You wonder why the electrical transformer rating is in KVA. Why don’t we specify the transformer rating in kW? If you want to know this then this article is for you.
Why is the transformer rating in KVA
We always specify transformer ratings in KVA or VA. We do not specify the transformer rating in kW. This is due to the following reasons.
If we connect an active load across the output of the electrical transformer, then active current will flow and power flow will be in kW or watts. It can be written in kW or KVA.
Now suppose we connect a capacitor as a load, then reactive current will flow in the transformer. And power flow will be in kVAR or VAR. The kW power flow will be zero. So, if we specify the transformer rating in kW then it looks like zero kW power flows in the transformer. And the transformer looks like safe with unlimited reactive power flow. That is not correct
So better to write transformer rating power in KVA. The kVAR power can be written in KVAR and KVA.
Further, suppose we connect an inductor as a load, then reactive current will flow in the transformer. And power flow will be in kVAR or VAR. It will not be in kW, This kVAR power can be written in KVAR and KVA.
So in all the above cases, it is always possible to define power flow in KVA. As kW does not give an idea of the limiting factor in the transformer, but KVA flow in the transformer is a limiting factor.
Basically, transformer size depends on voltage and the current flowing in the wire in addition to a few other factors. The KVA has voltage as well as electrical current. KW does not give an idea of the current flowing in the transformer.
So we specify the transformed rating in kVA and not in kW.
Further knowledge as per experience
Just specifying the transformer rating in KVA is not enough to design a transformer.
The electrical transformer rating depends on many other factors like frequency, voltage drop in the transformer, accuracy, voltage etc.
However, KVA gives a rough idea of the size and cost of the transformer at specified voltage levels and general applications. So we start with KVA and Voltage ratings almost always.
Watch the following video to learn in detail ( but in Hindi)
Also, watch the above video in Hindi
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About the author – G K Agrawal B.Sc and B.Tech (from HBTU Kanpur), Retd. Sr DGM Design (BHEL), the inventor of patents, has lifelong industry experience in the electrical and electronics design field of R&D. He worked for BHEL. He shares his experience and knowledge on blogs and YouTube. Read the profile here.
