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The two most important factor to consider when selecting an electric motor are:
1. The electricity supply to which the motor will be connected - AC or DC. If AC three phase or single phase.
2. Type of enclosure or housing
Type of Electric Motor Enclosure
There are two basic enclosure options available: drip proof in steel or totally enclosed, in aluminium, steel and cast iron.
The totally enclosed fan cooled (TEFC) motor is the predominant standard for industrial applications, today. The versatile TEFC is fully enclosed within the motor frame, with cooling air directed over it by an externally mounted fan.
Other Key Factors Required for Motor Selection
Loading (KW)
Loading is determined by the equipment to be driven, and the torque available at the shaft. Electric motors have standard outputs per frame size from which any KW loading required can be selected from.
Speed
Choose the required speed of the motor. The induction motor is a fixed single speed machine. Its speed is dependent on the frequency of the electricity supply and the stator winding design. The no load speed of an induction motor is slightly lower than synchronous speed due to the no load losses in the machine. Full load speed is typically a further 3-4 per cent lower than no load speed.
Mounting
The mounting position must always be given when a motor is to be selected. Improper motor mounting can affect performance.
Power Supply
The supply voltage and frequency must be given when selecting an Electric motor
Operating Environment
This is one of the major factors that affect motor performance. The environment in which the motor is to operate is an important factor to consider when selecting a motor, as the ambient temperature, humidity and altitude can all affect performance
Checklist for Ordering a Fixed Speed TEFC Motor:
1. The electricity supply to which the motor will be connected - AC or DC. If AC three phase or single phase.
2. Type of enclosure or housing
Type of Electric Motor Enclosure
There are two basic enclosure options available: drip proof in steel or totally enclosed, in aluminium, steel and cast iron.
The totally enclosed fan cooled (TEFC) motor is the predominant standard for industrial applications, today. The versatile TEFC is fully enclosed within the motor frame, with cooling air directed over it by an externally mounted fan.
Other Key Factors Required for Motor Selection
Loading (KW)
Loading is determined by the equipment to be driven, and the torque available at the shaft. Electric motors have standard outputs per frame size from which any KW loading required can be selected from.
Speed
Choose the required speed of the motor. The induction motor is a fixed single speed machine. Its speed is dependent on the frequency of the electricity supply and the stator winding design. The no load speed of an induction motor is slightly lower than synchronous speed due to the no load losses in the machine. Full load speed is typically a further 3-4 per cent lower than no load speed.
Mounting
The mounting position must always be given when a motor is to be selected. Improper motor mounting can affect performance.
Power Supply
The supply voltage and frequency must be given when selecting an Electric motor
Operating Environment
This is one of the major factors that affect motor performance. The environment in which the motor is to operate is an important factor to consider when selecting a motor, as the ambient temperature, humidity and altitude can all affect performance
Checklist for Ordering a Fixed Speed TEFC Motor:
| 1. Power Supply | Voltage (Volts) | No. of Phases | Frequency (Hertz) |
| 2. Power Rating | KW |
| 3. Speed | Rev/min | No. of Poles |
| 4. Duty | Type | Mounting IM |
| 5. Motor Drive | Direct | Belt |
| 6. Insulation Class/Temperature Rise | Insulation Class | Temperature Rise (oC) |
| 7. Torque Type | Quadratic | Constant |
| 8. Environmental Conditions | IP Rating | Ambient Temperature (oC) | Relative Humidity |
Checklist for Ordering a TEFC Variable Speed Electric Motor
| 1. Power Supply | Voltage (Volts) | No. of Phases | Frequency (Hertz) |
| 2. Power Rating | KW |
| 3. Speed | Rev/min | No. of Poles |
| 4. Duty | Type | Mounting IM |
| 5. Motor Drive | Direct | Belt |
| 6. Insulation Class/Temperature Rise | Insulation Class | Temperature Rise (oC) |
| 7. Torque Type | Quadratic | Constant |
| 8. Environmental Conditions | IP Rating | Ambient Temperature (oC) | Relative Humidity |
| 9. Variable Speed Drive Specifications | ||
| a. Type of Controller | Direct Torque Control (DTC) | Pulse Width Modulation (PWM) |
| b. Speed Range | Maximum Rev/min | Minimum Rev/min |
| c. Absolute Power (KW) | Maximum (KW) | Minimum (KW) |
| d. Output Fitters | Fitted | Non-Fitted |
| e. Maximum Cable Length (Meters) | Cable length (m) | |
