【JJG314-2010】5.1.3.4 The standard must have a valid verification or calibration certificate.
When the standard is two accuracy levels higher than the voltage transformer being tested, its actual secondary load should not exceed the rated and lower limit load range.
When the standard is one accuracy level higher than the voltage transformer being tested, the difference between the actual value of the secondary load during use and the load marked on the certificate should not exceed ±10%.
The differential pressure circuit load and the leakage load generated by the capacitive current flowing from the primary winding to the secondary winding should also be included in the actual secondary load.
For a standard with a rated load of zero, the impact of the actual secondary circuit load on the standard should not be greater than 1/10 of the error limit of the voltage transformer being tested.
【JJG314-2010】5.1.3.5 The error change (voltage coefficient) of the capacitive voltage proportional device at each calibration percentage point shall not exceed 1/10 of the error limit of the current transformer being tested.
【JJG313-2010】5.1.4 Error measurement device
The measurement error caused by the error measurement device shall not exceed 1/10 of the error limit of the current transformer being tested.
Among them, the measurement error caused by the device sensitivity shall not exceed 1/20, the measurement error caused by the minimum division value shall not exceed 1/15, and the measurement error caused by the additional secondary load of the differential current measurement circuit shall not exceed 1/20.
【JJG314-2010】5.1.4 Error measurement device
The measurement error caused by the error measurement device shall not exceed 1/10 of the error limit of the voltage transformer being tested.
Among them, the measurement error caused by the device sensitivity shall not exceed 1/20, and the measurement error caused by the minimum division value shall not exceed 1/15. The measurement error caused by the additional secondary load of the differential pressure measurement circuit is not greater than 1/20.
【JJG313-2010】 5.1.5 Monitoring ammeter
During calibration, the accuracy level of the ammeter used to monitor the secondary working current of the current transformer shall not be lower than level 1.5, and the relative error of the ammeter at all error measurement points shall not be greater than 20%.
In all indication ranges of the same range, the internal impedance of the ammeter shall remain unchanged.
【JJG314-2010】5.1.5 Monitoring voltmeter
During calibration, the accuracy level of the voltmeter used to monitor the secondary working voltage of the voltage transformer shall not be lower than level 1.5, and the relative error of the voltmeter at all error measurement points shall not be greater than 20%.
In all indication ranges of the same range, the internal impedance of the voltmeter shall remain unchanged.
【Article Interpretation】The error of the measuring transformer is usually determined by measuring several thousand current and voltage percentage points.
The error of the transformer at other measuring points is limited by the broken line formed by the measured error value points.
Therefore, it is necessary to have a monitoring current and voltage meter to indicate the measurement percentage.
In JJG 313-1994, the monitoring ammeter is required to be level 1.5, and the error characteristic is the reference error.
The reference value is the scale value corresponding to 100% rated current.
According to the allowable error calculation, when the ammeter indicates the current at the 5% point, due to the measurement error, the actual test current percentage is 3.5%~6.5%.
Taking the 0.2S level as an example, the change in the allowable error of the 1% and 5% points is 0.75%-0.35%=0.4%.
The average error is calculated as 0.1 when the current changes by 4%.
The current change of 1.5% may cause the error to change by 0.1x1.5%=0.15%.
This means that when the current at the 1% point is indicated by an ammeter, the inaccurate measurement result at the 1% point may cause the deviation of the measurement result to reach more than 0.15%, which is equivalent to 20% of the 1% point error limit (0.75% x 20% = 0.15%), and the reproducibility of the measurement result cannot be guaranteed.
In order to make up for this defect, in the past, when measuring the S-level current transformer with a rated secondary current of 5A, the ammeter range was changed to 1A at the 5% and 1% points.
But now the current transformer with a rated secondary current of 1A also has S-level, and its 1% point measurement will also face the same problem. In fact, most of the current calibrators now use digital ammeters to indicate the working current.
In theory, the error requirements can be proposed according to the indication characteristics of the digital meter, but it is also necessary to take into account the original production of current transformer calibrators, and it is not appropriate to propose too high requirements.
Based on possibility and need, the JJG313-2010 regulation adds additional error requirements for the indication of the ammeter, specifically, the relative error of the measurement point is not more than 20%.
According to this requirement, the actual value allowed when adjusting the 1% point current is 0.8%~1.2%.
It is estimated that the additional error introduced by the deviation of the current percentage point can be reduced to 1~2 rounding units, which greatly improves the repeatability of the measurement results.
For monitoring voltmeters, the lower limit of the voltage verification point is usually 20%.
If a standard voltage transformer is used as a standard, the 1.5% indication error generally does not affect the reproducibility of the measurement.
However, in actual operation, the calibration laboratory sometimes needs to use a high-voltage double-stage voltage transformer or inductive voltage divider as a standard, so that it is possible to measure at 20% lower than the rated voltage of the standard.
In order to be comparable, requirements must be made for the error of the voltmeter in the low voltage section.
Considering the consistency of the current and voltage regulations, JJG 314-2010 also adds the requirement that "the relative error of the voltmeter at all error measurement points is not greater than 20%" for the error of the monitoring voltmeter.
