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er TEPV or TEWAC enclosure. See 6.13. same AC source as the motor, or from a shaft-driven perma- nent-magnet generator. There are no brushes, commutator, or collector rings; these have been the disadvantages of syn- chronous machines in the past. Since there are no arcing devices in the brushless mo...

er TEPV or TEWAC enclosure. See 6.13. same AC source as the motor, or from a shaft-driven perma- nent-magnet generator. There are no brushes, commutator, or collector rings; these have been the disadvantages of syn- chronous machines in the past. Since there are no arcing devices in the brushless motor, it can be used in Class I, Division 2, or Zone 2 locations. When a synchronous motor installation is made, it is rec- ommended that the motor’s DC excitation be arranged so that it is not readily adjustable by untrained personnel, and it can be seen that the proper excitation is maintained. Otherwise, it may be found that excitation is not being maintained at a nor- mal value; with the result that the anticipated amount of power factor improvement is not being realized in actual ser- vice. Also, the performance of the motor may be adversely affected. Unless there is a clear economic justification for prefening a synchronous motor over an induction motor (under the pre- ceding conditions), the squirrel-cage induction motor, gener- ally, would be recommended because of its greater simplicity, reliability, and maintainability. 6.10.4 Adjustable Speed Drives The use of an adjustable speed drive and motor instead of a constant speed motor to meet process service conditions or save energy is often desirable. Typically, an adjustable-speed motor drive is one of the following types: a DC drive and motor, an adjustable-frequency AC drive and motor, or a wound-rotor motor drive. Although the applications of adjustable-speed drives are somewhat limited, their use in today’s facilities is gaining popularity. Pump, compressor, and blower applications may allow changes in flow by speed control without utilizing con- trol valves or dampers. Elimination of conventional control valves, dampers, and gearboxes may result in added energy and investment savings; and the use of adjustable-speed drives where load varies will allow for more efficient energy utilization because these drives can be very efficient, even at reduced speeds. 6.10.4.1 DC Motor Drives The DC motor design, one of the initial arrangements of electromechanical conversion, has existed for many years. DC motors may be used over their entire speed range, from 0% to 100% of their rated speed. Some characteristics which make DC motors desirable, besides adjustable speed use, Fe: excellent starting torque characteristics; relatively high effi- ciency throughout the speed range; and reliability. Most DC motors are powered from AC-to-DC rectifiers, and the rectifiers are typically installed in locations that have controlled environments. These drives are available in a wide range of sizes. Some of the ways that DC motor drives are used in petro- leum facilities are as follows: a. Vessel agitators. b. Conveyor systems. c. Continuous mixers and extruders and pelletizers (mainly in the petrochemical industry). d. Blenders. e. Fans. f. Production drilling top drive and draw works. g. Production drilling mud pumps. DC motor drives have some disadvantages: they require more maintenance compared to other motor types and, espe- cially in larger horsepower sizes, they are more difficult to apply in a classified location. DC motor drives using AC-to- DC rectifiers also have relatively poor power factors at low speeds, which is typical of static converter drives. 6.10.4.2 Adjustable Frequency Drives Adjustable-frequency drives are available in sizes ranging from fractional horsepower units to units over 60,000 HP, depending on the manufacturer. Both squirrel-cage induction and synchronous motors may be used with adjustable-fre- quency drives. The AC drives typically. may operate within the range of 10% to 100% of their rated speed, with some units capable of operating in excess of their rated speed. Speeds in excess of ‘1 1,000 rpm at an output rating of 3,500 HP have been achieved. Use of the higher output rating or higher speed motors requires care in application, opera- tion, and maintenance. Some characteristics which make adjustable-frequency AC drives desirable, besides their adjustable speed, are their good starting-torque characteris- tics; their capability to provide a soft start; their high effi- ciency; their reliability; their low maintenance needs; and their no-fault contribution. Large adjustable-frequency drives generally use a AC-to- DC rectifier coupled through a smoothing reactor to a DC-to- AC inverter. The power module enclosure for large machines requires a controlled environment and adequate clearhces for maintenance. Among the uses of adjustable-frequency AC drives in the petroleum facilities are the following: a. Continuous mixers, extruders, and pelletizers (mainly in the petrochemical industry). b. Vessel agitators. c. Conveyors. d. Pumps. e. Blowers. f. Compressors. g. Fans. Some disadvantages of adjustable-frequency AC drives are their initial cost, which is higher than some other speed control systems, and their controls, which may require more space than most other drive systems. These drives also produce harmonics that, if not controlled, may cause distribution system problems, such as excessive distribution’ system voltage distortion and overheating of the driven motor. These characteristics vary by manufacturer and dive type and should be reviewed individu- ally. Special considerations may include filtering of the dive’s output to prevent overstress of the motor winding insulation from excessive dvldt, or providing motor winding insulation capable of withstanding the additional voltage stress. Operating duty requirements, such as efficiency, power factor, harmonics, speed range, and current in-rush, should be specified for all applications. Depending on the criticality of the application, a bypass arrangement, or a backup drive, or a drive control module should be considered. 6.1 0.4.3 Wound-Rotor Motor Drives The wound-rotor motor is similar to the squirrel-cage induction motor except that the rotor cage winding is con- nected to a set of collector (or “slip”) rings and carbon brushes. An external adjustable resistance is connected to the collector rings, which allows the motor speed to be varied. Incremental steps are obtained through an arrangement of contractors and heavy duty (cast iron or steel) resistors. Near infinite variability is achieved with a liquid rheostat system. The wound-rotor motor drive typically operates within the 250/0-100% range of its base rated speed. As other adjustable- speed drive systems have improved, the use of wound-rotor motor drives has diminished. Some characteristics which make the wound-rotor motor desirable are: high starting torque; reduced in-rush current; and suitability for high-inertia loads requiring closely con- trolled acceleration. Except for the addition of the rotor circuit speed control, the starting method for the wound-rotor motor drive is similar to the starting method for the AC induction motor. The uses of the wound-rotor motor drive in petroleum facilities are rather limited, though. Some disadvantages of the wound-rotor motor drive are as follows: a. The motor collector rings cause enclosure problems in classified areas. This motor is complicated to build because of the rotor. b. The limited speed adjustment range is generally smaller than other systems. c. The motors have lower efficiency at lower speeds due to heat dissipation of rotor current through external resistors. Slip recovery systems can be used to help improve efficiency. 6.1 1 INSTALLATION 6.1 1.1 General Generally, electrical and mechanical equipment for petro- weather. This applies particularly to pumps, drivers, and asso- ciated equipment which are well-suited for outdoor service. In most cases, using equipment well-suited for outdoor ser- vice saves substantial expenditures for buildings in which to house equipment. Since these buildings tend to confine and accumulate the volatile hydrocarbons released by the process equipment located within their walls and in their immediate area, outdoor installations may also simplify the problem of preventing the accumulation of such releases. Experience has shown that outdoor operation of electric motors is practical and economical with properly selected equipment. 6.1 1.2 Outdoor Service The following types of totally enclosed motors for outdoor service are obtainable: a. Nonexplosionproof. b. Explosionproof. c. Pipe-ventilated, either self-ventilated or forced-ventilated. d. Water-air-cooled. e. Air-to-air-cooled. Open weather-protected motors of various designs (NEMA Type I or II) are available, with air filters as an optional acces- sory. In sizes above 250 HP, weather-protected Type II motors have gained wide acceptance. Dripproof types have been used in various applications but are not usually recommended for general outdoor use in processing plants. (NEMA MG 1, Part 1, provides a full description of enclosure types.) 6.1 1.3 Accessibility All motors should be designed to permit ready removal of the rotor and the bearings and facilitate the flushing and relu- brication of the bearings. To facilitate inspections, adjust- ments, and repairs, all enclosed brush-type synchronous, enclosed wound-rotor, and enclosed commutating motors should have removable covers to allow ready access to the brushes, slip rings, and commutator. Eyebolts, or the equiva- lent, should be provided for lifting motors or parts weighing more than 65 kg (150 lbs). 6.12 CONSTRUCTION OFTOTALLY ENCLOSED MOTORS External housings should completely encase totally enclosed motors. Designs in which the stator laminations form a part of the enclosure, or in which the stator laminations are otherwise exposed to the external cooling air, are not recommended. Motor frames and enclosures preferably should be’of cast iron because motors of this construction are best suited for con- ditions where they are used outdoors or exposed to corrosive conditions. Cast iron is not always available for the very small or very large horsepower sizes. For these cases, steel of ade- quate thickness with a proper protective coating is acceptable. The conduit or terminal box should be of cast construction and should have a hub threaded for rigid conduit. For larger horsepower sizes, only sheet steel boxes may be available (see IEEE Std 841), particularly where auxiliary devices such as surge capacitors, lightning arresters, or differential current transformers are used. Vertical motors should have a drip shield over the fan. 6.13 MOTORS FOR CLASS I LOCATIONS 6.13.1 Division 1 or Zone 1 6.13.1.1 Suitable Types Motors for use in Class I, Division 1, locations, as defined in NFPA 70, should be the explosionproof type and must be suit- able for use under the specific conditions to be encountered in service. Depending on the specific conditions, a motor may have to be suitable for Class I, Groups A, B, C, or D. If a motor size is not available as explosionproof for Groups A and B, then totally enclosed pipe-ventilated motors, totally enclosed inert-gas-filled motors, or submersible-type motors must be used. For more complete details, NFPA 70 may be referenced. An increased safety type “Ex e” motor is suitable for areas classified as Zone 1, but not for Division 1 areas. Motors are not recommended for installation in Zone O areas. This type of motor is designed to have excellent winding integrity; lim- its on internal and external temperatures during starting, oper- ation, and stalled con&tions; defined clearances between the rotating and stationary parts; and power terminals that have provisions against loosening. It is generally a TEFC motor, but can be of any totally enclosed type. An integral part of the increased safety type “Ex e” motor application is the use of a specific overload relay with the motor to limit temperatures during a stall or overload. 6.13.1.2 Nationally RecognizedTesting Laboratory (NRTL) Approval When available, motors should bear an NRTL label of approval for the gas or vapor involved. The label shall include temperature limits or other items as required by NFF’A 70 for approved equipment. Most laboratories cannot test larger motors, particularly those with voltage ratings exceeding 600 V. Where third-party approval is desired, the manufacturer can generally perform the tests required for conformance at the manufacturing site and submit the results to the third party for approval. Site approval may also be required and the user should work with the local “authority having jurisdiction” (see the NFPA 70) to determine the approval or labeling requirements. 6.13.1.3 Care in Inspection The hazardous approval label becomes void when the motor enclosure is opened unless the work is performed by a repair facility which is duly authorized (generally by the orig- inal NRTL). 6.13.2 Division 2 or Zone 2 6.13.2.1 Motors Having Arc-Making Devices Motors for use in Class I, Division 2, locations, or in Zone 2 locations, as defined in NFPA 70, shall be the totally enclosed, explosionproof-type approved for Class I, Division 1, loca- tions when the following devices are used in the motors: a. Sliding contacts. b. Centrifugal or other types of switching mechanisms, including motor overcurrent devices. c. Integral resistance devices, used while the motors are either starting or running. If these devices, however, are provided with separate explo- sionproof enclosures approved for Class I locations, then motor enclosures complying with 6.13.2.2 may be utilized. 6.13.2.2 Motors Having No Arc-Making Devices In Class I, Division 2, locations, or in Zone 2 locations, NFPA 70 permits the installation 6f squirrel-cage induction motors in enclosures other than explosionproof-type. This is permitted because it is not probable that a motor will fail elec- trically during those rare periods when gases or vapors are present in ignitable quantities. A motor intended for use in Class I, Division 2 or Zone 2 service should be constructed so that induced currents will not produce arcing, nor produce surface temperatures capable of causing ignition of the flammable vapor. 6.1 3.3 General 6.13.3.1 Mechanical Requirements Motors for use in a Class I area, either Division 1 or Divi- sion 2, should be nonsparking mechanically as well as electri- cally. For example, the fan or fans of a fan-cooled motor should be made of nonsparking material. 6.13.3.2 Other Factors ’ Even when other considerations may not dictate the use of totally enclosed motors, factors like dust, dirt, drifting snow, and corrosive fumes may influence the type of enclo- sure to be used. 6.13.4 Totally Enclosed Forced-Ventilated (TEFV) Motors (also known as Totally Enclosed Pipe Ventilated VEPVI) If an application for a classified location requires a syn- chronous or wound-rotor induction motor, a motor with a Totally Enclosed Forced-Ventilated (or TEPV) enclosure may be used to meet the requirements of the classified location. In some cases, the design will permit a pressurized enclosure around the collector or slip rings only; an example of this type of motor is one built with a gasketed steel metal housing. If a motor has brushes or slip rings, it is recommended that its enclosure be provided with pressure-tight windows which permit observation of the blush or slip-ring operation. A sepa- rate source of ventilating air is provided for this type of motor, usually by a separate motor-driven blower, and the ventilating air must be drawn from a unclassified location. The air passage should also have filters to minimize the air- borne dust. A common arrangement is to interlock the blower with the main motor controller so that the blower must be started and must remain in operation for some fixed period to assure that at least ten air changes have occurred before the main motor can be started. If air ventilation is lost, interlocks are often provided to shut down the main motor. Other interlocks are as follows: a. An auxiliary contact to detect the opening of the ventila- tion motor controller. b. An air flow switch installed in the duct near the main motor to detect actual flow. The switch enclosure shall be suitable for the location classification. 6.13.5 Totally Enclosed Inert Gas-Filled Pressurized (TEIGF) Motors For applications requiring a large induction or synchronous motor in a Class I, Division 1 location, a totally enclosed motor, pressurized internally with inert gas and arranged for water cooling or surface-air cooling, may be used (see NEMA MG 1 and NFPA 496). TEIGF-type of motors are rare and not readily available. In this type of application, the motor housing must be specially designed to be airtight and to provide tight closure around the shaft to prevent excessive loss of the pres- surizing medium. In the event of a pressure failure, it is required to disconnect the motor from its power source. An alarm should be provided to signal an alarm if there is any increase in temperature of the motor beyond design limits. Nitrogen is the preferred pressurizing medium. When a motor uses nitrogen as its pressurizing medium, the oil seals should be of a type that will prevent oil from being drawn into the motor when the. motor is shut down. Where a water- cooled motor is used in this application, the cooling water should continue to flow through the motor heat exchanger when the motor is shut down. The following accessories should be considered: a. Indicators to show whether cooling water is flowing in the proper amount. desired in the event of loss of pressure inside the motor, loss i b. Warning alarms or automatic shut-off devices to operate as of the cooling water supply, water leakage from the cooler, and overheating of the stator windings or bearings. c. Other devices required to give the degree of protection warranted for the particular application. 6.13.6 Totally Enclosed Water-to-Air Cooled Motors Totally Enclosed Water-to-Air Cooled motors use water-to- air heat exchangers. A source of cooling water or glycol- water mixture is piped to the motor heat exchanger, and the internal air is circulated over the exchanger tubes. This cooled air is then passed through the stator and rotor cores to cool the motor. The majority of the heat generated in the motor is taken up by the water supplied to it with a small portion being radiated from the frame. Totally enclosed water-to-air-cooled motors have an advantage when medium- and large-size motors are required, and where there is an environment that is hostile to motor windings and that might otherwise require the use of NEMA Type I or Type II weather-protected motors. Totally enclosed water-to-air cooled motors, however, require protection from the possibilities of loss of cooling water or low flow. Embed- ded winding temperature detectors are usually used in this type of motor. In many cases, the motor enclosure may have a “make-up” air inlet to provide an air inlet for bearing seals. Even though the air flow rate is relatively small, this air inlet should be provided with adequate filtration. 6.14 MOTORS FOR CLASS II LOCATIONS 6.14.1 SuitableTypes Motors for use in Class II locations, as defined in NFPA 70, shall be suitable for use in locations that are hazardous because of the presence of combustible dust. 6.14.2 Division 1 Motors should bear a third-party label of approval for Class II, Division 1, locations or be totally enclosed pipe- ventilated, meeting the temperature limitations for the spe- cific dust on them or in their vicinity. Some explosionproof motors approved for Class I, Division 1 locations are also dust ignitionproof and are approved for Class II, Division 1 locations. 6.1 4.3 Division 2 For Class II, Division 2 locations, motors should be totally enclosed nonventilated, totally enclosed pipe-venti- lated, totally enclosed fan-cooled, or totally enclosed dust- ignitionproof. The maximum full-load external temperature for these motors shall not exceed 120°C (248°F) for opera- tion in free air (not dust blanketed). Certain exceptions are permitted by NFPA 70. 6.15 MOTOR SERVICE FACTOR To apply a motor properly and economically, its service factor must be taken into account. A standard, integral-horse- power NEMA-frame open motor; or a high-efficiency, totally enclosed fan-cooled motor will generally have a service fac- tor of 1.15 and will carry its rated nameplate load continu- ously without exceeding its rated temperature rise. It will continuously carry 115% of its rated full load without attain- ing excessive temperature, although its insulation temperature limit will be approached, thus reducing winding insulation life. The bearings will also operate at a higher temperature, affecting bearing lubrication and bearing life. It is recom- mended that the service factor rating be reserved for contin- gency use. Consideration should also be given to the speed and torque characteristics of the motor, which are based on a 1 .O service factor. For the above NEMA-frame and other non-NEMA-frame motors the service factor is generally 1 .O with no margin for exceedmg the naineplate rating. It is not good practice to on such motors; therefore, it is advisable to determine defin- itive load requirements and to size motors conservatively. As an example, a certified copy of the characteristic curve of a centrifugal pump should be examined over its entire range to determine the maximum load the curve can impose on its driver. Regardless of service, motors with a service fac- tor of 1.0 should not be operated continuously nor for extended periods at loads exceeding the nameplate rating. When heavier loading is permitted, it should be done only with the understanding that the reliability and motor life expectancy will be reduced. Additionally, other specifications may effect motor sizing, such as API Std 610. i impose continuous loads in excess of the nameplate rating 6.16 FREQUENCY OF STARTING “A-frame motors are capable of multiple starts per hour. The number of which is defined by NEMA Std MG 1, paragraph 12.54.1, and NEMA Std MG-10 paragraph 2.8.1. Medium voltage motors are limited in their starting capa- bility, usually to two starts from cold (or ambient) condition and one start from hot (or running temperature) condition. This is on the basis of a) the load inertia is within NEMA lim- its, b) the load start curve is a”square-of-speed" type curve, and c) the voltage at the motor terminals is greater than 90% (see 6.20). In between starts (while the motor is at rest), these units