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Electrical Installation Practice 2

Electrical Installation Practice 2. LSEGG304A 9080D. Protection Devices Circuit Breakers. Content. Types of circuit breakers Operating principles of circuit breakers Inverse time/current characteristic of circuit breakers Circuit breakers and fault loop impedance Circuit breaker selection.

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Electrical Installation Practice 2

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  1. Electrical Installation Practice 2 LSEGG304A 9080D

  2. Protection DevicesCircuit Breakers

  3. Content • Types of circuit breakers • Operating principles of circuit breakers • Inverse time/current characteristic of circuit breakers • Circuit breakers and fault loop impedance • Circuit breaker selection

  4. Parts of A Circuit Breaker Thermal/Magnetic

  5. Parts of A Circuit Breaker Bimetal strip Used to detect overloads Bends when heat from current passes through it. It then mechanically trips the breaker

  6. Parts of A Circuit Breaker Bimetal strip

  7. Parts of A Circuit Breaker Solenoid Used to detect Short Circuits At a pre set current the coil attracts a metallic part of the trip, tripping the breaker

  8. Parts of A Circuit Breaker Solenoid

  9. Thermal/Magnetic Three basic time/current curves • Type B • Type C • Type D Used to protect • Generators • Long submains • General loads Power & Light • Motors

  10. Moulded Case

  11. Hydraulic Magnetic magnetic force produced by a load current flowing through a series connected coil Hermetically sealed tube containing an iron core, a spring and dampening fluid.

  12. Hydraulic Magnetic Overload • Magnetic flux in the solenoid pulls on the core. • Movement toward the pole piece is regulated by the hydraulic fluid. • Controlled time delay which is inversely proportional to the magnitude of the current.

  13. Hydraulic Magnetic Overload • If overload persists, core reaches the pole • Reluctance of the magnetic circuit drops • The armature is attracted to pole face • Breaker trips.

  14. Hydraulic Magnetic • Magnetic flux produced is large enough to attract armature to the pole face and trip the breaker even though the core has not moved. • Called the instantaneous trip region of the circuit breaker. Short Circuit

  15. Hydraulic Magnetic Advantages • Because magnetic operation, Trip curve not affected by ambient temperature • Can be re-closed immediately as there is no heating element • Possible to obtain any variation of time/current characteristic

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