Views: 0 Author: Site Editor Publish Time: 2025-03-25 Origin: Site
With an older-type 1000kVA transformer currently handling a load of approximately 200kW, can this transformer accommodate the increased demand if we plan to add a new load of approximately 600kW? This question primarily revolves around a fundamental concept: the relationship and distinction between kVA and kW.
kVA (kilovolt-ampere) is the unit of apparent power, while kW (kilowatt) represents the unit of active power. In addition to apparent power and active power, there is also reactive power, measured in kvar (kilovar).
Active Power: Measured in watts (W), it represents the actual energy consumed or useful work done by a circuit (e.g., heating, lighting).
Reactive Power: Measured in volt-amperes reactive (VAR), it supports magnetic fields in inductive loads (e.g., motors) but does no real work. For example, if an electrical device contains capacitors or coils, these components will continuously charge and discharge while the device operates. Since capacitors/coils do not actually consume electrical energy during this charging/discharging process, the associated power is termed reactive power.
Apparent Power: Measured in volt-amperes (VA), it is the combination of active and reactive power, representing the total power in a circuit. A power source (usually a transformer or generator) must supply not only active power but also reactive power to electrical devices. This is because, even though capacitors in the device do not consume active power, their continuous charging and discharging still require the power source to allocate a portion of its capacity to support this process.
After clarifying these concepts, we can now examine their interrelationships, which leads us to another critical concept: power factor. The amount of active power a power source can deliver depends directly on the power factor.
Power factor (cosΦ) is the ratio of active power (P) to apparent power (S):
For instance, a 1000kVA transformer can deliver 600kW of active power when the power factor (cosφ) is 0.6, whereas it can output 900kW of active power when the power factor increases to 0.9.
If electricity is priced at $1 per kilowatt-hour (kWh), a transformer operating at a power factor of 0.6 can generate $600/hour in economic revenue. When the power factor improves to 0.9, the same transformer can generate ¥900/hour in revenue45. While the financial benefits of improving power factor are evident, its broader technical implications (e.g., optimizing grid stability and reducing energy losses) extend far beyond these immediate gains.
With the foundational knowledge established above, we can now address the core question of this article with clarity and precision.
The capacity of a transformer is measured in kVA (kilovolt-amperes), while the power consumption of electrical equipment is measured in kW (kilowatts). The key distinction lies in the fact that calculating the active power (kW) of a device requires multiplying its apparent power (kVA) by the power factor (cosφ). For example, a 1000kVA transformer can only deliver a full-load output of 1000kW when operating at a power factor of 1.0. However, achieving this ideal condition (PF = 1.0) is virtually impossible in real-world applications.
In the design phase, if we implement power factor compensation to achieve a power factor of 0.95, the active power output of the transformer should be calculated as 1000×0.95=950kW. Important Notice: Power utilities mandate a power factor (PF) of ≥0.9 to avoid penalties; however, exceeding PF = 1.0 may cause system voltage rise and compromise grid stability.
A 1000kVA transformer originally supplies a 200kW electrical load. After adding a new 600kW load, the total active power demand reaches 800kW, which remains within the calculated safe operating limit of the transformer.
Therefore, a 1000kVA transformer originally supplying 200kW of electrical load can safely operate long-term even after adding a new 600kW load (total 800kW), provided the power factor is optimized to the required level.
