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This value is determined from a mathematical relationship that assumes that the worst efficiency of any motor in the batch — used to determine the average (nominal) value — could have losses as much as 20% higher than the average. As a result, each nominal efficiency value would have a corresponding minimum efficiency value. You can view these values in Table 12-8 in NEMA MG-1.
Power factor — Power factor is the ratio of motor load watts divided by volt-amps at the full-load condition. Power factor for a motor changes with its load. Power factor is minimum at no load and increases as additional load is applied to the motor. Power factor usually reaches a peak at or near full load on the motor.
Final spin. Changing motors out becomes a lot easier when you can quickly recognize the key items that describe a motor's size, speed, voltage, physical dimensions, and performance characteristics. All of this information and more is usually available on the motor's nameplate. It's your responsibility to be able to correctly interpret the information on this nameplate, correctly apply it in the field, and verify conformance to NEMA, IEC, or other industry standards.
Editor's Note: This text was written by Ed Cowern when he was a district manager for Baldor Electric Co. in Wallingford, Conn. He has since …show more content…
The plot shows what happens in terms of output torque and motor speed when a motor is started with full voltage applied.
The motor is initially at zero speed and develops locked-rotor torque (Point A). As the motor accelerates, some motor designs produce a slight dip in torque. If they do, the lowest point on this curve is called the pull-in or pull-up torque (Point B). As the speed increases further, the torque generally increases to the highest point on the curve (Point C), which is called the pullout or breakdown torque. Finally, when the motor is loaded to its full-load torque, the motor speed stabilizes (Point D).
If the motor isn't driving anything, its speed goes up to its no-load speed or synchronous speed (Point E). For example, on a four-pole motor operating at 60 Hz, the no-load speed might be 1,799 RPM and synchronous speed would be 1,800 RPM.
Each of these points (A, B, C, and D) has absolute values (usually expressed in pound-feet). However, they're frequently given in terms of a percentage of the full-load torque. For example, a 20-hp, 60-Hz, four-pole motor could have a full-load torque of 59.5 pound-feet and a locked-rotor torque of 116 pound-feet. This is shown as:
Power factor — Power factor is the ratio of motor load watts divided by volt-amps at the full-load condition. Power factor for a motor changes with its load. Power factor is minimum at no load and increases as additional load is applied to the motor. Power factor usually reaches a peak at or near full load on the motor.
Final spin. Changing motors out becomes a lot easier when you can quickly recognize the key items that describe a motor's size, speed, voltage, physical dimensions, and performance characteristics. All of this information and more is usually available on the motor's nameplate. It's your responsibility to be able to correctly interpret the information on this nameplate, correctly apply it in the field, and verify conformance to NEMA, IEC, or other industry standards.
Editor's Note: This text was written by Ed Cowern when he was a district manager for Baldor Electric Co. in Wallingford, Conn. He has since …show more content…
The plot shows what happens in terms of output torque and motor speed when a motor is started with full voltage applied.
The motor is initially at zero speed and develops locked-rotor torque (Point A). As the motor accelerates, some motor designs produce a slight dip in torque. If they do, the lowest point on this curve is called the pull-in or pull-up torque (Point B). As the speed increases further, the torque generally increases to the highest point on the curve (Point C), which is called the pullout or breakdown torque. Finally, when the motor is loaded to its full-load torque, the motor speed stabilizes (Point D).
If the motor isn't driving anything, its speed goes up to its no-load speed or synchronous speed (Point E). For example, on a four-pole motor operating at 60 Hz, the no-load speed might be 1,799 RPM and synchronous speed would be 1,800 RPM.
Each of these points (A, B, C, and D) has absolute values (usually expressed in pound-feet). However, they're frequently given in terms of a percentage of the full-load torque. For example, a 20-hp, 60-Hz, four-pole motor could have a full-load torque of 59.5 pound-feet and a locked-rotor torque of 116 pound-feet. This is shown as: