Question

Why is a transformer called kVA?

Answer 1

A transformer is rated in kVA (kilovolt-amperes) because it represents the **apparent power** that the transformer can handle. Let’s break it down:

1. **Apparent Power**: Power in an electrical system can be classified into three types:
   - **Active Power (kW)**: The actual power that does useful work (like lighting or heating).
   - **Reactive Power (kVAR)**: Power that supports the voltage levels necessary for equipment to work (but doesn't do any real work).
   - **Apparent Power (kVA)**: The total power supplied by the transformer, which is a combination of both active and reactive power.

2. **Why kVA, not kW?**:
   - A transformer doesn’t "care" about the power factor (the ratio between active power and apparent power) because it’s a passive device. It only transfers power from one side to the other.
   - The kVA rating tells us how much total power the transformer can safely handle, whether it is real or reactive power.
   
3. **Power Factor Dependence**: The **power factor** is the ratio of real power (kW) to apparent power (kVA). If the power factor is 1 (perfect), then the kVA rating equals the kW rating. But most electrical loads are inductive (like motors), so the power factor is less than 1, and the real power (kW) will be lower than the apparent power (kVA).

In summary, **kVA** is used for transformers because it indicates the maximum total power (both real and reactive) that the transformer can handle, regardless of the power factor.