induction motor delta star connection

[panthripu]

Hi
Once again looking for some information. An induction motor delta connected 110kW-460V/60Hz with full load current 200A. At present taking around 75 A (almost below 40% of full load ). If it is terminated in star , It will take more current (may be almost double of what it is taking now) with same load. Is it correct ?
How much energy consumption can i expects to reduce ?

 

[templdl]

Hi
Once again looking for some information. An induction motor delta connected 110kW-460V/60Hz with full load current 200A. At present taking around 75 A (almost below 40% of full load ). If it is terminated in star , It will take more current (may be almost double of what it is taking now) with same load. Is it correct ?
How much energy consumption can i expects to reduce ?

May you be referring to a motor for used with a reduced star delta motor starter?
This start is used to start the motor in the star configuration to reduce the motor's starting current and after it accelerates it reconfigures the winding connections to a delta in the run mode.
In the start mode the starter configures the 3 windings to be essentially connected in series from phase to phase connected in a common connection forming a ?star? with the 3 phase supply connected at each tip of the star.
When reconnected in a delta you will see that each winding will be across two of the phases and will no linger be connected in series with another winding.

 

[Electric-Light]

Hi
Once again looking for some information. An induction motor delta connected 110kW-460V/60Hz with full load current 200A. At present taking around 75 A (almost below 40% of full load ). If it is terminated in star , It will take more current (may be almost double of what it is taking now) with same load. Is it correct ?
How much energy consumption can i expects to reduce ?

If you wire it as wye, it will only make 1/3 the starting torque. It is used for reduced current starting. The running current, though, as you said will increase.

If you wire it wye, it would be like running it on 277v.

 

[Jraef]

This is a scheme that the government in India is promoting all over as a way to try to reduce energy consumption. They tell people to permanently connect lightly loaded motors in Star rather than Delta as a way to reduce the magnetic losses in the motor, knowing full well that the motor power capacity is cut to 1/3 of normal. They do this because they know that many users in India cannot afford to upgrade to more energy efficient motors, so this is a low cost alternative. What they don't tell people is that the energy savings benefit is minimal at best, but the risk of overloading the motor is high, so in my opinion the risk/reward ratio is too low to bother with.

Bottom line:

1. It does theoretically work in that reducing the motor terminal voltage by virtue of connecting t in Star (Wye), will reduce the magnetic losses in the motor. As a rough rough guess, the total magnetic losses in a modern energy efficient AC induction motor are around 1% of the absorbed power, so by reducing the terminal voltage, you can save maybe 1/4 of that 1% (0.0025 factor) of the consumed energy.

2. It does also reduce the mechanical kW capacity of the motor to 33% of what it is rated for, so to work at all, your load MUST be permanently reduced to that level or less.

3. At this point, all you know is the running load amps are 75A compared to the FLC of 200A. That does not accurately tell you what the connected load is in kW, because you do not know the Power Factor. But off-hand at first glance, it appears as though this is right on the border of being able to function, and if it does not, then the motor stalls and over loads, either causing a trip and therefore a failed application, or (if you fail to compensate the motor protection scheme), the motor overloads and is damaged, also resulting in a failed application.

4. If it works, and your mechanical load is truly 36kW or less and NEVER demands more from the motor, then you will save approximately 90W of energy.​

 

[Besoeker]

Hi
Once again looking for some information. An induction motor delta connected 110kW-460V/60Hz with full load current 200A. At present taking around 75 A (almost below 40% of full load ). If it is terminated in star , It will take more current (may be almost double of what it is taking now) with same load. Is it correct ?
How much energy consumption can i expects to reduce ?

There is no "one size fits all" answer to this. It depends on the particular motor and the loading. Induction motors typically run at around 30% -35% FLC on no load so your 40% indicates quite light load. At that, reducing terminal voltage a bit would reduce stator current and increase rotor current. Losses would likely reduce. But, in order to predict the operation at a voltage of 1/sqrt(3) of nominal would need a lot more data.

 

[panthripu]

induction motor delta star

induction motor delta star

Thanks guys for your valuable words.
I believe ,its not only in india but now a days everywhere in the world ,the people are talking about the sustainability.
Some time back , I started another thread asking you guys about using VFD to save energy. Now what I could understand is, converting delta to star or reducing speed of motor using VFD in no load condition will not result more than 1 to 3%. Even switching off the motor in no load condition is also not going to save more than 5%. But if the unnecessary loaded motor if switch off can give you a big impact.
Any other comments or ideas ....??

 

[mull982]

This is a scheme that the government in India is promoting all over as a way to try to reduce energy consumption. They tell people to permanently connect lightly loaded motors in Star rather than Delta as a way to reduce the magnetic losses in the motor, knowing full well that the motor power capacity is cut to 1/3 of normal. They do this because they know that many users in India cannot afford to upgrade to more energy efficient motors, so this is a low cost alternative. What they don't tell people is that the energy savings benefit is minimal at best, but the risk of overloading the motor is high, so in my opinion the risk/reward ratio is too low to bother with.

Bottom line:

1. It does theoretically work in that reducing the motor terminal voltage by virtue of connecting t in Star (Wye), will reduce the magnetic losses in the motor. As a rough rough guess, the total magnetic losses in a modern energy efficient AC induction motor are around 1% of the absorbed power, so by reducing the terminal voltage, you can save maybe 1/4 of that 1% (0.0025 factor) of the consumed energy.

2. It does also reduce the mechanical kW capacity of the motor to 33% of what it is rated for, so to work at all, your load MUST be permanently reduced to that level or less.

3. At this point, all you know is the running load amps are 75A compared to the FLC of 200A. That does not accurately tell you what the connected load is in kW, because you do not know the Power Factor. But off-hand at first glance, it appears as though this is right on the border of being able to function, and if it does not, then the motor stalls and over loads, either causing a trip and therefore a failed application, or (if you fail to compensate the motor protection scheme), the motor overloads and is damaged, also resulting in a failed application.

4. If it works, and your mechanical load is truly 36kW or less and NEVER demands more from the motor, then you will save approximately 90W of energy.​

You mention that when connected in wye the motor will operate at 1/3 of normal. I had thought that the motor starting torque was a function of the % voltage reduction squared but the running torque was equal to the % voltage reduction.

So when wired in wye with .58 rated voltage across the motor terminal the starting torque would be .58^2 which would be approx .33 or 1/3. The motor running tourque I thought would be equivelent to the .58 voltage reduction so therfore have a reduced running torque of 58% or nomal.

Is the 1/3 reduction factor you are talking about above referencing the starting torque/power or the running torque/power?

 

[weressl]

This is a scheme that the government in India is promoting all over as a way to try to reduce energy consumption. They tell people to permanently connect lightly loaded motors in Star rather than Delta as a way to reduce the magnetic losses in the motor, knowing full well that the motor power capacity is cut to 1/3 of normal. They do this because they know that many users in India cannot afford to upgrade to more energy efficient motors, so this is a low cost alternative. What they don't tell people is that the energy savings benefit is minimal at best, but the risk of overloading the motor is high, so in my opinion the risk/reward ratio is too low to bother with.

Bottom line:

1. It does theoretically work in that reducing the motor terminal voltage by virtue of connecting t in Star (Wye), will reduce the magnetic losses in the motor. As a rough rough guess, the total magnetic losses in a modern energy efficient AC induction motor are around 1% of the absorbed power, so by reducing the terminal voltage, you can save maybe 1/4 of that 1% (0.0025 factor) of the consumed energy.

2. It does also reduce the mechanical kW capacity of the motor to 33% of what it is rated for, so to work at all, your load MUST be permanently reduced to that level or less.

3. At this point, all you know is the running load amps are 75A compared to the FLC of 200A. That does not accurately tell you what the connected load is in kW, because you do not know the Power Factor. But off-hand at first glance, it appears as though this is right on the border of being able to function, and if it does not, then the motor stalls and over loads, either causing a trip and therefore a failed application, or (if you fail to compensate the motor protection scheme), the motor overloads and is damaged, also resulting in a failed application.

4. If it works, and your mechanical load is truly 36kW or less and NEVER demands more from the motor, then you will save approximately 90W of energy.​

It's more insidious than that. The overloaded motors will fail sooner than normal life expectancy, so the Owner will be forced to replace it or repair it. The Governments gets its pound of flesh one way or the other, citizens be damned.

 

[Jraef]

You mention that when connected in wye the motor will operate at 1/3 of normal. I had thought that the motor starting torque was a function of the % voltage reduction squared but the running torque was equal to the % voltage reduction.

So when wired in wye with .58 rated voltage across the motor terminal the starting torque would be .58^2 which would be approx .33 or 1/3. The motor running tourque I thought would be equivelent to the .58 voltage reduction so therfore have a reduced running torque of 58% or nomal.

Is the 1/3 reduction factor you are talking about above referencing the starting torque/power or the running torque/power?

:roll::angel:
Mull982
I'm on my way to a job site, but later I'm going to PM you on this and go from there.