Overhead Travelling Cranes Quiz

Questions and Answers

What is one major disadvantage of pneumatic motors compared to electric motors?

They contain a high proportion of moisture. (correct)

They require complex enclosures for protection.

They are less robust in design.

They are larger and heavier.

Why are pneumatic motors suitable for use in steamy atmospheres?

They consume less energy than electric motors.

They require special protective enclosures.

They operate using electrical power.

They are self-purging. (correct)

What can occur when pneumatic motors are idle?

Condensation can occur. (correct)

They require additional lubrication.

They generate excess heat.

They become less efficient.

What is a potential hazard of small leaks in pneumatic systems, especially in dusty environments?

They can cause particles to be propelled through the air. Signup and view all the answers

What precaution should be taken when inspecting power supply wires?

They should be checked for burns exceeding 25% of diameter. Signup and view all the answers

What is the primary reason pneumatic motors require less protective measures than electrical equipment in harsh environments?

They operate without electrical components. Signup and view all the answers

What is a consequence of not taking steps to remove moisture from pneumatic systems?

Corrosion and contamination of lubricants. Signup and view all the answers

What is a major cause of burns on power supply wires and collector mechanisms?

Vibrations or defective mechanisms. Signup and view all the answers

What is a primary advantage of the tracked cable system over the taut wire system?

Ability to support greater loads Signup and view all the answers

What is a typical feature of tracked festoon systems?

Perfect insulation to prevent energy loss Signup and view all the answers

Which of the following is likely a requirement for long track installations of tracked festoon systems?

Heavier cables to reduce voltage drop Signup and view all the answers

In a lifting appliance with two festoon tracks, what does one track typically provide?

Power to the hoist Signup and view all the answers

What could be a limiting factor for the operation of a festoon system?

Bunching of the trolleys Signup and view all the answers

What track shape do most tracked cable systems incorporate?

Inverted 'U' or 'C' section Signup and view all the answers

What is an expected outcome of employing a mobile pendant push button box with a festoon cable?

Termination in the pendant control box Signup and view all the answers

What is a characteristic of typical components of a tracked festoon cable supply?

Designed for various loading conditions Signup and view all the answers

What is the primary function of a hook operated limit switch?

To trip hoisting movement when the hook reaches the adjustable lever Signup and view all the answers

Which statement is true about the automatic reset of a hook operated limit switch?

Hoisting movement can resume after the hook is lowered from the switching area Signup and view all the answers

Where is the rotary limit switch unit for hoisting typically found?

In the connection box on the hoist gearbox Signup and view all the answers

What is the purpose of the ultimate limit switch in a hoist?

To provide an additional safety mechanism in case of limit switch failure Signup and view all the answers

How are most electric power hoists' limit switches arranged in the control circuit?

In a parallel arrangement Signup and view all the answers

What occurs in the control circuit when one limit switch is ‘open’?

The other switch is ‘closed’ allowing motion in that direction Signup and view all the answers

Which limit switch is used when the control limit switch fails?

Ultimate limit switch Signup and view all the answers

What is the main advantage of using hook operated limit switches in hoisting operations?

They can serve as a working limit before reaching standard upper limit Signup and view all the answers

What sound indicates that a bearing is in good condition?

A whirling sound Signup and view all the answers

What is the primary function of the cupped washers in the lever arm mechanism?

To push the lever arm back into its upper position when the load is reduced Signup and view all the answers

Which of these is NOT a benefit of using VFD inverters in industrial applications?

Increased equipment wear Signup and view all the answers

At what percentage of the Working Load Limit (WLL) is the load limiter set?

110% Signup and view all the answers

What is the primary function of a listening rod when checking equipment?

To detect bearing conditions Signup and view all the answers

What action does the strain gauge perform when it reaches the preset limit under load?

It opens a micro-switch that cuts power to the hoist motor Signup and view all the answers

What operation mode allows for changing the speed and running direction of a motor?

Variable Frequency Drive operation Signup and view all the answers

According to BS EN 14492-2, what must hoist brakes be designed to do?

Automatically engage to prevent unintended movements Signup and view all the answers

What are pulses of positive and negative direct current used for in a VFD inverter?

To simulate AC sine waves Signup and view all the answers

Which scenario requires the hoist brakes to engage automatically?

When the control device returns to its neutral position Signup and view all the answers

What happens if two phases of the power supply to a three-phase motor are interrupted?

The brakes must engage automatically Signup and view all the answers

What should be checked along with motor bearings to ensure proper operation?

Connecting shafts and gears Signup and view all the answers

How does using a VFD inverter contribute to operational efficiency?

By improving reliability of drive mechanisms Signup and view all the answers

Which condition does NOT trigger the engagement of hoist brakes?

When the control device is actively lowering a load Signup and view all the answers

What is PWM an acronym for in the context of VFDs?

Pulse Width Modulation Signup and view all the answers

What component connects the rope to the load limiter in the rope-operated load limiter?

The strain gauge anchor Signup and view all the answers

Study Notes

Festoon Systems Overview

Tracked cable systems enhance taut wire systems, accommodating greater loads and higher speeds.
Typically feature an inverted ‘U’ or ‘C’ shaped track for cable support trolleys on inner ledges.
Offer a range of profile sections tailored to various loading conditions, from light to heavy duty.
Safe design ensures insulation and prevents energy loss or voltage drop during current transfer.
For long installations, larger cables may be required to limit voltage drop, necessitating stronger tracks.

Components and Considerations

Festoon systems may include two tracks: one for power supply and another for a mobile pendant control box.
Pendant control boxes are suspended from the festoon cable to facilitate operator control.
Systems must address potential hoist travel loss due to trolley bunching, particularly in long applications.

Pneumatic Motors

Pneumatic motors are lighter and typically smaller than electric motors for similar capacities.
Designed to withstand high heat and moisture, ideal for environments like laundries and paper mills.
Self-purging feature minimizes internal contamination, making them robust for harsh conditions.
Compressed air is less efficient than electricity, requiring moisture removal to prevent corrosion.

Safety and Inspection Protocols

Implement Lock Out-Tag Out (LOTO) procedures for safety during inspections.
Check copper wires for burn damage due to arcing; replacements are warranted if burns exceed 25% of diameter.
Monitor collector shoes and roller collectors for burns and wear, primarily caused by vibrations or faulty mechanisms.

Limit Switches

Hook operated limit switches stop hoist movement at adjustable lever positions; can have automatic or manual reset.
Rotary limit switches contain contacts for essential operations and are located in the hoist's gearbox connection box.
Ultimate limit switches are critical for preventing damage by halting motor operation if other switches fail.
Control limit switches in electric hoists are arranged in parallel, allowing motion even if one switch is open.

Load Limiting and Braking Systems

Load limiters detect excessive loads and cease motor power to prevent damage; calibrated to 110% of the Working Load Limit (WLL).
BS EN 14492-2 outlines requirements for hoist braking systems to ensure safety during movements.
Brakes must automatically engage under specific conditions, like loss of control device position or power interruption.

Variable Frequency Drives (VFDs)

VFDs control speed and direction of 3-phase motors through changes in supply frequency.
Essential for applications requiring precise speed control, particularly in overhead cranes.
Offer benefits such as improved reliability, reduced downtime, lower energy consumption, and minimized maintenance costs.
VFD operation often utilizes Pulse Width Modulation (PWM) to simulate an AC motor's sine wave through controlled pulses.

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Description

Test your knowledge on overhead travelling cranes with a focus on festoon trolleys and cables. This quiz covers the technical aspects of different cable systems and their applications. Perfect for those studying cranes and lifting systems.