What are the effects of too large or too small secondary load of current transformer?

1. Effect of too large secondary load:
1. Increased measurement error: If the secondary load of current transformer is too large, the core will be saturated, resulting in increased measurement error. This is because after the core is saturated, its magnetic permeability decreases, which makes the linear relationship between primary current and secondary current worse, thus affecting the measurement accuracy. For example, in the power system, if the secondary load of current transformer is too large, it may cause inaccurate energy metering and affect the settlement of electricity bills.
2. Degraded protection performance: If the secondary load of current transformer is too large, the action current of protection device will increase, resulting in decreased protection performance. This is because the action current of protection device is set according to the secondary current of current transformer. If the secondary current is inaccurate, the action current of protection device will be inaccurate, thus affecting the performance of protection device. For example, in the power system, if the secondary load of current transformer is too large, it may cause the protection device to malfunction or refuse to operate, affecting the safe operation of power system.
3. Severe heating: If the secondary load of current transformer is too large, the current in secondary winding will increase, resulting in severe heating. This is because the increase in the current in the secondary winding will increase the resistance loss of the secondary winding, thereby generating more heat. If the heat is severe, it may cause the insulation of the current transformer to be damaged, affecting its service life. For example, in the power system, if the secondary load of the current transformer is too large, it may cause the current transformer to burn out, affecting the normal operation of the power system.
2. The impact of too small secondary load:
1. Reduced measurement accuracy: If the secondary load of the current transformer is too small, the secondary current will be too small, thus affecting the measurement accuracy. This is because if the secondary current is too small, the sensitivity of the measuring instrument will be reduced, making it impossible to accurately measure the size of the primary current. For example, in the power system, if the secondary load of the current transformer is too small, it may cause inaccurate energy metering and affect the settlement of electricity bills.
2. Misoperation of the protection device: If the secondary load of the current transformer is too small, the action current of the protection device will be too small, resulting in misoperation of the protection device. This is because the action current of the protection device is set according to the secondary current of the current transformer. If the secondary current is too small, the action current of the protection device will be too small, causing the protection device to misoperate during normal operation. For example, in a power system, if the secondary load of a current transformer is too small, it may cause frequent false trips of the protection device, affecting the safe operation of the power system.