Why should a series motor always start with a load?

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SUMMARY

A series motor must always start with a load to prevent excessive speed and potential damage. When starting without a load, the current is high, but the flux produced is moderate due to the fewer turns in the series winding. This results in an increase in speed and back EMF, which reduces current and further decreases flux, leading to dangerously high speeds. Therefore, starting with a load ensures safe operation, making series motors ideal for applications like trains that require high torque under load.

PREREQUISITES
  • Understanding of DC motor types, specifically series and shunt motors
  • Knowledge of back EMF and its relationship with motor speed
  • Familiarity with motor winding configurations and their effects on performance
  • Basic principles of electrical circuits and current flow
NEXT STEPS
  • Research the operational characteristics of DC series motors
  • Study the effects of load on motor performance and efficiency
  • Learn about protective measures for preventing motor damage during startup
  • Explore applications of series motors in transportation and heavy machinery
USEFUL FOR

Electrical engineers, motor control specialists, and anyone involved in the design or maintenance of DC motors, particularly in high-torque applications like trains.

mahima
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Why should a series motor always start with a load?
Why should a shunt motor always start without a load?
 
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I'm pretty sure this is a homework question, so what do you think? By the way, there must be more to this question since it is not correct as written.
 
In any DC motor the speed depends inversely on the flux. Consider when starting a series motor the current flowing will be high, but the flux that the motor produces will be moderate since the series winding has less number of turns. If u start the motor without load the speed will increase. as speed increases the back emf increases. this decreases the current through the series winding and hence flux decreases and the speed further increases. Theorerically speaking the speed becomes infinite. But practically the motor will accelerate to very high speed , which will damage the motor. But if you start the motor with the load, you are actually reducing the starting speed hence the motor runs safely. Since series motors has this property it is used in trains to pull high load.
 
It is correct to say that a dc series motor can start at quite (even startlingly) high speeds, but don't you use any control? Are there no power electronics people on your railroad?

BTW, the OP was about series motors not specifically dc series.
 

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