能源使用先期管理資訊平台

Many electrical devices have inductive loads, such as:
●AC single-phase and 3-phase motors (see Section 3.6)
●variable speed drives (see Section 3.6.3)
●transformers (see Section 3.5.4)
●high intensity discharge lighting (see Section 3.10)
These all require both active electrical power and reactive electrical power. The active electrical power is converted into useful mechanical power, while the reactive electrical power is used to maintain the device’s magnetic fields. This reactive electrical power is transferred periodically in both directions between the generator and the load (at the same frequency as the supply). Capacitor banks and buried cables also take reactive energy.
Vector addition of the real (active) electrical power and the reactive electrical power gives the apparent power. Power generation utilities and network operators must make this apparent power available and transmit it. This means that generators, transformers, power lines, switchgear, etc. must be sized for greater power ratings than if the load only drew active electrical power.
Power supply utilities (both on-site and off-site) are faced with extra expenditure for equipment and additional power losses. External suppliers, therefore, make additional charges for reactive power if this exceeds a certain threshold. Usually, a certain target power factor of cos ϕ of between 1.0 and 0.9 ( lagging) is specified, at which point the reactive energy requirement is significantly reduced. A simple explanation is given in Annex 7.17.

If the power factor is corrected, for example by installing a capacitor at the load, this totally or partially eliminates the reactive power draw at the power supply company. Power factor correction is at its most effective when it is physically near to the load and uses state-of-the-art technology.
The power factor can change over time so needs to be checked periodically (depending on site and usage, and these checks can be anything from 3 to 10 years apart), as the type of equipment and the supplies listed (above) change over time. Also, as capacitors used to correct the power factor deteriorate with time, these also require periodic testing (most easily carried out by checking if the capacitors are getting warm in operation).
Other measures to take are:
●to minimise operation of idling or lightly loaded motors (see Section 3.6)
●to avoid operation of equipment above its rated voltage
●to replace standard motors as they burn out with energy efficient motors (see Section 3.6)
●even with energy efficient motors, however, the power factor is significantly affected by variations in load. A motor must be operated near its rated capacity to realise the benefits of a high power factor design (see Section 3.6).

有些電氣設備都有電感性負載，例如：
●單相與三相馬達
●變速裝置
●變壓器
●高光度放電燈(HID).
這些都是需要實功率和虛功率，前者轉換成有用的機械功率，後者則用來維持設備的磁場。虛功電力在發電機與負載間呈週期性以同一頻率雙向轉換。電容器組和地下電纜也需要虛功電力。
實功率和虛功率所形成的向量叫視在(表觀)功率。發電廠和電網操作者必須利用這視在功率將電力輸送出去。意即發電機、變壓器、電力線路等必須比只用實功率的負載加大些電力功率額定值。
電力供應系統設施，不論是現場或不在現場都面臨額外的開銷及電力損失。所以外部電力供應者會就超過某一門檻的虛功率收取額外費用。通常功率因素(cos ϕ)的值約訂在1.0到0.9(落後)之間，以抑低虛功需求量。

電功率因素(cos ϕ) =實電力/視在(表觀)電力

如果可以利用裝在負載上的電容器，則可全部或大幅度減少自電力公司抽的虛功電力。當負載實體很接近且採用先進技術時，功率因素修正是最有效的方法。
電功率因素會因時間、設備型態而改變，所以需要定期檢查(根據現場與使用方法此定期檢查為3到10年)。
同時，用來修正電功率的電容器也會隨時間而功能衰退，所以也要定期測試，最簡單的檢查方法是在運轉中視其是否發燙。
其他可採用的方法有：
●減少馬達空轉或輕載運轉
●避免設備在超過其額定電壓運轉
●改用能效馬達以替代燒毀的傳統馬達(標準型)
●即使是能效馬達，其電功率還是會受到負載變動的影響。所以馬達應該在其額定容量運轉，以達到其高功率設計的目標。