Max. Load For Given Transformer Capacity

The question is an ideal one for the transformer manufacturer, whose name wil be on the side of it, and whose phone number is in the public domain. Please let the forum know the outcome of the telephone discussion.

Consider this: why would the transformer manufacturer rate one to X kVA if it were neither possible nor advisable to run the transformer up to 100% of that rating (rhetorical question - NNTR)?

Carnac, the Magnificent can answer that.

What is the question behind the question?

Transformers are not loaded on inductive or capacitive or resistive basis. They are loaded on apparent power basis (i.e.) kVA basis. If you want to know the maximum reactive load that can be loaded on to a particular transformer, then arrive at the kVAr of the reactive load by multiplying the kVA rating of the transformer with Sin (theta), theta being the power factor angle of the inductive load that is proposed to be connected to the transformer.

you should google the tearm impeandence....its the % of voltage drop on secondary side at the full load...transformer upto 500 kva have around 4-6 % impedance while large power transformer have upto 12% ....this is the beat term(impedance) for your question

WTH????

Nonsense.............

You can load a transformer up to 100% inductive/ Capacitive/Resistive Load. But Inductive or Capacitive Load can not be switched on in a single step. Reason being

Current lags or lead voltage by 90 Deg - hence if suddenly switched on it will be like a Short circuit on the transformer.

Depending upon how frequently you switch on the 100% load in one step - every time you are subjecting windings of the Transformer to Heavy Mechanical Shock due to Electromagnetic Reaction between adjacent turns and Coils.

If it is new Transformer to be ordered yet - specify your application to manufacturer so that he takes extra care in bracing of winding (manufactures Transformer similar to used in Short Circuit Labs).

If it is existing transformer - one solution is to switch on Series Resistor and short the resistor few seconds after first switching.

As said before, Steady state Performance of Transformer is not affected, as long as, its temperature is within operating limit.

What you say is true for capacitive, but not for inductive. The problem with inductive load is when they are switch off, not on. This does not bother transformers however, just the switch mechanism. Switching surges are a very real part of transformer design and usually the transformer impeadance handles the inrush surge to capacitive loads if the ratio of capacitance to resistance and inductance is anywhere near normal. It is hard to have pure capacitance unless a huge bank of power factor correction is in place. Increased inductance will limit inrush, not increase it.

No Sir/Madam,

What I said is true for magnetic core inductor or capacitor.

What I said may not be true for air core Inductor.

For magnetic core Inductor at times it is worst than capacitor switching, depending upon remanence magnetism in the core and point of switching on synocydle AC wave.

In case of doubt please go through my previous posts on transformer charging on this forum which is equivalent of switching on the Transformer.

The core is requiring energy to build up magnetism, the inductance is trying to limit the inrush. The higher the inductance, the lower the inrush. If you compare a 12% impeadance transformer to a 6% impeadance transformer you will see what I mean. Most of the impeadance is inductance.

That is true in case of Steady state operation.

Here we are talking of Transient condition at the time of switching.

Why do not you take the trouble of reading earlier posts on this site regarding switching on a Transformer (which is same as a Single winding reactance)?

I would not be answering your posts further, please do study on Transient conditions on switching on an Inductor.

Best of luck

= , X, kVA x power factor of Inductive load.

In my opinion the question is what is the maximum capacity ( In MVA ) of down stream transformer should be if it is to be switched on from 'X' MVA rated upstream transformer. Suppose 'X' is MVA of a transformer with V1/V2 voltage ratio so how much should be the maximum capacity or rating of the transformer down stream transformer in MVA to be swithed on at V2 side. For example: Can 25 MVA/ 66kV/33kV Trafo be switched on from 30 MVA 220kV/66kV Trafo.