The higher the power ,so the  machine can be operated at higher efficiency and can make the operation can be done quickly .This can increase company profit and economic of our country .

Heat is a concern when it comes to operating motors. They often have a specific temperature range at which they should be run. Motors produce heat when running, therefore fully-enclosed areas with no air circulation may cause motors to overheat.Certain motors will only draw the amount of current needed to perform a move or hold position. These motors tend to run cooler as they are not constantly drawing large amounts of current. 

Surrounding factor, because we need to know what kind motor that suitable with the surrounding. Some material in motor not suitable like plastic casing in motor will damage if in heat situation. Torque also the main point because certain machine need motor that required high power for operation machine beside that, power supply also important because  high torgue required high power supply . tq

Important factor selected motor is power, torque and rpm, electrical specs like some dimensions, voltage, number of phases, as well like axle diameter for choosing pulley. Let is say it is some kind of midsize project that want to operate from shop or garage electric supply, 110 volts 60 cycle. Large variety of motors available. A small motor, say 1/2 hp or 3/4 hp it might do well but if the weight to be turned is heavy, like a truck wheel, you would either get very slow response or you would just burn out the motor devices.

The reason why we consider this factor due to energy required to start electric motors is much higher than for steady-state operation. It could overheat electric motor or most probability overheat the motor. And when operating cycle need to operate for more than 25% of the time in accordance with its operating cycle, it becomes vital in sizing the motor.

as for me i think it is important to consider the motor sizing. motor sizing refer to the process of picking the correct motor for a given load. let say if the motor is too small  so it may not have sufficient torque to start the load and run it up to the correct speed. even if it does get the load up  to speed the motor will overheat and burn. same goes if  the motor if too large the n it will operate inefficiently due to run below rated load plus money wasted here of buying large motor. 

In my opinion,the most important factors required to be considered when selecting a motor for any of particular application:

·        ->> Output In Kilowatt/Horsepower-Mechanical limitations and electrical limitations

 

·         ->>Speed Of The Motor-Most of the motors are directly coupled with the driven equipment where in the speed of the motor and the driven equipment will be same. In order to meet the speed of the driven equipment, the devices like gearbox, chains or belts are introduced between motor and driven equipment.

 

·         ->>Power Supply, Voltage And Frequency Variations-The permissible voltage variations is ±5 to ±10%,permissible frequency is 50Hz, ±3% and permissible combined variation is ±6%.The effect of under voltage is more serious than that of overvoltage. Continuous operation with under voltage condition increases the current at the rate of about 20% for every 5% reduction in the supply voltage, increasing the rated copper loss. This results into heating and prolonged temperature rise and finally the burning of winding. The  motor offers reduced efficiency at their overvoltage or under voltage.

 

·         ->>Different Rotor Classes-The rotor classes indicate against what quantum of the load torque the motor would be able to start easily. Have motor with KL10 class of rotor than KL16 class of rotor, because KL10 class of rotor could take maximum starting torque up to 180% of the full load torque. Such practice reduces the motor life in no uncertain terms.

 

  

·         ->>Motor Efficiency-The new motor efficiency standard could have major energy-saving impact for motors worldwide. Though standard motors are now available with a better efficiency, this factor (motor efficiency)requires due attention when making the selection of the motor for a specific application in view of substantial quantum of power consumed by the motors in the particular applications.

·         ->>Ambient Temperature-As per normal standards, the motor output is given by the vendors based on 40ºC ambient temperature. In order to maintain the motor output at higher temperature as per the power requirement of driven equipment, it may be necessary that the motor with a higher frame size for the same rating is selected to avoid adverse effect of derating.

·         ->>Altitude- Standard motor output  are specified by the manufacturers for site altitude up to 1000m.For altitudes of more than 1000m,the motor ratings required to be checked for its suitability to maintain the specified output, or otherwise the duration factor is to be applied to know actual anticipated output at higher altitude.

·         ->>Method Of Starting And Number Of Starts-The starting performance of the motor depends on the method starting deployed, i.e. Direction-line, star-delta, high resistance, auto transformer, variable frequency drive. Where the starting torque requirement is not so critical, the star-delta starting or any other reduced voltage method of starting is used. Where the starting with very heavy load, such as with hoist or crane drives and speed control over a wide range is required, it is advantageous to consider the slip-ring type(or wound rotor type)motor with a drum controller starter or resistance starter.

·         ->>Duty Cycle-Duty cycle is the load that a motor must handle over the period when it starts, runs, and stops. Continuous duty is by far the simplest and most efficient application. The duty cycle begins with startup, then long periods of steady operation where the heat in the motor can stabilize as it runs. A motor in continuous duty can be operated safely at or near its rated capacity because the temperature has a chance to stabilize. Intermittent duty is more complicated. The life of commercial airplanes is measured by their number of landings; in the same way, the life of a motor is proportional to the number of starts it makes. Frequent starts shorten life because inrush current at startup heats the conductor rapidly. Because of this heat, motors have a limited number of starts and stops that they can make in an hour.

In a constant speed application, a motor often runs at an approximate speed with little or no concern about acceleration and deceleration ramps. This type of application is usually run using across-the-line on/off control. The control circuits often consist of a branch circuit fusing with a contactor, an overload motor starter, and a manual motor controller or soft starter.

Both ac and dc motors are suitable for constant speed applications. DC motors provide full torque at zero speed and have a large installed base. AC motors are also a good choice because they have a high power factor and require little maintenance. 

Variable speed applications usually require tight velocity and speed changes as well as defined acceleration and deceleration ramps. Reducing the motor speed in application, such as fans and centrifugal pumps often improves efficiency by matching the power consumed to the load instead of running at full speed and throttling or dampening the output. 

those criteria to be consider and acknowledge before selecting a motor : 
1. What the load need to move?
2. What the speed need to run?
3. Does the load vary throughout the move?
4. Should recognize any special function needed on the application.
5. Suitable to use AC Power or DC power?
6. Finally the budget.

Some grades need to be climbed at a minimum speed some others don’t. Sometimes the maximum power is found simply at maximum speed (this is the case where the vehicle as a large frontal area or goes at very high speed). This translates to having a motor powerful enough to go through all the different conditions the vehicle can be submitted to!