CT dimensioning
CT dimensioning
(OP)
how can you dimension the proper rating of the CT given the characteristics of a relay, say the GE Multilin SR750?
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RE: CT dimensioning
RE: CT dimensioning
ANSI rated CT's for protection applications are specified in terms of the saturation voltage with a standard burden. The standard burden is (CT class) / (20* Isec) ohms at 0.5pf. So a class C100 with 5A secondary can provide roughly 100V secondary into a standard burden of 1.0ohm, 0.5pf at 20x rated secondary current. For multi-tap CT's be aware that the sauration voltage is less on lower taps.
For a single SR750 with short leads, C100 or better will be adequate for most applications. Suggest consulting a good protective relaying book for details, such as Blackburn, "Protective Relaying".
IEC rated CT's are sized based on VA burdens and use different accuracy classifications.
RE: CT dimensioning
RE: CT dimensioning
Quote from Multilin relay instruction book-
GE Multilin also provides phase and ground fault CTs
if required. Dimensions for these are shown in Figure
2.2a, Figure 2.2b, Figure 2.2c, and Figure 2.2d. Note:
Dimensions of a are for 100:5 to 1000:5 phase CT's;
for the dimensions of 50:5 and 75:5 CT's, consult factory.
Unquote
Details of the CT that can be seen in their relay instruction book are:
Rct, C***, Current Tranformation Ratio, Physical Dimension, typ. Magnetizing characteristics, etc along with the Multilin code for the CT. You may find an equivalent one in the market.
Best of luck!
RE: CT dimensioning
Also available are the CT Burden in both VA and milli-Ohms due to the connection of the relay, CT Thermal Withstand, Relay Overload Withstand, etc
This might be all that you look for while sizing the CT.
Best regards,
RE: CT dimensioning
thanks to all.