Motor Enclosures and Adjustable-Speed Drives in Petroleum Facilities Quiz
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Questions and Answers

What type of motor can be used in Class I, Division 2, or Zone 2 locations due to the absence of arcing devices?

  • Synchronous motor (correct)
  • Wound-rotor motor drive
  • DC drive and motor
  • Adjustable-frequency AC drive and motor

    • What is recommended to ensure proper excitation and performance of a synchronous motor installation?

  • Using a wound-rotor motor drive
  • Utilizing an adjustable-frequency AC drive and motor
  • Preferring a squirrel-cage induction motor
  • Arranging the motor's DC excitation to be not readily adjustable by untrained personnel (correct)

    • What is the primary reason for preferring a squirrel-cage induction motor over a synchronous motor?

  • Higher power factor improvement
  • Greater simplicity, reliability, and maintainability (correct)
  • Adjustable speed capabilities
  • Ability to be used in hazardous locations

    • What type of motor drive is often desirable to meet process service conditions or save energy?

    <p>Adjustable-frequency AC drive and motor</p> Signup and view all the answers

    Which type of motor is recommended for Class II, Division 1 locations?

    <p>Totally enclosed dust-ignitionproof motor</p> Signup and view all the answers

    What is the maximum full-load external temperature for motors in Class II, Division 2 locations?

    <p>120°C (248°F)</p> Signup and view all the answers

    What is the service factor for a standard, integral-horsepower NEMA-frame open motor?

    <p>1.15</p> Signup and view all the answers

    What is recommended regarding the service factor rating for motors?

    <p>It should be used for contingency use only</p> Signup and view all the answers

    What is the maximum load a motor with a service factor of 1.0 should carry?

    <p>115% of its rated full load</p> Signup and view all the answers

    What should be examined to determine the maximum load a centrifugal pump can impose on its driver?

    <p>The motor's speed and torque characteristics</p> Signup and view all the answers

    What determines the number of starts per hour for A-frame motors?

    <p>NEMA Std MG 1, paragraph 12.54.1</p> Signup and view all the answers

    What limits the starting capability of medium voltage motors?

    <p>Voltage at the motor terminals</p> Signup and view all the answers

    What is the basis for limiting the starting capability of medium voltage motors?

    <p>The load start curve</p> Signup and view all the answers

    At what voltage should medium voltage motors be limited in their starting capability?

    <p>90%</p> Signup and view all the answers

    What action is not recommended for motors with a service factor of 1.0?

    <p>Continuous operation at loads exceeding the nameplate rating</p> Signup and view all the answers

    What should be given consideration for motor sizing?

    <p>API Std 610</p> Signup and view all the answers

    Which type of motors are suitable for outdoor service in petro-weather conditions?

    <p>Totally enclosed motors</p> Signup and view all the answers

    What type of motors should be used in Class I, Division 1 locations?

    <p>Explosionproof motors</p> Signup and view all the answers

    What type of motors are suitable for areas classified as Zone 1?

    <p>Increased safety type 'Ex e' motors</p> Signup and view all the answers

    What happens to the hazardous approval label when the motor enclosure is opened?

    <p>It becomes void</p> Signup and view all the answers

    What type of motors should be used in Class I, Division 2 locations or Zone 2 locations when certain arc-making devices are used in the motors?

    <p>Totally enclosed, explosionproof type approved for Class I, Division 1 locations</p> Signup and view all the answers

    What should the external housings of totally enclosed motors do?

    <p>Completely encase the motors</p> Signup and view all the answers

    What can help improve efficiency in various industrial applications?

    <p>Slip recovery systems</p> Signup and view all the answers

    What should motors for use in hazardous locations bear?

    <p>An NRTL label of approval for the gas or vapor involved</p> Signup and view all the answers

    What should motors for use in hazardous locations have for easy access to for inspections and repairs?

    <p>Rotor, bearings, brushes, slip rings, and commutator</p> Signup and view all the answers

    What type of electric motors is practical and economical for outdoor operation with properly selected equipment?

    <p>Totally enclosed motors</p> Signup and view all the answers

    What type of motors can be used if explosionproof motors are not available for certain conditions?

    <p>Totally enclosed pipe-ventilated, inert-gas-filled, or submersible-type motors</p> Signup and view all the answers

    What should increased safety type 'Ex e' motors be suitable for?

    <p>Areas classified as Zone 1</p> Signup and view all the answers

    Which type of motor enclosure may be used in Class I, Division 2, or Zone 2 locations according to NFPA 70?

    <p>Totally Enclosed Forced-Ventilated (TEFV) Motors</p> Signup and view all the answers

    What type of motors may be used in Class I areas and should be nonsparking mechanically and electrically?

    <p>Non-fan-cooled motors</p> Signup and view all the answers

    Which factor may influence the type of enclosure to be used for motors in hazardous locations?

    <p>Corrosive fumes</p> Signup and view all the answers

    What is a requirement for Totally Enclosed Inert Gas-Filled Pressurized (TEIGF) Motors used in Class I, Division 1 locations?

    <p>Airtight housing and special design to prevent pressure failure</p> Signup and view all the answers

    What type of motors use water-to-air heat exchangers and require protection from loss of cooling water or low flow?

    <p>Totally Enclosed Water-to-Air Cooled Motors</p> Signup and view all the answers

    What should motors intended for use in Class I, Division 2 or Zone 2 service be constructed to prevent?

    <p>Induced currents from producing arcing</p> Signup and view all the answers

    What is provided for TEFV motors to assure proper ventilation?

    <p>Separate motor-driven blower, with interlocks to assure proper ventilation</p> Signup and view all the answers

    What type of motors shall be suitable for use in hazardous locations due to the presence of combustible dust?

    <p>Totally Enclosed Forced-Ventilated (TEFV) Motors</p> Signup and view all the answers

    What does NFPA 70 allow for the installation of in hazardous locations for Class II locations?

    <p>Explosionproof enclosures approved for Class I locations</p> Signup and view all the answers

    What should motors intended for use in Class I, Division 2 or Zone 2 service be constructed to prevent?

    <p>Induced currents from producing arcing</p> Signup and view all the answers

    Which type of motor drives offer excellent starting torque characteristics, relatively high efficiency throughout the speed range, and reliability?

    <p>DC motor drives</p> Signup and view all the answers

    Which type of motor drives are available in sizes ranging from fractional horsepower units to over 60,000 HP and can operate within the range of 10% to 100% of their rated speed?

    <p>Adjustable-frequency AC drives</p> Signup and view all the answers

    What is a disadvantage of wound-rotor motor drives?

    <p>They offer limited speed adjustment range</p> Signup and view all the answers

    What special consideration may be needed for adjustable-frequency AC drives to prevent overstress of the motor winding insulation?

    <p>Filtering the drive's output</p> Signup and view all the answers

    Which type of motor drives are suitable for high-inertia loads requiring closely controlled acceleration?

    <p>Wound-rotor motor drives</p> Signup and view all the answers

    What may be a consequence of not controlling the harmonics produced by adjustable-frequency AC drives?

    <p>Overstress of the motor winding insulation</p> Signup and view all the answers

    In which type of motor drives do motor collector rings pose enclosure problems in classified areas?

    <p>Wound-rotor motor drives</p> Signup and view all the answers

    What is a characteristic of adjustable-frequency AC drives that may lead to higher initial cost compared to some other speed control systems?

    <p>Potential to produce harmonics</p> Signup and view all the answers

    Which type of motor drives operate within the 25% to 100% range of their base-rated speed?

    <p>Wound-rotor motor drives</p> Signup and view all the answers

    What is a drawback of DC motor drives compared to other motor types?

    <p>More maintenance requirements</p> Signup and view all the answers

    What characteristic of adjustable-speed drives allows changes in flow by speed control without using control valves or dampers?

    <p>Good starting-torque characteristics</p> Signup and view all the answers

    What is a benefit of adjustable-frequency AC drives compared to some other speed control systems?

    <p>Soft start capability</p> Signup and view all the answers

    What type of motors frequently require temperature, current, vibration, air flow, water flow, or differential pressure monitoring?

    <p>Motors complying with API Std 541 and Std 546</p> Signup and view all the answers

    For motors larger than 1,000 HP, what should be observed in relation to the size and direction of conduit entrances to motor terminal boxes?

    <p>Sizing requirements of the local electrical code</p> Signup and view all the answers

    What is a consideration for space heaters in motors?

    <p>They should be suitable for hazardous locations</p> Signup and view all the answers

    What is recommended for motors driving high inertia loads or operating under high power system voltage drops?

    <p>Special consideration</p> Signup and view all the answers

    Which reduced-voltage controller method may be required where specific high-inertia loads or system limitations are encountered?

    <p>Autotransformer</p> Signup and view all the answers

    What type of starting method usually requires an 'open transition' where the motor is disconnected for a couple of seconds when changing from the wye to the delta configuration?

    <p>Wye-Delta</p> Signup and view all the answers

    Which type of starting method reduces the current in-rush and starting torque to one-third of the full-voltage starting values?

    <p>Wye-Delta</p> Signup and view all the answers

    Which type of controller provides the means to start, regulate speed, and stop electric motors?

    <p>Motor controllers</p> Signup and view all the answers

    What is used with or without a standard contactor to bypass the solid-state starter in soft-start controllers?

    <p>Solid-state devices</p> Signup and view all the answers

    What is switched onto the same bus as the motor an instant before the motor is connected in capacitor-assisted starting?

    <p>Relatively large capacitor bank</p> Signup and view all the answers

    What provides most of the reactive requirements of the motor during the motor acceleration in capacitor-assisted starting?

    <p>Capacitors</p> Signup and view all the answers

    What is typically implemented through sets of fixed contactors and resistors, or a stepless liquid rheostat in wound rotor control?

    <p>Speed control rheostat</p> Signup and view all the answers

    What does the typical wiring diagram for a wound rotor motor begin with?

    <p>The basic control system for a full-voltage type motor</p> Signup and view all the answers

    What is obtained through the addition of a speed control rheostat external to the motor enclosure in wound rotor control?

    <p>Rpm adjustment</p> Signup and view all the answers

    What do motor controllers afford protection against?

    <p>Abnormal operating conditions</p> Signup and view all the answers

    What is the basis for limiting the starting capability of medium voltage motors?

    <p>Power system capacity</p> Signup and view all the answers

    What is the recommended operating voltage rating for space heaters?

    <p>115 V or 230 V, single phase</p> Signup and view all the answers

    What type of bearings are commonly found in most NEMA and IEEE-841 motors?

    <p>Antifriction bearings</p> Signup and view all the answers

    What is the typical voltage applied for low-voltage winding heating in small motors?

    <p>25% of the voltage</p> Signup and view all the answers

    What can lead to bearing failures in motors?

    <p>Frequent greasing</p> Signup and view all the answers

    What type of bearings are usually used in ball-bearing motors for horizontal motors?

    <p>Grease-lubricated bearings</p> Signup and view all the answers

    Which type of motors generally use the same lubricant for all bearings?

    <p>Vertical motors</p> Signup and view all the answers

    What does the net torque delivered by motors to driven equipment become when voltages are below rated levels?

    <p>Less than the rated torque</p> Signup and view all the answers

    What is the purpose of constant-visible-level automatic oilers in sleeve-bearing motors?

    <p>To provide constant lubrication</p> Signup and view all the answers

    What should be compatible with the oil when oil mist lubrication is used?

    <p>Internal and noncontacting external shaft seals</p> Signup and view all the answers

    What is the maximum torque developed by a motor proportional to?

    <p>The square of the voltage</p> Signup and view all the answers

    What type of motors are available with antifriction or hydrodynamic radial bearings?

    <p>Horizontal motors</p> Signup and view all the answers

    What may exist due to system design or characteristics during motor starting?

    <p>Low voltage</p> Signup and view all the answers

    What should be used for larger motors with sleeve bearings?

    <p>Forced-oil lubrication</p> Signup and view all the answers

    What type of motors exhibit characteristic torque variations with respect to applied voltage?

    <p>Synchronous motors</p> Signup and view all the answers

    What is the purpose of using low-voltage winding heating in small motors?

    <p>Maintain the internal temperature above ambient</p> Signup and view all the answers

    What is the primary factor determining the type of bearing used in motors?

    <p>External thrust</p> Signup and view all the answers

    What should be considered for vertical weather-protected motors used for water well service?

    <p>Using space heaters</p> Signup and view all the answers

    What is the primary equipment driven by motors in petroleum processing?

    <p>Pumps</p> Signup and view all the answers

    What do high-thrust driven equipment require specification of?

    <p>Maximum thrust loads</p> Signup and view all the answers

    What do motors subject to high thrust need to be equipped with?

    <p>Bearings capable of carrying thrusts from driven equipment</p> Signup and view all the answers

    What are normal-torque motors suitable for in petroleum processing?

    <p>Centrifugal or rotary pumps</p> Signup and view all the answers

    What do low-voltage conditions during motor starting result from?

    <p>High voltage drop</p> Signup and view all the answers

    What do motors subject to high thrust need to be equipped with?

    <p>Bearings capable of carrying thrusts from driven equipment</p> Signup and view all the answers

    What is the power factor range at which inrush current at start can be several times the rated full-load current?

    <p>0.2 to 0.4</p> Signup and view all the answers

    What percentage greater than the driven equipment starting-speed-torque curve may the motor torque need to be, as per minimum torque specifications?

    <p>10%</p> Signup and view all the answers

    What should be the motor-generated voltage level before restarting a motor driving a high-inertia load?

    <p>25% or less of the rated voltage</p> Signup and view all the answers

    What type of motor controllers offer the simplest and most economical method for starting induction motors?

    <p>Full-voltage magnetic controllers</p> Signup and view all the answers

    For which type of motors are high-torque options available?

    <p>Synchronous motors</p> Signup and view all the answers

    What may be a consequence of using reduced-voltage controllers for motors?

    <p>Complicated starting</p> Signup and view all the answers

    What type of loads may require calculations to ensure the motor has sufficient torque and thermal capacity to bring the equipment up to rated speed?

    <p>High-inertia loads</p> Signup and view all the answers

    What type of motor may require reduced-voltage starting to prevent undesirable voltage drops and in-rush during reacceleration?

    <p>Large motors</p> Signup and view all the answers

    What is a characteristic of reduced-voltage controllers compared to full-voltage magnetic controllers for starting motors?

    <p>Complicates starting</p> Signup and view all the answers

    What increases in complexity as the motor sizes become larger?

    <p>Motor control</p> Signup and view all the answers

    What may be required for certain conditions of operation such as with a centrifugal blower or pump?

    <p>Greater torque</p> Signup and view all the answers

    What may be a drawback of reduced-voltage controllers for starting motors?

    <p>Complicated starting process</p> Signup and view all the answers

    What is the full-voltage starting current range for squirrel-cage induction motors and synchronous motors?

    <p>350% to 700%</p> Signup and view all the answers

    In what units are motor controllers typically rated?

    <p>Horsepower</p> Signup and view all the answers

    What must the power distribution system be able to handle in relation to motor starting loads?

    <p>Increased kilovolt-amperes</p> Signup and view all the answers

    What determines the selection of control equipment to a large extent?

    <p>Power supply system's ability to handle motor starting loads</p> Signup and view all the answers

    What is the primary control device for starting a wound-rotor motor?

    <p>Magnetic full-voltage starter</p> Signup and view all the answers

    What is typically applied for motor starting due to its simplicity and adaptability to full-voltage starting?

    <p>Magnetic full-voltage starting</p> Signup and view all the answers

    What method offers variations in starting torque through selective starting taps for a wound-rotor motor?

    <p>Autotransformer method</p> Signup and view all the answers

    What is employed to reduce the starting current on power systems of limited capacity if the reduced-starting torque is adequate for the connected equipment?

    <p>Series resistor or reactor method</p> Signup and view all the answers

    What is the most desirable starting method for a squirrel-cage induction motor?

    <p>Magnetic full-voltage starting</p> Signup and view all the answers

    What is the primary control device for starting a squirrel-cage induction motor?

    <p>Magnetic full-voltage starter</p> Signup and view all the answers

    What provides selective speed control under varying conditions of load for a wound-rotor motor?

    <p>Series resistor or reactor method</p> Signup and view all the answers

    What is employed when the driven load demands smooth starting for a wound-rotor motor?

    <p>Variable resistor or regenerative system</p> Signup and view all the answers

    What is the secondary device for regulating the speed of a wound-rotor motor?

    <p>Series resistor or reactor</p> Signup and view all the answers

    What is usually the same as the primary control device used for a squirrel-cage induction motor?

    <p>Magnetic full-voltage starter</p> Signup and view all the answers

    What is employed to prevent restart of motors after the return of failed voltage?

    <p>Magnetic full-voltage starting</p> Signup and view all the answers

    What is imperative in cases where automatic restarting is necessary due to critical process requirements?

    <p>Time-delay relaying</p> Signup and view all the answers

    What is the standard control type in the petroleum industry that utilizes a magnetic contactor and pushbutton or automatic control device(s) to start and stop the motor?

    <p>Magnetic contactor control</p> Signup and view all the answers

    What provides undervoltage protection against automatic restart of motors after voltage restoration?

    <p>Time-delay relaying</p> Signup and view all the answers

    What is the basis for limiting the starting capability of medium voltage motors?

    <p>Standard air ambient temperature reference</p> Signup and view all the answers

    What is applied to de-energize overloaded motors automatically before winding or conductor damage occurs?

    <p>Overload protection</p> Signup and view all the answers

    What is responsive to variations in ambient temperature unless temperature compensated?

    <p>Thermal elements</p> Signup and view all the answers

    What is used to distinguish between abnormal equipment operation and system failures?

    <p>Protective relaying</p> Signup and view all the answers

    What should be selective in de-energizing only the affected units in a comprehensive installation?

    <p>Protective relaying</p> Signup and view all the answers

    What is frequently used in large motors as the best indication of motor temperature?

    <p>Embedded detection-type thermal protection</p> Signup and view all the answers

    What is available to permit motors to ride through momentary voltage dips, but the delay interval is critical?

    <p>Time-delay relaying</p> Signup and view all the answers

    What is used to provide disconnect and short-circuit protection for motors?

    <p>Motor circuit protectors</p> Signup and view all the answers

    Which type of control is mainly for starting fractional horsepower, single-phase motors in the 120-V to 240-V range?

    <p>Manual operation control</p> Signup and view all the answers

    What is used to start and stop the motor in the petroleum industry?

    <p>Magnetic contactor control</p> Signup and view all the answers

    What type of protective relays are recommended for large motors (1,500 HP and over) for various forms of protection?

    <p>Differential, undervoltage, phase-sequence voltage, and induction disk overcurrent relays</p> Signup and view all the answers

    For motors operated on grounded systems over 600 V, what type of protection should they have?

    <p>Ground-fault protection</p> Signup and view all the answers

    What type of controllers may show substantial savings compared to remotely located general-purpose or weatherproof controllers for classified locations?

    <p>Explosionproof controllers</p> Signup and view all the answers

    What is the purpose of control centers or grouping of control equipment?

    <p>Potential cost savings and maintenance convenience</p> Signup and view all the answers

    What are NEMA enclosure types for AC motor controllers detailed to provide protection against?

    <p>Various environmental factors</p> Signup and view all the answers

    What do severe service conditions, such as humidity and corrosion, necessitate a discussion with the equipment manufacturer about?

    <p>Availability of corrosion-resistant enclosure parts</p> Signup and view all the answers

    What are control power transformers used for in the context of motor controllers?

    <p>Magnetically operated controllers with motor voltages of 480 V or more, and for process instrumentation</p> Signup and view all the answers

    What should the control equipment selected be able to handle?

    <p>The assigned duty</p> Signup and view all the answers

    What type of motor controllers are extensively used in petroleum processing facilities and are closely related to protective relaying?

    <p>Partial and fully automatic control</p> Signup and view all the answers

    What are multifunction motor protection relays available to provide?

    <p>Comprehensive protection</p> Signup and view all the answers

    For motors larger than 1,500 HP, what type of protective relays are recommended?

    <p>Differential, undervoltage, phase-sequence voltage, and induction disk overcurrent relays</p> Signup and view all the answers

    What should be considered for potential cost savings and maintenance convenience in the context of control equipment?

    <p>Control centers or grouping of control equipment</p> Signup and view all the answers

    Which NEMA enclosure type is suitable for submersion in water, such as in quarries, mines, and manholes?

    <p>Type 6</p> Signup and view all the answers

    In which type of location are NEMA Type 7 enclosures designed to be used?

    <p>Chemical plants</p> Signup and view all the answers

    Which NEMA enclosure type is suitable for locations with corrosive acid or fumes, such as chemical plants and sewage plants?

    <p>Type 11</p> Signup and view all the answers

    What are NEMA Type 8 enclosures designed for?

    <p>Chemical plants</p> Signup and view all the answers

    Where are NEMA Type 4X enclosures suitable for outdoor installation?

    <p>Chemical plants</p> Signup and view all the answers

    Which type of NEMA enclosure protects against windblown dust, water, and external ice or sleet?

    <p>Type 3</p> Signup and view all the answers

    Where are NEMA Type 12 enclosures suitable for industrial use?

    <p>Indoors</p> Signup and view all the answers

    Which NEMA enclosure type is designed to protect pilot devices against lint, dust, and spraying water, oil, or coolant?

    <p>Type 13</p> Signup and view all the answers

    For which type of areas are NEMA Type 9 enclosures designed?

    <p>Class II areas with combustible dusts</p> Signup and view all the answers

    Where are NEMA Type 11 enclosures suitable for installation?

    <p>Chemical plants</p> Signup and view all the answers

    In which locations are NEMA Type 3 and 3R enclosures typically used?

    <p>Office buildings</p> Signup and view all the answers

    Where are NEMA Type 4 enclosures used?

    <p>Chemical plants</p> Signup and view all the answers

    Study Notes

    Motor Enclosures for Hazardous Locations

    • NFPA 70 permits the installation of squirrel-cage induction motors in enclosures other than explosionproof-type in Class I, Division 2, or Zone 2 locations.
    • Motors for use in Class I areas should be nonsparking mechanically and electrically, for example, the fan of a fan-cooled motor should be made of nonsparking material.
    • Factors like dust, dirt, drifting snow, and corrosive fumes may influence the type of enclosure to be used for motors.
    • Totally Enclosed Forced-Ventilated (TEFV) Motors may be used to meet the requirements of a classified location, with a separate source of ventilating air drawn from an unclassified location and interlocks to ensure proper ventilation.
    • Totally Enclosed Inert Gas-Filled Pressurized (TEIGF) Motors may be used in Class I, Division 1 locations, requiring airtight housing and special design to prevent pressure failure. Nitrogen is the preferred pressurizing medium.
    • Accessories for TEIGF motors include indicators for cooling water flow, warning alarms for loss of pressure or water leakage, and devices for protection.
    • Totally Enclosed Water-to-Air Cooled Motors use water-to-air heat exchangers and require protection from loss of cooling water or low flow, with embedded winding temperature detectors and adequate filtration for air inlets.
    • Motors for use in Class II locations shall be suitable for use in hazardous locations due to the presence of combustible dust.
    • NFPA 70 allows the installation of motors with explosionproof enclosures approved for Class I locations in hazardous locations.
    • Motors intended for use in Class I, Division 2 or Zone 2 service should be constructed to prevent induced currents from producing arcing or surface temperatures capable of causing ignition of flammable vapor.
    • A separate source of ventilating air is provided for TEFV motors, usually by a separate motor-driven blower, with interlocks to assure proper ventilation.
    • TEIGF motors require airtight housing, special design to prevent pressure failure, and the use of nitrogen as the preferred pressurizing medium, with accessories for protection and warning alarms.

    Adjustable-Speed Drives in Petroleum Facilities

    • Adjustable-speed drives are gaining popularity in today's facilities for pump, compressor, and blower applications, allowing changes in flow by speed control without using control valves or dampers.
    • DC motor drives offer excellent starting torque characteristics, relatively high efficiency throughout the speed range, and reliability.
    • DC motor drives are used in petroleum facilities for vessel agitators, conveyor systems, continuous mixers, blenders, fans, and production drilling equipment.
    • DC motor drives require more maintenance compared to other motor types and are more difficult to apply in a classified location, especially in larger horsepower sizes.
    • Adjustable-frequency drives are available in sizes ranging from fractional horsepower units to over 60,000 HP and can operate within the range of 10% to 100% of their rated speed.
    • Adjustable-frequency AC drives offer good starting-torque characteristics, soft start capability, high efficiency, reliability, and low maintenance needs.
    • Adjustable-frequency AC drives are used in petroleum facilities for continuous mixers, vessel agitators, conveyors, pumps, blowers, compressors, and fans.
    • Adjustable-frequency AC drives have a higher initial cost than some other speed control systems and may produce harmonics that, if not controlled, can cause distribution system problems.
    • Special considerations for adjustable-frequency AC drives may include filtering the drive's output to prevent overstress of the motor winding insulation and providing motor winding insulation capable of withstanding the additional voltage stress.
    • Wound-rotor motor drives are similar to squirrel-cage induction motors but offer high starting torque and reduced in-rush current.
    • Wound-rotor motor drives operate within the 25% to 100% range of their base-rated speed and are suitable for high-inertia loads requiring closely controlled acceleration.
    • Disadvantages of wound-rotor motor drives include enclosure problems in classified areas due to motor collector rings, limited speed adjustment range, and lower efficiency at lower speeds due to heat dissipation of rotor current through external resistors.

    Motor Starting Considerations

    • Inrush current at start can be several times the rated full-load current with a low power factor of 0.2 to 0.4.
    • Voltage conditions at the instant of pull-in should be checked when using a synchronous motor.
    • Minimum torque specifications may require the motor torque to be 10% greater than the driven equipment starting-speed-torque curve.
    • High-torque motors are available for applications requiring higher-than-normal torque.
    • For high-inertia loads, calculations should ensure the motor has sufficient torque and thermal capacity to bring the equipment up to rated speed.
    • Restarting a motor driving a high-inertia load should be delayed until the motor-generated voltage has decayed to 25% or less of the rated voltage.
    • Recognition should be given to the requirement for greater torque under certain conditions of operation, such as with a centrifugal blower or pump.
    • Larger motors may require reduced-voltage starting to prevent undesirable voltage drops and in-rush during reacceleration.
    • Full-voltage magnetic controllers offer the simplest and most economical method for starting induction motors.
    • Reduced-voltage controllers reduce the net torque exerted by the motors and may complicate the starting problem, especially for synchronous motors.
    • The method of starting control for all motors is essentially the same, but complexity increases with larger motor sizes.
    • Control circuits which provide for the reacceleration of motors are complex and require additional considerations.

    NEMA Enclosure Types for AC Motor Controllers

    • NEMA Type 3 and 3R enclosures are typically combined and designed to protect against windblown dust, water, and external ice or sleet
    • These enclosures are used in various locations such as office buildings, warehouses, and locations subject to heavy rain or icing conditions
    • Type 4 enclosures protect against splashing water and are used in chemical plants and locations subject to splashing or dripping water
    • Type 4X enclosures are corrosion-resistant and suitable for outdoor locations in chemical plants
    • Type 6 enclosures are suitable for submersion in water, such as in quarries, mines, and manholes
    • Type 7 enclosures are designed for Class I, Division 1 locations with flammable gases and vapors
    • Type 8 enclosures are designed for Class I, Division 1 locations with flammable gases and vapors and apparatus immersed in oil
    • Type 9 enclosures are designed for Class II areas with combustible dusts
    • Type 10 enclosures meet the latest requirements of MSHA
    • Type 11 enclosures are suitable for locations with corrosive acid or fumes, such as chemical plants and sewage plants
    • Type 12 enclosures are provided with an oil-resistant synthetic gasket and suitable for industrial use indoors
    • Type 13 enclosures protect pilot devices against lint, dust, seepage, and spraying water, oil, or coolant, and are intended for indoor use

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    Description

    Test your knowledge of motor enclosures for hazardous locations and adjustable-speed drives in petroleum facilities with this informative quiz. Explore the specific requirements and considerations for motor enclosures in hazardous locations, as well as the various types of adjustable-speed drives used in petroleum facilities, their applications, and advantages and disadvantages.

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