Lowering speed

In many large plants, an intermediate pressure (IP) turbine is located on the same shaft as either the HP turbine or the low pressure (LP) turbine. In this arrangement, a common gearbox translates the torque from the high speed turbine shaft to a generator shaft turning at a much lower speed. Unless reheat is used, the steam exiting the HP turbine is typicaHy used directly in the IP turbine. 

Suction and/or discharge vessel levels are not correct, a problem mostly seen in lower-speed pumps. 

Note A slightly higher derating for higher-speed motors, 1500 r.p.m. and above, is required in view of the cooling which in higher-speed motors will be affected more than in lower-speed motors. 

In fact, it would be even worse as a result of the equally reduced cooling effect of the fan at lower speeds. Since kW oc Nr T, kW would vary with speed, the torque remaining almost the same throughout the speed range. The motor would draw the same power from the supply as before, which, proportional... 

Note The speed of the motor ean be varied by vai-ying the frequeney alone but this docs not provide satisfactory performance, A variation in frequeney causes an inverse variation in the flux, for the same system voltage. The strength of magnetic field, p, develops, the torque and moves the rotor, but at lower speeds. / would be reduced, which would raise 0 , and lead the magnetic circuit to saturation. For higher s )ccds, / would be r.nised, but that would reduee which would adversely diminish the torque. Hence frequency variation alone is not recommended practice for speed control. The recommended practiee is to keep V/fas constant, to maintain the motor s vital operatin.c parameters, i.e. its torque and 0 ,. within acceptable limits. 

Drooping torque at lower speeds. At higher speeds loo, the torque profile is variable... 

In a V/f control generally, only the frequency is varied to obtain the required speed control. Based on this frequency, the switching logistics of the inverter control circuit control the inverter s output voltage using the PWM technique to maintain the same ratio of V/f. A W/control is, however, not suitable at lower speeds. Their application is limited to fan, pump and compressor-type loads only, where speed regulation need not be accurate, and their low-spccd performance or transient response is not critical and they are also not required to operate at very low speeds. They arc primarily used for soft starts and to conserve energy... 

At lower speeds more than the a.c. drives as remains the same and a relatively higher /... 

At rated speed 90% and more. Reduces slightly at lower speeds because of poor efficiency of the... 

No loss except in the form of motor inefficiency at lower speeds... 

Losses are high because of field system, but comparatively much less than fluid and eddy current couplings. At lower speeds the losses rise in the form of motor inefficiency... 

Just as heating in the daytime occurs more quickly over land than over water, at night radiational cooling occurs more quickly over land. The pressure pattern tends to be the reverse of that in the daytime. The warmer air tends to rise over the water, which is replaced by the land breeze from land to water, with the reverse flow (water to land) completing the circular flow at altitudes somewhat aloft. Frequently at night, the temperature differences between between land and water are smaller than those during the daytime, and therefore the land breeze has a lower speed. 

Turbomachines can be compared with each other by dimensional analysis. This analysis produces various types of geometrically similar parameters. Dimensional analysis is a procedure where variables representing a physical situation are reduced into groups, which are dimensionless. These dimensionless groups can then be used to compare performance of various types of machines with each other. Dimensional analysis as used in turbomachines can be employed to (1) compare data from various types of machines—it is a useful technique in the development of blade passages and blade profiles, (2) select various types of units based on maximum efficiency and pressure head required, and (3) predict a prototype s performance from tests conducted on a smaller scale model or at lower speeds. 

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