Docsity
Docsity
Prepare for your exams
Prepare for your exams

Study with the several resources on Docsity

Earn points to download
Earn points to download

Earn points by helping other students or get them with a premium plan

Guidelines and tips
Guidelines and tips
Sell on Docsity
Sell on Docsity
Docsity AI
Docsity AI
Log inSign up

Prepare for your exams

Study with the several resources on Docsity

Find documents

Prepare for your exams with the study notes shared by other students like you on Docsity

Search for your university

Find the specific documents for your university's exams

Docsity AINEW

Summarize your documents, ask them questions, convert them into quizzes and concept maps

Explore questions

Clear up your doubts by reading the answers to questions asked by your fellow students

Earn points to download

Earn points by helping other students or get them with a premium plan

Share documents
download point icon20 Points

For each uploaded document

Answer questions
download point icon5 Points

For each given answer (max 1 per day)

All the ways to get free points
Get points immediately

Choose a premium plan with all the points you need

Study Opportunities

Choose your next study program

Get in touch with the best universities in the world. Search through thousands of universities and official partners

Community

Ask the community

Ask the community for help and clear up your study doubts

Free resources

Our save-the-student-ebooks!

Download our free guides on studying techniques, anxiety management strategies, and thesis advice from Docsity tutors

Capacitive Circuit - Electrical Engineering - Exam, Exams of Electrical Engineering

Dr. Bhim Rao Ambedkar UniversityElectrical Engineering

Main points of this exam paper are: Capacitive Circuit, Switchboard, Distribution Transformer, Short Circuit, Primary Voltage, Secondary Voltage, Percentage Impedance, Switchfuse, Resistive Heating Load, Motive Power Load

Typology: Exams

2012/2013

Uploaded on 04/09/2013

shabo-rani
shabo-rani 🇮🇳

4.3

(27)

97 documents

1 / 8

Toggle sidebar

This page cannot be seen from the preview

Don't miss anything!

bg1
Cork Institute of Technology
Bachelor of Engineering in Electrical Engineering – Award
(National Diploma in Engineering in Electrical Engineering – Award)
(NFQ – Level 7)
Autumn 2005
Electrical Engineering
(Time: 3 Hours)
Instructions
Answer any FIVE questions.
All questions carry equal marks.
Examiners: Mr. J. Buckley
Mr. M. Ahern
Mr. K. O Connell
Q1. (a) “When a complex current wave exists in a circuit, each of the components harmonics can
be looked upon as acting independently”.
(i) Discuss this in the context of the following circuits:
(a) An inductive circuit in which the resistance can be regarded as negligible.
(b) A capacitive circuit in which the resistance can be regarded as negligible.
(ii) Derive an expression for the current value of the third, fifth and seventh harmonic
for (a) and (b) above. The expression to express the current in terms of the
fundamental reactance x1 and the respective harmonic e.m.f. E3, E5 and E7.
(10 marks)
(b) An e.m.f. in which the amplitude of the fundamental (frequency 50 Hz) is 500 volts, and
which contains a 21st harmonic having an amplitude of 1 per cent of the fundamental,
exists in a circuit in which R = 2 ohms, L = 0.115 henry, and C = 0.2 microfarad.
Calculate the amplitude of :
(i) the harmonic current and the harmonic p.d. across the capacitor
(ii) the fundamental current. (10
marks)
pf3
pf4
pf5
pf8

Partial preview of the text

Download Capacitive Circuit - Electrical Engineering - Exam and more Exams Electrical Engineering in PDF only on Docsity!

Cork Institute of Technology

Bachelor of Engineering in Electrical Engineering – Award

(National Diploma in Engineering in Electrical Engineering – Award)

(NFQ – Level 7)

Autumn 2005

Electrical Engineering

(Time: 3 Hours)

Instructions Answer any FIVE questions. All questions carry equal marks.

Examiners: Mr. J. Buckley Mr. M. Ahern Mr. K. O Connell

Q1. (a) “When a complex current wave exists in a circuit, each of the components harmonics can be looked upon as acting independently”.

(i) Discuss this in the context of the following circuits: (a) An inductive circuit in which the resistance can be regarded as negligible. (b) A capacitive circuit in which the resistance can be regarded as negligible. (ii) Derive an expression for the current value of the third, fifth and seventh harmonic for (a) and (b) above. The expression to express the current in terms of the fundamental reactance x 1 and the respective harmonic e.m.f. E 3 , E 5 and E 7. (10 marks) (b) An e.m.f. in which the amplitude of the fundamental (frequency 50 Hz) is 500 volts, and which contains a 21 st^ harmonic having an amplitude of 1 per cent of the fundamental, exists in a circuit in which R = 2 ohms, L = 0.115 henry, and C = 0.2 microfarad. Calculate the amplitude of : (i) the harmonic current and the harmonic p.d. across the capacitor (ii) the fundamental current. ( marks)

Q2. A switchboard is fed via a 1500 kVA distribution transformer as shown in Fig. 1 attached. (a) Calculate the maximum short circuit current that can arise in the system. (6 marks) (b) Calculate the short circuit current that would arise in the event of a short circuit occurring at the entry to the cable box of the 250 kW squirrel cage motor. You may assume: (i) the primary voltage is 12 kV, 3-phase, 50 Hz (ii) the secondary voltage is 500 V, 3-phase, 50 Hz (iii) the percentage impedance of the transformer is 5% (iv) the impedance of the 800 A switchfuse is (0.651 x 10 -3^ + j0)Ω (v) the impedance of the 350 A starter is (1.341 x 10 -3^ +j0) Ω (vi) the impedance of the 2000 A ACB is (0.032 x 10 -3^ + j0) Ω. (14 marks)

Q3. The electrical loads taken from a 380 V, 3φ, 50 Hz, A.C. supply consists of: (i) A 3φ resistive heating load of 15 kW; (ii) A 3φ motive power load of 15 kW; at a P.F. of 0.8 lagging; (iii) A 3φ lighting load of 20 kW at P.F. 0.9 lagging; (iv) A 1φ load (R phase) 30 A @ P.F. 0.9 lagging; (v) A 1φ load (s phase) 20 A @ P.F. 0.8 lagging.

Q6. (a) With the aid of a neat sketch outline a method for connecting the secondary side of two 1000 kVA 10 kV/400 V distribution transformers to two sets of 400 V bus-bars such that under normal working conditions, the transformers are not connected in parallel, but in the event of the failure of one transformer, the remaining transformer may be connected to the two sets of bus-bars. (6 marks) (b) Two 1000 kVA oil immersed distribution transformers parallel feed a distribution system, via two 400 V 3φ 50 Hz air circuit breakers. The transformer has dual primaries 20 kV/10 kV. The secondary voltage is 400 V 3φ 50 Hz and the percentage impedance is 4.5%. (i) Calculate the maximum prospective short circuit current that can occur on the low tension (400 V) side. (ii) Calculate the full load current for each of the 400 V circuit breakers. (iii) Calculate the breaking capacity of each of the 400 V circuit breakers. (8 marks) (c) Discuss the conditions necessary for satisfactory operation of transformers in parallel. (6 marks) Q7. (a) Explain why reverse active current protection and reverse reactive current protection are necessary in an industrial installation which is fed in parallel by the ESB and an onsite generator. (10 marks) (b) Describe an experiment you carried out in the laboratory as part of your year’s work where you measured reverse reactive current. What was the function of this experiment and discuss (with graphical support) the results you got. (10 marks)