The T.M.Haja Sahib Transformer efficiency thread

[T.M.Haja Sahib]

Bes;
How can you be sure that maximum capacity i.e 471 KVA of the transformner will in no case be exceeded?Thanks.

 

[Besoeker]

Bes;
How can you be sure that maximum capacity i.e 471 KVA of the transformner will in no case be exceeded?Thanks.

Because it is correctly rated for purpose in accordance with my explanation of how the calculation is performed.

 

[T.M.Haja Sahib]

Sorry,I am not convinced.

 

[Besoeker]

Sorry,I am not convinced.

Not convinced about what exactly?
The fact that we have made dozens of such systems from 200kW to 6,600kW and that they operating in industries as diverse as water pumping and petrochem and have been doing so for thirty years does not convince you?

Then maybe you had better demonstrate to me what I'm doing wrong in my calculations so that you can set me straight on the error of my ways.

 

[T.M.Haja Sahib]

If you lay down the assumptions or the limitations on which the maximum capacity of the transformer of your case are based,it would be helpful to further discussion.

 

[Besoeker]

If you lay down the assumptions or the limitations on which the maximum capacity of the transformer of your case are based,it would be helpful to further discussion.

Again you are making an assumption. You're assuming that there are assumptions.
In actual fact, the parameters are all pretty well defined. We know motor rating, load characteristics.

Maybe this will help your understanding......all in PU values and treated on a per phase basis.

V - rotor voltage
I - rotor current
n - speed
P - Rotor power

V = (1-n)
I = n²

P = VI
= n² - n³...................(1)

Whence:
dP/dn = 2n-3n²


For a turning value:
2n-3n² = 0

From which you get:
n = 2/3

Substituting in Equation (1)
P = (2/3)² - (2/3)³
= 0.148

which is where the 15% comes from - all of which you could or should have been able to deduce from the information I provided in post #158.

Now, what assumptions did you assume I assumed?

 

[T.M.Haja Sahib]

One assumption,I naturaaly assume is about the pump discharge.If the pump discharge should increase above the design limit,the maximum transformer capacity should also rise.So reasonable provision for this should be made in the design stage.Has it been made in your case?

 

[Besoeker]

One assumption,I naturaaly assume is about the pump discharge.If the pump discharge should increase above the design limit,the maximum transformer capacity should also rise.So reasonable provision for this should be made in the design stage.Has it been made in your case?

Sadly my explanations seem to have been wasted on you.
First of all you assume its a wind turbine application and now you're making it a pump.
From my post #158:

This application was a wound rotor variable speed drive on a centrifugal fan.

You should be aware that the a fan has a cube law load power curve. To get it to take more power than its rating you would have to run it above rated speed, all other things being equal. But this is a sub-synchronous system (not a doubly fed system as you also assumed) so there is no possibility of increasing the load by increasing the speed beyond the rating. And, at maximum rating the transformer in question is at its most lightly loaded duty point anyway. See the curves I provided for you.

Of course, you can't exclude the possibility of the motor being overloaded possibly owing to bearing problems or other causes but then the motor overcurrent overcurrent protection on the stator side would operate. That's what the protection is for.
Beefing up the recovery transformer rating won't affect the protection settings.

 

[T.M.Haja Sahib]

Sadly my explanations seem to have been wasted on you.
First of all you assume its a wind turbine application and now you're making it a pump.

Sorry.I misread your application and I hope it did not cause excessive distress to you.

...there is no possibility of increasing the load by increasing the speed beyond the rating. And, at maximum rating the transformer in question is at its most lightly loaded duty point anyway.

You are considering only the fan speed as the variable to increase the discharge from it.One more parameter that can increase the fan discharge is its inlet air pressure and if it is greater,greater will be the discharge and so maximum transformer capacity should also increase.

 

[Besoeker]

You are considering only the fan speed as the variable to increase the discharge from it.One more parameter that can increase the fan discharge is its inlet air pressure and if it is greater,greater will be the discharge and so maximum transformer capacity should also increase.

At the risk of repeating the same information....
If the motor load increases beyond it's rating for ANY reason whatsoever, the overload protection will operate and shut the system down. That's what the protection is for after all.
So why should I uprate the recovery transformer to cover for abnormal operation outside the rating of the drive system and for which adequate protection exists?
Next you'll be telling me that I should uprate the motor just in case......the cables to it, the switchgear......gets a bit silly doesn't it?

Note also that, at the highest output from the drive, the recovery transformer is at its lowest loading anyway.
You do understand that, don't you?

 

[T.M.Haja Sahib]

At the risk of repeating the same information....
If the motor load increases beyond it's rating for ANY reason whatsoever, the overload protection will operate and shut the system down. That's what the protection is for after all.
So why should I uprate the recovery transformer to cover for abnormal operation outside the rating of the drive system and for which adequate protection exists?Next you'll be telling me that I should uprate the motor just in case......the cables to it, the switchgear......gets a bit silly doesn't it?

So you are designing it that way treating some design parameters as abnormal to be taken care of by O/L protection devices and shutting down the system instead of suitably allowing for in the system design as modern electrical design would do so?

Note also that, at the highest output from the drive, the recovery transformer is at its lowest loading anyway.

That is when speed is considered as the only variable.Isn't it?

 

[Besoeker]

So you are designing it that way treating some design parameters as abnormal to be taken care of by O/L protection devices and shutting down the system instead of suitably allowing for in the system design as modern electrical design would do so?

I'm not treating any of the DESIGN parameters as abnormal. Protection is for abnormal circumstance that might occur as a result of a fault or impending failure of some sort.
Prudent modern electrical system design has protection features that provide protection in the event that any design parameter is exceeded. A simple fixed speed motor starter would have protection.

In the system I have explained, the motor has a fairly sophisticated P&B Engineering motor protection relay taking measurements on the stator side.
This quite separate from any of the recovery side protection.

That is when speed is considered as the only variable.Isn't it?

It is not.
For a centrifugal load, maximum power is at maximum speed. Not at any other so speed is not a variable. It is a single duty point.

 

[T.M.Haja Sahib]

I'm not treating any of the DESIGN parameters as abnormal. Protection is for abnormal circumstance that might occur as a result of a fault or impending failure of some sort.
Prudent modern electrical system design has protection features that provide protection in the event that any design parameter is exceeded. A simple fixed speed motor starter would have protection.
In the system I have explained, the motor has a fairly sophisticated P&B Engineering motor protection relay taking measurements on the stator side.
This quite separate from any of the recovery side protection.

I am afraid you misunderstood.Reasonable allowance for any increase in inlet pressure to the subject centrifugal fan is a prudent design choice.It should not be disallowed by operation of O/L protection devices,because that would cause shut down of the system.It should be allowed for by suitable increase in the size of the recovery transformer etc.,This is what the modern electrical design does.

It is not.
For a centrifugal load, maximum power is at maximum speed. Not at any other so speed is not a variable. It is a single duty point.

Then what happens if inlet air pressure parameter is also added in ?
Answer:It results in the increase in the maximum size of the recovery transformer.

 

[Besoeker]

I am afraid you misunderstood.

There you go again. Telling me that I don't understand the equipment I have been designing and manufacturing for several decades and supplying to major blue chip companies.
And in field in which you clearly lack experience. That's an observation, not a criticism.

Reasonable allowance for any increase in inlet pressure to the subject centrifugal fan is a prudent design choice.It should not be disallowed by operation of O/L protection devices,because that would cause shut down of the system.It should be allowed for by suitable increase in the size of the recovery transformer etc.,This is what the modern electrical design does.

You really don't understand, do you?
We know the rating of the motor. There are no circumstances where you would want it to be operating continuously beyond that rating. Prudent modern design thus dictates that you include motor protection to prevent this from happening. Surely you are not suggesting that we ditch that protection?
Yet, that's exactly what you are suggesting:

It should not be disallowed by operation of O/L protection device

Unbelievable. Or ought to be....but somehow.........

Then what happens if inlet air pressure parameter is also added in ?
Answer:It results in the increase in the maximum size of the recovery transformer.

Answer: The motor rating determines the recovery system rating. Including that of the transformer. Stop digging.

 

[T.M.Haja Sahib]

We know the rating of the motor. There are no circumstances where you would want it to be operating continuously beyond that rating. Prudent modern design thus dictates that you include motor protection to prevent this from happening. Surely you are not suggesting that we ditch that protection?

You stated that maximum capacity of the transformer occurs at 15% of the drive rating.This might be for a given inlet air pressure.If the inlet air pressure is higher,the maximum capacity of the recovery transformer should also be higher.Clear,isn't it?

 

[Besoeker]

You stated that maximum capacity of the transformer occurs at 15% of the drive rating.

Yes and I actually showed you how you could calculate the 15% so I'm assuming that you don't dispute that.

This might be for a given inlet air pressure.If the inlet air pressure is higher,the maximum capacity of the recovery transformer should also be higher.Clear,isn't it?

Wrong.
The entire drive train rating would have to be higher. The recovery side would still be 15% of that rating.

 

[T.M.Haja Sahib]

Wrong.
The entire drive train rating would have to be higher. The recovery side would still be 15% of that rating.

If the drive rating is higher,15% of it is higher than the original 15% of original drive rating.

 

[Besoeker]

If the drive rating is higher,15% of it is higher than the original 15% of original drive rating.

Yes, but it isn't the original drive, is it?

 

[T.M.Haja Sahib]

Yes, but it isn't the original drive, is it?

Yes.It is not original drive,but of higher rating to meet future requirement,if any.

 

[Besoeker]

Yes.It is not original drive,but of higher rating to meet future requirement,if any.

Let me repeat what I said in post #153:

What if the transformer is designed for purpose and future expansion isn't a consideration?