The standard TP current transformer is divided into four levels: TPS, TPX, TPY and TPZ.
    TPS and TPX cores have no air gap, so there is no restriction on remanence, and the characteristics of the two are similar. When the current transformer is severely saturated, the primary current will be cut off, and the secondary current will rapidly decrease to the remanence level from the saturation state with the magnetic flux, that is, the residual current of the secondary current is small, so it is suitable for circuit breaker failure protection with strict requirements on the protection reset time On the other hand, this type of current transformer has a higher magnetizing resistance and a small current draw, which is suitable for applications where current transformers are connected in parallel.
The core of TPY and TPZ transformers has an air gap, so the magnetic resistance is large, which increases the time for the transformer to reach saturation, and is not easy to saturate, that is, it has a longer time to maintain the linear conversion and transfer relationship, so that the transient characteristics are greatly improved. . The time constant of the transformer is reduced, and the core area can be reduced; the reduction of residual magnetism is also conducive to the improvement of transient characteristics, so the TPY level can ensure the maximum peak instantaneous error of the full current under the accurate limit condition ε=10%; while the TPZ level only Ensure that the maximum peak instantaneous error of the AC component εac=10%. Since the TPZ level can only transfer the AC component, it is used for protection devices that only need to react to the AC component. It cannot guarantee the low-frequency component error and the excitation impedance is too low. Therefore, it is not recommended for the protection of main equipment such as generator sets and circuit breaker failure protection. . In general comparison, the core of the TPY current transformer has an appropriate air gap, and the residual magnetism is limited to the appropriate value (below 10% of the saturation magnetic flux value), and the peak value of the full current can be guaranteed under the specified accurate limit conditions. The instantaneous error is below 10%, which has good transient characteristics and is more suitable for generator set protection.