Description of the parameters of the current transformer

1. Current transformer model:
First letter: L—current transformer
Second letter: A - through-wall; Z—Pillar type; M—busbar type; D—single-turn through-type; V—structure inverted; J—Zero order
For grounding detection; W—anti-pollution; R—Bare winding
The third letter: Z - epoxy resin casting type; C—porcelain insulation; Q—gas-insulated medium; W—Dedicated to microcomputer protection
Fourth letter: B - with protection level; C—differential protection; D—D; Q—Enhanced type; J—Enhanced ZG
Fifth number: voltage level Product serial number

2. Main technical requirements
2.1 Rated capacity: the apparent power consumed when the rated secondary current passes through the secondary rated load. The rated capacity can be expressed in terms of apparent power V.A or in terms of secondary rated load impedance Ω.
2.2 Primary rated current: the current load allowed through the primary winding of the current transformer. The primary rated current of the current transformer used in the power system is 5~25000A, and the precision current transformer used for the test equipment is 0.1~50000A. The current transformer can operate for a long time under a rated current, when the load current exceeds the rated current value, it is called overload, and the current transformer is overloaded for a long time, which will burn the winding or reduce the service life.
2.3 Secondary rated current: allows the primary induced current through the secondary winding of the current transformer.
2.4 Rated current ratio (transformation ratio): the ratio of the primary rated current to the secondary rated current.
2.5 Rated voltage: The maximum voltage that the primary winding can withstand to the ground for a long time (the effective value is measured in kV) should not be lower than the rated phase voltage of the connected line. The rated voltage of the current transformer is divided into several voltage levels such as 0.5, 3, 6, 10, 35, 110, 220, 330, 500kV and so on.
2.6 10% multiple: The multiple of the current current of the current transformer when the current error of the current transformer is -10% under the specified secondary load and arbitrary power factor. The 10% multiple is a technical indicator related to relay protection.
2.7 Accuracy class: indicates the level of error (ratio difference and angle difference) of the transformer itself. The accuracy level of the current transformer is divided into 0.001~1 levels, and the accuracy is greatly improved compared with the original. The electrical instruments used on the distribution control panel of power plants, substations and power consumption units generally adopt 0.5 or 0.2 level; the relay protection used for equipment and lines is generally not less than 1 level; When used for energy measurement, it is selected according to the requirements of the regulations depending on the measured load capacity or the amount of electricity consumed (see Lecture 1).
2.8 Ratio difference: The error of the transformer includes two parts: specific difference and angle difference. The ratio error is referred to as the ratio difference, generally expressed by the symbol f, which is equal to the difference between the actual secondary current and the primary current converted to the secondary side, and the ratio of the primary current converted to the secondary side, expressed as a percentage.
2.9 Angle difference: The phase angle error is referred to as the angle difference, generally expressed by the symbol δ, which is the phase difference between the secondary current vector and the primary current vector after rotation of 180°. It is specified that the secondary current vector is ahead of the primary current vector δ which is positive, and vice versa, and the minute (') is used as the calculation unit.
2.10 Thermal stability and dynamic stability multiple: When the power system fails, the current transformer is subjected to the thermal effect and electrodynamic action of the huge current caused by the short-circuit current, and the current transformer should have the ability to withstand without being damaged, and this ability to withstand is expressed by thermal stability and dynamic stability multiple. The thermal stability factor refers to the ratio of the rated current of the current transformer within 1s that does not cause the heat generation of the current transformer to exceed the allowable limit. The dynamic stability factor is the ratio of the instantaneous value of the maximum current that a current transformer can withstand to its rated current.