Explain the construction of over-current protection devices

Circuit Protection and Polyphase Motors
Explain the construction of over-current protection devices
Explain the operating principles of circuit over-current protection devices
Explain the operating principles of earth fault protection devices

1. Explain, with the aid of diagrams, the construction and operating principles of the following types of protection devices:

a. Airblast circuit breaker

b. Oil-filled circuit breaker

c. High rupture capacity fuse

d. Residual current device

e. Earth fault relay

Task 2 – Learning Outcome 5.1
Describe the types and explain the construction of induction motors

2. Describe the construction of the following types of three-phase induction motors; you may use diagrams to aid your description.

a. Single cage

b. Double cage

c. Wound rotor

Task 3 – Learning Outcome 5.2
Explain the operating principles and methods of starting induction motors
3. Explain the operating principles of a three-phase cage rotor induction motor. Your explanation must include the terms:

a. Rotating magnetic field
b. Mutual inductance
c. Slip
d. Synchronous speed
e. Torque
4. The following are all methods of starting a three-phase induction motor. In each case, explain how the starting method works, state the type of motor the starter is used on, and a typical power range for that motor.

a. Direct-on-line

b. Star-Delta

c. Inverter / soft start

Task 4 – Learning Outcomes 5.3
Analyse the methods of speed control of induction motors

5. Describe and analyse two different methods of controlling the speed of three-phase induction motors.

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