1 Overview
Measuring transformers and their test instruments are classical electrical instruments and have been developed for about a century now. For such instruments, whether there is a possible development and innovation answer is positive. Because with the development of production technology, on the one hand put forward all kinds of new requirements for transformers, on the other hand, new materials and new technologies have improved the performance of transformers.
An important way to improve the performance of the measuring transformer is to compensate for the error. Therefore, all transformers use corresponding compensation methods to increase their accuracy. The research on compensation methods began in the 1920s and many compensation methods were proposed successively. They mainly include two-stage current transformers and load compensation methods, zero-flux current transformers and zero magnetic flux compensation methods, and magnetic shunt compensation. Principles and so on.
In current transformers used in power systems, the simplest number of turns or fractional åŒ compensation is used, and the above complex compensation methods are basically not used. In precision current transformers, in addition to using branch number compensation, multi-capacitance (lithium ion capacitor market prospects) is generally used to compensate the phase difference, and only magnetically coupled transformer calibrators use dual-stage current transformers that match them. As a standard current transformer. In voltage transformers, what is actually used is the number of turns or fractional compensation.
In the 40s and 50s, current transformers produced in the former Soviet Union used anti-excitation and magnetic shunt compensation for ring cores and square-stacked iron core transformers, respectively.
Transformer calibrator is the main test instrument for transformers. It was a direct comparison in the early days. Because the instrument was limited by the accuracy of the resistance and capacitance components, it was later made into a differential type, which simplified the line and structure of the calibrator and improved its performance. Its accuracy as long as there are 13 can meet the requirements.
2. Transformer Development and Innovation
21 Ring Magnetic Shunt Compensated Current Transformer With the development of cold rolling silicon steel sheet production in the 50's, in the various cold rolled silicon steel cores, the toroidal core made of rolled steel core has the highest magnetic permeability, and thus it is in the current transformer product. First, cold-rolled silicon steel annular cores are used to replace the annular cores and square-shaped laminated cores of the original hot rolled silicon steel sheet. This requires the study of new compensation methods that are compatible with this and have better results. To this end, the author used the transformer calibrator to test the relevant parameters of the transformer and the core. Based on the original anti-excitation compensation and magnetic shunt compensation, the principle of the ring magnetic shunt compensation structure and its calculation formula were proposed. The compensation method can not only compensate the ratio difference and phase difference of the current transformer, but also improve the linearity of the ratio difference and phase difference, and thus develops a ring magnetic shunt compensation current transformer. In 1968, it was adopted for the unified design of transformers in China and was included in the Electrical Engineering Handbook. It has been produced so far and has become the largest current transformer in the country. The current annual output reaches several million units and the output value is nearly 100 million yuan.
22 High-accuracy current transformers In the 1960s, the highest accuracy of domestic transformers was 01, while high-accuracy transformers of level 005 and above were all imported.
After detailed analysis of various compensation methods, the author proposes a low-flux RC compensation method for the characteristics of small changes in the secondary load of high-accuracy current transformers. That is, using an auxiliary core to bear most of the load, so that the main core load is small, the magnetic flux is low, coupled with the capacitance compensation, so that the error is significantly reduced. Based on this, it has been developed into a high-accuracy current transformer with good performance, small size and light weight. Based on this research, the current methods for error compensation of various current transformers are summarized, and the principle of error magnetic potential compensation and potential compensation for current transformers and their calculation formulae are proposed. In this way, a systematic and complete understanding of the current transformer error compensation method is derived, many new compensation methods are deduced from it, and a more reasonable and effective compensation method is selected according to actual needs. Therefore, the 001-005 high-accuracy current transformers with various specifications such as 01100A/5A and 55000A/5A have been developed to meet domestic needs.
In 1991, West et al. proposed a new two-stage compensation circuit to compensate for the fixed double-stage load to increase the accuracy of the current transformer and verify it with a sampler with a single current ratio of 100A/1A. Similar compensation methods have been used domestically in high-accuracy current transformers as early as the 1980s. This shows that the development and innovation of high-accuracy current transformers at home and abroad are different and have similarities.
23 High-accuracy voltage transformer Based on the research results of current transformers, systematically studies the error compensation of voltage transformers, and proposes principles and formulas for error current compensation and voltage compensation of voltage transformers, filling in this research. Whitespace. The voltage transformer no-load error compensation method was derived from this, and a 001-level high-accuracy voltage transformer was developed accordingly.
In the development of high-voltage, high-accuracy voltage transformers, the errors caused by distributed capacitance currents in high-voltage multi-voltage-to-voltage transformers were mainly discussed. Two schemes for one tap and two taps were proposed and analyzed. The advantages and disadvantages and the corresponding measures taken were developed into a 310kV/01kV high accuracy voltage transformer.
Since the 1970s, high-accuracy voltage transformers of various specifications from grades 001 to 005 of domestic 10kV and below have met domestic needs.
24 Current transformers with current transformers and voltage transformers with voltage boosters Precision current transformers and current transformers or step-up transformers (ie small single-phase power transformers) are often used together. Square laminated cores for small transformers Cold rolled silicon steel ring cores have been used. In this way, it is possible to integrate transformers and transformers. Through research, a new type 001-005 current transformer with a current transformer and a voltage transformer with a booster were proposed and developed. The current transformer and the current transformer share the primary (upstream output) winding; the voltage transformer and the booster share a core. It can be used as a standard transformer to verify the accuracy of 005 level and below the transformer, with a simple wiring, easy to use and other characteristics, has been widely used in the country.
3. Development and Innovation of Current and Voltage Ratio Standards
To verify a high-accuracy transformer, a ratio of 0002 and above is required. Current ratio standards include two-stage current transformers, zero-flux current transformers, and current comparators. The voltage ratio standards mainly include two-stage voltage transformers of sense voltage dividers and resistors or capacitor voltage dividers.
31 Current ratio standard In order to test high-accuracy current transformers, in the 1960s, on the basis of low-flux compensation, methods and structures for adjusting zero-flux were studied, and zero-flux current transformers and their zero-setting lines were proposed. Make the current transformer really run under zero flux, with high accuracy. At the same time, with reference to the current comparators (which also operate at zero flux, which is equivalent to the zero-flux current transformer) and their verification circuits, the zero flux magnetic current transformer self-test of 0110000A/5A was developed. The system has the highest accuracy of 05X10-6.
The analysis of the above three current ratio standards shows that in addition to the line described in [1] (a potential compensation line and no detection winding), the zero-flux current transformer also has multiple types of magnetic potential compensation and potential compensation. line. The two-stage current transformer and the compensating current comparator have the same basic circuit. From the former to the latter, after about 40 years of development, a detection winding is added to monitor the zero flux of the current comparator. It is this difference that the former operates at low magnetic flux and the latter operates at zero flux, so the accuracy of the latter is an order of magnitude higher than the former. The compensated current comparator plus zero-adjustment structure can also be a two-stage compensated zero-flux current transformer. Therefore, whether it is a general current transformer or a two-phase current transformer or a current comparator, if there is a detection winding and the corresponding zero-adjustment structure, it can become a zero-flux current transformer.
On this basis, the structure and compensation methods for improving the accuracy of the current comparator are studied, a new zero-adjustment structure is designed, and a variety of current comparators and their self-checking systems are developed. Its performance: the highest accuracy reaches 02X10-6; the primary current reaches 01A at minimum, the accuracy is 5X10-6, the maximum reaches 5kA, the accuracy is 1X10-6; at the end of the 80's, it was compared with the German current comparator. : The difference in error is only 05X10-6. The author also communicated with the Canadian authors of the literature.
In the 1990s, according to the needs of users, it also developed a 05500A/5A IF current comparator self-checking system with an accuracy of 5X10-52X10-6.
Since the 1970s, China has produced 0002 or 0001 class 01100A/5A and 55000A/5A (or 10000A/5A) current comparators more than 200 sets and more than 10 sets of current comparators self-checking system. There are many current comparators and their self-checking systems in China, which is the highest in the world.
32 Voltage Proportional Standard Similarly, in order to verify a high-accuracy voltage transformer, the low-voltage double-stage voltage transformer was developed by referring to the principle of a two-stage current transformer. In the research of high-voltage two-stage voltage transformers, the problem of leakage current under high voltage was mainly discussed. Since 1975, a series of double-stage voltage transformers with various voltages of 50V35kV have been developed, with an accuracy of 0001 or higher. 0002 level. On this basis, a compensation device was used to develop a voltage ratio of (110/3) kV and (220/3) kV. The accuracy is 0002 and 0005 respectively.
In the development of the inductive voltage divider, based on the domestic common reference potential verification method, the reference potential is integrated with the inductive voltage divider. In 1987, a multi-disc induction divider product with self-calibration was developed and its accuracy was improved. Achieved 1X10-6 (at the same time foreign countries the same size of the sensing voltage divider accuracy is 2X10-6, and can not self-school), can be used as the highest proportion of voltage ratio of the use of units.
The above-mentioned voltage ratio standards of various specifications below 10 kV have been widely used domestically since the 1980s.
4. Transformer calibrator development and innovation
Before the 1960s, the domestic transformer calibrators used were not imported from abroad or were imitations of foreign ones, and these calibrators were only able to certify transformers below 01. With the successful development of high-accuracy transformers with grade above 005 in China, it is urgent to be able to calibrate calibrators with high accuracy transformers. At the same time, there are current comparators and their verification circuits in foreign countries. However, such circuits are specifically designed for the verification of high-accuracy current transformers. In order to expand the function of the comparator test circuit, after years of exploration, the use of current comparator to expand the current transformer error limit, use different resistance to change the voltage transformer error limit, and thus successfully developed the first domestic Instrument calibrator? ? ? The comparison ceremonial transformer calibrator can test current transformers and voltage transformers from level 10 to level 001. The two-stage current transformer originally used only for magnetic coupling in Austria can also be used on a comparison ceremonial calibrator, which provides favorable conditions for the development of a two-stage current transformer. The new calibrator not only has a simple structure, a wide range of applications, but also performs well. It has quickly replaced all transformer calibrators in China and has been widely used.
For the verification of the transformer calibrator, domestically used in the 70 years ago, the original Soviet Union put forward a method for the verification of the parts of their products, and verified the calibrators of the corresponding models. In the 1970s, China proposed the use of an overall verification method that can use a unified verification method for different types of calibrators. Based on this, we have successfully developed an overall verification device for transformer calibrators. It consists of a single-phase power supply and a standard transformer calibrator. The latter is the above comparison ceremonial transformer calibrator. The entire device has been carefully designed and manufactured, and its accuracy has reached level 01. It can be used to verify all 13 transformer calibrators.
In the 1980s, a variety of applied electronic circuits and microcomputer-based automatic transformer calibrators (referred to as digital calibrators) began to appear abroad. In the 1990s, various kinds of digital calibrators have also been successfully developed in the country, and the test of transformers has embarked on the road of automatic detection. And created a microcomputer in the transformer and its test equipment applications.
As mentioned above, the use of a general current comparator with an accuracy of 0002 enables the verification of high accuracy current transformers, but the use of comparators must be used to verify the line. At this time, if the transformer is used to verify the circuit, the comparator becomes a two-stage current transformer, and the accuracy is reduced to 005 to 001. Comparator verification lines use comparison ceremonial transformer calibrators and still need to manually adjust the balance. The digital calibrator can be tested without adjusting the balance, and there is no comparator verification circuit. At home in the late 1980s, a self-balanced digital calibrator with a comparator test circuit was produced. The performance is not ideal and needs improvement. Therefore, it is imperative to be able to verify high accuracy current transformers on all digital calibrators. After years of hard work, it has developed 0002-level 01120A/5A and 510000A/5A dual-phase current transformers that can be used for all calibrators. In this way, a highly accurate current transformer is tested for automatic detection. At the same time, the accuracy of the 550A/5A two-stage current transformer has reached 1X10-6.
The principle of a two-stage current transformer was proposed in 1922. It was used in a magnetically coupled transformer calibrator (accuracy 001), and it has been further developed and applied in the 1990s.
5. Outlook for Development and Innovation
In summary, since the end of the 1950s, with the development of production and market demand, domestic precision transformers and their test instruments have been greatly developed and innovated. The precision transformers and their test instruments used by various experimental research institutes in China are scientific and technological achievements in the past 20-30 years. With the widespread use of computers, there will be far-reaching implications for transformers and their test instruments.
51 Secondary low-current or small-voltage transformers and their test instruments require the voltage of the input signal to be 055V, so the current and voltage are required to be converted to 055V by the transformer.
For current transformers, the smaller the secondary current, the smaller the capacity. The mA current transformer with a secondary current of 25100 mA, the current/voltage converter converted to the above voltage, and the small voltage transformer with a secondary voltage of 055 V have appeared and are required to be equipped with corresponding test instruments.
At present, the primary current of the above-mentioned small current transformer is mostly 5A, and the primary voltage of the small voltage transformer is mostly 100V, which is mainly used as a component of an electrical instrument and a control system. In the future, it may be developed as a transformer directly used in the power system. The current ratio is 51000A/005A and the voltage ratio is 10010000V/5V.
There are two trends in the calibrators that test these transformers: one is to develop a calibrator with a small current and a small voltage, and the second is to use an existing calibrator or slightly improved to use a 5A or 100V supply. The former may have more calibrator specifications, while the latter will require calibrator direct reading. For the verification of a small current transformer, if a current comparator is used and a comparison ceremonial calibrator is used, it can be directly read by one power supply, which is a better verification method.
There are two schemes for verifying the current/voltage converter: First, the entire converter is used to verify the tested converter. The verification is more convenient and the verification result is intuitive, but it is difficult to formulate a high-accuracy resistor and the existing calibrator is The resolution used to certify the converter is not enough. It is only suitable for the verification of low-level converters or linear converters only; second, the current transformers and resistors of the converter are separately verified, which is relatively easy to implement, that is, the above-mentioned standard converters. It also needs to be individually verified.
No matter which test method is adopted, a new set of standard transformers or proportional standards are needed. At the same time, it is necessary to study the connection of these new proportional standards with the original current ratio of 5A.
52 Improving the level of automation and intelligence of transformer testing In the testing of common transformers, there have been a variety of automatic transformer calibration tables made using high-tech microcomputers, and some have been able to perform data processing on test results. . Its level of automation and intelligence can be further improved, and testing is easier.
At present, the verification of the current comparator self-checking system and the detection of the inductive voltage divider still rely on manual operations. In particular, the workload of the self-inspection system is large and cumbersome, and it needs to be automated and intelligent.
53 Field calibrator and virtual calibrator Transformer verification In addition to the transformer calibrator, a standard transformer and power supply are also required. When verifying large current transformers and high voltage voltage transformers at the substation site, it is necessary to carry the above-mentioned cumbersome testing equipment. In order to facilitate the verification of the field transformer, the Australian Red Phase recently proposed an on-site current transformer calibrator that does not use standard current transformers and current sources. Its working principle is based on the current transformer error calculation formula, the corresponding parameters are determined and calculated by the microcomputer software to achieve the current transformer error measurement. This on-site current transformer calibrator calculates the transformer error using the measured parameters and can deduct the compensation value. However, the verification of this calibrator still needs further exploration and improvement. In this way, it is possible to further expand the scope of application of the new principle calibrator.
In addition, the use of computer-generated virtual calibrators is another direction for the development and innovation of calibrators.
The above vision is only a small part of it. This requires a closer integration of transformers' electrical measurement expertise and computer expertise, and looks forward to the close cooperation and joint efforts of related professional scientific and technical personnel to achieve greater development.
Measuring transformers and their test instruments are classical electrical instruments and have been developed for about a century now. For such instruments, whether there is a possible development and innovation answer is positive. Because with the development of production technology, on the one hand put forward all kinds of new requirements for transformers, on the other hand, new materials and new technologies have improved the performance of transformers.
An important way to improve the performance of the measuring transformer is to compensate for the error. Therefore, all transformers use corresponding compensation methods to increase their accuracy. The research on compensation methods began in the 1920s and many compensation methods were proposed successively. They mainly include two-stage current transformers and load compensation methods, zero-flux current transformers and zero magnetic flux compensation methods, and magnetic shunt compensation. Principles and so on.
In current transformers used in power systems, the simplest number of turns or fractional åŒ compensation is used, and the above complex compensation methods are basically not used. In precision current transformers, in addition to using branch number compensation, multi-capacitance (lithium ion capacitor market prospects) is generally used to compensate the phase difference, and only magnetically coupled transformer calibrators use dual-stage current transformers that match them. As a standard current transformer. In voltage transformers, what is actually used is the number of turns or fractional compensation.
In the 40s and 50s, current transformers produced in the former Soviet Union used anti-excitation and magnetic shunt compensation for ring cores and square-stacked iron core transformers, respectively.
Transformer calibrator is the main test instrument for transformers. It was a direct comparison in the early days. Because the instrument was limited by the accuracy of the resistance and capacitance components, it was later made into a differential type, which simplified the line and structure of the calibrator and improved its performance. Its accuracy as long as there are 13 can meet the requirements.
2. Transformer Development and Innovation
21 Ring Magnetic Shunt Compensated Current Transformer With the development of cold rolling silicon steel sheet production in the 50's, in the various cold rolled silicon steel cores, the toroidal core made of rolled steel core has the highest magnetic permeability, and thus it is in the current transformer product. First, cold-rolled silicon steel annular cores are used to replace the annular cores and square-shaped laminated cores of the original hot rolled silicon steel sheet. This requires the study of new compensation methods that are compatible with this and have better results. To this end, the author used the transformer calibrator to test the relevant parameters of the transformer and the core. Based on the original anti-excitation compensation and magnetic shunt compensation, the principle of the ring magnetic shunt compensation structure and its calculation formula were proposed. The compensation method can not only compensate the ratio difference and phase difference of the current transformer, but also improve the linearity of the ratio difference and phase difference, and thus develops a ring magnetic shunt compensation current transformer. In 1968, it was adopted for the unified design of transformers in China and was included in the Electrical Engineering Handbook. It has been produced so far and has become the largest current transformer in the country. The current annual output reaches several million units and the output value is nearly 100 million yuan.
22 High-accuracy current transformers In the 1960s, the highest accuracy of domestic transformers was 01, while high-accuracy transformers of level 005 and above were all imported.
After detailed analysis of various compensation methods, the author proposes a low-flux RC compensation method for the characteristics of small changes in the secondary load of high-accuracy current transformers. That is, using an auxiliary core to bear most of the load, so that the main core load is small, the magnetic flux is low, coupled with the capacitance compensation, so that the error is significantly reduced. Based on this, it has been developed into a high-accuracy current transformer with good performance, small size and light weight. Based on this research, the current methods for error compensation of various current transformers are summarized, and the principle of error magnetic potential compensation and potential compensation for current transformers and their calculation formulae are proposed. In this way, a systematic and complete understanding of the current transformer error compensation method is derived, many new compensation methods are deduced from it, and a more reasonable and effective compensation method is selected according to actual needs. Therefore, the 001-005 high-accuracy current transformers with various specifications such as 01100A/5A and 55000A/5A have been developed to meet domestic needs.
In 1991, West et al. proposed a new two-stage compensation circuit to compensate for the fixed double-stage load to increase the accuracy of the current transformer and verify it with a sampler with a single current ratio of 100A/1A. Similar compensation methods have been used domestically in high-accuracy current transformers as early as the 1980s. This shows that the development and innovation of high-accuracy current transformers at home and abroad are different and have similarities.
23 High-accuracy voltage transformer Based on the research results of current transformers, systematically studies the error compensation of voltage transformers, and proposes principles and formulas for error current compensation and voltage compensation of voltage transformers, filling in this research. Whitespace. The voltage transformer no-load error compensation method was derived from this, and a 001-level high-accuracy voltage transformer was developed accordingly.
In the development of high-voltage, high-accuracy voltage transformers, the errors caused by distributed capacitance currents in high-voltage multi-voltage-to-voltage transformers were mainly discussed. Two schemes for one tap and two taps were proposed and analyzed. The advantages and disadvantages and the corresponding measures taken were developed into a 310kV/01kV high accuracy voltage transformer.
Since the 1970s, high-accuracy voltage transformers of various specifications from grades 001 to 005 of domestic 10kV and below have met domestic needs.
24 Current transformers with current transformers and voltage transformers with voltage boosters Precision current transformers and current transformers or step-up transformers (ie small single-phase power transformers) are often used together. Square laminated cores for small transformers Cold rolled silicon steel ring cores have been used. In this way, it is possible to integrate transformers and transformers. Through research, a new type 001-005 current transformer with a current transformer and a voltage transformer with a booster were proposed and developed. The current transformer and the current transformer share the primary (upstream output) winding; the voltage transformer and the booster share a core. It can be used as a standard transformer to verify the accuracy of 005 level and below the transformer, with a simple wiring, easy to use and other characteristics, has been widely used in the country.
3. Development and Innovation of Current and Voltage Ratio Standards
To verify a high-accuracy transformer, a ratio of 0002 and above is required. Current ratio standards include two-stage current transformers, zero-flux current transformers, and current comparators. The voltage ratio standards mainly include two-stage voltage transformers of sense voltage dividers and resistors or capacitor voltage dividers.
31 Current ratio standard In order to test high-accuracy current transformers, in the 1960s, on the basis of low-flux compensation, methods and structures for adjusting zero-flux were studied, and zero-flux current transformers and their zero-setting lines were proposed. Make the current transformer really run under zero flux, with high accuracy. At the same time, with reference to the current comparators (which also operate at zero flux, which is equivalent to the zero-flux current transformer) and their verification circuits, the zero flux magnetic current transformer self-test of 0110000A/5A was developed. The system has the highest accuracy of 05X10-6.
The analysis of the above three current ratio standards shows that in addition to the line described in [1] (a potential compensation line and no detection winding), the zero-flux current transformer also has multiple types of magnetic potential compensation and potential compensation. line. The two-stage current transformer and the compensating current comparator have the same basic circuit. From the former to the latter, after about 40 years of development, a detection winding is added to monitor the zero flux of the current comparator. It is this difference that the former operates at low magnetic flux and the latter operates at zero flux, so the accuracy of the latter is an order of magnitude higher than the former. The compensated current comparator plus zero-adjustment structure can also be a two-stage compensated zero-flux current transformer. Therefore, whether it is a general current transformer or a two-phase current transformer or a current comparator, if there is a detection winding and the corresponding zero-adjustment structure, it can become a zero-flux current transformer.
On this basis, the structure and compensation methods for improving the accuracy of the current comparator are studied, a new zero-adjustment structure is designed, and a variety of current comparators and their self-checking systems are developed. Its performance: the highest accuracy reaches 02X10-6; the primary current reaches 01A at minimum, the accuracy is 5X10-6, the maximum reaches 5kA, the accuracy is 1X10-6; at the end of the 80's, it was compared with the German current comparator. : The difference in error is only 05X10-6. The author also communicated with the Canadian authors of the literature.
In the 1990s, according to the needs of users, it also developed a 05500A/5A IF current comparator self-checking system with an accuracy of 5X10-52X10-6.
Since the 1970s, China has produced 0002 or 0001 class 01100A/5A and 55000A/5A (or 10000A/5A) current comparators more than 200 sets and more than 10 sets of current comparators self-checking system. There are many current comparators and their self-checking systems in China, which is the highest in the world.
32 Voltage Proportional Standard Similarly, in order to verify a high-accuracy voltage transformer, the low-voltage double-stage voltage transformer was developed by referring to the principle of a two-stage current transformer. In the research of high-voltage two-stage voltage transformers, the problem of leakage current under high voltage was mainly discussed. Since 1975, a series of double-stage voltage transformers with various voltages of 50V35kV have been developed, with an accuracy of 0001 or higher. 0002 level. On this basis, a compensation device was used to develop a voltage ratio of (110/3) kV and (220/3) kV. The accuracy is 0002 and 0005 respectively.
In the development of the inductive voltage divider, based on the domestic common reference potential verification method, the reference potential is integrated with the inductive voltage divider. In 1987, a multi-disc induction divider product with self-calibration was developed and its accuracy was improved. Achieved 1X10-6 (at the same time foreign countries the same size of the sensing voltage divider accuracy is 2X10-6, and can not self-school), can be used as the highest proportion of voltage ratio of the use of units.
The above-mentioned voltage ratio standards of various specifications below 10 kV have been widely used domestically since the 1980s.
4. Transformer calibrator development and innovation
Before the 1960s, the domestic transformer calibrators used were not imported from abroad or were imitations of foreign ones, and these calibrators were only able to certify transformers below 01. With the successful development of high-accuracy transformers with grade above 005 in China, it is urgent to be able to calibrate calibrators with high accuracy transformers. At the same time, there are current comparators and their verification circuits in foreign countries. However, such circuits are specifically designed for the verification of high-accuracy current transformers. In order to expand the function of the comparator test circuit, after years of exploration, the use of current comparator to expand the current transformer error limit, use different resistance to change the voltage transformer error limit, and thus successfully developed the first domestic Instrument calibrator? ? ? The comparison ceremonial transformer calibrator can test current transformers and voltage transformers from level 10 to level 001. The two-stage current transformer originally used only for magnetic coupling in Austria can also be used on a comparison ceremonial calibrator, which provides favorable conditions for the development of a two-stage current transformer. The new calibrator not only has a simple structure, a wide range of applications, but also performs well. It has quickly replaced all transformer calibrators in China and has been widely used.
For the verification of the transformer calibrator, domestically used in the 70 years ago, the original Soviet Union put forward a method for the verification of the parts of their products, and verified the calibrators of the corresponding models. In the 1970s, China proposed the use of an overall verification method that can use a unified verification method for different types of calibrators. Based on this, we have successfully developed an overall verification device for transformer calibrators. It consists of a single-phase power supply and a standard transformer calibrator. The latter is the above comparison ceremonial transformer calibrator. The entire device has been carefully designed and manufactured, and its accuracy has reached level 01. It can be used to verify all 13 transformer calibrators.
In the 1980s, a variety of applied electronic circuits and microcomputer-based automatic transformer calibrators (referred to as digital calibrators) began to appear abroad. In the 1990s, various kinds of digital calibrators have also been successfully developed in the country, and the test of transformers has embarked on the road of automatic detection. And created a microcomputer in the transformer and its test equipment applications.
As mentioned above, the use of a general current comparator with an accuracy of 0002 enables the verification of high accuracy current transformers, but the use of comparators must be used to verify the line. At this time, if the transformer is used to verify the circuit, the comparator becomes a two-stage current transformer, and the accuracy is reduced to 005 to 001. Comparator verification lines use comparison ceremonial transformer calibrators and still need to manually adjust the balance. The digital calibrator can be tested without adjusting the balance, and there is no comparator verification circuit. At home in the late 1980s, a self-balanced digital calibrator with a comparator test circuit was produced. The performance is not ideal and needs improvement. Therefore, it is imperative to be able to verify high accuracy current transformers on all digital calibrators. After years of hard work, it has developed 0002-level 01120A/5A and 510000A/5A dual-phase current transformers that can be used for all calibrators. In this way, a highly accurate current transformer is tested for automatic detection. At the same time, the accuracy of the 550A/5A two-stage current transformer has reached 1X10-6.
The principle of a two-stage current transformer was proposed in 1922. It was used in a magnetically coupled transformer calibrator (accuracy 001), and it has been further developed and applied in the 1990s.
5. Outlook for Development and Innovation
In summary, since the end of the 1950s, with the development of production and market demand, domestic precision transformers and their test instruments have been greatly developed and innovated. The precision transformers and their test instruments used by various experimental research institutes in China are scientific and technological achievements in the past 20-30 years. With the widespread use of computers, there will be far-reaching implications for transformers and their test instruments.
51 Secondary low-current or small-voltage transformers and their test instruments require the voltage of the input signal to be 055V, so the current and voltage are required to be converted to 055V by the transformer.
For current transformers, the smaller the secondary current, the smaller the capacity. The mA current transformer with a secondary current of 25100 mA, the current/voltage converter converted to the above voltage, and the small voltage transformer with a secondary voltage of 055 V have appeared and are required to be equipped with corresponding test instruments.
At present, the primary current of the above-mentioned small current transformer is mostly 5A, and the primary voltage of the small voltage transformer is mostly 100V, which is mainly used as a component of an electrical instrument and a control system. In the future, it may be developed as a transformer directly used in the power system. The current ratio is 51000A/005A and the voltage ratio is 10010000V/5V.
There are two trends in the calibrators that test these transformers: one is to develop a calibrator with a small current and a small voltage, and the second is to use an existing calibrator or slightly improved to use a 5A or 100V supply. The former may have more calibrator specifications, while the latter will require calibrator direct reading. For the verification of a small current transformer, if a current comparator is used and a comparison ceremonial calibrator is used, it can be directly read by one power supply, which is a better verification method.
There are two schemes for verifying the current/voltage converter: First, the entire converter is used to verify the tested converter. The verification is more convenient and the verification result is intuitive, but it is difficult to formulate a high-accuracy resistor and the existing calibrator is The resolution used to certify the converter is not enough. It is only suitable for the verification of low-level converters or linear converters only; second, the current transformers and resistors of the converter are separately verified, which is relatively easy to implement, that is, the above-mentioned standard converters. It also needs to be individually verified.
No matter which test method is adopted, a new set of standard transformers or proportional standards are needed. At the same time, it is necessary to study the connection of these new proportional standards with the original current ratio of 5A.
52 Improving the level of automation and intelligence of transformer testing In the testing of common transformers, there have been a variety of automatic transformer calibration tables made using high-tech microcomputers, and some have been able to perform data processing on test results. . Its level of automation and intelligence can be further improved, and testing is easier.
At present, the verification of the current comparator self-checking system and the detection of the inductive voltage divider still rely on manual operations. In particular, the workload of the self-inspection system is large and cumbersome, and it needs to be automated and intelligent.
53 Field calibrator and virtual calibrator Transformer verification In addition to the transformer calibrator, a standard transformer and power supply are also required. When verifying large current transformers and high voltage voltage transformers at the substation site, it is necessary to carry the above-mentioned cumbersome testing equipment. In order to facilitate the verification of the field transformer, the Australian Red Phase recently proposed an on-site current transformer calibrator that does not use standard current transformers and current sources. Its working principle is based on the current transformer error calculation formula, the corresponding parameters are determined and calculated by the microcomputer software to achieve the current transformer error measurement. This on-site current transformer calibrator calculates the transformer error using the measured parameters and can deduct the compensation value. However, the verification of this calibrator still needs further exploration and improvement. In this way, it is possible to further expand the scope of application of the new principle calibrator.
In addition, the use of computer-generated virtual calibrators is another direction for the development and innovation of calibrators.
The above vision is only a small part of it. This requires a closer integration of transformers' electrical measurement expertise and computer expertise, and looks forward to the close cooperation and joint efforts of related professional scientific and technical personnel to achieve greater development.
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