ETO ETO Exam papers 📅 Jul 2023

Exam Question

Direct online starting for large induction motors such as those for bow thrust units, may not be viable.

(a) State the reasons for this. (5)

(b) Sketch a starting system that may be used for such motors. (6)

Reference Answer

(a) Reasons for Not Using Direct Online (DOL) Starting for Bow Thruster Units:
High Operating Voltage: Bow thruster units typically operate at high voltages (3.3 kV to 6.6 kV), making DOL starting unsuitable.
High Starting Current: DOL starting draws 3–4 times the normal operating current, which poses risks such as arc blast and safety device failure, especially in HV systems.
Low Starting Torque: Bow thrusters require immediate and high torque response, which DOL starting cannot provide efficiently.

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