Chapter 9: Q3MCQ (page 576)
When calculating symmetrical three-phase fault currents, only ________ sequence network needs to be considered.
When calculating symmetrical three-phase fault currents, only positive sequence network needs to be considered.
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Repeat Problem 9.21 for a bolted line-to-line fault.
Question:For the system of Problem 9.11, compute the fault current and voltages at the fault for the following faults at point F: (a) a bolted single line-to-ground fault; (b) a line-to-line fault through a fault impedance ZF =j0.05; (c) a double line-to-ground fault from phase B to C to ground, where phase B has a fault impedance ZF =j0.05 , phase C also has a fault impedance ZF =j0.05, and the common line-to-ground fault impedance is ZG =j0.033 per unit.
A single-line diagram of a four-bus system is shown in Figure 9.27. Equipment ratings and per-unit reactances are given as follows.
Machine and:
Transformers and:
On a base of 100 MVA and 345 kV in the zone of the transmission line, the series reactances of the transmission line areand . (a) Draw each of the sequence networks and determine the bus impedance matrix for each of them. (b) Assume the system to be operating at nominal system voltage without prefault currents when a bolted line-to-line fault occurs at bus 3. Compute the fault current, the line-to-line voltages at the faulted bus, and the line-to-line voltages at the terminals of machine 2. (c) Assume the system to be operating at nominal system voltage without prefault currents, when a bolted double line-to ground fault occurs at the terminals of machine 2. Compute the fault current and the line-to-line voltages at the faulted bus.
The zero-, positive-, and negative-sequence bus impedance matrices for a two-bus three-phase power system are
Determine the per-unit fault current and per-unit voltage at bus 2 for a bolted three-phase fault at bus 1. The pre fault voltage is 1.03 per unit.
Using the bus impedance matrices determined in Problem 9.47, verify the fault currents for the faults given in Problems 9.4(b), 9.4(c), and 9.19 (a through d).
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