উপকেন্দ্র ও উপকেন্দ্রের যন্ত্রপাতি সম্পর্কে ১০০ টি গুরুত্বপূর্ণ ভাইভা প্রশ্ন ও উত্তর

1. What is a substation?
   A substation is an electrical facility that transforms voltage levels and facilitates the transmission and distribution of electric power.

1. What are the main components of a substation?
   The main components of a substation include transformers, circuit breakers, busbars, isolators/disconnectors, instrument transformers, and control panels.

2. What is the purpose of a transformer in a substation?
   Transformers are used to step up or step down the voltage levels for efficient power transmission and distribution.

3. What are the different types of transformers used in substations?
   The different types of transformers used in substations are power transformers, distribution transformers, and instrument transformers (current transformers and voltage transformers).

4. What is the function of a circuit breaker in a substation?
   Circuit breakers are used to interrupt the flow of current in case of faults or abnormal conditions to protect the electrical equipment and the system.

5. How does a circuit breaker differ from a fuse?
   Circuit breakers can be reset and reused, whereas fuses need to be replaced after they blow.

6. What is a busbar in a substation?
   A busbar is a conductor used to connect different electrical equipment in a substation.

7. What is the significance of isolators or disconnectors in a substation?
   Isolators or disconnectors are used to isolate equipment for maintenance or repair purposes without interrupting the power supply to the rest of the system.

8. What is the purpose of instrument transformers?
   Instrument transformers are used to step down high currents and voltages to measurable levels for protection and metering purposes.

9. What is the difference between a current transformer (CT) and a voltage transformer (VT)?
   A current transformer steps down high currents to a lower value, while a voltage transformer steps down high voltages to a lower value.

10. What are the commonly used insulating materials in substation equipment?
    Common insulating materials include oil, air, and solid materials like porcelain or composite insulators.

11. What are the different types of substation layouts?
    The different types of substation layouts are radial, ring, and breaker-and-a-half.

12. What is the purpose of lightning arresters in a substation?
    Lightning arresters protect the substation equipment from voltage surges caused by lightning strikes.

13. What are shunt reactors, and why are they used in substations?
    Shunt reactors are used to compensate for reactive power in long transmission lines and maintain voltage stability.

14. What are auto-transformers, and where are they used in substations?
    Auto-transformers have a single winding and are used for voltage transformation in specific applications where the transformation ratio is not significant.

15. What is a capacitor bank, and what is its role in substations?
    A capacitor bank is used to improve power factor and reduce reactive power in the system, leading to improved efficiency.

16. What is a gas-insulated substation (GIS)?
    A gas-insulated substation uses sulfur hexafluoride (SF6) gas as an insulating medium for high-voltage equipment, enabling compact designs and better environmental protection.

17. What are the advantages of a GIS over an air-insulated substation (AIS)?
    GIS offers smaller footprint, higher reliability, lower maintenance requirements, and enhanced protection against environmental elements.

18. What is a switchgear, and how is it different from a circuit breaker?
    Switchgear is a general term for a combination of electrical disconnect switches, fuses, or circuit breakers used to control, protect, and isolate electrical equipment. A circuit breaker is a specific type of switchgear used to interrupt currents in case of faults.

19. What is the role of a control panel in a substation?
    A control panel houses the control and monitoring devices for the substation equipment, enabling operators to manage the substation effectively.

20. What is a step-up transformer, and where is it used?
    A step-up transformer increases the voltage level from the generator output to the transmission voltage level for long-distance power transmission.

21. What is the purpose of a step-down transformer, and where is it used?
    A step-down transformer decreases the transmission voltage level to distribution voltage levels suitable for consumer use.

22. What are the factors considered while selecting the location for a substation?
    Factors include load demand, proximity to the load center, availability of land, accessibility, and environmental considerations.

23. How is a ground grid beneficial in a substation?
    A ground grid provides a low-resistance path for fault currents to flow, ensuring safety and reducing the risk of damage to equipment.

24. What is the main difference between a distribution substation and a transmission substation?
    A distribution substation steps down the voltage for local distribution to consumers, while a transmission substation steps up the voltage for long-distance transmission.

25. What is the difference between an indoor substation and an outdoor substation?
    An indoor substation is housed in an enclosed building, whereas an outdoor substation is open-air and may be protected by fences or walls.

26. Why are substation fences and access gates essential?
    Fences and access gates help protect the substation from unauthorized entry, ensuring safety and security.

27. What are the various methods used to detect and locate faults in a substation?
    Methods include current differential protection, distance protection, and overcurrent protection.

28. What are the challenges faced in substations located in areas with extreme weather conditions?
    Extreme weather conditions can affect equipment performance, and measures such as insulation, heating, and cooling systems are implemented to mitigate these effects.

29. What is the purpose of a surge arrester in a substation?
    Surge arresters protect equipment from voltage surges caused by lightning or other transient events.

30. What is the difference between an outdoor and an indoor surge arrester?
    An outdoor surge arrester is designed to withstand weather conditions, while an indoor surge arrester is intended for indoor use and may be housed in a metal container for protection.

31. How are substation transformers cooled?
    Substation transformers are commonly cooled using mineral oil, air, or in some cases, liquid dielectric coolants.

32. What is a tap changer in a transformer, and what is its function?
    A tap changer is a device used to adjust the turns ratio of a transformer, enabling voltage regulation and load voltage control.

33. What is the significance of a relay in a substation?
    Relays are protective devices that detect faults and issue trip signals to circuit breakers, isolating faulty sections to protect the system.

34. How is a substation maintained to ensure optimal performance?
    Regular inspections, testing, and preventive maintenance measures are undertaken to ensure the substation's efficiency and reliability.

35. What is the purpose of a substation battery bank?
    A substation battery bank provides backup power for control and protection systems during power outages.

36. How are fault currents interrupted in a substation?
    Fault currents are interrupted using protective devices like circuit breakers or fuses.

37. What is the difference between a power substation and a distribution substation?
    A power substation is a large facility that handles high-voltage transmission, while a distribution substation is closer to consumers and steps down the voltage for local distribution.

38. What is the significance of an auxiliary transformer in a substation?
    An auxiliary transformer provides power for auxiliary systems, control circuits, and lighting within the substation.

39. What are the safety precautions to be taken while working in a substation?
    Safety precautions include wearing appropriate personal protective equipment (PPE), following lockout-tagout procedures, and adhering to safety protocols to prevent electric shock and other hazards.

40. What are the main differences between a three-phase and a single-phase transformer?
    A three-phase transformer has three windings and is used in three-phase power systems, while a single-phase transformer has only one winding and is used in single-phase power systems.

41. What is the purpose of a substation grounding grid?
    A grounding grid ensures that the substation equipment and structures are at the same electrical potential, reducing the risk of electrical shock and equipment damage.

42. How is the oil quality of a transformer maintained?
    The oil quality of a transformer is maintained by periodically testing and filtering the oil to remove impurities and moisture.

43. What is a static var compensator (SVC), and why is it used in substations?
    An SVC is a power electronics-based device used to control reactive power flow and voltage levels, improving system stability and voltage regulation.

44. What are the different types of cooling methods used for power transformers?
    Power transformers can be cooled using oil, air, or water-cooling systems.

45. Why are substation transformers equipped with Buchholz relays?
    Buchholz relays are used to detect internal faults and gas accumulation in oil-filled transformers.

46. What is the function of a load tap changer (LTC) in a transformer?
    A load tap changer adjusts the transformer's turns ratio to maintain the output voltage within specified limits during load variations.

47. What is the role of sulfur hexafluoride (SF6) gas in gas-insulated substations?
    SF6 gas acts as an insulating and arc-quenching medium in gas-insulated substations, making them more compact and efficient.

48. How are substation equipment protected against animal intrusions?
    Animal guards and fencing are used to protect equipment from animals, reducing the risk of electrical faults and damage.

49. What is the purpose of lightning masts in substations?
    Lightning masts are tall structures installed in substations to intercept and divert lightning strikes away from critical equipment.

50. How is the safety of substation personnel ensured during maintenance activities?
    Safety measures include proper training, the use of appropriate PPE, and compliance with lockout-tagout procedures to de-energize and isolate equipment.

51. What is the difference between an open-air substation and a compact substation?
    An open-air substation is typically larger and uses outdoor equipment, while a compact substation is designed for limited space and is enclosed within a compact structure.

52. What are the factors that determine the insulation level of substation equipment?
    The insulation level is determined by the system voltage, lightning overvoltages, and switching overvoltages.

53. What is a capacitor voltage transformer (CVT), and where is it used?
    A CVT is a type of voltage transformer that uses capacitive voltage division to provide accurate voltage measurement for protection and metering purposes.

54. What are the various types of relay protection schemes used in substations?
    Overcurrent, differential, distance, and differential/distance schemes are commonly used for various protection requirements.

55. What are the key requirements for a substation's control room design?
    The control room should have adequate space, proper ventilation, ergonomic design, and clear visibility of the equipment and displays.

56. What are the primary functions of a substation automation system (SAS)?
    SAS is used for remote monitoring, control, and data acquisition of substations, enhancing operational efficiency and reducing maintenance costs.

57. How are oil leaks detected and repaired in a power transformer?
    Oil leaks are detected through regular inspections and treated by replacing faulty gaskets or seals.

58. Why are substation buildings equipped with lightning protection systems?
    Lightning protection systems protect substation buildings and equipment from direct lightning strikes, reducing the risk of damage.

59. What is a load break switch, and where is it used?
    A load break switch is used to interrupt or establish electrical circuits under load conditions and is often employed in distribution networks.

60. What are the factors that determine the insulation level of substation equipment?
    The insulation level is determined by the system voltage, lightning overvoltages, and switching overvoltages.

61. What is a capacitor voltage transformer (CVT), and where is it used?
    A CVT is a type of voltage transformer that uses capacitive voltage division to provide accurate voltage measurement for protection and metering purposes.

62. What are the various types of relay protection schemes used in substations?
    Overcurrent, differential, distance, and differential/distance schemes are commonly used for various protection requirements.

63. What are the key requirements for a substation's control room design?
    The control room should have adequate space, proper ventilation, ergonomic design, and clear visibility of the equipment and displays.

64. What are the primary functions of a substation automation system (SAS)?
    SAS is used for remote monitoring, control, and data acquisition of substations, enhancing operational efficiency and reducing maintenance costs.

65. How are oil leaks detected and repaired in a power transformer?
    Oil leaks are detected through regular inspections and treated by replacing faulty gaskets or seals.

66. Why are substation buildings equipped with lightning protection systems?
    Lightning protection systems protect substation buildings and equipment from direct lightning strikes, reducing the risk of damage.

67. What is a load break switch, and where is it used?
    A load break switch is used to interrupt or establish electrical circuits under load conditions and is often employed in distribution networks.

68. What are the different types of substation bus schemes?
    The different types of bus schemes include single bus, double bus, main and transfer bus, and ring bus configurations.

69. How are substation equipment and structures protected against corrosion?
    Regular maintenance, painting, and the use of corrosion-resistant materials help protect against corrosion.

70. What is a substation feeder, and what is its role?
    A substation feeder is a set of conductors used to distribute power from the substation to the end-users.

71. What are the safety measures taken to protect against electrical fires in a substation?
    Fireproof construction materials, fire detection systems, and firefighting equipment are installed to prevent and mitigate electrical fires.

72. How is the condition of transformer insulation assessed during maintenance?
    Insulation resistance testing and dissolved gas analysis (DGA) are commonly used methods to assess the condition of transformer insulation.

73. What is the purpose of a substation grounding system?
    The grounding system ensures safety by providing a low-impedance path for fault currents, thereby preventing dangerous voltage buildup.

74. How are substation transformers protected against overloading and overheating?
    Temperature sensors and protective relays monitor the transformer's temperature and issue trip signals if it exceeds safe limits.

75. What is the role of a Buchholz relay in a transformer?
    A Buchholz relay detects internal faults and gas accumulation in oil-filled transformers and sends alarms or trip signals.

76. How are substation equipment protected against animal intrusions?
    Animal guards and fencing are used to protect equipment from animals, reducing the risk of electrical faults and damage.

77. What is the purpose of lightning masts in substations?
    Lightning masts are tall structures installed in substations to intercept and divert lightning strikes away from critical equipment.

78. How is the safety of substation personnel ensured during maintenance activities?
    Safety measures include proper training, the use of appropriate PPE, and compliance with lockout-tagout procedures to de-energize and isolate equipment.

79. What is the difference between an open-air substation and a compact substation?
    An open-air substation is typically larger and uses outdoor equipment, while a compact substation is designed for limited space and is enclosed within a compact structure.

80. What are the factors that determine the insulation level of substation equipment?
    The insulation level is determined by the system voltage, lightning overvoltages, and switching overvoltages.

81. What is a capacitor voltage transformer (CVT), and where is it used?
    A CVT is a type of voltage transformer that uses capacitive voltage division to provide accurate voltage measurement for protection and metering purposes.

82. What are the various types of relay protection schemes used in substations?
    Overcurrent, differential, distance, and differential/distance schemes are commonly used for various protection requirements.

83. What are the key requirements for a substation's control room design?
    The control room should have adequate space, proper ventilation, ergonomic design, and clear visibility of the equipment and displays.

84. What are the primary functions of a substation automation system (SAS)?
    SAS is used for remote monitoring, control, and data acquisition of substations, enhancing operational efficiency and reducing maintenance costs.

85. How are oil leaks detected and repaired in a power transformer?
    Oil leaks are detected through regular inspections and treated by replacing faulty gaskets or seals.

86. Why are substation buildings equipped with lightning protection systems?
    Lightning protection systems protect substation buildings and equipment from direct lightning strikes, reducing the risk of damage.

87. What is a load break switch, and where is it used?
    A load break switch is used to interrupt or establish electrical circuits under load conditions and is often employed in distribution networks.

88. What are the different types of substation bus schemes?
    The different types of bus schemes include single bus, double bus, main and transfer bus, and ring bus configurations.

89. How are substation equipment and structures protected against corrosion?
    Regular maintenance, painting, and the use of corrosion-resistant materials help protect against corrosion.

90. What is a substation feeder, and what is its role?
    A substation feeder is a set of conductors used to distribute power from the substation to the end-users.

91. What are the safety measures taken to protect against electrical fires in a substation?
    Fireproof construction materials, fire detection systems, and firefighting equipment are installed to prevent and mitigate electrical fires.

92. How is the condition of transformer insulation assessed during maintenance?
    Insulation resistance testing and dissolved gas analysis (DGA) are commonly used methods to assess the condition of transformer insulation.

93. What is the purpose of a substation grounding system?
    The grounding system ensures safety by providing a low-impedance path for fault currents, thereby preventing dangerous voltage buildup.

94. How are substation transformers protected against overloading and overheating?
    Temperature sensors and protective relays monitor the transformer's temperature and issue trip signals if it exceeds safe limits.

95. What is the role of a Buchholz relay in a transformer?
    A Buchholz relay detects internal faults and gas accumulation in oil-filled transformers and sends alarms or trip signals.

96. What are the measures taken to protect against electrical faults caused by vegetation near substations?
    Vegetation clearance and regular trimming are conducted to prevent tree branches from coming into contact with electrical equipment.

97. How are substation control systems secured against cybersecurity threats?
    Firewalls, intrusion detection systems, and regular software updates are implemented to protect against cyberattacks.

98. What is the purpose of a substation annunciator panel?
    An annunciator panel provides visual and audible alarms to indicate specific conditions or faults in the substation.

99. How are substation equipment and structures protected against vandalism and theft?
    Security measures such as surveillance cameras, fencing, and access control systems are employed to deter vandalism and theft.

100. Please note that the scope of these questions can vary based on the level of the viva (e.g., undergraduate, graduate, or professional). Additionally, some questions may require more detailed answers, and further elaboration may be necessary during the viva examination.