Calculation of torque of a DC motor

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Discussion Overview

The discussion revolves around calculating the torque of a DC motor based on its specifications, including voltage, frequency, number of poles, power, and RPM. The context includes a final year project requirement for motor replacement.

Discussion Character

  • Homework-related, Technical explanation

Main Points Raised

  • Fawaaz presents the specifications of a DC motor and requests assistance in calculating its torque.
  • One participant questions the RPM and number of poles, suggesting that the specifications may actually pertain to an induction motor, noting that a 6-pole motor at 50 Hz should yield about 1000 RPM synchronous, with a typical slip leading to approximately 990 RPM.
  • Fawaaz acknowledges the mistake in the RPM, correcting it to 1000 RPM and asks if torque can now be calculated.
  • Another participant suggests using the known power and RPM to find the torque, referencing a relationship found in introductory physics resources.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the motor type or the implications of the specifications, and there is uncertainty regarding the correct RPM and its impact on torque calculation.

Contextual Notes

The discussion includes assumptions about motor types and specifications that may not be fully clarified, such as the distinction between DC and induction motors, and the implications of slip on RPM.

fawaaz
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Hi everyone,

Im currently doing my final year project and I need to calculate the torque of a DC motor so that I can replace it accordingly by another motor. Here are the motor's specification : 400V, 50Hz, 6poles, 200kW, 1400rpm, 371A
Can anyone please help me sort this out.

regards,
Fawaaz
 
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I think the RPM (or number of poles) listed is incorrectk assuming specs above are for an induction motor.
A 6 pole motor at 50 Hz should give about 1000 rpm synchronous. With 1% slip, you should expect about 990 rpm.
50 Hz with 4 poles gives 1500 rpm synchronous. The motor would have to slip over 6% to make 1400 rpm.
 
Last edited:
oooh god... i made a mistake... itz 1000rpm... :(

now u can calculate the torque??
 
You know the power (200kw) and you know the rpm (1400). Open any first year physics book and look up the relationship between hp-rpm-torque.
 

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