15-01-2013, 02:28 PM
Basic Components Of An Electric Drives System
[attachment=46976]
The basic criterion in selecting an electric motor for a given
drives application
1. Power level and performance required by the loads during steady steady-state and dynamic operation.
Ex: In application for which a high starting torque is needed a dc series motor might be a better choice than an ac induction motor.
In Constant speed applications, synchronous motor be more suitable than induction or dc motors
2. Environmental factors (determine the motor type)
Ex: In food processing, chemical industries, aviation, where the environment must be clean and free from arcs, dc motor can not be used unless they are encapsulated.
3. The cost of the electric motors.
In general, brushless dc motors are more expensive, whereassquirrel cage induction motors are the choppers
4. The function of converters (wave forms)
Ex: If the power source is an ac type and the motor is a dcmachine. The converter transforms the ac waveform to dc. (stability, efficiency and performance of motor that using this converter.
Electric Motors Speed Speed-Torque Characteristics
Shunt or separately excited dc motor(speed slightly reduced when the load torque increase)Curve III : Series dc motor(speed is high at light loading condition and low at heavy loading)Curve IV : Induction motor(during steady state, they operation at the linear portion of speed-torque characteristic speed is high at light loading, the maximum developed torque is limited to TmaxIn electric drive application, electric motors should be selected to match the intended performance of loads. Ex: In constant speed application, the synchronous motor is probably the best option.
Power Sources
Two major type of power sources are used in industrial
applications:
1. Alternating Current (ac), single phase or three three-phase, 60Hz or
60 Hz,
2. Direct Current (dc)
Extensive industrial installation usually have more than one type of power sources at different voltages and frequencies, Commercial airplanes, for examples, may have a 400Hz ac sources in additional a 270 volt sources.
[attachment=46976]
The basic criterion in selecting an electric motor for a given
drives application
1. Power level and performance required by the loads during steady steady-state and dynamic operation.
Ex: In application for which a high starting torque is needed a dc series motor might be a better choice than an ac induction motor.
In Constant speed applications, synchronous motor be more suitable than induction or dc motors
2. Environmental factors (determine the motor type)
Ex: In food processing, chemical industries, aviation, where the environment must be clean and free from arcs, dc motor can not be used unless they are encapsulated.
3. The cost of the electric motors.
In general, brushless dc motors are more expensive, whereassquirrel cage induction motors are the choppers
4. The function of converters (wave forms)
Ex: If the power source is an ac type and the motor is a dcmachine. The converter transforms the ac waveform to dc. (stability, efficiency and performance of motor that using this converter.
Electric Motors Speed Speed-Torque Characteristics
Shunt or separately excited dc motor(speed slightly reduced when the load torque increase)Curve III : Series dc motor(speed is high at light loading condition and low at heavy loading)Curve IV : Induction motor(during steady state, they operation at the linear portion of speed-torque characteristic speed is high at light loading, the maximum developed torque is limited to TmaxIn electric drive application, electric motors should be selected to match the intended performance of loads. Ex: In constant speed application, the synchronous motor is probably the best option.
Power Sources
Two major type of power sources are used in industrial
applications:
1. Alternating Current (ac), single phase or three three-phase, 60Hz or
60 Hz,
2. Direct Current (dc)
Extensive industrial installation usually have more than one type of power sources at different voltages and frequencies, Commercial airplanes, for examples, may have a 400Hz ac sources in additional a 270 volt sources.