What factors affect the secondary load of the current transformer?

1. Resistance of the secondary circuit: The wire resistance, contact resistance, etc. in the secondary circuit will increase the secondary load. If the wire cross-sectional area of ​​the secondary circuit is too small, the length is too long, or the connection point is poorly contacted, the resistance will increase, thereby increasing the secondary load. For example, when the cable used in the secondary circuit is thin, its resistance is relatively large, which will increase the secondary load.
2. The number of connected measuring instruments and relays: The more measuring instruments (such as ammeters, power meters, etc.) and relays (such as protection relays, differential relays, etc.) connected to the secondary circuit of the current transformer, the greater the total load impedance. This is because each measuring instrument and relay has a certain internal resistance. When they are connected in parallel to the secondary circuit, the total impedance of the secondary circuit will be reduced, resulting in an increase in the secondary load. For example, in a power system, if multiple ammeters and protection relays are connected at the same time, their impact on the secondary load of the current transformer needs to be considered.
3. Types of measuring instruments and relays: Different types of measuring instruments and relays have different internal resistances, which also affect the secondary load of the current transformer. For example, the internal resistance of electromagnetic relays is relatively small, while the internal resistance of electronic relays is relatively large. If an electronic relay with a large internal resistance is used in the secondary circuit, the secondary load will increase.
4. Wiring method of the secondary circuit: The wiring method of the secondary circuit will also affect the secondary load. For example, if the secondary circuit adopts a series wiring method, the total load impedance will increase; if a parallel wiring method is adopted, the total load impedance will decrease. Therefore, when designing the secondary circuit, it is necessary to select a suitable wiring method according to the actual situation to reduce the secondary load.
5. Transformation ratio of current transformer: The transformation ratio of current transformer refers to the ratio of primary current to secondary current. When the transformation ratio of the current transformer increases, the secondary current will decrease, thereby increasing the power factor of the secondary load, the angle difference will increase, and the ratio difference will decrease. This is because under the same primary current, the larger the transformation ratio, the smaller the secondary current, and the greater the total impedance of the secondary circuit, which leads to an increase in the secondary load.
6. System frequency: The change of system frequency has little effect on the secondary load of the current transformer and can be ignored.
7. Capacity of current transformer: The larger the capacity of the current transformer, the greater its excitation impedance and the larger the allowable secondary load. This is because the core cross-section of the current transformer with large capacity is larger and can withstand a larger magnetic flux density, thereby reducing the saturation of the core and reducing the error.
8. Ambient temperature: Changes in ambient temperature will affect the secondary load of the current transformer. When the ambient temperature rises, the winding resistance of the current transformer will increase, thereby increasing the secondary load. Therefore, in practical applications, it is necessary to consider the impact of ambient temperature on the secondary load of the current transformer and take corresponding measures to compensate. For example, a temperature compensation resistor can be connected in series in the secondary circuit to reduce the impact of ambient temperature changes on the secondary load.
9. Primary current size: The size of the primary current will also affect the secondary load of the current transformer. When the primary current increases, the secondary current will also increase accordingly, thereby increasing the secondary load. In addition, the waveform of the primary current will also affect the secondary load. If the primary current contains more harmonic components, the secondary load will also increase accordingly.
10. Capacitance of the secondary circuit: The capacitance in the secondary circuit will also affect the secondary load. If there is a large capacitor in the secondary circuit, then under the action of the AC voltage, the capacitor will produce a certain capacitive reactance, which will reduce the total impedance of the secondary circuit and increase the secondary load. Therefore, when designing the secondary circuit, it is necessary to minimize the capacitance in the secondary circuit to avoid adverse effects on the secondary load.