Adapting a 60Hz trasnfomer to 50Hz

[Mbrooke]

13200/23000Y HV 277 LV double bushing 50kva transformer. Applied on a 50Hz system at 11,000 volts primary would give about 230 volts secondary and a 5/6th kva of 41 kva. Does this look right thus far?


MY question is, provided that the volt/hertz ratio matches, will operating on a lower frequency have any unforeseen negative impact? For example I am told that the lamination width and grain material is different on a 60Hz core which might lead to excessive eddy currents and hysteresis heating as a result even with matching V/Hz ratios. But my understanding is that this applies only to very large power transformers?

 

[waross]

Hysteresis losses increase with increased frequency. Hysteresis losses will be less at 50 Hz than at 60 Hz.
Skin effect increases with increased frequency, so the effective resistance and the I^√2R losses will be slightly less at 50 Hz.
Also remember that the applied voltage at 50 Hz will be less.
I believe that any issues will be with increased frequency, and will be slight.



Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[HamburgerHelper]

The laminations on your core have to be thinner as you go up in frequency. The eddy current power dissipation will be proportion to the square of your frequency and lamination depth. By going to a lower frequency, I am failing to see why your lamination width would matter. You just have a transformer that that happens to have thinner laminations than is necessary when you go from 60 to 50hz. If you go from a lower frequency to a higher frequency, I think then you will see higher eddy currents losses due to your laminations not being thin enough to provide adequate eddy current resistance.

 

[Mbrooke]

Guess I had this backward then. And the quality of grain material won't matter either, correct? Thanks to everyone for clarifying this.

Since we are on the subject of 50 vs 60Hz, how will my % impedance look on this transformer?

 

[waross]

From basics, the inductive reactance will be lower so the impedance will be lower. However, the PU will be a percentage of a lower voltage. The resistance won't change enough to matter. With a changing reactance and a fixed resistance the X:R ratio will change slightly.
Overall, with an X:R ratio of 6:1 or higher I expect the change in PU impedance to be less than 1%.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[magoo2]

With 11 kV applied to a 13.2 kV winding, the resulting secondary voltage will be 11/13.2*277 or 230.8 V. Agrees with you.

As far as the V/Hz ratio, I would use the nameplate as the 'not to exceed' value. So, 13200/60 works out to be 220. With it applied at 11 kV and 50 Hz, you get the same ratio of 220. My point is you don't need to have the same ratio. You just need the new ratio to be less than or equal to the initial design basis and it will be OK.

From what I've worked with, a 50 kVA unit has an impedance of around 2.0 to 2.5% IZ, with the %IX being around 1.8 to 2.0%. Using the 2 %IX as an example, if we connect it to 50 Hz, its resulting IX will be 5/6*2% or 1.7%. So the change in IX will be lower and it will result in a lower IZ as Bill points out.

I wouldn't be too concerned with the excitation losses since you're applying only 83% of rated voltage to the winding.

 

[Mbrooke]

Normally all transformer have a saturation safety factor, so at 5/6 that factor is equal like on 60Hz?

 

[waross]

The impedance voltage will be lower, but it will be a ratio to the lower 50 Hz rated voltage and so will result in the same PU impedance with probably less than 1% error.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Mbrooke]

Sounds good, thanks

 

[waross]

MY question is, provided that the volt/hertz ratio matches, will operating on a lower frequency have any unforeseen negative impact?

As my rusty memory slowly responds, there may be one possible negative impact.
Your full load losses are expressed as a percentage of KVA.
Although your full load losses will be the same at 50Hz as at 60 Hz, they will be expressed as a percentage or P.U. value of a lower KVA.
I worked in an area where the customer was required to supply their own transformer(s) for any thing bigger than a single family dwelling.
The utility required the customer supplied transformer(s) to be tested for efficiency and charged a monthly surcharge for less efficient transformers.
There may be instances where the higher P.U. losses may push a transformer into monthly surcharges.
This is the only "unforeseen negative impact?" I can think of. This issue will probably not be an issue in most 60Hz/50Hz conversions.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Mbrooke]

None extra charge hear. As long as it works everyone is happy.

BTW, when someone orders a 50Hz transformer from a north American IEEE manufacture, do they really go to the trouble of building individual coils? Using a de-rated 60hz coil sounds much more economical.

 

[lansford]

Just as a comment, at our mining facility we had a number of large old 25 cycle transformers that were operating fine for many years on 60 Hz.
Jim