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ElectricalEconomics for Engineers
PrevNext

Light duty cranes are generally used in

A

Power houses

B

Pumping stations

C

Automobile workshops

D

All of these

Correct Answer

Concept & PrincipleElectricalEconomics for Engineers
Option D

All of these

Quick Summary: Light duty cranes are defined as hoisting equipment designed for intermittent, low-frequency operation, typically handling loads significantly lower than their rated capacity. They are selected for environments where the operational demand is sporadic rather than continuous, ensuring cost-effectiveness in installation and maintenance.

ЁЯТб Explanation

Light duty cranes are defined as hoisting equipment designed for intermittent, low-frequency operation, typically handling loads significantly lower than their rated capacity. They are selected for environments where the operational demand is sporadic rather than continuous, ensuring cost-effectiveness in installation and maintenance.

ЁЯФв Key Formulas

Ud=nN├Ч100U_d = \frac{n}{N} \times 100UdтАЛ=NnтАЛ├Ч100 тАФ Duty factor calculation, where nnn is operating time and NNN is total time

Lavg=тИСPi3tiтИСti3L_{avg} = \sqrt[3]{\frac{\sum P_i^3 t_i}{\sum t_i}}LavgтАЛ=3тИСtiтАЛтИСPi3тАЛtiтАЛтАЛтАЛ тАФ Cubic mean load for duty cycle assessment

тЪЩя╕П Working Principle

The operational duty cycle of a crane, classified as light, medium, heavy, or extra-heavy, depends on the 'Class of Mechanism' determined by the frequency of usage and the load spectrum. Light duty cranes utilize smaller motor ratings and lighter structural frameworks because they are designed for fewer stress cycles over their service life, minimizing the required fatigue resistance compared to heavy-duty industrial cranes.

ЁЯУМ Key Points
  • тЦ╕

    Light duty cranes are classified under FEM or ISO standards based on low utilization rates.

  • тЦ╕

    Commonly found in maintenance shops or service areas where repairs are infrequent.

  • тЦ╕

    Energy consumption and mechanical wear are minimized by appropriate duty-class selection.

  • тЦ╕

    Power houses and pumping stations use them primarily for occasional equipment maintenance (e.g., turbine or pump motor assembly).

тЬЕ Advantages
  • тЦ╕

    Reduced capital investment due to lighter structural requirements.

  • тЦ╕

    Lower maintenance costs for intermittent operation profiles.

тЭМ Disadvantages / Limitations
  • тЦ╕

    Not suitable for continuous production lines or high-throughput logistics.

  • тЦ╕

    Risk of thermal overload if operated beyond the specified duty cycle.

ЁЯЫая╕П Applications / Uses
  • тЦ╕

    Maintenance of heavy pumping station motors.

  • тЦ╕

    Assembly and repair of automobile components.

  • тЦ╕

    Periodic servicing of power house electrical machinery.

ЁЯУД Additional Information
  • тЦ╕

    Light duty usually corresponds to ISO classification M1 to M3.

  • тЦ╕

    Selecting a crane with a duty cycle higher than the actual requirement increases installation costs unnecessarily, while choosing a lower class leads to premature mechanical failure.

ЁЯУК Diagram / Illustration
Crane Duty ClassificationTotal Load Cycles (N)Service Life Duration (T)
Light Duty: Low NNN / High TTT interval
тЬЕ

D is correct тАФ Light duty cranes are versatile machines ideal for intermittent maintenance tasks found in power houses, pumping stations, and workshops.

Core Concepts Used
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Duty Cycle Rating Mechanical Fatigue Installation Economics
ЁЯТб EXAM TIP

Always verify the duty cycle of electrical motors and mechanical hoists before selection; over-specifying equipment leads to wasted capital expenditure (CapEx), while under-specifying leads to excessive operational expenditure (OpEx) due to downtime.

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