Application Examples; Example: Radial System With Three Grading Levels - Siemens SENTRON 3WA1 Manual

2.10.6

Application examples

The functionality of the ZSI system will be explained using four application examples.
• Radial system with three grading levels
• Multiple infeed with coupler circuit breakers
• Branch circuit with fuse
• Integrating the medium-voltage protection device
Grading levels
Due to the high accuracy and processing speed of the ETU600 electronic trip unit, up to
seven independent grading levels can be selectively set up relative to each other. For the
coordination of short-circuit protection, the response characteristics of the circuit
breakers can be selectively graded with the times 0.4 / 0.33 / 0.265 / 0.2 / 0.135 / 0.07 /
0 s (via INST):
2.10.6.1

Example: radial system with three grading levels

The following figure shows a power distribution system with three grading levels. The
three errors A, B and C are considered in more detail.
The left side of the figure shows the settings of the ZSI function and the delays for the
short-time-delayed short-circuit protection ST.
3WA1 air circuit breaker
Equipment Manual, 02/2023, 92310000002-06
2.10 Zone-selective interlocking ZSI
Description
191