Use Of Ansi C-Class Cts - GE MiCOM P40 Agile Technical Manual

P14x
Metrosils for devices with a 5 Amp CT
These Metrosil units have been designed to comply with the following requirements:
The Metrosil current should be less than 100 mA rms (the actual maximum currents passed by the devices
●
shown below their type description.
At the maximum secondary internal fault current the Metrosil should limit the voltage to 1500 V rms for
●
0.25secs. At the higher relay settings, it is not possible to limit the fault voltage to 1500 V rms so higher fault
voltages have to be tolerated.
The Metrosil units normally recommended for use with 5 Amp CTs and single pole relays are as shown in the
following table:
Secondary Internal Fault Current
Amps RMS
50A
100A
150A
In some situations single disc assemblies may be acceptable, contact Alstom Grid for detailed applications.
Note:
The Metrosils recommended for use with 5 Amp CTs can also be used with triple pole devices and consist of three single pole
units mounted on the same central stud but electrically insulated from each other. To order these units please specify "Triple
pole Metrosil type", followed by the single pole type reference. Metrosil for higher voltage settings and fault currents are
available if required.
2.9

USE OF ANSI C-CLASS CTS

Where American/IEEE standards are used to specify CTs, the C class voltage rating can be used to determine the
equivalent knee point voltage according to IEC. The equivalence formula is:
V 1 05 . ( C rating in volts
=
K
P14xEd1-TM-EN-1
Recommended Metrosil types for various voltage settings
Up to 200 V RMS 250 V RMS
600A/S1/S1213 600A/S1/S1214
C = 540/640 C = 670/800
35 mA RMS 40 mA RMS
600A/S2/P/
600A/S2/P/S1215
S1217
C = 570/670
C = 470/540
75 mA RMS
70 mA RMS
600A/S3/P/
600A/S3/P/S1220
S1219
C = 520/620
C = 430/500
100 mA RMS
100 mA RMS
) 100 R
+
CT
Chapter 9 - Current Transformer Requirements
275 V RMS
600A/S1/S1214
C =670/800
50 mA RMS
600A/S2/P/S1215
C =570/670
100 mA RMS
600A/S3/P/S1221
C = 570/670
100 mA RMS
300 V RMS
600A/S1/S1223
C = 740/870
50 mA RMS
600A/S2/P/S1196
C =620/740
100 mA RMS
600A/S3/P/S1222
C =620/740
100 mA RMS
205