The transformer is rated in KVA and not in KW. The transformer supplies power to electrical loads like motors,heaters. The electrical loads have their own power factor.

The power factor at the transformer secondary and primary is equal to the combined power factor of all types of electrical loads connected to the transformer. Thus the transformer does not have fixed power factor and the power factor varies with types of load connected to it and also on percentage loading on transformer.

The transformer is a link between alternator and the load.The alternator supplies active and reactive power to the load. Similarly, the transformer is sort of power supply source which supplies the active kW and reactive kVAR to electrical loads. Volts x Amps equation of the transformer gives the maximum current that the winding can carry. The transformer winding can’t carry current more than its rated current carrying capacity. The same kVA, more MVA means winding can carry more current without overheating.

If transformer is rated in kW,the designer has to fixed the kVAR capacity of the transformer.However, kVAR depends on the types of loads connected to the transformer and it is not possible to fix the kVAR delivering capacity of the transformer.

In other words, if transformer is rated on the basis of KW, the user has to operate the transformer **at the designed power factor of the transformer.** However, it is not pragmatic to operate the transformer at particular power factor or at particular kVAr because the load power factor varies and the system power factor changes with variation in power factor of the connected loads.

The transformer designer does not know at what power factor the customer will operate the transformer. The designer gives the choice to operate the transformer at whatever power factor by giving the rating of transformer in apparent power (KVA or MVA).

Apparent power(kVA) of the transformer is equal to the vector sum of active power(kW) and reactive power(kVAr).

kVA^{⃗}= kW^{⃗}+ kVAr^{⃗}kVA^{2}= kW^{2} + kVAr^{2}kVA =√(kW^{2} +kVAr^{2}) ——–(1)

Where,

kVA – Apparent Power

kW – Active Power

kVAr – Reactive Power

If power factor is low, the kVAR supplied by transformer will increase and correspondingly the active power delivery will gets decreased.The transformer will be underutilized if the power factor of the loads is low.

From above table, it is clear that the active power delivering capacity of the transformer gets lowered with lower power factor.

The power factor can be improved by installation of capacitor banks to neutralize the reactive kVAr with capacitive kVAr.

**Related Posts on Transformer**

**Transformer Interview Questions & Answers Part-3****Difference Between High, Medium and Low Voltage Transformers****Why is the core of a power transformer grounded?****No Load Losses in Transformer****Copper Loss In Transformer**

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Very informative article, thanks.

Very good knowledge sir

Aap ke es matter se bahut knowledge mila

Very very thanks