Using the current tap settings and time dial settings that you have selected in Problem 10.12, evaluate relay coordination for the minimum fault currents. Are the fault-to-pickup current ratios \(\geqslant 2.0\), and are the coordination time delays \(\geqslant 0.3\) seconds in all cases?

Problem 10.12

Repeat Example 10.4 for the following system data. Coordinate the relays for the maximum fault currents.

Example 10.4

Data for the \(60-\mathrm{Hz}\) radial system of Figure 10.16 are given in Tables 10.3, 10.4, and 10.5. Select current tap settings (TSs) and time-dial settings (TDSs)

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Bus 1 2 23 3 Breaker B1 B2 B3 MVA 9.0 9.0 9.0 Maximum Load Lagging p.f. 0.95 0.95 0.95 Breaker Operating Time 5 cycles 5 cycles 5 cycles Symmetrical Fault Current Minimum A 3750 2250 1500 Maximum A 5000 3000 2000 CT Ratio 600:5 400:5 200:5 Relay CO-8 CO-8 CO-8