Overload Ratings of Transformer and inductor

[Manojcheers]

Dear sir,

How to find the overload rating of AC inductor For eg : 150% of rms rating for 1 Minute and 200% of rms for 10 secounds .

How to find the inductance curve for increas in current rating For eg : 100% inductance at 100 % current , 80% inductance at 150%..etc


Best regards

Manoj

 

[smijesh]

The ratting of inductor determined by theoretically or by test result.
Inductors AC or DC design based on the applied current and required inductance, Inductance value depend on the applied current. If applied current exceeds the rated( designed) current, inductance value will start to drop. If the current further increase, the magnetic core of the inductor will lose its magnetic property due to high flux density. This condition is called saturation at this point the inductance value should be very less or zero. For ferrite core and iron powder core, manufactures will specify the inductance drop due to applied current.

 

[Manojcheers]

Dear sir,

Will be helpfull if i come to know the background calculation behind your therotical explinations for my better understanding .

best regards
Manoj

- - - Updated - - -

Dear sir ,

I do understand the saturation point can be calculated using B-H relationship and wher H = N*I/L and B/H = Uo*Ur

But i can notice that the inductor is overloaded for 150%,200% ..For particular time period say 1 minute , 10 sec ..etc

How do i calcualte it ????

Best regards
Manoj

 

[schmitt trigger]

Being a passive component, the overload ratings are given by the thermal losses. Which in turn are given by the core and copper losses. You can estimate those via the core losses plot provided by the core manufacturer, plus I2R copper losses.

To validate those estimates, you have to perform experiments, and measure the average wire temperature via the cold vs hot resistance method.

However, since the internal layers always run hotter than the external layers (for obvious reasons), the best method is to insert a temperature sensor on the inner layer and read the actual temperature.
Ultimately, the insulation's thermal rating is what will be the limiting factor.

 

[Manojcheers]

Dear sir,

But, I design transformers and inductors for the given regulation (Copper Loss) .If our efficiency goal is 95% Remainig 5% will be the remainig total losses.

" overloaded for 150%,200% ..For particular time period say 1 minute , 10 sec "

In the above statement which includes some time period it involves" Duty cycle "


Best regards
Manoj

 

[FvM]

Hope you already understood that ratings for intermittent overload of inductors or transformers and inductance versus current curve of inductors are two different, essentially unrelated topics.

Intermittent overload specifications are based on winding temperature ratings and thermal time constants.

 

[Manojcheers]

Dear sir,

I understood the inductance versus current. But, im not clear about overload specification for a particular time period . Will you share any paper regarding this .

Best regards
Manoj

 

[FvM]

I have no paper about it. Guess temporary overload is discussed in transformer design handbooks. Anyway, the permissible current versus time respectively duty cycle is ruled by simple physical law (P = I²*R, stationary and ballistic heating of windings, thermal resistance, thermal capacity).

If you don't have exact thermal data of a particular transformer design, you're required to derive it by empirical measurements anyway.

 

[Manojcheers]

Dear sir,

Suggest me a Transformer and inductor design book ,

Best regards
Manoj

 

[smijesh]

Handbook of Transformer Design and Applications by William M. Flanagan
Power Transformers Principles and Applications by John J. Winders,

Below book is the authorized book for transformer and inductor

Transformer and Inductor Design Handbook (Electrical engineering and electronics)
McLyman, William T.

 

[FvM]

I have seen the 1993 Handbook of Transformer Design and Applications which isn't bad, but there are surely many others.

 

[Manojcheers]

Dear sir,

I reffered a Electrical standard notes and they have mentioned a formula

ED ( Duty cycle ) = ((Load duration in min )/( Cycle duration in min ))* 100
Cycle Duration =Idle time +Load Duration (Load duration must not exceed 10 MIn)


NT (Type power fo STL) = N *(Sqrt(ED%)/100)
NT = Type power of short time loading
N = Nominal Power .


Will u be able to explain me with an example .

Best regards
Manoj

 

[FvM]

As said, can be derived from simple physical law, e.g. P = I²*R. Related technical term is adiabatic loading (Paragraph 9.4 in suggested text book), you assume that the winding power dissipation can be averaged over a load cycle.

 

[Manojcheers]

Dear sir,


"I have seen the 1993 Handbook of Transformer Design and Applications which isn't bad, but there are surely many others"


Kindly let me know the book name .

Best regards
Manoj

 

[FvM]

Handbook of Transformer Design and Applications, also suggested in post #10