6.4.1 The calibration data shall be recorded in the original format. The original records shall be kept for at least two calibration cycles.
6.4.2 The error of the transformer under test obtained according to this regulation at all calibration points shall be considered qualified if it does not exceed the basic error limit, and the stability, operation variation and magnetic saturation margin meet the provisions of Article 4.3, Article 4.4 and Article 4.5 of this regulation.
If one or more operation variations exceed the tolerance, but the actual error absolute value plus the absolute value of each operation variation exceeding the tolerance does not exceed the basic error limit, the transformer error is also considered qualified.
The error of the transformer under test obtained according to this regulation at one or more calibration points shall be considered unqualified if it exceeds the basic error limit in Table 2 or Table 3, or the stability exceeds the provisions of Article 4.3 of this regulation, or the operation variation exceeds the provisions of Article 4.4 of this regulation, or the magnetic saturation margin exceeds the provisions of Article 4.5 of this regulation, and the actual error absolute value plus the absolute value of each operation variation exceeding the tolerance exceeds the basic error limit.
The error of the unqualified transformer is allowed to be re-inspected under the reference conditions of Table 11, combined with the content of Article 6.4.2, and finally a qualified or unqualified conclusion is made based on the re-inspection results.
[Article Interpretation] Power transformers are working measuring instruments and are not used for value transfer.
Therefore, as long as its error can meet the measurement accuracy requirements, it should be allowed to be used.
Some power transformers allocate the operating variation as part of the basic error during design, and appropriately compress the error of the transformer under reference conditions.
This is also a reasonable industrial design method and should be supported.
Therefore, the verification certificate part of the JJG1021-2007 regulations adopts a corresponding treatment method for this situation, that is, if one or more operating variations exceed the tolerance, but the actual error absolute value plus the absolute value of each additional error does not exceed the basic error limit, the transformer error is also considered qualified.
The power transformer is installed on site, and the reference conditions cannot be met during verification under on-site conditions.
Since the transformer has different structures, among the multiple factors that affect the transformer error, some are positively correlated and some are negatively correlated.
Even if the transformer deviates from the reference condition, it is not necessarily out of tolerance.
Therefore, the transformer must be designed with an error margin to ensure that it will not exceed the tolerance during verification.
The value of this margin is the verification uncertainty, which is usually equal to 113 of the basic error limit of the transformer being tested.
In many years of on-site verification work, it is found that the on-site verification pass rate of current transformers is higher than 90%, and the remaining 10% is mainly caused by residual magnetism, which is generally qualified after demagnetization.
Therefore, the problem of large-scale out-of-tolerance will not occur if verified according to this regulation.
However, the regulations require that each item of running variation is not greater than 113 of the basic error, so the error caused by residual magnetism is limited in the regulations.
This is different from JJG 313 "Current Transformer for Measurement".
There are two ways to deal with this provision. One is to verify the current transformer on-site and find that the error exceeds 1.5 times the basic error, and directly determine that it is out of tolerance.
The basis is the provisions of Article 4.4 of the regulations on operational variation.
After multiple influencing factors act, the maximum possible operational variation is equivalent to 1/2 of the basic error limit.
The other is to calibrate the current transformer on site. After finding the deviation, no conclusion is drawn first.
Demagnetization and re-inspection with improved environmental conditions are used to determine whether it is out of tolerance.
The first treatment is applicable to power transformers produced according to the technical conditions of this regulation.
After the promulgation of the verification regulations, it must be publicized to the manufacturer.
The second treatment method is applicable to the original products. However, most of the original products still meet the error requirements under field conditions.
For transformers that do not meet this regulation, they should be used under controlled conditions.
For example, some capacitive voltage transformers should reduce their rated secondary load range, so that margin can be allocated to operational variation.
In addition, if the on-site verification result is not greater than 1.5 times the basic error, but exceeds the basic error, the verification personnel need to evaluate the environmental impact.
If the verification environment does not meet the reference conditions, resulting in a relatively large operational variation, and the size and direction can be estimated, after deducting the error amount affected by the environmental conditions, if the basic error of the tested sensor is qualified, a qualified conclusion can be made.
If it is difficult to evaluate the impact, you can negotiate with the user to try to improve the environmental conditions on site to make it close to the reference conditions, and then conduct a re-inspection, and finally make a qualified or unqualified conclusion based on the re-inspection results.
If the site cannot approach the reference conditions, the transformer can only be removed and transferred to the laboratory for re-inspection, and the qualification is determined based on the verification results.
6.4.3 If the appearance inspection, polarity test and insulation test of the tested transformer are qualified, and all errors meet the requirements of Article 6.4.2, the transformer is qualified and a verification certificate is issued.
The error verification results of the transformer are given on the verification certificate.
Transformers with unqualified items in the verification results are allowed to be downgraded if they can meet all the technical requirements of the level after downgrading.
Transformers that are not suitable for downgrading are issued a verification result notice.
The unqualified items shall be stated in the notice and the calibration data shall be given.
[Article Interpretation]Generally speaking, the tolerance rate of transformers is very low.
If an abnormality is found, the test circuit, load box and calibration instrument shall be checked first to see if they are normal.
Finally, the factors and directions affecting the error shall be analyzed to determine whether there is indeed a tolerance.
Transformers with unqualified items in the calibration results are allowed to be downgraded for use if they can meet all technical requirements of the level after downgrading.
