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Power System Analysis and Design

Mulukutla S Sarma, J D Glover, Thomas Overbye

Computer Science

6th Edition · 925 pages

ISBN: 9781305632134

Chapter 7: Q20MCQ (page 464)

Breakers of the 115kV class and higher have a voltage range factor k = _____, such that their symmetrical interrupting current capability remains constant.

Short Answer

Expert verified

Answer

Breakers of the 115kV class and higher have a voltage range factor k = 1, such that their symmetrical interrupting current capability remains constant.

Step by step solution

01

Definition of voltage range factor in circuit breaker.

The voltage range factor (k-factor) is normally up to 1 to 1.3 and is the range over which the breaker operates at a specific voltage and current. But the interrupting capability of the current remains constant.

02

Determine the voltage range factor in circuit breaker.

The voltage range factor is mainly a high-class factor of a 115 kV circuit breaker. The voltage range is over one because interrupting capability increases at a specific voltage and current, and symmetrical interrupting current holds true.

$I = I_{m a x} (k - 1) V = V_{m a x} (k = 1)$

Therefore, the breakers of the 115kVclass and higher have a voltage range of factor k = 1.

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Most popular questions from this chapter

A single-line diagram of a four-bus system is shown in Figure 7.20, for which $Z_{bus}$ is given below:

$Z_{bus} = j [\begin{matrix} 0.25 & 0.2 & 0.16 & 0.14 \\ 0.2 & 0.23 & 0.15 & 0.151 \\ 0.16 & 0.15 & 0.196 & 0.1 \\ 0.14 & 0.151 & 0.1 & 0.195 \end{matrix}] per unit$

Let a three-phase fault occur at bus 2 of the network.

(a) Calculate the initial symmetrical rms current in the fault.

(b) Determine the voltages during the fault at buses 1, 3, and 4.

(c) Compute the fault currents contributed to bus 2 by the adjacent unfaulted buses 1, 3, and 4.

(d) Find the current flow in the line from bus 3 to bus 1. Assume the prefault voltage $V_{f}$ at bus 2 to belocalid="1655403112082" $1 ∠ 0^{\circ}$ and neglect all prefault currents.

For distribution systems, standard reclosers are equipped for two or more reclosers, whereas multiple-shot reclosing in EHV systems is not a standard practice.

(a) True (b) False

For the power system given in Problem 7.14, a three-phase short circuit occurs at bus 4, where the prefault voltage is $138 kV$ . Prefault load current is neglected. Determine (a) the Thévenin equivalent at the fault, (b) the subtransient fault current in per unit and in $kA rms$ , and (c) contributions to the fault from transformer $T 2$ and from line 3–4.

(a) The bus impedance matrix for a three-bus power system is

$Z_{bus} = J [\begin{matrix} 0.12 & 0.08 & 0.04 \\ 0.08 & 0.12 & 0.06 \\ 0.04 & 0.06 & 0.08 \end{matrix}] per unit$

Where subtransient reactance were used to compute $Z_{bus}$ . Prefault voltage is and prefault current is1.0 per unit and prefault current neglected. (a) Draw the bus impedance matrix equivalent circuit (rake equivalent). Identify the per-unit self- and mutual impedances as well as the prefault voltage in the circuit. (b) A three-phase short circuit occurs at. Determine the subtransient fault current and the voltages at buses 1, 2 and 3 during the fault.

(c) Repeat for the case of

$Z_{bus} = J [\begin{matrix} 0.4 & 0.1 & 0.3 \\ 0.1 & 0.8 & 0.5 \\ 0.3 & 0.5 & 0.2 \end{matrix}] per unit$

In the system shown in Figure 7.16, a three-phase short circuit occurs at point. Assume that prefault currents are zero and that the generators are operating at rated voltage. Determine the fault current.

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