Metrosils for devices with a 5 Amp CT
These Metrosil units hav
e 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 Recommended Metrosil types for various voltage settings
Amps RMS Up to 200 V RMS 250 V RMS 275 V RMS 300 V RMS
50A
600A/S1/S1213
C = 540/640
35
mA RMS
600A/S1/S1214
C = 670/800
40 mA RMS
600A/S1/S1214
C =670/800
50 mA RMS
600A/S1/S1223
C = 740/870
50 mA RMS
100A
600A/S2/P/
S1217
C = 470/540
70 mA RMS
600A/S2/P/S1215
C = 570/670
75 mA RMS
600A/S2/P/S1215
C =570/670
100 mA RMS
600A/S2/P/S1196
C =620/740
100 mA RMS
150A
600A/S3/P/
S1219
C = 430/500
100 mA RMS
600A/S3/P/S1220
C = 520/620
100 mA RMS
600A/S3/P/S1221
C = 570/670
100 mA RMS
600A/S3/P/S1222
C =620/740
100 mA RMS
In some situations single disc assemblies may be acceptable, contact Alstom Grid for detailed applications.
Note:
The Metr
osils 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 v
oltage according to IEC. The equivalence formula is:
V Cratinginvolts R
K CT
= +1 05 100. ( )
P14x Chapter 9 - Current Transformer Requirements
P14xEd1-TM-EN-1 205
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