Construction

Eddy-current couplings are available in both horizontal (Figure 5) and vertical (Figure 6) configurations as might be required for any pump mechanical arrangement. Horizontal machines in smaller sizes are frequently close-coupled to the drive motor in what is known as integral construction. Larger sizes are usually flexibly coupled to the drive motor and pump load.

FIGURE 5 Horizontal centrifugal pump driven by a 1000-hp (746-kW), 1780-rpm induction motor through a stepup gear and an eddy-current coupling (Electric Machinery)
FIGURE 6 Vertical centrifugal pumps driven by 40-hp (30-kW), 1750-rpm induction motors and eddy-current couplings (Electric Machinery)

Vertical motors and slip couplings are close-coupled to limit overall height and to prevent vibration problems. Pump hydraulic thrust requirements can be accommodated, when necessary, in much the same way as in constant-speed motor applications. Because of mechanical limitations, thrust bearings are frequently located in the bottom of the adjustable-speed drive.

FIGURE 7 Interconnection block diagram of eddy-current clutch and speed control

Enclosures available will vary depending on the type of cooling involved. Obviously water-cooled types need little if any enclosure adaptation for virtually any installation. However, caution should be exercised in outdoor use where freezing can occur. Also, vertical installations utilizing water cooling may require special considerations.

Air-cooled couplings are more universally used for centrifugal pump loads but do require attention on enclosure design. Indoor installations in clean atmospheres need only open or drip-proof enclosures where heat rejection is not a problem. In some cases, intake and discharge covers for connection to ductwork may be necessary for environmental isolation.

Weather-protected enclosures are available for outdoor installations, A NEMA Type I rating is normally adequate because of the slip coupling's inherent mechanical design and relatively low field winding voltage levels.

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