【JJG313-2010】This regulation applies to the initial verification, subsequent verification and in-use inspection of 0.001~0.5 level measuring current transformers (hereinafter referred to as current transformers) with a rated frequency of S0Hz (60Hz).
【JJG314-2010】This regulation applies to the initial verification, subsequent verification and in-use inspection of 0.001~0.5 level measuring voltage transformers (hereinafter referred to as voltage transformers) with a rated frequency of 50Hz (60Hz).
[Article Interpretation] 50Hz is the standard frequency of the mains electricity in China's power industry. Some countries or regions (such as America) set it at 60Hz.
1. Classification of measuring current transformers
The 0.001~0.5 level measuring current transformers covered by the JJG313-2010 verification regulation can be divided into four categories according to the accuracy level in terms of manufacturing process and structure, as described below:
(1) Accuracy 0.5 The first category is 0.05 and 0.1, which are working current transformers.
This type of current transformer is made of rolled or laminated silicon steel core, and the ratio error is adjusted by calculating the secondary compensation turns.
(2) The second category is 0.05~0.02, which are standard current transformers.
This type of current transformer is made of high magnetic permeability core.
Commonly used materials include 1J79 or 1J85 iron-nickel alloy rolled core, amorphous, microcrystalline and ultra-microcrystalline core.
The ratio error is adjusted by calculating the compensation turns.
This standard current transformer will have a positive phase error at low ampere turns.
If necessary, an appropriate capacitor should be connected in parallel on the secondary side to compensate for the phase error.
Therefore, a current ratio standard with an accuracy of 0.005 or above is required.
(3) The third category is 0.01 and 0.005 The double-core current transformer of level 0.002 is a metrological standard.
One of the cores in the secondary winding is used for magnetic potential compensation.
The compensation amount can be obtained by calculation, but it must be adjusted on the error measurement circuit in the end, so a current ratio standard with an accuracy of 0.001 or above is required.
(4) The fourth category is the double-core current transformer with an accuracy of 0.002 and 0.001, which belongs to the industrial frequency current ratio standard.
The double-core current transformer uses an auxiliary core to generate secondary current.
The excitation ampere-turns of the main core are the difference ampere-turns of the primary winding and the secondary winding.
The compensation winding is wound on the main core, and the secondary load is zero, so that the secondary compensation current has a very small load error.
The S in the 0.001S~0.5S measurement current transformer involved in the JJG313-2010 verification regulations is the English The first letter of Special, the accuracy level without S is ordinary level, and the accuracy level with S is enhanced level, which means current transformer for special purpose.
S-level current transformer is specially designed to expand the measurement range of electromechanical energy meter with rated current of 5A.
Usually, the effective lower limit working current of the current magnetic field coil of electromechanical energy meter is 0.05A, while the lower limit working current percentage of ordinary current transformer is 5%.
When the rated current of the transformer is 5A, the lower limit of normal working current is 0.25A, which is inconsistent with the 0.05A of the energy meter.
If the effective range of the energy meter is defined in 0.25A~6A, that is, covering the interval of 5%~120% of the rated current of the current transformer, the metering capacity of the energy meter is not fully utilized.
If the effective range of the energy meter can be expanded to 0.05A, when the rated current of the energy meter is set to 1A, in addition to having a working range of 5%~120% of the rated current, it can also maintain the original accuracy within a range of 5 times the rated current, that is, it has a 5-fold overload capacity.
In fact, most power users have peak and valley values of electricity consumption, and the range of variation is very large.
Generally, the peak-to-valley difference reaches dozens of times.
Wide-load energy metering devices are more suitable for actual electricity consumption and have more accurate metering performance.
