6.1.6 Current and voltage percentage meters for monitoring
The accuracy level of current and voltage percentage meters shall not be lower than level 1.5. Within the specified measurement range, the internal impedance shall remain unchanged.
[Article interpretation] Traditionally, the percentage meter attached to the calibrator is used for monitoring, so there are also accuracy requirements for the percentage meter attached to the calibrator.
JJG1021-2007 does not stipulate the error limit of the accuracy level.
Because S-level current transformers are widely used, current current transformer calibrators use digital meters as percentage meters.
For digital percentage meters, their error limits are usually expressed as inherent errors plus errors proportional to the measured indication.
The error of the 1% point is mainly determined by the inherent error, which is usually 0.1a% of the full scale value, and a is the accuracy level index.
When a-1.5, the relative error is 15%, which will not have a substantial impact on the calibration results.
6.2 Verification Items
[Article Interpretation] In the verification items of power transformers, demagnetization is not a routine item, but is only performed in the re-inspection after the verification fails.
This is because JJG1021-2007 has already limited the residual magnetism error, requiring it to be no more than 1/3 of the basic error.
Generally, the error of the transformer has a certain margin, and the error of the current transformer without demagnetization generally does not exceed the basic error.
This regulation helps to reduce the workload of the verification personnel.
JJG 1021-2007 stipulates that after the operation variation, it is necessary to test the operation variation to determine whether its size meets the requirements.
In order to reduce the verification workload and improve work efficiency while controlling the operation variation, the regulations propose that the operation variation value of the test product can be obtained based on the design book and test report data provided by the manufacturer or research and testing institution according to the characteristics of the operation variation.
This is done because the design and process of the transformer can completely determine the electrical performance of the transformer.
The transformers mass-produced by the manufacturer have nearly consistent electrical performance, and therefore have similar operating variations.
The regulations allow the verification department to conditionally adopt the test data provided by the manufacturer entrusted by a qualified test research institution, which can avoid the waste of manpower and material resources caused by repeated tests.
In fact, all transformers used in power grids need to undergo type tests.
After the release and implementation of JJG1021-2007, the power grid construction department can require the manufacturer to provide a test report on operating variations when bidding and ordering transformer products.
The manufacturer can entrust a qualified test research institution to conduct type tests, and extract the contents related to operating variations from the type test report to form an operating variation report, which is provided as product performance parameters.
In this way, it is not necessary for the verification personnel to repeat the test of these items during verification, and only the relevant items of the verification certificate need to be qualified.
In addition, the regulations take the operating variation test as the first verification content, and the conclusion of the first verification on the operating variation can be directly quoted during the periodic verification.
This treatment can ensure the accuracy of the transformer in use without increasing the workload of the verification personnel.
