Squirrels

Naphthaleneamine is a dye intermediate and is used as the starting material in the manufacture of the rodenticide, Antii (8), l-naphthalenethiourea/5 %< < -4/, which is prepared by heating a mixture of 1-naphthylamine hydrochloride, NH SCN, and a large amount water for 14—16 h while keeping its volume constant by a dding an additional amount of water, to give a 97% yield. Its LD q is 600 mg in squirrels (46). 

Ara-A-5 -monophosphate [29984-33-6] (ara-AMP), C2QH24N OyP, is more water-soluble than ara-A, and therefore can be used in higher dosage during the first hours of treatment of viral infections. Ara-AMP has been shown to decrease virion-associated DNA polymerase concentrations in ground squirrels carrying ground squirrel hepatitis vims. The hypoxanthine derivative, ara-HxMP [54656-49-4] (24) is more water-soluble, appears to have a similar antiviral spectmm to ara-A, and is considerably less toxic (48). 

Head pulleys for belt elevators are crowned to help train and guide the belt and quite often are mbber lagged to increase traction with the belt. Wing-type pulleys, which resemble a squirrel cage, are often used as a tail pulley to minimise any pinching of materials between the belt and tail pulley surface. 

The most popiilar form of motor speed control for adjustable-speed pumping is the voltage-controlled pulse-width-modulated (PWM) frequency synthesizer and AC squirrel-cage induction motor combination. The flexibility of apphcation of the PWM motor drive and its 90 percent- - electric efficiency along with the proven ruggedness of the traditional AC induction motor makes this combination popular. 

Alternating-Current Squirrel-Cage Induction Motors. 29-4... 

Four-Speed, Two-Winding Squirrel-Cage Motors. 29-7... 

Alternating-Current Squirrel-Cage Induction Motors These motors are by far the most common constant-speed drives. They are relatively simple in design and therefore both low in cost and highly reliable. Representative prices are shown in Fig. 29-1 for various speeds and horsepowers. 

The typic medium-sized squirrel-cage motor is designed to operate at 2 to 3 percent shp (97 to 98 percent of synchronous speed). The synchronous speed is determined by the power-system frequency and the stator-winding configuration. If the stator is wound to produce one north and one south magnetic pole, it is a two-pole motor there is always an even number of poles (2, 4, 6, 8, etc.). The synchronous speed is... 

FIG. 29-2 Typical speed versus torque curves for various NEMA-design squirrel-cage induction motors. (See Table 29-2 for an explanation of design types.)... 

Squirrel-cage induc tion motors are inherently single-speed machines, but multispeed operation can be obtained by reconnecting the stator windings of motors designed for this purpose. 

In the preceding discussion of multispeed ac motors note that only induction motors are considered. These have no discrete physical rotor poles, so that only the stator-pole configuration need be modified to change speed. To operate multispeed, a synchronous motor would require a distinct rotor structure for each speed. Thus multispeed is practical only for squirrel-cage induction motors. 

This is a vital relationship, which reveals that during start-up and until such speed, the reactance of the motor windings / 2> the rotor current will also remain almost the same as the starting current and will fall only at near the rated speed. (Refer to the current curves in Figures 1.5(a) and (b)). The initial inrush current in a squirrel cage induction motor is very high. In a slip-ring motor, however, it can be controlled to a desired level. (Refer to Section 5.2.1.)... 

The higher the full load slip, the higher will be the rotor losses and rotor heat. This is clear from the circle diagram and also from equation (1.9). An attempt to limit the start-up current by increasing the slip and the rotor resistance in a squirrel cage motor may thus jeopardize the motor s performance. The selection of starling current and rotor resistance is thus a compromise to achieve optimum performance. 

Because of heavy start-up inrush eurrents, the use of LT motors should be preferred up to a medium sized ratings, say, up to 160 kW, in squirrel eage motors and up to 750 kW in slip-ring motors. For still higher ratings, HT motors should be used. 

Figure 1.18(a) Screen protected drip proof (SPDP) squirrel cage motor (Cooling system ICOA1)... 

Figure 1.21 Closed air circuit, air cooled (CACA) squirrel cage motors (likely cooling systems IC6A1A1 or IC6A1A6) (Courtesy BHEL)...

Figure 2.4(a) Equivalent circuit diagram of a single squirrel cage motor... 

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