Question: "There is an old 1000kVA transformer currently supporting a 200kW load. If we add a new 600kW load, can the transformer handle it?"
This question revolves around understanding the relationship and difference between kVA (apparent power) and kW (active power).
Key Concepts:
- kVA (kilovolt-ampere): Unit of apparent power, representing the total power supplied by the transformer.
- kW (kilowatt): Unit of active power, representing the actual power consumed by equipment.
- kVAR (kilovar): Unit of reactive power, which temporarily stores and releases energy in systems with capacitors or coils (e.g., motors).
Power Factor (cosφ):
The ratio of active power (kW) to apparent power (kVA). For example:
- A 1000kVA transformer with a power factor of 0.6 can deliver 600kW of active power.
- With a power factor of 0.9, it can deliver 900kW.
Economic Impact:
A higher power factor improves efficiency. For instance:
- At cosφ = 0.6, a 1000kVA transformer generates 600kW (equivalent to ¥600/hour at ¥1/kWh).
- At cosφ = 0.9, it generates 900kW (¥900/hour).
Analysis:
Transformer capacity is measured in kVA, while equipment loads are in kW. To convert kVA to kW, multiply by the power factor:
kW=kVA×cosφ
In practice:
- A 1000kVA transformer typically operates at 90% load (900kVA) for safety and efficiency.
- With power factor correction (e.g., cosφ ≥ 0.95), the active power output becomes:
900kVA×0.95=855kW
Answer to the Question:
The total load after adding 600kW is 800kW. If the power factor is corrected to ≥0.95, the transformer can safely support 855kW, exceeding the required 800kW. Thus, the 1000kVA transformer can handle the new load if the power factor is optimized.
