Littelfuse Startco Protection Relays Technical Note - Current Transformers CT-11: FPL ZERO-SEQUENCE SENSORS WITH LITTELFUSE RELAYS
Toroidal (Type T) zero-sequence sensors manufactured by Federal Pioneer Ltd. can be used with Littelfuse Startco ground-fault and motor-protection relays. Table 1 lists compatible FPL sensors and window sizes. These sensors can be used on resistance-grounded systems and on solidly grounded systems where the maximum ground-fault current is less than 50 kA.
When using an FPL sensor with the SE-701 Ground-Fault Monitor, the CT-primary rating is 50 A. The SE-701 set-point range is 1 to 99% in 1% increments, which corresponds to 0.5 to 49.5 A in 0.5-A steps. If the ground-fault current can exceed 400 A, a voltage-clamping device must be used as shown in Fig. 1. An SE-EFVC is recommended for these applications.
When using an FPL sensor with an FPS, FPU-32, MPS, or MPU-32, the earth-fault CT-primary rating should be set to 50 A. This will provide correct earth-leakage metering information and trip levels. The set-point range is 1 to 100% in 1% increments, which corresponds to 0.5 to 50 A in 0.5-A steps. For the MPS, the set-point range is 5 to 100% in 1% increments, which corresponds to 2.5 to 50 A in 0.5-A increments.
If the earth-fault current can exceed 200 A, a voltage-clamping device must be used. An SE-EFVC is recommended for these applications, as shown in Figs. 2, 3a, and 3b.
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Application note & Design Guide |
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Please see the document for details |
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English Chinese Chinese and English Japanese |
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January 22, 2013 |
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