Safety electric motors

Underwriters Laboratories Inc. (UL), UL 674, Safety Electric Motors and Generators for Use in Division 1 Hazardous (Classified) Locations, Third Edition, UL, Northbrook, IL, 1994. 

MG 2 Safety Standard for Construction and Guide for Selection, Installation, and Use of Electric Motors and Generators MG 10 Energy Guide for Selection and Use of Polyphase Motors VE 1 Cable Tray Systems... 

Determination of Reliability Characteristic Factors in the Nuclear Power Plant Biblis B, Gesellschaft fur Reaktorsicherheit mbH Nuclear Failure rates with upper and lower bounds and maintenance data for 17,000 components from 37 safety systems Data for pumps, valves, and electrical positioning devices, electric motors and drives from an operating power plant 66. 

The aforementioned reviews and assessments were assimilated to characterize the effect of dielectric, rotational, and mechanical hazards on motor performance and operational readiness. Functional indicators were identified that can be monitored to assess motor component deterioration caused by aging or other accidental stressors. The study also includes a preliminary discussion of current standards and guides, maintenance programs, and research activities pertaining to nuclear power plant safety-related electric motors. Included are motor manufacturer recommendations, responses from repair facilities to a questionnaire, in-service inspection data, expert knowledge, USNRC-IE audit reports, and standards and guides published by the Institute of Electrical and Electronics Engineers (IEEE). 

Because of the magnitude of the task of preparing the material for this new edition in proper detail, it has been necessary to omit several important topics that were covered in the previous edition. Topics such as corrosion and metallurgy, cost estimating, and economics are now left to the more specialized works of several fine authors. The topic of static electricity, however, is treated in the chapter on process safety, and the topic of mechanical drivers, which includes electric motors, is covered in a separate chapter because many specific items of process equipment require some type of electrical or mechanical driver. Even though some topics cannot be covered here, the author hopes that the designer will find design techniques adaptable to 75 percent to 85-1- percent of required applications and problems. 

Electric motors are not designed to absorb side loads, such as those induced by V-belt drives. In applications where V-belts or other radial loads are placed on the motor, the primary radial transducer (X-axis) should be oriented opposite the direction of induced load and the secondary radial (Y-axis) point should be positioned at 90° in the direction of rotation. If, for safety reasons, the primary transducer cannot be positioned opposite the induced load, the two radial transducers should be placed at 45° on either side of the load plane created by the side load. 

Electric installations should be hermetically sealed and non-sparking. The bulbs should be enclosed in safety shields. Electric motors should not be installed in premises in which powder is manufactured. 

Examples of common safe practices are pressure relief valves, vent systems, flare stacks, snuffing steam and fire water, escape hatches in explosive areas, dikes around tanks storing hazardous materials, turbine drives as spares for electrical motors in case of power failure, and others. Safety considerations are paramount in the layout of the plant, particularly isolation of especially hazardous operations and accessibility for corrective action when necessary. 

This pump uses a closed impeller, mechanical seals, and is constructed of stainless steel 304L. The small power load of approximately 3.5 kW is supplied by an electric motor drive employing a horizontal shaft. The design casing pressure is sufficient to give a 30% safety factor above the total head required. Mechanical seals are preferred to a packed box arrangement due to their superior ability to contain the corrosive and toxic acid liquor. 

Experiments for testing the flameproofness of specially protected electrical motors and apparatus and for the determination of suitable safety devices for such apparatus, performed at the Berggewerkschaftliche Versuchsstrecke, Gelsenkirchen-Bismarck... 

Because electric motors are available in standard sizes from Table 5.1a, select a standard 3000 hp (2.24x10 kW) motor. This choice results in a safety factor of 9%. 

Select a standard electric-motor horsepower using Table 5.10 to obtain approximately a 10% safety factor. 

From Table 5.10, a standard-size electric motor is 30 hp (22.4 kW), which results in a safety factor of 15.4%. 

From Table 5.10, the nearest standard size electric motor is 5 hp (373 kW). The safety factor for this selection will only be 2.5 %. Therefore, select the next larger-size motor, which is 7.5 hp (559 kW). The safety factor for this selection is 53.8 %. 

Now, calculate the electric-motor horsepower. For an electric motor, the efficiency is about 88%. Therefore, the motor horsepower is 8.002 hp (5.97 kW). The next standard-size electric motor is 10 hp (7.46 kW), which results in a safety factor of 25.0%. 

Most electronic equipment shares the television set s need for a number of differing voltages for the operation of individual components. This alone may be sufficient justification for the inclusion of a direct current to alternating current converter in fuel cell power systems. In addition, alternating current electric motors are more suitable in most applications. They tend to operate at a rotational speed controlled by the frequency of the current. If completely unloaded they speed up to this fixed velocity and accelerate no further. Many types of direct current motors, if operated unloaded, will continue to accelerate until they fail. A belt driven fan operated by an alternating current motor is undamaged by the failure of the belt. A direct current motor will require a special safety circuit to shut it down in case of belt failure. If the belt and the safety circuit both fail, the motor will speed up until it destroys itself. 

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