Scope

Update time : 2024-11-29 08:19:58

At present, S-class current transformers generally use amorphous or microcrystalline high magnetic permeability material cores, which can easily reach S-class without special design.

In the past, only current transformers with a secondary rated current of 5A had S-class.

With the development of technology, electronic electric energy meters have been used in large quantities.

This type of electric energy meter does not require a large power drive, so S-class current transformers with a secondary current of 1A are also used in power grids.

At present, current transformers with a secondary rated current of 1A are mainly used at electric energy metering gateways, and are used in conjunction with electronic multi-function meters at electric energy metering gateways.

The gateway meter with a rated current of 1A does not have the problem of 4 times overload, and the use of S-class transformers also greatly reduces the measurement error of high-voltage electric energy metering devices when the line is running at low load, so it has been promoted and applied.

The revised IEC60044-1 "Current Transformer" also allows current transformers with a secondary current of 1A to have S-class.

In addition, the measurement lower limit of the miniature current transformer produced according to JB/T10665-2016 "Miniature Current Transformer for Electric Energy Meter" is 1%, and the error measurement also needs to be carried out according to Class S.

In order to verify the error of the measuring current transformer and the miniature current transformer at 1% of the rated current point, a Class S standard current transformer is required, and to verify the Class S standard current transformer, a Class S metering standard current transformer and a power frequency current ratio standard are required.

Therefore, the entire range of measuring current transformers must be expanded to Class S to achieve the requirement of value transfer of the 1% point error of the rated current.

2. Classification of Measuring Voltage Transformers

The measuring voltage transformers involved in the JJG 314-2010 verification regulations can be divided into three categories according to the accuracy level in terms of manufacturing process and structure, as described below:

(1) The first category is the accuracy level 0.5~0.05, which belongs to the working voltage transformer.

This type of voltage transformer is made of laminated or ring-wound silicon steel core.

The error is adjusted by increasing or decreasing the number of turns of the primary winding at 20% of the rated voltage.

(2) The second type has an accuracy of 0.02~0.01, which belongs to the standard voltage transformer.

This type of voltage transformer is also made of laminated or ring-wound silicon steel core.

In addition to adjusting the error by increasing or decreasing the number of turns of the primary winding at 20% of the rated voltage, it is also necessary to use an auxiliary small core fractional turn compensation on the secondary side to adjust the ratio difference at 50%~120% voltage percentage.

The compensation of phase difference is generally obtained by connecting a compensation capacitor and a resistor element in series in the secondary compensation winding to obtain an orthogonal compensation potential, and then adjusting the primary or secondary turns of the small core after coupling it to the compensation small core for accurate compensation.

Therefore, a voltage ratio standard with an accuracy of 0.005 or above is required when adjusting the error.

(3) The third category has an accuracy of 0.005~0.001.

This category mainly includes voltage transformers or inductive voltage dividers, which belong to voltage ratio standards.

Voltage ratio standards with a rated voltage of more than 1kV generally have two cores, on which the excitation and ratio windings are wound respectively.

The primary excitation current mainly flows through the excitation winding, and the primary ratio winding has basically no excitation voltage drop, so it has good linearity.

For a properly designed two-stage voltage transformer, the correlation between the transformer error.

Since the excitation current of the ratio winding needs to be limited, the secondary load of the two-stage voltage transformer's ratio output should be 0VA.

The two-stage voltage transformer also has winding capacitance error and magnetic error, so it is also necessary to perform error adjustment at 20%~120% of the rated voltage, and a voltage ratio standard with an uncertainty of less than it is required.

The inductive voltage divider is an autocoupled or two-stage voltage transformer with multiple voltage ratios.

The inductive voltage divider (such as a single-disk inductive voltage divider or an autocoupled voltage transformer) that uses a fixed tap to provide a voltage ratio is suitable for the error specified in JJG314-2010, and the ratio error is expressed as a proportional error.

The error definition of a multi-disk inductive voltage divider should be based on the provisions of JJF1067-2014 "Calibration Specification for Power Frequency Voltage Ratio Standard Devices", and its ratio error is expressed as a reference error.

It is also necessary to mention JJG 244-2003 "Verification Procedure for Inductive Voltage Dividers", which is applicable to "autocoupled and isolated audio inductive voltage dividers, inductive audio attenuators, and inductive audio voltage ratio standards".

The transfer ratio error is calculated using the modulus value and is not applicable to power frequency inductive voltage dividers.

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