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Join Date: Apr 2012
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Effect of Temperature Stability on Induction Motor

04/03/2012 6:11 AM

During type testing of induction motor the losses tends to decrease why??

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#1

Re: Effect of temperature stability on Induction motor

04/03/2012 6:17 AM

According to IEC 600034-1 Clause 3.31 Type test is a test of one or more machines made to a certain design to show that the design meets certain specifications but According to IEC 60034-1 Clause 3.32 a routine test is a test to which each individual machine is subjected during or after manufacture to ascertain whether it complies with certain criteria.

The criteria which is checked in 3 phase induction motor is the value of No load current at rated voltage and the value of lock rotor voltage at rated full load current. The No Load loss coming out during cold running is much more than the loss coming during hot running.

In routine test the No load test is done in cold condition while in type test the no load test is done in hot conditions of motor. Infact immediately after the temperature rise test when the motor winding got saturated.It is a phenomenon of induction motor that in starting the losses are high which gradually decreases while running on load. In routine test the no load current will also be high in comparison to the no load current during type test.

Why this happens???

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#3
In reply to #1

Re: Effect of temperature stability on Induction motor

04/03/2012 6:31 AM

Something in the motor changes its properties with temperature?

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#4
In reply to #3

Re: Effect of temperature stability on Induction motor

04/03/2012 6:36 AM

Yeah I want to know the "something"

What is that property which makes the losses to come down ??

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#2

Re: Effect of temperature stability on Induction motor

04/03/2012 6:23 AM

According to IEC 600034-1 Clause 3.31 Type test is a test of one or more machines made to a certain design to show that the design meets certain specifications but According to IEC 60034-1 Clause 3.32 a routine test is a test to which each individual machine is subjected during or after manufacture to ascertain whether it complies with certain criteria.

The criteria which is checked in 3 phase induction motor is the value of No load current at rated voltage and the value of lock rotor voltage at rated full load current. The No Load loss coming out during cold running is much more than the loss coming during hot running.

In routine test the No load test is done in cold condition while in type test the no load test is done in hot conditions of motor. Infact immediately after the temperature rise test when the motor winding got saturated.It is a phenomenon of induction motor that in starting the losses are high which gradually decreases while running on load. In routine test the no load current will also be high in comparison to the no load current during type test.

Why this hapeens???

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#5

Re: Effect of temperature stability on Induction motor

04/03/2012 6:49 AM

What is that property which makes the losses in induction motor to decrease???

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Guru
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#6
In reply to #5

Re: Effect of temperature stability on Induction motor

04/03/2012 10:09 AM

The resistance of copper increases @ 4% per degree Celsius. Could that be a reason?

My goodness, you really seem anxious. Just repeating your posts several times won't get you any answers. Once is enough.

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#7

Re: Effect of Temperature Stability on Induction Motor

04/03/2012 10:45 AM

AC motors have what is called a "negative coefficient of resistance", which means as the temperature changes, the winding resistance changes in the opposite direction. So as temperature goes up, resistance goes down. BUT... when you FIRST energize a motor that has been cold, moisture may have infiltrated the winding insulation, however slightly, and for the first few moments the resistance will exhibit positive coefficiency properties until the windings warm up enough to evaporate the moisture.

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#8

Re: Effect of Temperature Stability on Induction Motor

04/05/2012 1:49 AM

No it is not like that I think it depends upon the properties of electrical steel used in making the stator and rotor stampings. The magnetic properties of iron and iron silicon alloys are only slightly affected by small temperature changes. As the temperature is increased, permeability usually improves , whereas hysteresis and eddy current losses are decreased.

When temperature is less there is less permeability and when temperature is slightly high there is greater permeability causing the losses to decrease.

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