During a tea break brainstorming session, we are looking for a rough estimate related to motor startup torque. We are considering connecting the motor to a high-quality VSD that has been properly configured. For the purpose of this discussion, we are focusing solely on the startup torque and will not be using any additional data such as motor nameplates. Let's assume all motors were manufactured by the same company at the same time and are identical apart from their power ratings and number of poles. Our target motor is a 90Kw 400V 6-pole motor with a speed of 990 rpm, which we will consider as our benchmark for 100% startup torque. We also have a 75Kw 400V 6-pole motor operating at 990 rpm and a 90Kw 400V 4-pole motor running at 1440 rpm. Could you provide a percentage estimate of the startup torque for these two motors in comparison to our ideal motor configuration?
The choice of motor manufacturer will play a key role.
Thank you for responding, friend. Could you please upload the power curve of a 90Kw 6 pole motor from the same source as the previous two you shared? I would greatly appreciate it whenever you have a moment. In the specific application I am working on, the initial startup is the issue, not once the machine shaft reaches 1 rpm. Based on the data provided, it seems reasonable to conclude that a 90Kw 4 pole motor will have better startup performance than a 75Kw 6 pole motor. Thanks once again for your help.
According to the formula "Power = Torque * Revolutions," it is evident that the 75kW motor will have a less-than-optimal torque ratio of 75/90. Similarly, the 4-pole, 90kW motor will also exhibit a lower-than-ideal torque ratio of 4/6. This implies that both motors may not be operating at their maximum efficiency levels in terms of power output.
In a recent communication, Zimmer expressed gratitude for the response and requested the upload of a speed/torque curve for a 90Kw 6 pole motor from the same source as previously shared curves. The concern lies with the initial start of the machine shaft, as performance seems to improve once it reaches 1 rpm. Based on the analysis of the curves, it seems likely that a 90Kw 4 pole motor will have an advantage over a 75Kw 6 pole motor during startup. For further information, visit the link below to access motor options and speed/torque curves based on specific criteria: https://www.weg.net/catalog/weg/CI/en/c/EU_MT_LV_NEMA_3PHASE_TEFC_W22_HIGH/list. Don't hesitate to reach out for assistance in selecting the appropriate motor for your application.
This is an interesting question. To proceed, we have to assume that torque output is directly proportional to the power of the motor and inversely proportional to its speed. This is a simplified assumption and actual results may vary. Considering the 75Kw 400V 6-pole motor at 990 rpm, it has 83.33% of the power of your 90Kw benchmark motor; thus, it should roughly produce the same percentage of startup torque, assuming other factors are equal. On the other hand, the 90Kw 400V 4-pole motor, despite having the same power rating as your benchmark motor, operates at a higher speed (1440 rpm). Due to the inverse relationship between speed and torque, it should produce less torque. If we compare the speed ratios, 990 rpm / 1440 rpm gives about 0.69, or 69% of your benchmark. Do keep in mind these are rough estimates and actual values would depend on more specific motor characteristics and setup.
To make an educated guess on startup torque, we need to know that torque is directly proportional to the power and inversely proportional to the speed, assuming other operating conditions being equal. To compare the former with the benchmark motor: the 75Kw has 83.33% of the power rating of the 90Kw motor, and the speed is the same. So, its startup torque should be roughly 83.33% of the benchmark. As for the 90kW 4-pole motor with higher speed, the power factor is the same as the benchmark, but it's running at 1440 rpm, which is 145.45% of the speed of our benchmark 990 rpm. To estimate, applying the inverse relation of speed to the torque, I'd suggest its startup torque relative to the benchmark would be approximately 68.75% (1/1.4545). Keep in mind this is an estimation and would require actual tests for more accurate results.
For the 75 kW 6-pole motor, I'd estimate the startup torque might be around 85-90% of the 90 kW motor since it's the same design but with a lower power rating, so it shouldn't deviate too much in terms of torque characteristics. As for the 90 kW 4-pole motor, given its higher speed, the startup torque could be roughly 70-75% of the benchmark. The increased RPM typically means a lower torque at startup, but the exact figure can vary depending on the specific design choices made by the manufacturer.
Based on the information you've provided, I'd estimate that the 75 kW 6-pole motor would have a startup torque roughly around 75-80% of the 90 kW motor, given that it's a slightly lower power rating but maintains the same pole configuration. As for the 90 kW 4-pole motor, its startup torque could be around 60-70% of the 90 kW 6-pole motor because it's designed for a higher speed and generally exhibits lower torque characteristics at startup due to fewer poles. Of course, these are just rough estimates, and actual performance could vary with specific application conditions and VSD settings!
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Answer: - Estimating startup torque is crucial for understanding the initial force required to accelerate a motor from rest to its operating speed. This helps in assessing the efficiency and performance of different motor configurations under startup conditions.
Answer: - The number of poles in a motor influences its speed and torque characteristics. Generally, motors with fewer poles (e.g., 4-pole) tend to have higher starting torque compared to motors with more poles (e.g., 6-pole) due to differences in their speed-torque curves.
Answer: - A high-quality VSD can optimize the startup torque of a motor by providing precise control over its speed and acceleration. Properly configuring the VSD ensures efficient motor performance during startup, reducing mechanical stress and energy consumption.
Answer: - By analyzing the power ratings, voltage, and speed of the motors, a percentage estimate of the startup torque for the
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