Part 1 — Electrical Engineering Queries Asked by Our Valuable Students

  1. Thermal Trip Curve: This is the trip curve for the bi-metallic strip, which is designed for slower overcurrent to allow for in rush/startup, as described above.
  2. Magnetic Trip Curve: This is the trip curve for the coil or solenoid. It is designed to react quickly to large overcurrent, such as a short circuit condition.
  3. The Ideal Trip Curve: This curve shows what the desired trip curve for the bi-metallic strip is. Because of the organic nature of the bi-metallic strip, and changing ambient conditions, it is difficult to precisely predict the exact tripping point.
  • Type 1 (Type A) SPD: The Type 1 SPD is recommended in the specific case of service-sector and industrial buildings, protected by a lightning protection system or a meshed cage. They are also intended for installation between the secondary of the service transformer and the line side of the service equipment overcurrent device, as well as the load side, including watt-hour meter socket enclosures, and are intended to be installed without an external overcurrent protective device.
    It protects electrical installations against direct lightning strokes. It can discharge the back-current from lightning spreading from the earth conductor to the network conductors.
  • Type 2 (Type B) SPD: The Type 2 SPD is the main protection system for all low voltage electrical installations. Installed in each electrical switchboard, it prevents the spread of over voltages in the electrical installations and protects the loads. connected Type 2 SPDs are intended for installation on the load side of the service equipment overcurrent device, including SPDs located at the branch panel.
  • Type 3 (Type C) SPD: They are installed as a supplement to Type 2 SPD and in the vicinity of sensitive loads. Type 3 Point-of-Use Surge Protection Point-of-use surge protectors such as surge receptacles are installed within 30 ft of conductor length from the service panel and are designed to offer premium surge protection for specific electronics while providing innovative features to enhance user convenience.
  • Type 4 (Type D) SPD: Type 4 SPDs may be intended as Type 1 SPDs, Type 2 SPDs, or Type 3 SPDs and must be considered based on their intended application.
  • 10 kA for Type 1 SPDs or Type 4 SPDs used for Type 1 SPD Applications
  • 3 kA, 5 kA, or 10 kA for Type 2 SPDs or Type 4 SPDs used for Type 2 SPD Applications and, optionally, for Type 3 SPDs
  1. Corrective: After failure occurs
  2. Preventive: Regular maintenance to prevent future failure
  • Availability of skillful maintenance worker
  • Tools and equipment for maintainability
  • Spare stocks for backup operations
  • Maintenance policy
  • Environmental factor (weather, size, working conditions)
  • Systematic maintenance data collection, analysis and continued reliability study
  • GMS (generator maintenance schedule) and TMS (transportation maintenance schedule) using different algorithm
  1. Equipment criticality and device significance
  2. Current condition
  3. Lubrication life
  4. Maintenance history
  5. Operational history
  6. Industry experience
  7. Maintenance philosophy
  8. Operating environment
  9. Time allowed for maintenance
  10. Manufacturer’s recommendations



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AllumiaX Engineering

AllumiaX Engineering

Leaders in Industrial & Commercial Power Systems Engineering