P-level current transformers can determine whether the accurate limit factor KALF is qualified by measuring the excitation curve. The method is as follows:
1、 Measure the DC resistance RCT of the secondary winding and calculate the impedance ZCT=RCT+jXCT of the secondary winding. XCT can be ignored or taken as 0.1~0.2 Ω.
2、 Calculate the rated load impedance Zbn based on the rated load Sbn on the nameplate of the current transformer
Zbn=Sbn/Isn2
Isn is the rated secondary current
3、 Calculate the secondary induced electromotive force Es=KALFDsn (Zct+Zbn)
4、 Create an excitation curve with US ≈ ES. When searching for the US value on the excitation curve, if the excitation current Ie value is less than the value calculated according to the formula Ie=ε KALFIsn, it is qualified; otherwise, it is unqualified. ε is a composite error of 5% or 10%.
