16.1.7 Current transformer requirements for CTs according toother standards SEMOD53771-1 v1M11623-4 v3All kinds of conventional magnetic core CTs are possible to use with the IEDs ifthey fulfill the requirements corresponding to the above specified expressed as therated equivalent limiting secondary e.m.f. Eal according to the IEC 61869-2standard. From different standards and available data for relaying applications it ispossible to approximately calculate a secondary e.m.f. of the CT comparable withEal. By comparing this with the required rated equivalent limiting secondary e.m.f.Ealreq it is possible to judge if the CT fulfills the requirements. The requirementsaccording to some other standards are specified below.16.1.7.1 Current transformers according to IEC 61869-2, class P, PR M11623-6 v4A CT according to IEC 61869-2 is specified by the secondary limiting e.m.f. EALF.The value of the EALF is approximately equal to the corresponding Eal. Therefore,the CTs according to class P and PR must have a secondary limiting e.m.f. EALFthat fulfills the following:ALF alreqE max EEQUATION1383 V4 EN-US (Equation 29)16.1.7.2 Current transformers according to IEC 61869-2, class PX, PXR (andold IEC 60044-6, class TPS and old British Standard, class X) M11623-14 v5CTs according to these classes are specified approximately in the same way by arated knee point e.m.f. Eknee (Ek for class PX and PXR, EkneeBS for class X and thelimiting secondary voltage Ual for TPS). The value of the Eknee is lower than thecorresponding Eal according to IEC 61869-2. It is not possible to give a generalrelation between the Eknee and the Eal but normally the Eknee is approximately 80 %of the Eal. Therefore, the CTs according to class PX, PXR, X and TPS must have arated knee point e.m.f. Eknee that fulfills the following:( )knee k kneeBS al alreqE E E U 0.8 maximum of E» » » > ×EQUATION2100 V2 EN-US (Equation 30)16.1.7.3 Current transformers according to ANSI/IEEE M11623-22 v6Current transformers according to ANSI/IEEE are partly specified in differentways. A rated secondary terminal voltage UANSI is specified for a CT of class C.UANSI is the secondary terminal voltage the CT will deliver to a standard burden at20 times rated secondary current without exceeding 10 % ratio correction. Thereare a number of standardized UANSI values for example, UANSI is 400 V for a C400Section 16 1MRK 511 423-UEN ARequirements298 Bay control REC650 2.2 IECApplication manual
