HV Exit Exam • Set 7 Question 3 of 30

Which type of protective relay is commonly used to protect electric motors against continuous moderate overload?

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Direct Answer

Option C: Bimetallic thermal overload relay

Thermal overload relays utilize bimetallic strips heated by motor load current to replicate the thermal heating curve of the motor windings and provide inverse-time tripping.

All Options

Impedance / Distance relay

Instantaneous electromagnetic relay

Bimetallic thermal overload relay (Correct Answer)

Buchholz gas relay

Detailed Explanation & Context

Thermal overload relays utilize bimetallic strips heated by motor load current to replicate the thermal heating curve of the motor windings and provide inverse-time tripping.

Relevant Framework: STCW 2010 Manila Amendments • DG Shipping E-Learning & Exit Exam Standards • High Voltage Safety Officer & Switchgear Operations (HV).

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Q1 High Rupturing Capacity (HRC) fuses provide the most effective and rapid protection under conditions of: Q2 For high-speed motor circuit breakers, the total closing time from command signal to contact touch is typically in the order of: Q3 Which type of protective relay is commonly used to protect electric motors against continuous moderate overload? Q4 According to Preece's Law, the fusing current (I) of a fuse wire is related to its wire diameter (D) by the relationship: Q5 In a circuit breaker contact gap, ionization of the medium is NOT facilitated by: Q6 An ideal fuse wire material should possess which combination of physical properties? Q7 For extra-high-voltage (EHV) transmission networks above 220 kV, which circuit breaker type is predominantly selected? Q8 The number of power-frequency AC cycles in which a modern high-speed circuit breaker completes its tripping and arc clearing operation is: Q9 Which of the following metals is best suited for manufacturing precision HRC fuse elements due to its resistance to oxidation and low specific resistance? Q10 In a circuit breaker, the current that is flowing through the contacts at the precise instant of contact separation is known as the: