Current Transformer Parameters

The main technical requirements of the current transformer
1. Rated capacity: the apparent power consumed when the rated secondary current passes through the secondary rated load. Rated capacity can be expressed in terms of apparent power V.A, can also be expressed in terms of secondary rated load impedance Ω.
2. Primary rated current: allowed through the primary winding of the current transformer load current. Used in the power system current transformer primary rated current of 5 ~ 25000 A, used for testing equipment precision current transformer 0.1 ~ 50000 A. Current transformer can be in the primary rated current for long-term operation, the load current exceeds the value of the rated current is called overload, the current transformer overload operation for a long period of time, it will burn out the windings or reduce the service life.
3. Secondary rated current: the primary induction current through the secondary winding of the current transformer.
4. Rated current ratio (ratio): primary rated current and secondary rated current ratio.
5. Rated voltage: the primary winding can withstand long-term maximum voltage to ground (rms value in kV), should not be less than the rated phase voltage of the connected line. Current transformer rated voltage is divided into 0.5, 3, 6, 10, 35, 110, 220, 330, 500kV and other voltage levels.
6. 10% times: in the specified secondary load and any power factor, the current transformer current error of -10%, the primary current to its rated value of the times. 10% times is related to the technical indicators of relay protection.
7. Accuracy level: indicates the level of the transformer’s own error (ratio difference and angular difference). Current transformer accuracy level is divided into 0.001 ~ 1 multiple levels, compared with the original accuracy is greatly improved. Used in power plants, substations, power units on the distribution control panel of the electrical instrumentation is generally 0.5 or 0.2 level; for equipment, line relay protection is generally not less than 1 level; used for power measurement, depending on the measured load capacity or how much power consumption based on the requirements of the regulations to choose (see the first lecture).
8. Ratio difference: the error of the transformer includes the ratio difference and angular difference of two parts. Ratio error is referred to as ratio difference, generally expressed by the symbol f, which is equal to the actual secondary current and the conversion to the secondary side of the difference between the primary current, and the conversion to the secondary side of the ratio of the primary current, expressed as a percentage.
9. Angular difference: phase angle error is referred to as angular difference, generally expressed by the symbol δ, which is the phase difference between the secondary current vector and the primary current vector after 180° rotation. Provide that the secondary current vector exceeds the primary current vector δ is a positive value, and vice versa is a negative value, with minutes (‘) as the unit of calculation.
10. Thermal stability and dynamic stability times: power system fault, current transformer by the short-circuit current caused by the thermal and electrodynamic effects of the huge current, current transformer should be able to withstand without damage to the ability to withstand the ability to use the thermal stability and dynamic stability multiplier expressed. Thermal stability times refers to the thermal stability of the current 1s does not cause the heating of the current transformer exceeds the permissible limit of the current and current transformer rated current ratio. Dynamic stability times is the current transformer can withstand the maximum current instantaneous value of its rated current ratio.

Configuration table of 10kV high voltage current transformer and low voltage current transformer

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