Why Do We Express the Connected Load in KW?

There are too many posts on this subject, well one more will not matter.

KW or W - measure of real power ie the power that is being converted to another form by the machine - heat, mechanical, Sound,...

KVA - Measure of the complex power - that is a vector summation of the real power (as above) and the imaginary power (this is the power that is being continually exchanged between the two types of reactances - capacitive and inductive- obviously it does not go the user as the useful power)

The load why in KW is clear from above - the output what we want.

The KVA ( or VA ) has two parts - V and A (or I) - these two define the capacity of the instruments (transformers, generators etc)

V - Voltage - limited by the insulation. however this is more or less pre-decided/predefined. This also is directly proportional to the flux density and hence defines the cross-section of the magnetic media (or in simple terms the iron cross-section)

A- Current - limited by the conducting media (as we call the copper) cross-section.

Also please note that the load - output is real power - the input (complex power) it takes from the line as KVA (based on power factor)

Generator - Input is real power (from turbine/Engine) - output is what is demanded by the electrical load (complex power)

Transformers- Input and output both are complex powers (it adds a bit complexity from it's side )

hi Dear,,,,

power sources or equipments are generally expressed in "KVA, MVA" Because these equipments need some sort of necessary protections against all abnormal working conditions, the protection devices in turns need the value of amperage that passes these devices without occurring problems in the power source itself... This happens because the high charge of such equipments.....

for example, a power transformer needs a differential protection which needs in turns a current transformer CT:

I(A) = POWER (VA)/ Voltage(v)

ON THE OTHER HAND, the small-sized apparatus "home devices" expressed in "Watt", as they're quite cheap in comparison with high voltage equipments, so, they dont need any protection.

THANKS......................

So because of the protection requirement, we are using the term KVA. Good...additional information for me.

The difference is Power Factor. When you get a motor or a resistance furnace or some such device which converts electricity to some other form of energy, the power factor is known. Motors may be at 0.8 pf while heaters will be 1 pf.

When you get a generator or a transformer, it is not known what kind of loads will be connected to it. May be a motor, maybe a furnace, and maybe a capacitor only (pf=zero!). So, one makes a generator or a transformer capable of delivering a maximum current A at a voltage V which is all that can be given, so VA, kVA, MVA etc.

If you want , you can express in KVA, but all equipment load shall be with unity power factor.

Explanation please.

Get any motor if designed with power factor 1, then you can say the load In KVA.(I didnt see yet)