Examination Authority - Maharashtra State Board of Technical Education, Mumbai
Examination - Winter 2014
Scheme - 'G'
Course Name - Diploma in Electrical Engineering
Medium - English
Time - 3 Hours
Marks - 100
Subject -Switchgear and Protection
Subject code -(17508)
Semester - Fifth
MSBTE Mumbai Previous Years Question Papers
3 Hours/100 Marks
Instructions : (1) All questions are compulsory.
(2) Illustrate your answers with neat sketches wherever necessary.
(3) Figures to the right indicate full marks.
(4) Assume suitable data, if necessary.
(5) Use of Non-programmable Electronic Pocket Calculator is permissible.
(6) Mobile Phone, Pager and any other Electronic Communication devices are not permissible in Examination Hall.
1. A) Attempt any three of the following : (3×4=12)
a) State any four abnormal conditions which can develop in power system and state its effect on power system.
b) State the necessity of current limiting reactors in power system and classify the reactors on the basis of their location.
c) State various causes of over voltages in an electrical power system.
d) What are fundamental requirements of protective relaying ? What qualities relay must posses for satisfactory functioning.
B) Attempt any one of the following : (1×6=6)
a) Two 11 KV, 3 phase, 3000 KVA generators having reactance of 15% operates in parallel. The generator supply power to a transmission line through a 6000 KVA transformer of ratio 11/22 KV and having leakage reactance of 5%. Calculate fault current and faults KVA on H.T. side of a
transformer.
b) A 3 phase transformer of 220/11000 volts is connected in star/delta is protected by Merz price circulating current scheme. The protective transformer on 220 volt side have a current ratio of 600/S. What should be the ratio on 11000 volt side. Draw a neat diagram and indicate given values at appropriate places.
2. Attempt any four of the following : (4×4=16)
a) Compare HRC Fuse and circuit brakers as an interrupting devices.
b) State the sequence of operation of isolator, circuit breaker and earthing switches :
i) while closing the circuit
ii) while opening the circuit.
c) Describe the construction and principle of operation of a typical lighting arrestor.
d) State necessity of neutral earthing and list the different methods.
e) Define the following terms related to relay :
i) Relay time
ii) Pick up
iii) Reset
iv) Fault clearing time.
f) State the abnormalities and faults in alternator with necessary protection.
3. Attempt any four of the following : (4×4=16)
a) Describe current zero method for arc extinction in circuit breaker operation.
b) What is ELCB ? Describe its working.
c) The current rating of an overcurrent relay is 5 Amp. Current setting is at 200%. Tsm = 0.4, CT ratio= 400/S. Fault current = 4000 Amp. Determine the operating time of the relay. Use the following table operating at various PSM at TMS = 1. PSM 2 4 8 20 Relay time in Sec. 10 5 3 2.4
d) State the common faults occurs in power transformer. Suggests the protection for these faults.
e) What are the difficulties in differential protection scheme used for transformer ?
4. A) Attempt any three of the following : (3×4=12)
a) Draw a diagram of differential protection scheme for a star connected alternator and explain its working.
b) Define the term insulation co-ordination. Draw the volt-time curve of an apparatus used in power system.
c) Define following terms related to C.B. :
i) Rated normal current
ii) Rated breaking current
iii) Short time rating
iv) Symmetrical breaking current.
d) Which are most commonly used schemes for bus bar protection ? Explain any one scheme in detail.
B) Attempt any one of the following : (1×6=6)
a) What type of motor protection is used for high capacity induction motors ? Describe the function of different relays used.
b) What are advantages of distance protection over other type of protection of feeder ? Explain distance protection of transmission line.
5. Attempt any four of the following : (4×4=16)
a) State any eight properties of SF6 gas which is suitable for arc quenching.
b) Describe the working principle, construction and advantages of vacuum e-circuit breaker with neat diagram.
c) Describe with the help of neat diagram the construction and operation of Induction type over current relay.
d) Explain how the plug setting and time setting can be done in induction relay.
e) State advantages and disadvantages of static relays over electromagnetic relays.
f) State salient features of microprocessor based protection relay. Draw blockdiagram of microprocessor based overcurrent relay.
6. Attempt any four of the following : (4×4=16)
a) Draw neat labelled diagram of Buchholz relay.
b) State the specifications of CT and PT as a protective transformer.
c) How negative phase sequence current are set up in an alternator ? Draw protective scheme for same.
d) Describe restricted earth fault-protection scheme for 3 phase Delta/Star transformer with neat diagram.
e) What are the requirements of transmission line protection ?
_________________
Examination - Winter 2014
Scheme - 'G'
Course Name - Diploma in Electrical Engineering
Medium - English
Time - 3 Hours
Marks - 100
Subject -Switchgear and Protection
Subject code -(17508)
Semester - Fifth
MSBTE Mumbai Previous Years Question Papers
3 Hours/100 Marks
Instructions : (1) All questions are compulsory.
(2) Illustrate your answers with neat sketches wherever necessary.
(3) Figures to the right indicate full marks.
(4) Assume suitable data, if necessary.
(5) Use of Non-programmable Electronic Pocket Calculator is permissible.
(6) Mobile Phone, Pager and any other Electronic Communication devices are not permissible in Examination Hall.
1. A) Attempt any three of the following : (3×4=12)
a) State any four abnormal conditions which can develop in power system and state its effect on power system.
b) State the necessity of current limiting reactors in power system and classify the reactors on the basis of their location.
c) State various causes of over voltages in an electrical power system.
d) What are fundamental requirements of protective relaying ? What qualities relay must posses for satisfactory functioning.
B) Attempt any one of the following : (1×6=6)
a) Two 11 KV, 3 phase, 3000 KVA generators having reactance of 15% operates in parallel. The generator supply power to a transmission line through a 6000 KVA transformer of ratio 11/22 KV and having leakage reactance of 5%. Calculate fault current and faults KVA on H.T. side of a
transformer.
b) A 3 phase transformer of 220/11000 volts is connected in star/delta is protected by Merz price circulating current scheme. The protective transformer on 220 volt side have a current ratio of 600/S. What should be the ratio on 11000 volt side. Draw a neat diagram and indicate given values at appropriate places.
2. Attempt any four of the following : (4×4=16)
a) Compare HRC Fuse and circuit brakers as an interrupting devices.
b) State the sequence of operation of isolator, circuit breaker and earthing switches :
i) while closing the circuit
ii) while opening the circuit.
c) Describe the construction and principle of operation of a typical lighting arrestor.
d) State necessity of neutral earthing and list the different methods.
e) Define the following terms related to relay :
i) Relay time
ii) Pick up
iii) Reset
iv) Fault clearing time.
f) State the abnormalities and faults in alternator with necessary protection.
3. Attempt any four of the following : (4×4=16)
a) Describe current zero method for arc extinction in circuit breaker operation.
b) What is ELCB ? Describe its working.
c) The current rating of an overcurrent relay is 5 Amp. Current setting is at 200%. Tsm = 0.4, CT ratio= 400/S. Fault current = 4000 Amp. Determine the operating time of the relay. Use the following table operating at various PSM at TMS = 1. PSM 2 4 8 20 Relay time in Sec. 10 5 3 2.4
d) State the common faults occurs in power transformer. Suggests the protection for these faults.
e) What are the difficulties in differential protection scheme used for transformer ?
4. A) Attempt any three of the following : (3×4=12)
a) Draw a diagram of differential protection scheme for a star connected alternator and explain its working.
b) Define the term insulation co-ordination. Draw the volt-time curve of an apparatus used in power system.
c) Define following terms related to C.B. :
i) Rated normal current
ii) Rated breaking current
iii) Short time rating
iv) Symmetrical breaking current.
d) Which are most commonly used schemes for bus bar protection ? Explain any one scheme in detail.
B) Attempt any one of the following : (1×6=6)
a) What type of motor protection is used for high capacity induction motors ? Describe the function of different relays used.
b) What are advantages of distance protection over other type of protection of feeder ? Explain distance protection of transmission line.
5. Attempt any four of the following : (4×4=16)
a) State any eight properties of SF6 gas which is suitable for arc quenching.
b) Describe the working principle, construction and advantages of vacuum e-circuit breaker with neat diagram.
c) Describe with the help of neat diagram the construction and operation of Induction type over current relay.
d) Explain how the plug setting and time setting can be done in induction relay.
e) State advantages and disadvantages of static relays over electromagnetic relays.
f) State salient features of microprocessor based protection relay. Draw blockdiagram of microprocessor based overcurrent relay.
6. Attempt any four of the following : (4×4=16)
a) Draw neat labelled diagram of Buchholz relay.
b) State the specifications of CT and PT as a protective transformer.
c) How negative phase sequence current are set up in an alternator ? Draw protective scheme for same.
d) Describe restricted earth fault-protection scheme for 3 phase Delta/Star transformer with neat diagram.
e) What are the requirements of transmission line protection ?
_________________
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