• 100% Satisfaction Guarantee

akch2002, Engineer
Category: Homework
Satisfied Customers: 3091
Experience:  Home work expert
46493125
akch2002 is online now

# 3.8 A 138 kV/13.8 kV, 20 MVA, three-phase transformer has

### Customer Question

3.8
A 138 kV/13.8 kV, 20 MVA, three-phase transformer has a reactance of 10% and a resistance of 0.4%. Calculate a reasonably close approximation the peak fault current in the low voltage winding under the worst conditions, if a three-phase fault occurs at the low voltage terminals. For the purpose of the calculation the impedance of the source can be considered negligible.
If the fault current is interrupted by a circuit breaker on the high voltage side of the transformer, and if the capacitance per phase of this winding is 5200 pF, determine the frequency of the transient recovery voltage seen by the breaker.

Then;
3.9
Refer again to Problem 3.8. Let us now assume that the impedance of the 138 kV source is not negligible and that it has the same X/R ration as the transformer itself. Let us further state that a symmetrical fault on the 138 kV bus would develop a fault current of 18 kA rms.
Determine the frequency and relative magnitude of the transient recovery voltage of the circuit breaker when it interrupts the fault described in Problem 3.2.
Assume that the stray capacitance on the source side of the breaker is 12,000 pF.
Submitted: 3 years ago.
Category: Homework
Expert:  akch2002 replied 3 years ago.
Kindly indicate time in hours by which you would like to have answers for these questions.
Customer: replied 3 years ago.

I'm trying to finish and need within 5 hours

Expert:  akch2002 replied 3 years ago.
I will try to solve by that time and upload the answers. Thanks.
Customer: replied 3 years ago.

Ok thanks, XXXXX XXXXX graduate level Power Systems Transients course problems and the use of laplace transforms is requested as needed by the prof, as much detail as possible would be helpful. Thanks

Expert:  akch2002 replied 3 years ago.
Where ever use of Laplace transform is required, I will try to use. For calculating transient recovery voltage, formulae are available and I will use them.
Expert:  akch2002 replied 3 years ago.
What is frequency as it is required to calculate frequency of recovery voltage? Kindly inform.
Customer: replied 3 years ago.

It is not stated in the problem so assume 60Hz

Expert:  akch2002 replied 3 years ago.
OK. Thanks.
Customer: replied 3 years ago.

I just noticed it requested information from question 3.2 so i'm uploading the question for reference.

Expert:  akch2002 replied 3 years ago.
I am working. If required, I will use it.
Expert:  akch2002 replied 3 years ago.
It seems that transformers in 3.8 and 3.9 are different. When we are assuming source impedance zero, fault current is coming 8.36kA.
In 3.9, it is stated that fault current is 18kA considering source impedance. It can not be with same same transformer as maximum fault current occurs with zero source impedance.
Kindly look into this aspect and reply. I have completed 3.8.
Customer: replied 3 years ago.

I have reviewed the problem and it is verbatim from the book.

Expert:  akch2002 replied 3 years ago.
OK. I will solve it considering 18kA fault current on HV side itself.
Customer: replied 3 years ago.

Ok, thank you, XXXXX XXXXX is much appreciated.

Expert:  akch2002 replied 3 years ago.

You need to spend \$3 to view this post. Add Funds to your account and buy credits.
akch2002, Engineer
Category: Homework
Satisfied Customers: 3091
Experience: Home work expert
Customer: replied 3 years ago.

thank you, I have another 3 questions i've posted under engineering, if you are interrested in looking at them for me. they are simpler than the other 2

Expert:  akch2002 replied 3 years ago.
Thanks for rating excellent.
Kindly post those questions under home work category as I am not authorized to reply in Engineering category.
Customer: replied 3 years ago.

* it keeps erroring out when i try to post a new question. Is it possible to increase pay for this problem?

3.3
Figure 3P.2 shows two capacitor banks, C1 and C2, in a substation. C1 is energized, but C2 is discharged. The three-phase, 60 Hz rating of the banks are: C1, 5 MVA; C2, 3 MVA, on a 13.8 kV base. The source has a short circuit rating of 20kA rms at 13.8 kV. The inductance of the loop between C1 and C2, represented by L2 is 30μH.

 Attachments are only available to registered users.Register Here Attachments are only available to registered users.Register Here Attachments are only available to registered users.Register Here View Full Image Attachments are only available to registered users.Register Here

Calculate the peak transient voltage that will appear on C2 and the peak transient current that will flow in L1, if the switch S is closed at the peak of the voltage cycle. Point out any assumptions you make.

3.5

 Attachments are only available to registered users.Register Here Attachments are only available to registered users.Register Here Attachments are only available to registered users.Register Here View Full Image Attachments are only available to registered users.Register Here

A line to ground fault occurs as indicated in Fig. 3P.4, close to the secondary terminals of a 230/34.5 kV transformer. The transformer has a three-phase rating of 100 MVA; it has 0.1 pu reactance on this base.
Calculate:
a.The fault current
b.The time to peak of the transient recovery voltage when the circuit breaker opens to interrupt the fault current. A value of 12.7nF can be assumed for the effective capacitance per phase of the transformer secondary winding.

3.12

 Attachments are only available to registered users.Register Here Attachments are only available to registered users.Register Here Attachments are only available to registered users.Register Here View Full Image Attachments are only available to registered users.Register Here

C1=100μF; C2=40μF; L1=10mH; L2=20mH;
C1 and L1 in Fig. 3P.8. are oscillating; C2 and L2 are de-energized. The switch is closed when V(C1 )=0 and I2=500A. Calculate:

a.Peak voltage reached on C2
b.Peak current reached in L2
c.Frequency of the current in L1
d.Maximum voltage on C1 prior to closing the switch

Expert:  akch2002 replied 3 years ago.

Kindly indicate time in hours by which you would like to have answers.
Customer: replied 3 years ago.

Soon, today preferably, I'm a web student and going to submit my assignment late but i'd rather late than never. I'm hoping by getting help i'll be able to drill down the funamentals of the problems more accurately.

Customer: replied 3 years ago.

I was finally able to resubmit the homework question if you would like to pick it up from there.

Expert:  akch2002 replied 3 years ago.
Here it is night time and I would like to work up to 1pm or so. If it is possible to finish by that time, I will upload the answers; otherwise I will wok tomorrow and will try to upload the answers in 12 hrs or so.
I will look in home work category for these questions.

Ask-a-doc Web sites: If you've got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers... Justanswer.com.
...leave nothing to chance.
Traffic on JustAnswer rose 14 percent...and had nearly 400,000 page views in 30 days...inquiries related to stress, high blood pressure, drinking and heart pain jumped 33 percent.
Tory Johnson, GMA Workplace Contributor, discusses work-from-home jobs, such as JustAnswer in which verified Experts answer people’s questions.
I will tell you that...the things you have to go through to be an Expert are quite rigorous.

### What Customers are Saying:

• Wonderful service, prompt, efficient, and accurate. Couldn't have asked for more. I cannot thank you enough for your help. Mary C. Freshfield, Liverpool, UK
< Previous | Next >
• Wonderful service, prompt, efficient, and accurate. Couldn't have asked for more. I cannot thank you enough for your help. Mary C. Freshfield, Liverpool, UK
• This expert is wonderful. They truly know what they are talking about, and they actually care about you. They really helped put my nerves at ease. Thank you so much!!!! Alex Los Angeles, CA
• Thank you for all your help. It is nice to know that this service is here for people like myself, who need answers fast and are not sure who to consult. GP Hesperia, CA
• I couldn't be more satisfied! This is the site I will always come to when I need a second opinion. Justin Kernersville, NC
• Just let me say that this encounter has been entirely professional and most helpful. I liked that I could ask additional questions and get answered in a very short turn around. Esther Woodstock, NY
• Thank you so much for taking your time and knowledge to support my concerns. Not only did you answer my questions, you even took it a step further with replying with more pertinent information I needed to know. Robin Elkton, Maryland
• He answered my question promptly and gave me accurate, detailed information. If all of your experts are half as good, you have a great thing going here. Diane Dallas, TX

• ### LogicPro

#### Satisfied Customers:

4925
Expert in Java C++ C C# VB Javascript Design SQL HTML
< Last | Next >

### LogicPro

#### Satisfied Customers:

4925
Expert in Java C++ C C# VB Javascript Design SQL HTML

### Manal Elkhoshkhany

#### Satisfied Customers:

4538
More than 5000 online tutoring sessions.

### Linda_us

#### Satisfied Customers:

3138
Post Graduate Diploma in Management (MBA)

### Chris M.

#### Satisfied Customers:

2602
Master's Degree, strong math and writing skills, experience in one-on-one tutoring (college English)

### F. Naz

#### Satisfied Customers:

2126
Experience with chartered accountancy

### Bizhelp

#### Satisfied Customers:

1887
Bachelors Degree and CPA with Accounting work experience