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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 13: Q1CSQ (page 857)

Why are circuit breakers and fuses ineffective in protecting against transient over voltages due to lightning and switching surges?

Short Answer

Expert verified

Therefore, due to the slower speed the circuit breaker and the fuses are not employed.

Step by step solution

01

Define transient overvoltage

The transient overvoltage is the overvoltage that arises in the system during the initial voltage of the cycle. The transient over voltage have the peak values of the voltage that can destroy the system if not properly taken into consideration.

02

Determine the description for the answer.

Note the circuit breakers have the operating speed of 50 ms. Although being so fast they are slower in operation for the protection against the transient stage of the lightning surges. This is why other faster protection schemes are employed to protect the transformer.

Therefore, the circuit breaker and the fuse have slower operation and are not effective for the protection against the transient surges.

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Most popular questions from this chapter

Rework Example 13.4 with $Z_{R} = 5 Z_{c}$ and $Z_{G} = \frac{Z_{c}}{3}$ .

As shown in Figure 13.34, an ideal current source consisting of a $10 - k A$ pulse with $50 - μ s$ duration is applied to the junction of a single-phase, lossless cable and a single-phase, lossless overhead line. The cable has a $200 - Ω$ characteristic impedance, $2 \times 10^{8} m / s$ velocity of propagation, and $20 - k m$ length. The overhead line has a $300 - Ω$ characteristic impedance, $3 \times 10^{8} m / s$ velocity of propagation, and $60 - k m$ length. The sending end of the cable is terminated by $400 - Ω$ resistor, and the receiving end of the overhead line is terminated by a $100 - Ω$ resistor. Both the line and cable are initially unenergized. (a) Determine the voltage reflection coefficients $T_{S}$ , $T_{R}$ , $T_{AA}$ , $T_{AB}$ , $T_{BA}$ , and $T_{BB}$ (b) Draw the Bewley lattice diagram for $0 \leq t \leq 0.8 m s$ . (c) Determine and plot the voltage $υ (0, t)$ at $x = 0$ versus time $t$ for $0 \leq t \leq 0.8 m s$ .

Figure 13.34

The single-phase, two-wire lossless line in Figure 13.3 has a series inductance $L = (1 / 3) \times 10^{- 6} H / m$ , a shunt capacitance, and a $50 K m$ line length. The source voltage at the sending end is a step $e_{G} (t) = 100 u_{- 1} (t) k V$ with $Z_{G} (s) = 100 Ω$ .The receiving-end load consists of a $100 Ω$ resistor in parallel with $2 m H$ a inductor. The line and load are initially unenergized. Determine (a) the characteristic impedance in ohms, the wave velocity in $m / s$ , and the transit time in $m s$ for this line; (b) the sending-and receiving-end voltage reflection coefficients in per-unit; (c) the Laplace transform of the receiving-end current $I_{R} (s)$ , ; and (d) the receiving-end current $i_{R} (t)$ as a function of time.

Referring to the single-phase two-wire lossless line shown in Figure 13.3, the receiving end is terminated by an inductor with $2 L_{R}$ Henries. The source voltage at the sending end is a step $e_{G} (t) = E u_{- 1} (t)$ with . Both the line and inductor are initially unenergized. Determine and plot the voltage at the centre of the line $v (l / 2, t)$ versus time $t$ .

Rework Example 13.2 if the source voltage at the sending end is a ramp, $e_{G} (t) = {Eu}_{- 2} M = {Etu}_{- 1} (t)$ with $Z_{G} = 2 Z_{c}$ .

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