Protection of Electrical Networks
Suitable for engineers, technicians, designers and operators working with electrical networks, this book discusses network structures and grounding systems, as well as problems that can occur in networks.
TABLE OF CONTENTS Protection of Electrical Networks
Chapter 10: Protection of Network Elements
10.1 Network protection
Notations
| ? t | selectivity interval (generally set at 0.3 seconds: see section 9.2) | |
| I setA | current threshold of the protection located at A ("A" for arrival) | |
| I setDi | current threshold of the protection located on the outgoing feeder Di ("D" for departure) | |
| I sc2,min, A | minimum phase-to-phase short-circuit current with protection located at A | |
| I sc2,min, Di | minimum phase-to-phase short-circuit current with protection located on the outgoing feeder Di | |
| I ? | resistance limited current | |
| I C | total capacitive current of the network when a phase-to-earth fault occurs, | |
| I Ci | capacitive current generated by the outgoing feeder Di when a phase-to-earth current occurs, I Ci=3 jC i ? V n | |
| I p | permanent current that the earthing resistor can withstand | |
| I nCT | current transformer rating | |
| t H | time delay of the protection located at H, H1 or H2 | |
| t A | time delay of the protection located at A, A1 or A2 | |
| t D | time delay of the protection located on the outgoing feeders Di | |
| t N | time delay of the protection located on the neutral earthing connection | |
| V set, A | threshold of the residual overvoltage protection that trips the circuit-breaker at A, A1 or A2 | |
| t R | directional protection time delay | |
| I set, R | directional protection current threshold |
We will first of all determine the requirements of the network and equipment for earth faults relevant...
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