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# Why the transformer ratings is given in "KVA" rather than in KW?

Why the transformer ratings is given in "KVA" rather than in KW?

#1

10-08-2013 09:09 AM

Top #2

Because even transformer has its power factor.

10-08-2013 11:35 AM

Top #3

Simply speaking, Power (say, from LV to HV) is transferred purely on the basis of No. of Turns on LV and on HV. Power Factor which depends on the nature of load, has no effect on the Turn Ratio - on transformation of Power.

10-08-2013 02:06 PM

Top #4

There are two types of losses within a transformer, copper losses and iron losses. Copper losses depend on current which passes through the transformer winding while iron losses

(core losses) depends on the voltage. That's the reason why the rating is in kVA and not in kW.

(core losses) depends on the voltage. That's the reason why the rating is in kVA and not in kW.

10-08-2013 04:26 PM

Top #5

Because it's the product of rated voltage (V) and rated current (A), irrespective of power factor, or power transformed, or losses.

10-08-2013 07:04 PM

Top #6

Simply because the load applied to a transformer is in terms of KVA. Now, understand that is comprised of KW and KVAR, where KW is the real component and KVAR is the reactive component. The result of the combination of KW and KVAR is KVA, the actual loading on the transformer. Review power triangle and power factor.

Also understand that capacitors can be applied at the transformer secondary to improve the power factor and thus unload the transformer. This is because capacitive reactance is 180 degrees out of phase with inductive reactance. Thus the magnitude of the KVAR component becomes smaller and KVA becomes close to KW. This is all about vector analysis..

Hope this helps.

Also understand that capacitors can be applied at the transformer secondary to improve the power factor and thus unload the transformer. This is because capacitive reactance is 180 degrees out of phase with inductive reactance. Thus the magnitude of the KVAR component becomes smaller and KVA becomes close to KW. This is all about vector analysis..

Hope this helps.

10-08-2013 09:19 PM

Top #7

in fact, you face with two kinds of limits, first, voltage limits, which is mostly depended on the type of dielectrics and isolation. and the second one is about current, and related to the type and diameter of conductors and the standard working temperature of the transformer. By multiplication of these two ratings(rated voltage and rated current), you can obtain rating KVA of the transformer, and as you can see, it doesn't relate to load's power-factor.

10-08-2013 11:20 PM

Top #8

Not only transformers, most loads are. KVA is the true power measure as it combines both the passive (KW) and reactive (KVAr) components of power consumption.

10-09-2013 01:46 AM

Top #9

Power and apparent power are two different things. Watts would be a measure of apparent power and VA a measure of possible power. Because of the efficiency of loads and power factor, the watts of a given system typically are lower than the system va. See http://www.power-solutions.com/watts-va for a pretty solid explanation.

10-09-2013 04:41 AM

Top #10

Transformers are rated in {VA, kVA, MVA etc.} due to flows of active and reactive power through transformer. In case of transformer we have active power losses as consequence of existence inside resistance of windings (primary and secondary) and existence of active power losses of ferromagnetic core and other side we have reactive power losses as consequence of existence losses of magnetic flux (primary and secondary) and existence of reactive power losses of ferromagnetic core... [VA]=sqrt(sqr[W]+sqr[VAr])