with the secondary current polarity terminal K ₁ of the current transformer TA _X of the test object; transformer calibration The instrument differential current loop test terminal D is grounded.

According to GB1208-2006 "Current Transformer" §5.2 Rated secondary current standard value: "The rated secondary current standard value is: 1A and 5A." Therefore, the method of the present invention only considers the rated secondary current of 1A and 5A current transformers Measurement of magnetic saturation margin.

Assuming: the transformation ratio of the current transformer TA _X of the test product is K _x , then:

…………⑶

The equivalent transformation ratio after cascading the current proportional converter and the current transformer TA _X of the test object is K _x1 :

…………⑷

It can be seen from formula (4) that the current proportional converter with a transformation ratio of 10A/5A can reduce the secondary circuit current of the current proportional converter by 50% after being cascaded with the tested current transformer TA _X. That is, when the primary current of the current transformer under test is 150% of the rated primary current, the secondary current of the current proportional converter is:

According to the requirements of China Southern Power Grid, when the primary current of the current transformer under test is 200% of the rated primary current, the secondary current of the current proportional converter is:

To compare the test current transformer TA _X with the above transformation ratio, a standard current transformer with the same transformation ratio must be selected, that is, the transformation ratio of the standard current transformer must be K _x1 . In the same way, the secondary current of the standard current transformer can be reduced by 50%, so that the standard current transformer can work at 50% or 100% of the rated current. The method simultaneously solves the overcurrent problem of the transformer calibrator and the standard current transformer. The rated current of the load box can be selected according to twice the rated secondary current of the current transformer of the test product. When the rated secondary current is 5A, a load box with a rated current of 10A can be selected to solve the overcurrent problem of the load box.

The steps of the method for directly measuring the magnetic saturation margin of the current transformer of the present invention are as follows:

(1) The equipment used, the equipment used in the embodiment of the present invention has (1): a standard current transformer (0.02 level), a transformer calibrator (2 level), and a load with a rated current of 10A box (3 levels), a current proportional converter with a transformation ratio of 10A/5A and an accuracy level of 0.01%;

(2) Carry out wiring according to the wiring method shown in Figure 2;

(3) Set the load box according to the parameter "rated secondary load" on the nameplate of the current transformer of the test product;

(4) Raise the primary current of the current transformer under test to 150% of the rated primary current according to the requirements of the regulations. At this time, the secondary current of the standard current transformer and current proportional converter is 75% of the rated secondary current. Or increase the primary current of the test current transformer to 200% of the rated primary current according to the requirements of China Southern Power Grid Corporation. At this time, the secondary current of the standard current transformer and current proportional converter is 100% of the rated secondary current.

(5) Read the errors f and δ of the current transformer of the test product on the transformer calibrator, f is the ratio difference, unit: (%); δ phase difference, unit: (′) minutes.

(6) Reduce the primary current of the current transformer under test to 0.

(7) Complete the measurement of the magnetic saturation margin of the current transformer of the test product.

The beneficial effect of the present invention is that when testing the magnetic saturation margin of the current transformer of the test product, a standard current transformer (0.02 level), a transformer calibrator (2 levels), and a rated current transformer of 10A are used. The load box (3 levels), a current proportional converter with a transformation ratio of 10A/5A and an accuracy level of 0.01%. The detection circuit for direct measurement of the magnetic saturation margin of the current transformer is formed, and the current transformer verification equipment such as the existing standard current transformer and the transformer calibrator can be used to realize the direct measurement of the magnetic saturation margin of the current transformer. Make the standard current transformer and transformer calibrator work at 50% or 100% of the rated current to ensure the traceability of the value of the detection device. The method has the advantages of simple, economical, scientific, practical, strong operability and low cost.

The invention is applicable to the technical field of current transformer detection.

Description of drawings

Figure 1 is a conventional current transformer detection wiring diagram;

Figure 2 is a wiring diagram for direct measurement and detection of the magnetic saturation margin of a current transformer;

Symbols in the figure: TA ₀ is the standard current transformer; TA _x is the test current transformer; TA _T is the current proportional converter; Z is the load box of the current transformer; I ₀ is the secondary current of the standard current transformer; I _x I T is the secondary current of the current transformer of the test product; I _T is the primary current _of the current proportional converter; ΔI is the difference current of the measurement circuit; I ₁ is the primary current of the detection circuit _; Transformer and current transformer primary current polarity terminals; K ₁ , K ₂ are standard current transformer, current proportional converter and secondary current polarity terminals of current transformer under test; T ₀ , T _X are mutual inductance The working current loop test terminals of the transformer calibrator; K and D are the differential current loop test terminals of the transformer calibrator.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings.

1. The equipment used in this method:

One standard current transformer (level 0.02), one transformer calibrator (level 2), one load box (level 3) with a rated current of 10A, and one with a transformation ratio of 10A/5A; the accuracy level is 0.01% class current proportional converter.

2. Wiring method

(1) Select the transformation ratio of the standard current transformer:

Assume: the transformation ratio of the current transformer under test is I _1n /I _2n , and the transformation ratio of the standard current transformer is 2I _1n /I _2n . For example: if the transformation ratio of the test current transformer is 100A/5A, then the transformation ratio of the standard current transformer is 200A/5A.

(2) Perform wiring according to the wiring diagram of the direct measurement method of the magnetic saturation margin of the current transformer, see Figure 2;

Connect the secondary current terminal K ₂ of the standard current transformer TA _O to the working current loop test terminal T ₀ of the transformer calibrator, and connect the secondary current polarity terminal K ₁ of the standard current transformer TA _O to the secondary current proportional converter Current polarity terminal K ₂ is connected to the differential current loop test terminal K of the transformer calibrator in parallel, and the secondary current polarity terminal K ₁ of the current proportional converter is connected to the working current loop test terminal T _X of the transformer calibrator; standard current The primary current polarity terminal L ₁ of the transformer TA _O is connected in series with the primary current polarity terminal L ₁ of the test current transformer TA _X , and the primary current polarity terminal L ₂ of the standard current transformer TA _O is connected with the test current transformer The primary current polarity terminal L ₂ of TA _X is respectively connected to the output terminal of the current booster; the primary current polarity terminal L ₁ of the current proportional converter passes through the load box Z and the secondary current polarity terminal K ₂ of the test current transformer TA _X The primary current polarity terminal L ₂ of the current proportional converter is connected with the secondary current polarity terminal K ₁ of the current transformer TA _X of the test object; the differential current loop test terminal D of the transformer calibrator is grounded.

3. Conduct testing according to the requirements of relevant regulations.

(1) Set the load box according to the parameter "rated secondary load" on the nameplate of the current transformer of the test product;

First calculate the impedance value of the load box:

According to the principle of electrical engineering:

…………⑸

For example: rated secondary load of the current transformer under test: S=20VA; rated secondary current: I=5A, then:

(2) Set the load box range according to the calculation result;

(3) Raise the primary current of the current transformer under test to 150% of the rated primary current according to the requirements of the regulations. At this time, the secondary current of the standard current transformer and current proportional converter is 75% of the rated secondary current. Or increase the primary current of the test current transformer to 200% of the rated primary current according to the requirements of China Southern Power Grid Corporation. At this time, the secondary current of the standard current transformer and current proportional converter is 100% of the rated secondary current.

(4) Read the errors f and δ of the current transformer of the test product on the transformer calibrator. f is the ratio difference, unit: (%); δ phase difference, unit: (′) points;

(5) Reduce the primary current of the current transformer under test to 0;

(6) Complete the measurement of the magnetic saturation margin of the current transformer of the sample.

Claims (2)

1. A method for directly measuring the magnetic saturation margin of a current transformer based on a proportional converter, characterized in that, the method is cascaded with the current proportional converter and the test product current transformer TAx, and is connected with a transformer calibrator, a standard The current transformer TA _O and the load box Z form a new circuit for measuring the magnetic saturation margin of the current transformer, and read the error of the current transformer TAx of the test product on the transformer calibrator, that is, the ratio difference f and the phase difference δ; Complete the magnetic saturation margin measurement of the current transformer TAx of the sample; The circuit for measuring the magnetic saturation margin of the current transformer is that the secondary current terminal _K2 of the standard current transformer _TA0 is connected to the working current loop test terminal _T0 of the transformer calibrator, and the secondary current terminal K2 of the standard current transformer _TA0 The current polarity terminal K ₁ and the secondary current polarity terminal K ₂ of the current proportional converter are connected in parallel to the differential current loop test terminal K of the transformer calibrator, and the secondary current polarity terminal K ₁ of the current proportional converter is connected to the transformer The test terminal T _X of the working current loop of the calibrator; the primary current polarity terminal L ₁ of the standard current transformer TA _O is connected in series with the primary current polarity terminal L 1 of the current transformer TA _X of the test object, and the primary current polarity terminal L ₁ of the standard current transformer TA _O The primary current polarity terminal L ₂ and the primary current polarity terminal L ₂ of the current transformer TA _X of the test object are respectively connected to the output terminal of the current booster; the primary current polarity terminal L ₁ of the current proportional converter passes through the load box Z and the current of the test object The secondary current polarity terminal K ₂ of the transformer TA _X is connected, and the primary current polarity terminal L ₂ of the current proportional converter is connected with the secondary current polarity terminal K ₁ of the test current transformer TA _X ; the transformer calibrator The differential current loop test terminal D is grounded. 2. a kind of current transformer magnetic saturation margin direct measurement method based on proportional converter according to claim 1, is characterized in that, the step of current transformer magnetic saturation margin direct measurement method is as follows: (1) Equipment used: a standard current transformer TA _O 0.02 level; a transformer calibrator level 2; a load box with a rated current of 10A level Z3; a transformation ratio of 10A/5A, accurate A current proportional converter with a degree of 0.01%; (2) Wiring according to the circuit for measuring the magnetic saturation margin of the current transformer; (3) Set the load box Z according to the parameter "rated secondary load" on the TAx nameplate of the test product current transformer; (4) Raise the primary current of the current transformer TAx of the test product to 150% of the rated primary current, at this time, the secondary current of the standard current transformer TA _O and the current proportional converter is 75% of the rated secondary current; or The primary current of the test current transformer TAx rises to 200% of the rated primary current, at this time, the secondary current of the standard current transformer TA _O and the current proportional converter is 100% of the rated secondary current; (5) Read the error f and δ of the current transformer TAx of the test product on the transformer calibrator; f is the ratio difference, unit: %; δ is the phase difference, unit: minute; (6) Reduce the current to 0; (7) Complete the measurement of the magnetic saturation margin of the current transformer TAx of the sample.