Starting loads

The increment size of the prime mover, starting loads, and sales value of fuel gas must be taken into consideration. Space/weight consideration determines whether individual gas-turbine drivers or a central power-generation station will be more economical. 

The configuration of power-generation increments depends on load phasing, prime-mover ratings, starting loads required, and the amount of backup needed to assure continuous operation. 

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Selecting a motor for an application depends on a number of fectors, including the speed of the motor (in rpm), the power requirement, and the type of load. Some applications deal with difficult starting loads, such as conveyors, while others deal with easy starting loads, such as a fen. For this reason, there are many diFferent types of motors. Here we will not discuss the principles of how various motors wodc. Instead, we will provide examples of various motors and their applications, as given in Table 12.3. Most of you will take some classes later that will be devoted to the theory and operation of motors. 

Ea Starting Loads 1 to tunes nmniug torque 6 to 8 times running current (1/20-3/4 hp) ... 

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High starting loads are especially expensive if variable speed drives are used, because of their limited starting torque characteristics, compared with direct-on-start squirrel cage motors that develop up to two to three times normal full-load torque for short periods on start-up. Similar considerations apply to hydraulic and pneumatic drives, the strength of safety clutches and shear pins fitted to safeguard the equipment. 

Furthermore, significant power in excess of normal running requirements causes other problems. In the case of an overload, such as the outlet of the machine becoming blocked, surplus power installed to overcome a starting load dispersed over the length of the feeder will be concentrated upon the final screw flight that is delivering material up to the blocked outlet. 

Bin discharge screws are intended to work in flooded conditions. Starting loads and extraction pattern are related, in that pressures developed at the screw interface, and the pattern of extraction imposed at this region, depend upon the design of the hopper section of the bin and how it operates. The selection of screw size, its form and geometry, and the hopper/screw interface design are interdependent within the overall bin design, for both cost and performance. 

Maximum starting load the DG set can take— to match with emergency loads planned by purchaser. 

Provide motors of optimum horsepower and torque if viscous fluids are to be handled, since high torque is required for operating at heavy starting loads (e.g. cmshers/grinders). 

CLUTCH AND TRANSMISSION Starts loaded unit smoothly Uses clutch properly Times gearshifts properly Shifts gears smoothly Uses proper gear sequence... 

It should be noted that filling the bin from near-empty while not extracting feed can result in abnormally high starting loads. These may be reduced by providing feeder supports which are relatively flexible, thereby inducing some movement of material relative to the bin as it is filled. 

Difference in elevation between the starting (loading) point and the end point (discharge point) and the distance over which the material is to be carried. 

Load currents tend to demagnetize the core, so output current is automatically limited. A ferroresonant transformer typically cannot deliver more than 125 to 150% of its full-load rated output without going into a current-limiting mode. Such transformers cannot support the normal starting loads of motors without a significant dip in output voltage. 

Only employees who are delegated the responsibility should start, load and unload conveyor systems. 

Voltage too low at motor terminals (because of line voltage drop or voltage drop in wiring to motor) Starting load too high Shorted or weak capacitor Low temperature (below 0°F)... 

As the term is used here, inertia loads are different from shock loads. Inertia loads are the occasional loads imposed on the chain by imusual, and often unexpected, events. They may come from starting a heavily loaded conveyor or a drive with a large flywheel. Or they may be caused by a sudden momentary jam in the driven machine or conveyor. The drive or conveyor designer should calculate expected starting loads and be sme that they are never more than the yield strength of the chain. 

Very high shock or inertial (starting) loads. 

In the design of an emergency electrical power system, the starting load requirements of the various items of equipment served by the system shall be taken into account. 

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