Does a Transformer Also Act as a Load?

Have a look at http://en.wikipedia.org/wiki/Transformer

Yes and dunno...
Del

Base on your study, how many percent do you think your friend is right?

Transformers, like most energy transformation devices, can be characterized by their No-Load and Full-Load losses. No-Load losses are a fixed by the physical characteristics of the device, Load-Losses vary according to the load imposed on the device. Use your engineering knowledge and the above mentioned Wikipedia article to do your homework for your "friend"-ly teacher. Consulting any handbook on electrical engineering will provide plenty of formulas for you to explore.

Transformer, in fact, is a "reactive" load on the system.

Yes it is....how much is determined by its design. We can't guess exactly how much.

let us say you have a 1000 watt transformer, isolation type 240 to 240 V 60 Hz.

You might find that at full power it dissipates 50 watts of heat, while sending 950 watts to the load and consuming 1000 watts = 95% efficient.

If you run it at 0 watts, you might find it consumes ~20-30 watts and sends nothing to the load = zero % efficiency. This 20-30 watts represents the cyclical magnetization and demagnetization of the core at 60 Hz, which shows up as heat. Smaller transformers are less efficient and the transformer will show as an inductive reactance, and shift the power factor accordingly. At 60 watts power out it might uses a total of 90 watts = 66% efficient.

So you can see a transformer that is exactly matched to its load has the highest efficiency = strive for this.

Transformer, though a static equipment, behaves as a load on the system if it does not deliver power. The load as seen by the system (which is equal to the No Load Losses of the Transformer and are drawn continuously and constantly till it is switched off) will be approximately 0.001 times the capacity.

For example, if we see a Transformer 5MVA, 33 / 11 kV with No Load losses = 4kW and Load losses = 25kW, the system sees a load of 4 kW from the very start.

Now if the Transformer is loaded to 20% its capacity, the Transformer's own losses (100% No load losses + Load losses corresponding to 20% Load) will be 4kW + 1.6kW = 5.7kW

So, it is always economical to operate the Transformer on at least 80% of its capacity.

That means, for a 5000 KVA Transformer, loaded at 20% its capacity, apart from the 20% load, the system will see an excess load of 5.7kW.

Hi Dnomchier, In a transformer you have constant losses these are called "Iron Losses" This loss is constant whatever load is applied to the transformer.

You also have other losses, these are Current Squared x Resistance Losses. Lets call this resistance losses for now.

Transformers that are designed correctly are of a general high efficiency nature, but a transformer should be designed to operate around about 80% to obtain optimum efficiency, below this the Iron Losses will cost you, above this the Resistance losses will also cost you.

Iron Losses is the energy that is required to create the magnetic field that a transformer needs, I think that this is due to the eddy current created in the transformer laminations.

Resistance losses, well they speak for them selves don't they, the more current that is required to supply the load creates heat, this is due to the resistance of the windings.

The Iron Losses is the main issue here, contact the transformer manufacture they should be able to tell you the Iron Losses, Don't quote me but I think that the Iron losses is the transformer energy efficiency ratting, IE; Power Factor

Cheers

Joe

Thanks to all, I really appreciate it..

More power!

Appreciate what ?The discussion or the contents of the technical discussion the participants projected by their replies . I do not know how much of the contents you understood or weather the replies satisfied your doubts.

If your or your friend's doubt is only " weather the the transformer act as a load"

The answer yes. But if you are serious to know about the subject ,it is a major problem faced by all transformer designers. Be serious in putting up threads here as participants spend lot of time in trying to reply your questions with good intension of helping needy engineers. Thanks

The load on the secondary side is reflected on the primary side, the ratio being the square of the turns ratio. For example, if the transformer is a 10:1 step down, 100 ohms on the secondary would appear as 10K ohms on the primary.

Yes; the transformer will look like a load to the supplying power source even when the transformer has no load. The transformer has a core and coils. The core has a constant watts drop across it. The coils watts drop increases with the power draw of the transformers load. Efficiencies vary depending upon load % and the materials used to make the tranformer. The losses are usually less than 5%.