Title 22524 SAP msbteallclear.com.pdf ✅

MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION (Autonomous) (ISO/IEC - 27001 - 2013 Certified) ________________________________________________________________________________________________________________ SUMMER – 2023 EXAMINATION Model Answer – Only for the Use of RAC Assessors Subject Name: Switchgear And Protection Page 1 of 17 22524: SAP Important Instructions to examiners: 1) The answers should be examined by key words and not as word-to-word as given in the model answer scheme. 2) The model answer and the answer written by candidate may vary but the examiner may try to assess the understanding level of the candidate. 3) The language errors such as grammatical, spelling errors should not be given more Importance (Not applicable for subject English and Communication Skills). 4) While assessing figures, examiner may give credit for principal components indicated in the figure. The figures drawn by candidate and model answer may vary. The examiner may give credit for any equivalent figure drawn. 5) Credits may be given step wise for numerical problems. In some cases, the assumed constant values may vary and there may be some difference in the candidate’s answers and model answer. 6) In case of some questions credit may be given by judgement on part of examiner of relevant answer based on candidate’s understanding. 7) For programming language papers, credit may be given to any other program based on equivalent concept. 8) As per the policy decision of Maharashtra State Government, teaching in English/Marathi and Bilingual (English + Marathi) medium is introduced at first year of AICTE diploma Programme from academic year 2021-2022. Hence if the students write answers in Marathi or bilingual language (English +Marathi), the Examiner shall consider the same and assess the answer based on matching of concepts with model answer. Q. No. Sub Q. N. Answer Marking Scheme 1. Attempt any FIVE of the following: 10 Marks a) State any two functions of protective system. Ans: Functions of Protective System: 1. To switch ON or OFF the electric power during normal conditions for operation and maintenance. 2. To protect the power system by isolating the faulty parts due to abnormal conditions within shortest possible time. 3. To provide the reliable and continuous supply to consumers. 4. To isolate only faulty sections of system without affecting the healthy sections of system. 5. Constantly monitor the electrical quantities of system so that occurrence of fault should be minimized. 6. To prevent the occurrence of major faults. 7. To ensure maximum safety conditions from generation stage to consumer’s premises. 1 Mark for each of any two functions = 2 Marks b) List any four applications of HRC fuse. Ans: Applications of HRC Fuse: 1. HRC fuses are used to protect the circuit from short circuits in HV switchgear. 2. Used for backup protection to the circuit breaker. 3. Used to protect electrical devices like motors, transformers etc. 4. Motor stators also require this kind of fuse. 5. Used to protect high selectivity radial and ring networks. 6. Used for protection of semiconductor devices. 1⁄2 Mark for each of any four applications = 2 Marks msbteallclear.com
MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION (Autonomous) (ISO/IEC - 27001 - 2013 Certified) ________________________________________________________________________________________________________________ SUMMER – 2023 EXAMINATION Model Answer – Only for the Use of RAC Assessors Subject Name: Switchgear And Protection Page 2 of 17 22524: SAP 7. Used for protection of cables. 8. Used for protection of LV distribution system against overload and short circuit. 9. Used for protection of automobiles circuits. 10. Used for protection of capacitor banks. 11. Used for protection of small loads in circuits having high fault levels. 12. Used for protection of AC drives. 13. Used for protection of DC drives. 14. Used for protection of UPS system. 15. Used for protection of electronic equipment. OR Equivalent Answer c) State function of RCBO and MPCB. Ans: Functions of RCBO: 1. It gives protection against short circuit fault. 2. It gives protection against over-current or overload fault. 3. It gives protection against leakage current fault, electrical shock. 4. It can give protection against current imbalance. 5. It automatically breaks the circuit when flow of current through it exceeds a certain level. Functions of MPCB: 1. Protection against faults such as short circuits, line-to-ground faults and line-to-line faults. The MPCB can interrupt any electrical fault that is below its breaking capacity. 2. Motor overload protection, when motor draws electric current above its nameplate value for an extended period of time. Overload protection is normally adjustable in MPCBs. 3. Protection against phase unbalances and phase loss. Both conditions can severely damage a three-phase motor, so the MPCB will disconnect the motor in either case as soon as the fault is detected. 4. Thermal delay to prevent the motor from being turned back on immediately after an overload, giving the motor time to cool down. An overheated motor can be permanently damaged if it is turned back on. 5. Fault Signalling – Most models of motor protection circuit breakers have a LED display that is turned on whenever the MPCB has tripped. This is a visual indication for nearby personnel that a fault has occurred and the electric motor must not be connected again until the fault is addressed. 6. Automatic Reconnection – Some MPCB models allow a cool down time to be input in case there is an overload, after which the motor will restart automatically. 1 Mark for any one function 1 Mark for any one function d) State the need of directional relay. Ans: Need of Directional Relay: In power system (power equipment / distribution lines / transmission lines etc.) fault can be in two different directions from relay and it is highly desirable for a relay to respond differently for faults in the forward or reverse direction. In fact, the relay should respond only when the fault is on one side, 2 Marks msbteallclear.com
MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION (Autonomous) (ISO/IEC - 27001 - 2013 Certified) ________________________________________________________________________________________________________________ SUMMER – 2023 EXAMINATION Model Answer – Only for the Use of RAC Assessors Subject Name: Switchgear And Protection Page 3 of 17 22524: SAP while for failures on the other side it remains inactive. In order to avoid disconnection of unnecessary circuits as normal overcurrent relay cannot provide this function directional relay is needed. Directional relay enables better discrimination of the faulty part of the network than with overcurrent protection. e) List any four protection scheme used for alternator. Ans: Protection Scheme Used for Alternator: 1. Mertz price protection. 2. Differential protection. 3. Percentage differential protection. 4. Over current protection. 5. Earth fault protection. 6. Inter turn fault protection. 7. Negative phase sequence protection against unbalanced loading. 8. Overheating protection. 9. Balanced earth fault protection. 10. Restricted earth fault protection. 11. Protection against loss of excitation. 12. Reverse power protection. 13. Protection against over speed. 14. Short circuit protection. 1⁄2 Mark for each of any four schemes = 2 Marks f) Draw time-current characteristics of IDMT relay. Ans: Time-Current Characteristics of IDMT Relay: 2 Marks for labeled diagram g) List any four faults related to busbar. Ans: Faults Related to Busbar: 1. Failure of support insulators resulting in earth faults. 2. Failure of circuit breakers to interrupt the fault current. 3. Foreign object accidentally falling across the busbar. 4. Flash over across support insulator causing flash over due to over-voltage. 5. Heavily polluted insulator, causing flash-over. 6. Earthquake, mechanical damages. 7. Failure of other related equipment. 8. Errors in operation and maintenance. 1⁄2 Mark for each of any four faults = 2 Marks msbteallclear.com