⑴Calculate the multiple of the primary current flowing through the current transformer according to the type of protection device. ⑵According to the model, transformation ratio and primary current multiple of the current transformer, determine the allowable secondary load of the current transformer on the 10% error curve. (3) Calculate the actual secondary load of the current transformer according to the type of short circuit that is the most serious to the secondary load of the current transformer. ⑷ Compare the actual secondary load with the allowable secondary load. If the actual secondary load is less than the allowable secondary load, it means that the error of the current transformer does not exceed 10%. 1) Increase the connection: the cross section of the wire or shorten the length of the connection wire to reduce the actual secondary load. 2) Choose a relatively large current transformer, reduce the primary current multiple, and increase the allowable secondary load. 3) Connect the secondary windings of the current transformer in series to double the allowable secondary load.