( )knee k kneeBS al alreqE E E U 0.8 maximum of E» » » > ×EQUATION2100 V2 EN-US (Equation 94)17.1.7.3 Current transformers according to ANSI/IEEE M11623-22 v6Current transformers according to ANSI/IEEE are partly specified in different ways. A ratedsecondary terminal voltage UANSI is specified for a CT of class C. UANSI is the secondaryterminal voltage the CT will deliver to a standard burden at 20 times rated secondary currentwithout exceeding 10 % ratio correction. There are a number of standardized UANSI values forexample, UANSI is 400 V for a C400 CT. A corresponding rated equivalent limiting secondarye.m.f. EalANSI can be estimated as follows:alANSI sr ct ANSI sr ct sr bANSIE 20 I R U 20 I R 20 I Z= × × + = × × + × ×EQUATION971 V2 EN-US (Equation 95)where:ZbANSI The impedance (that is, with a complex quantity) of the standard ANSI burden for the specific C class(W)UANSI The secondary terminal voltage for the specific C class (V)The CTs according to class C must have a calculated rated equivalent limiting secondary e.m.f.EalANSI that fulfils the following:alANSI alreqE maximum of E>EQUATION1384 V2 EN-US (Equation 96)A CT according to ANSI/IEEE is also specified by the knee point voltage UkneeANSI that isgraphically defined from an excitation curve. The knee point voltage UkneeANSI normally has alower value than the knee-point e.m.f. according to IEC and BS. UkneeANSI can approximately beestimated to 75 % of the corresponding Eal according to IEC 61869-2. Therefore, the CTsaccording to ANSI/IEEE must have a knee point voltage UkneeANSI that fulfills the following:kneeANSI alreqV 0.75 (max imum of E )> ×EQUATION2101 V2 EN-US (Equation 97)17.2 SNTP server requirements GUID-588FCD12-C494-445E-8488-8287B34EFD9A v4The SNTP server to be used is connected to the local network, that is not more than 4-5switches or routers away from the IED. The SNTP server is dedicated for its task, or at leastequipped with a real-time operating system, that is not a PC with SNTP server software. TheSNTP server should be stable, that is, either synchronized from a stable source like GPS, orlocal without synchronization. Using a local SNTP server without synchronization as primary orsecondary server in a redundant configuration is not recommended.1MRK 505 355-UEN A Section 17Requirements265Application manual
