What is the effect of the secondary load of the current transformer on its accuracy?

1. The effect of excessive secondary load on accuracy:
1. Increased error: When the secondary load impedance exceeds the allowable secondary load impedance of the current transformer, the excitation current will increase greatly, causing the core to enter a saturated state. In this case, a large part of the primary current will be used to provide the excitation current, resulting in a significant increase in the error of the transformer and a decrease in accuracy. For example, in some large industrial power systems, if the secondary load design is unreasonable, excessive load may cause the measurement error of the current transformer to exceed the allowable range, affecting the accurate judgment of the operating status of the power system.
2. Impact on the measurement range: Excessive secondary load will narrow the measurement range of the current transformer. For a given current transformer, it is designed with a certain rated secondary load. When the actual secondary load exceeds the rated value, the transformer may not be able to accurately measure larger current values, or the error increases when measuring small currents. For example, in an electric power metering system, if the secondary load of the current transformer is too large, it may lead to inaccurate energy metering during low load periods.
3. Reduced protection performance: In protection applications, current transformers need to accurately detect fault currents in order to trigger the protection device to operate in time. Excessive secondary load may cause the current transformer to fail to accurately reflect the change in primary current during a fault, thereby delaying the action time of the protection device or causing inaccurate action, reducing the reliability and effectiveness of the protection system. For example, when a short-circuit fault occurs, if the secondary load of the current transformer is too large, the protection device may not be able to detect the increase in short-circuit current in time, resulting in the failure to remove the fault in time, causing greater damage to the power equipment.
2. The impact of too small secondary load on accuracy:
1. Too small measurement signal: If the secondary load is too small, the measurement signal may be too small, affecting the measurement accuracy. For example, in some high-precision measurement occasions, a smaller secondary load is required to ensure the accuracy of the measurement. However, if the secondary load is too small, the measurement signal may be disturbed, affecting the reliability of the measurement results.
2. Affecting the normal operation of the protection device: In protection applications, the secondary load of the current transformer needs to match the input impedance of the protection device. If the secondary load is too small, the protection device may not work properly or fail to operate in time during a fault. For example, in some overcurrent protection devices, if the secondary load of the current transformer is too small, the starting current of the protection device may increase, causing the protection device to fail to operate in time when a fault occurs, causing greater damage to the power equipment.