(Please try to make the title of your post specific to the question)
It is due to the voltage applied to the motor stator coil. When the motor is connected in Delta, full voltage is applied to the motor coil and the speed is more. The same motor when connected in Y and same voltage is applied to the motor terminal, only 58% (1/√3) voltage is applied to the stator coil and hence the speed is less, the motor torque also will be 1/3rd. A motor having both Star/Delta configuration must have dual voltage system (higher voltage for Y and lower voltage for Delta) and you must run the motor with the correct voltage system. However, you can apply Delta voltage in Y connection only during the Star/Delta starting period.
- MS
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"All my technical advices in this forum must be consulted with and approved by a local registered professional engineer before implementation" - Mohammed Samad (Linkedin Profile: http://www.linkedin.com/in/msamad)
"(1/√3) voltage is applied to the stator coil and hence the speed is
less, the motor torque also will be 1/3rd."
Technically... in an AC squirrel cage motor, motor SPEED is only a function of the number of poles and the applied frequency, voltage has no bearing (but you know that). I'm being pedantic here because there are plenty of non-engineers who will read this and not understand the subtlety of what your statement can be interpreted as.
How about this tweak...
"(1/√3) voltage is applied to the stator coil and hence the torque will be 1/3rd, so if the load does not decrease on the the motor, the speed will drop as well. This will also cause a severe increase in slip, so the motor cannot actually sustain the same load with the reduced torque and resultant speed."
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** All I every really wanted to be, was... A LUMBERJACK!.**
Thanks JRaef for pointing it out. I should have explained it clearly.
- MS
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"All my technical advices in this forum must be consulted with and approved by a local registered professional engineer before implementation" - Mohammed Samad (Linkedin Profile: http://www.linkedin.com/in/msamad)
That's why I first stated that his premise was faulty, he was assuming that speed did in fact change because of the effective voltage drop, when in fact it may or may not change, and if it does, it will not likely be sustainable.
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** All I every really wanted to be, was... A LUMBERJACK!.**
Motor torque % = (supplied voltage / winding voltage) raised to the power of 2 x 100.
Therefore 400 v feed to a 690 v winding (Star connected) will result in a torque of 33.6 % this will result in an increase in motor slip due to rotor stalling against mechanical load. It is obvious that this will result in lower shaft rpm.
Try riding a bicycle from a flat road to an up hill and see if you can maintain the same speed without having to push harder on the pedals.
Motor Speed
Re: el
