why is transformers rated in kva not in kw
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Originally Answered: Why transformer rating kVA?
Hello.
Transformer is a static device which transfers electrical power from one AC circuit to the other AC circuit by means of increasing or decreasing voltage (or current) & by keeping frequency constant.
Now, there are mainly 3 types of powers in case of AC circuit.
1. Active Power, P=VI*cos(phi) watt
2. Reactive Power, Q=VI*sin(phi) VAr
3. Apparent/Total Power, S=VI VA
There are three reasons why we rate transformer in kVA or MVA:
1. The transformer has to supply transfer both active and reactive power from one AC circuit to the other.
And hence, it has to transform total power i.e. nothing but apparent power(S)=(P^2 + Q^2)^(1/2). The "S" is having unit of VA and hence transformers are rated in terms of kVA or MVA.
2. At the time of manufacturing of transformer it is not known that which type of load the transformer is going to serve (i.e.R, RL, RC or RLC or any other) hence its beneficial to rate it in terms of total apparent power "S". (kVA or MVA)
3. Transformer has two types of losses, *Copper loss, which are dependent on current(Current is having unit Ampere)*Iron losses, which are dependent on voltage(voltage is having unit Volts)Hence total losses=Iron Losses + Copper losses, which are dependent on VA.
Hello.
Transformer is a static device which transfers electrical power from one AC circuit to the other AC circuit by means of increasing or decreasing voltage (or current) & by keeping frequency constant.
Now, there are mainly 3 types of powers in case of AC circuit.
1. Active Power, P=VI*cos(phi) watt
2. Reactive Power, Q=VI*sin(phi) VAr
3. Apparent/Total Power, S=VI VA
There are three reasons why we rate transformer in kVA or MVA:
1. The transformer has to supply transfer both active and reactive power from one AC circuit to the other.
And hence, it has to transform total power i.e. nothing but apparent power(S)=(P^2 + Q^2)^(1/2). The "S" is having unit of VA and hence transformers are rated in terms of kVA or MVA.
2. At the time of manufacturing of transformer it is not known that which type of load the transformer is going to serve (i.e.R, RL, RC or RLC or any other) hence its beneficial to rate it in terms of total apparent power "S". (kVA or MVA)
3. Transformer has two types of losses, *Copper loss, which are dependent on current(Current is having unit Ampere)*Iron losses, which are dependent on voltage(voltage is having unit Volts)Hence total losses=Iron Losses + Copper losses, which are dependent on VA.
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