Understanding Apparent Power vs. Real Power
Transformers are rated in kVA (kilovolt-amperes), while most electrical loads are measured in kW (kilowatts). To determine if a 1000kVA transformer can support a combined load of 200kW (existing) + 600kW (new) = 800kW, we must first clarify the relationship between these units—rooted in three types of power: active, reactive, and apparent.
Active, Reactive, and Apparent Power: What’s the Difference?
- Active power (kW): The actual energy consumed by devices to perform work (e.g., heating, lighting, or mechanical motion). This is what appears on your electricity bill.
- Reactive power (kvar): Energy temporarily stored and released by components like capacitors or inductors. It powers processes like magnetic field generation in motors but doesn’t contribute to useful work. Think of it as “standby” power that equipment borrows and returns to the grid.
- Apparent power (kVA): The total power supplied by the transformer, combining active and reactive power. It reflects the transformer’s full capacity to serve both types of demand.
The Role of Power Factor
The link between kVA and kW lies in the power factor (cosφ), defined as the ratio of active power to apparent power (kW/kVA). A higher power factor means more of the transformer’s capacity is used for useful work. For example:
- At cosφ = 0.6, a 1000kVA transformer delivers only 600kW (1000kVA × 0.6).
- At cosφ = 0.9, it delivers 900kW (1000kVA × 0.9).
In practice, power companies enforce a minimum power factor (often ≥0.9) to avoid penalties, as low factors strain the grid unnecessarily.
Analyzing the Load Scenario
Originally, the 1000kVA transformer supports 200kW. Adding 600kW brings the total to 800kW. Can it handle this?First, consider design margins. Transformers are rarely operated at 100% capacity long-term; a 90% safety margin is typical, capping usable apparent power at ~900kVA. With proper power factor correction (targeting ≥0.95), the transformer’s active power capacity becomes 900kVA × 0.95 ≈ 855kW—well above the 800kW demand.Even without correction, if the existing load already operates at a reasonable power factor (say 0.8), the original 200kW would use 200kW / 0.8 = 250kVA of apparent power. Adding 600kW at the same factor would require 600kW / 0.8 = 750kVA, totaling 1000kVA—exactly the transformer’s rating. But with modern power factor correction (common in industrial settings), achieving ≥0.95 is feasible, leaving ample headroom.Conclusion: With appropriate power factor management, the 1000kVA transformer can safely support the combined 800kW load.