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For the circuit given in Problem 13.8, replace the circuit elements by their discrete-time equivalent circuits. Use t10=50sμs=5-5and E=100kV. Determine and show all resistance values on the discrete-time circuit. Write nodal equations for the discrete-time circuit, giving equations for all dependent sources. Then solve the nodal equations and determine the sending-and receiving-end voltages at the following times: t=50,100,150,200,250and 300ms.

Short Answer

Expert verified

Answer

For t=50μs

The value for role="math" localid="1656760999733" Vk(50×10-6),Vm(50×10-6),Ik(50×10-6),Im(50×10-6),and IC(50×10-6), are 0.0025kV,0V,0kA,1.675×10-50kAand 0kArespectively.

For t=100μs

The value for Vk(100×10-6),Vm(100×10-6),Ik(100×10-6),Im(100×10-6),and IC(100×10-6), are 0.005kV,0V,0kA,3.35×10-5kAand 0kArespectively.

For t=100μs

The value for Vk(150×10-6),Vm(150×10-6),Ik(150×10-6),Im(150×10-6),and IC(150×10-6), are 0.0075kV,0V,0kA,5.025×10-5kAand0kArespectively.

For t=200μs

The value for Vk(200×10-6),Vm(200×10-6),Ik(200×10-6),Im(200×10-6),and IC(200×10-6), are0.01kV,0V,0kA,6.7×10-5kAand0kArespectively.

For t=250μs

The value for Vk(250×10-6),Vm(250×10-6),Ik(250×10-6),Im(250×10-6),and IC(250×10-6),arerole="math" localid="1656762238787" 0.0125kV,0V,3.24×10-4V,1.446×10-5kA,8.375×10-5kAand 2.592×10-5kArespectively.

For t=300μs

The value for Vk(300×10-6),Vm(300×10-6),Ik(300×10-6),Im(300×10-6),and IC(300×10-8), are 0.015kV,1.816×10-4kV,3.229×10-5kA,1.005×10-4kAand 1.1392×10-5kArespectively.

Step by step solution

01

Write the given data from the from the question.

The voltage source,E=100kV

Time,t=5×10-5s

The series inductance,L=0.999×10-6Hm

The shunt capacitance,C=1.112×10-11Fm

The length of the line,I=60kM

The source impedance,ZGs=Zc

The source voltage,

eGt=Etu-1tkVeGt=Etu-2tkV

02

Determine the equation to calculate the sending-end receiving end voltages.

The equation to calculate characteristics impedance is given as follows.

Zc=LC …… (1)

The equation to calculate the value of velocity is given as follows.

v=1LC …… (2)

The equation to calculate the transit time is given as follows.

T=Iv …… (3)

03

Calculate the sending-end receiving end voltages.

Consider the diagram using the terminal variables in the time domain.

Redraw the circuit diagram by using the equivalent and also convert the voltage and current sources with the help of source transformation.

Calculate the characteristics impedance.

Substitute 0.999×10-6Hmfor L, and 1.112×10-11Fmfor C into equation (1).

Zc=0.999×10-61.112×10-11ZC=8.983×104ZC=299.73Ω

Calculate the value of the velocity.

Substitute 0.999×10-6Hmfor L, and 1.112×10-11Fmfor C into equation (2).

v=10.999×10-6×1.112×10-11v=9×1016v=3×108ms

Calculate the value of the transit time.

Substitute 60 km for I and 3×108msfor v into equation (3).

ζ=60×1033×10Sζ=200μs

Apply the nodal analysis at node 1.

role="math" localid="1656766636362" Vk(t)(ZcZG)-iG(t)+Ik(t-ζ)=0Vk(t)(ZcZG)=iG(t)-Ik(t-ζ)Vk(t)=[iGkt-ζt-I](ZcZG)

Substitute role="math" localid="1656766648626" eG(t)ZGfor iGinto above equation.

Vk(t)=[eG(t)ZG-IK(t-ζ)](ZcZG)

Substitute 200μsfor ζ,100tu-1(t)kVfor eG(t),299.73Ωfor ZGinto above equation.

Vk(t)=[100t299.73-Ikt-200×10-6](299.73299.73)Vk(t)=[0.334t-Ikt-200×10-6]149.87kV …… (4)

Therefore, the expression for the voltage Vk(t)is [0.334t-Ik(t-200×10-6)]149.87V.

Apply the nodal analysis at node 2,

Vm(t)(ZcRt2C)-Im(t-ζ)-IC(t-t)=0Vm(t)=[Imt-ζ-Ict-t](ZCRt2C)

Substitute 200μsfor ζ,50msfor t,299.73Ωfor Zc,150Ωand 1μFfor C into above equation.

Vm(t)=[Imt-200×10-6-Ict-50×108](299.7315050×10-62×1×10-6)Vm(t)=[Imt-200×10-Ict-50×10-6](10025)

Vm(t)=[Im(t-200×10)-Ic(t-50×10-6)]×20kV …… (5)

Hence the expression for the voltage Vm(t)is [Imt-200×10-6-Ict-50×10-6]×20kV.

The expression for the current Ik(t-ζ).

Ik(t-ζ)=Im(t-ζ)-2Zcvm(t)

Replace t-ζwith t into above equation.

Ik=Im(t-ζ)-2ZCvm(t)

Substitute 200μsfor ζand 299.73Ωfor Zcinto above equation.

Ik(t)=Im(t-200×10-6)-2299.73vm(t)

Ik(t)=Im(t-200×10-6)-0.0067vm(t)kA …… (6)

Hence the expression for the currentis.

The expression for the current.

Imt-ζ=Ikt-2ζ+2Z0vkt-ζ

Replacewithinto above equation.

Im(+t)=Ik(t-ζ)+2Z0vk(t)

Substituteforandforinto above equation.

Im(t)=Ik(t-200×106)+2299.73vk(t)

Im(t)=Ik(t-200×10-6)+0.0067vk(t)kA …… (7)

Hence the expression current Im(t)isIk(t-200×10-6)+0.0067vk(t)kA.

The expression for the current Ic(t-t).

Ic(t-t)=-IC(t-t)+vm(t)t/4C

Replacewithinto above equation.

Substituteforandforinto above equation.

…… (8)

Hence the expression foris.

For

Recall the equation (4).

Substituteforinto above equation.

The value of the termis zero since input is composed of unit function.

Recall equation (5),

Substituteforinto above equation.

The value of the termis zero since input is composed of unit function.

Recall the equation (6),

Substituteforinto above equation.

The value of the termis zero since input is composed of unit function.

Substituteforinto above equation.

Recall equation (7).

Substituteforinto above equation.

The value of the termis zero since input is composed of unit function.

Substituteforinto above equation.

Recall the equation (8),

Substituteforinto above equation.

Substituteforandforinto above equation.

Hence the value forand are,,,andrespectively.

For

Recall the equation (4).

Substituteforinto above equation.

The value of the termis zero since input is composed of unit function.

Recall equation (5),

Substituteforinto above equation.

The value of the termis zero since input is composed of unit function.

Substituteforinto above equation.

Recall the equation (6),

Substituteforinto above equation.

The value of the termis zero since input is composed of unit function.

Substituteforinto above equation.

Recall equation (7).

Substituteforinto above equation.

The value of the termis zero since input is composed of unit function.

Substituteforinto above equation.

Recall the equation (8),

Substituteforinto above equation.

Substituteforandforinto above equation.

Hence the value forand are,,,andrespectively.

For

Recall the equation (4).

Substituteforinto above equation.

The value of the termis zero since input is composed of unit function.

Recall equation (5),

Substituteforinto above equation.

The value of the termis zero since input is composed of unit function.

Substituteforinto above equation.

Recall the equation (6),

Substituteforinto above equation.

The value of the termis zero since input is composed of unit function.

Substituteforinto above equation.

Recall equation (7).

Substituteforinto above equation.

The value of the termis zero since input is composed of unit function.

Substituteforinto above equation.

Recall the equation (8),

Substituteforinto above equation.

Substituteforandforinto above equation.

Hence the value forand are,,,andrespectively.

For

Recall the equation (4).

Substituteforinto above equation.

Recall equation (5),

Substituteforinto above equation.

Substituteforinto above equation.

Recall the equation (6),

Substituteforinto above equation.

Substituteforinto above equation.

Recall equation (7).

Substituteforinto above equation.

Substituteforinto above equation.

Recall the equation (8),

IC(t)=Ic(t-50×10-6)+0.08vm(t)kA

Substituteforinto above equation.

IC(200×10-6)=-IC(200×10-6-50×10-5)+0.08vm(200×10-6)Im(250×10-6)=Ic(150×10-6)+0.08vm(200×10-6)

Substituteforandforinto above equation.

Im(200×10-6)=0-0.8(0)Im(200×10-6)=0kA

Hence the value for Vk200×10-6,Vm200×10-6,Ik200×10-6,Im200×10-6and IC200×10-6, are 0.01kV,0V,6.7×10-6kAand 0kArespectively.

For t=250μs

Recall the equation (4).

Vk(t)=[0.334t-Ik(t-200×10-6)]149.87kA

Substitutefor t into above equation.

Im(250×10-6)=[0.334×250×10-6-Ik250×10-6-200×10-6]149.87Im(250×10-6)=[83.5×10-6-Ik50×10-6]149.87

The value of the termis zero since input is composed of unit function.

Im(250×10-6)=[83.5×10-6-0]149.87Im(250×10-6)=0.0125kV

Recall equation (5),

Vm(t)=[Im(t-200×10-8)-Ic(t-50×10-6)]×20kA

Substituteforinto above equation.

Vm(250×10-6)=[Im250×10-6-200×10-6-Ic250×10-6-50×10-6]×20Vm(250×10-6)=[Im50×10-6-Ic200×10-6]×20

Substituteforandforinto above equation.

Vm(250×10-6)=[1.675×10-5-0]×20Vm(250×10-6)=3.24×10-4kV

Recall the equation (6),

Im(t)=Im(t-200×10-6)+0.0067vk(t)kA

Substituteforinto above equation.

Im(250×10-6)=Im(250×10-6-200×10-6)+0.0067vk(250×10-6)Im(250×10-6)=Ik(50×10-6)+0.0067vk(250×10-6)

Substituteforandinto above equation.

Im(250×10-6)=1.675×10-5-0.0067(3.24×10-4)Im(250×10-6)=1.675×10-5-2.2378×10-4kAIk(250×10-6)=1.446×10-5kA

Recall equation (7).

Im(t)=Ik(t-200×10-8)+0.0067vk(t)kA

Substituteforinto above equation.

Im(250×10-6)=Ik(250×10-6-200×10-6)+0.0067vk(250×10-6)Im(250×10-6)=Ik(50×10-6)+0.0067vk(250×10-6)

Substituteforandforinto above equation.

Im(250×10-6)=0+0.0067(0.0125)Im(250×10-5)=8.375×10-5kA

Recall the equation (8),

Ic(t)=-Ic(t-50×10-6)+0.08vm(t)kA

Substituteforinto above equation.

Ic(250×10-6)=-Ic(250×10-5)+0.08vm(250×10-6)IC(250×10-6)=-IC(200×10-6)+0.08vm(250×10-6)

Substituteforandforinto above equation.

Ic(250×10-6)=0-0.08(3.24×10-4)IC(250×10-6)=2.592×10-5kA

Hence the value for Vk250×10-6,Vm250×10-6,Ik250×10-6,Im250×10-6and IC250×10-6, are 0.0125kV,3.24×10-4V,1.446×10-5kA,8.375×10-5kAand 2.592×10-5kArespectively.

For t=300μs

Recall the equation (4).

Vk(t)=[0.334t-Ik(t-200×10-6)]149.87kV

Substitute 300μsfor into above equation.

Vk(300×10-6)=[0.334×300×10-6-lk300×10-6-200×10-6]149.87Vk(300×10-6)=[100.2×10-6-Ik100×10-6]149.87

The value of the term Vk(300×10-6)is zero since input is composed of unit function.

Vk(300×10-6)=[100.2×10-6-0]149.87Vk(300×10-6)=0.015kV

Recall equation (5),

Vm(t)=[Imt-200×10-6-ICt-50×10-6]×20kV

Substitute 300μsfor t into above equation.

Vm(300×10-6)=[Im300×10-6-200×10-6-IC300×10-6-50×10-6]×20Vm(300×10-6)=[Im100×10-6-Ic250×10-6]×20

Substitute 2.592×10-5kAfor Ic(250×10-6)and 3.35×10-5kAfor Im(100×10-6)into above equation.

Vm(300×10-6)=[3.35×10-5-2.592]×20Vm(300×10-6)=1.816×10-4kV

Recall the equation (6),

IK(t)=Im(t-200×10-6)-0.0067vm(t)kA

Substituteforinto above equation.

Ik(300×10-6)=Im(300×10-6-200×10-6)-0.0067m(300×10-6)Ik(300×10-6)=Im(100×10-6)-0.0067vm(300×10-6)

Substitute 1.816×10-4kVfor Vm(300×10-6)and 3.35×10-5kAfor Im(100×10-6) into above equation.

Ik(300×10-6)=3.35×10-5-0.0067(1.816×10-4)Ik(300×10-6)=3.35×10-5-0.121×10-5IK(300×10-6)=3.229×10-5kA

Recall equation (7).

Im(t)=Ik(t-200×10-6)+0.0067vk(t)kA

Substitute 300μsfor t into above equation.

Im(300×10-6)=IK(300×10-6-200×10-6)+0.0067vk(300×10-6)Im(300×10-6)=IK(300×10-6)+0.0067vk(300×10-6)

Substitute 0.015 kV for Vk(300×10-6)and 0 A for Ik(100×10-6)into above equation.

Im(300×10-6)=0+0.0067(0.015)Im(300×10-6)=1.005×10-4kA

Recall the equation (8),



IC(t)=-IC(t-50×10-6)+0.08vm(t)kA

Substitute 300μsfor t into above equation.

IC(300×10-6)=-IC(300×10-6-50×10-6)+0.08vm(300×10-6)IC(300×10-6)=-IC(250×10-6)+0.08vm(300×10-6)

Substitute 1.816×10-4kVfor Vm(300×10-6)and 2.592×10-5kVfor IC(250×10-6)into above equation.

IC(300×10-6)=2.592×10-5kA-0.08(1.816×10-4kV)IC(300×10-6)=1.1392×10-5kA

Hence the value forVk(300×10-6),Vm(300×10-6),Ik(300×10-6),Vm(300×10-6),and Ic(300×10-6), are 0.015kV,1.816×10-4kV,3.229×10-5kV,1.005×10-4kAand 1.005×10-4kArespectively.

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Most popular questions from this chapter

Repeat Example 13.8 for a 500 - kV system with a 1.08 per-unit maximum 60 - Hz voltage under normal operating conditions and with a 2000 - kVBIL.

As shown in Figure 13.33, two identical, single-phase, two-wire, lossless lines are connected in parallel at both the sending and receiving ends. Each line has a 400Ω characteristic impedance,3×108m/s velocity of propagation, and100km line length. The source voltage at the sending end is a100kV step with source impedance ZG=100Ω. The receiving end is shorted (ZR=0). Both lines are initially unenergized. (a) Determine the first forward traveling voltage waves that start at timet=0 and travel on each line toward the receiving end. (b) Determine the sending- and receiving-end voltage reflection coefficients in per-unit,

(c) Draw the Bewley lattice diagram for 0t2.0ms.

(d) Plot the voltage at the center of one line versus timet for 0t2.0ms.

Where are the surge arrestor located in the power system.

Rework Example 13.4 with ZR=5Zcand ZG=Zc3.

As shown in Figure 13.34, an ideal current source consisting of a 10-kApulse with 50-μsduration is applied to the junction of a single-phase, lossless cable and a single-phase, lossless overhead line. The cable has a 200-Ωcharacteristic impedance, 2×108m/svelocity of propagation, and 20-kmlength. The overhead line has a 300-Ωcharacteristic impedance, 3×108m/svelocity of propagation, and 60-kmlength. The sending end of the cable is terminated by 400-Ωresistor, and the receiving end of the overhead line is terminated by a 100-Ωresistor. Both the line and cable are initially unenergized. (a) Determine the voltage reflection coefficients TS, TR, TAA, TAB, TBA, and TBB(b) Draw the Bewley lattice diagram for 0t0.8ms. (c) Determine and plot the voltage υ(0,t)at x=0versus time tfor 0t0.8ms.

Figure 13.34

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