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2. Application Notes
2.1 Protection Schemes
The GRL100 provides the following protection schemes (Appendix A shows block diagrams of the
GRL100-700 series):
• Segregated-phase current differential protection
• Zero-phase current differential protection
• Three-stepped distance protection and command protection
• Directional earth fault protection
• SOTF and Stub protection
• Overcurrent backup protection
• Thermal overload protection
• Overvoltage and undervoltage protection
• Broken conductor detection
• Out-of-step protection
• Breaker failure protection
• Transfer trip protection
Zero-phase current differential protection enables sensitive protection for high-impedance earth
faults.
Overcurrent backup protection provides both inverse time overcurrent and definite time
overcurrent protection for phase faults and earth faults.
Out-of-step protection performs phase comparison of the local and remote voltages and operates
only when the out-of-step loci cross the protected line.
Furthermore, the GRL100 incorporates autoreclose functions, charging current compensation
for cable or long-distance lines and fault location. The autoreclose mode can be selected from
single-phase, three-phase, single- and three-phase and multi-phase modes.
The current differential protection utilises with the microwave or fibre optic digital
telecommunication systems to transmit instantaneous current values sampled synchronously at
each terminal.
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6 F 2 S 0 8 5 0
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