AC Electric Motor Design - Software

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AC Electric Motor Design - Software
Softbit presents an easy way to design LT, 3 ph, TEFC, squirrel cage ac electric motors with the help of "AC Electric Motor Design Software". You just need to enter a few preliminary inputs and click a button. What you get is an output "Design Sheet" containing more than 100 output parameters required to build an ac squirrel cage electric motor. You can start to design from a small fractional horse power ac electric motor to a 50 hp ac electric motor using this design software. Higher hp modules are also available on request. You have the options to change any of the values from output design data to match your specifications and need. With the change in any of these values, the remaining parameters change automatically, without affecting the output design and performance of the motor.

What you can Change
You can change any parameter from the design data sheet like no. of slots, type of cage, material of cage conductor (Al or Cu), length of stator, bore of stator, core type / material, rotor dimensions, stator length, shaft diameter, shaft length, supply voltage etc.,. to get a better and most suited design for your requirement. Accordingly motor winding data will also change.

Why to change the output parameter
What ever results you get through this design software are as per calculations done using the formulae used to design a squirrel cage ac electric induction motor. Now suppose you get a rotor diameter as X and rotor length as Y but the job and place do not permit you to use these dimesions of rotor or say motor then you just change the value of either X or Y to best suit your requirement and all the related output parameters will change automatically. So you can customize the design as per yours , your client's or job's requirement.

Values you need to enter at the start
When you start designing a squirrel cage ac electric motor, certain preliminary values are required to be fed to the software to give the out put parameters. So you need to enter - capacity of motor in hp / kw, poles, supply voltage, rpm, frequency and certain more that the software will ask you at the time of start.

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Factors affecting the Design of an ac electric induction motor
"An electric motor converts electrical energy into rotating mechanical energy or an electric motor is a machine that converts electrical energy into rotating mechanical energy. AC electric motor works on the principle of electro - magnetic induction".
Design of an ac electric motor is directly affected by the length of the air gap. Ampere Conductors value also affects the design of an ac electric motor. The value of average flux density over the air gap of an ac electric motor also affects the design of an ac electric motor. The size or dimensions of an ac electric motor depend upon the speed of an ac electric motor. It can also be said that the volume of active parts of an ac electric motor varies inversely as the speed of an ac electric motor. The value of output co-efficient is directly responsible for the dimensions of an ac electric motor. In other words the volume of active parts of an ac electric motor is inversely proportional to the value of output co-efficient of the ac electric motor. The total flux around the armature (or stator of an ac electric motor) periphery at the air gap is called the total magnetic loading. While total electric loading is the total number of ampere conductors around the armature (or stator of an ac electric motor) periphery. Since the output coefficient of an ac electric motor is proportional to the product of specific magnetic and specific electric loading of an ac electric motor, we conclude that the size and hence the cost of ac electric motor decreases if increased values of specific magnetic and electric loading are used. The flux density in iron parts of an ac electric motor is directly proportional to the average flug density in the air gap of the ac electric motor. In a well designed ac electric motor the maxmium density occurs in the teeth of the ac electric motor and therefore let us relate the flux density in the teeth with flux density in the air gap of ac electric motor. Th magnetising current of an ac electric motor is directly proportional to the mmf required to force the flux through the air gap and the parts of the ac electric motor. The mmf required for the air gap of an ac electric motor is directly proportional to the gap flux density i.e. the specific magnetic loading of an ac electric motor. The consideration of magnetising current is very important in ac electric induction motor(s) as an increased value of magnetising current means of a low operating power factor of ac electric motor. Therefore specific magnetic loading in the case of ac electric induction motor(s) is lower than that in dc electric motor(s). The core loss in any part of the magnetic circuit of an ac electric motor is directly proportional to the flux density for which the ac electric motor is going to be designed. Thus a large value of specific magnetic loading in an ac electric motor indicates an increased core loss in ac electric motor and consequently a decreased efficiency of ac electric motor and an increased temperature rise of ac electric motor. In case of high frequency ac electric motor, specific magnetic loading must be reduced in order to get lower iron losses in ac electric motor so that reasonable values of efficiency may be maintained in an ac electric motor. The max. temperature rise of an ac electric motor is determined by the type of insulation material used in the ac electric motor. If the cooling co-efficient of the ac electric motor is small, a high value of specific loading may be used in the ac electric motor. The value of cooling co-efficient while designing an ac electric motor depends upon the ventilation conditions in the ac electric motor. An ac electric motor with better ventila- tion has a lower value of cooling co-efficient. If the current density in conductors of an ac electric motor and the slot space factor of ac electric motor are assumed constant, then specific electric loading of an ac electric motor is proportional to the diameter of the core of ac electric motor as depth usually depends upon the diameter of core of ac electric motor. Typical values of current density are in the range of 2 - 5 A/mm sq. in case of an ac electric motor. While desining an ac electric motor, temperature rise is usually 40 deg C for normal applications of ac electric motor and co-efficient is between 0.02 to 0.035 CW-m sq. The larger ac electric motor is intrinsically more efficient. As the size of an ac electric motor increases, better ventilation and cooling conditions have to be provided in the ac electric motor. Iron loss in an ac electric motor increases with increased value of air gap flux density. The value of air gap flux density of an ac electric motor determines the overload capacity of the ac electric motor. A large value of ac in an ac electric motor means that a greater amount of copper is employed in the ac electric motor. This results in higher copper losses in the ac electric motor and large temperature of embedded conductors in ac electric motor. A small value of ac should be taken for high voltage ac electric motor. And also higher value of ac in an ac electric motor, the lower would be the overload capacity of ac electric motor. For a normal design of an ac electric motor the dia of core of ac electric motor be so choosen that the peripheral speed of rotor of ac electric motor does not exceeds about 30 m/s. The three phases of an ac electric motor can be connected in either star or delta. The power factor of ac electric motor with agreater gap length is smaller. The harmonic fields in an ac electric motor are due to: i) windings of ac electric motor, ii) Slotting of ac electric motor, iii) Saturation of air gap of an ac electric motor and iv) Irregularities in the air gap of ac electric motor. The harmonic fields in an ac electric motor are responsible for increase in stray load losses in ac electric motor and increased ac electric motor heating. The choice of rotor slots of an ac electric motor is particularly important in the case of ac squirrel cage electric motors. The Cogging effect can be over come in an ac electric motor by the way that the number of stator slotes of ac electric motor should not be equal to the number of rotor slots of ac electric motor. Better to have 15 to 30 percent more or less rotor slots of ac electric motor than the number of stator slots of ac electric motor. The difference of stator slots of an ac electric motor and rotor slots of an ac electric motor should not be equal to 2p or 5p to avoid synchronous cups in ac electric motor. The difference between the number of stator slots of ac electric motor and rotorslots of ac electric motor should not be equal to 3p for 3 phase ac electric motor in order to avoid magnetic locking in ac electric motor. The difference between the number of stator slots of ac electric motor and rotor slots of ac electric motor should not be equal to 1, 2, (p+/-1) or (p+/-2) to avoid noise and vibrations in ac electric motor. The ac electric motor noise and vibrations, cogging effects in ac electric motor and synchronous cups in ac electric motor can be reduced or even entirely eliminated be skewing either the stator slots of ac electric motor or the rotor of ac electric motor. Also, in order to eliminate the effects of any harmonic in the ac electric motor, the rotor bars of ac electric motor should be skewed through an angle so that the bars lie under alternate harmonic poles of the polarity or in other words, bar must be skewed through two pitches in ac electric motor. A rotor of an ac electric motor with a high resistance has the disadvantage the I sq. R loss is greater in the ac electric motor and therefore its efficiency is lower under running conditions of ac electric motor. A rotor of an ac electric motor designed with a high value of current density results in high starting torque and a lower efficiency for the ac electric motor. The current density of rotor bars of an ac electric motor may be taken between 4 to 7 A/mm sq. The flux density in the rotor core of an ac electric motor is generally equal to the stator core density of ac electric motor. The total losses in an ac electric motor are equal to the sum of total copper losses in ac electric motor, iron losses in ac electric motor, friction losses in ac electric motor and windage losses in ac electric motor. A small value of leakage reactance of ac electric motor means that the power factor of the ac electric motor is good. The high starting torque of ac electric induction motor can be achieved by either using double cage rotor in ac electric motor or deep bar rotor in an ac electric motor. Design of shaft of an ac electric motor. The shaft of an ac electric motor must be strong enough throughout its section to withstand all loads causing residual strain. The diameter of shaft of ac electric motor in the bearings is less than the diameter under the armature of ac electric motor. Plain bearings are used for horizontal shaft ac electric motor and thrust bearings are used for vertical shaft ac electric motor.

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