How to select the APF capacity in the design of distribution system drawing?
Overall, for new projects, Users can configure the APF capacity according to the following reference.
Firstly understand the distribution system of the drawing, estimate the harmonic current value, select the capacity of APF according to the harmonic current value; then select the corresponding APF model according to this capacity; then determine the installation location and installation method according to the product size, and finally reflect the product model on the drawing to complete the type selection process. Details can be done following the following procedures:
1.?Capacity Select
This step is mainly to determine the installation capacity of APF. During the design, the electrical designer first estimates the harmonic current effective value of the power distribution system first. The detailed real?process of the capacity design stage is described as follows:
The calculation of harmonic current value involves many factors. For the calculation of harmonic current?value, we suggest a special power quality analysis instrument. However, for new projects, only in the design stage, electrical designers can not obtain enough electrical equipment harmonic data, take this into consideration, we configure APF for this kind of new project based on the?test and experience summary of many industries, the experience formula for electrical designers in the design selection as reference. Using the following formula meets the design requirements to select the APF according to the calculated harmonic current.
1.1 Centralized treatment
Formula-1:
Noted: This formula is suitable for centralized treatment on the secondary side of the transformer.
Formula data explanation：
S: Transformer capacity；
U: Transformer secondary side rated voltage；
K: Load Ratio；
IHR: Harmonic Current；
THDi: Total Harmonic Current Distortion ratio
The taken value range:
1）K?Represents the load rate of the transformer， The taken value range of transformer design is?0.6-0.85.
2）THDI?is the only variable value in the formula above formula， Its range of value depends on different industries and industry loads.?
1.2 Local treatment
The above formula is determined for the centralized treatment of the harmonic on the secondary side of the transformer. Here, it is recommended to treat the harmonic at?the secondary side of the transformer, it can also be treated locally at the input end of the load.Calculation can be performed using formula 2 below.
Formula-2:
In this formula, IN?represents the rated current of APF. The above formula only considers the load running at full load (K=1). Actual operational K values should be considered in the design, as in Formula 3.
Formula-3:
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1.3. Partial treatment
If we know the?know?capacity/power, then the harmonic current value can be calculated. For example, the total load capacity (power) below a branch A is P (and here can be a single device or multiple devices), then the harmonic current can be calculated by Formula?4.
Formula-4:
Where, the Un represents the rated voltage (line voltage) of the device.The P represents the total capacity (power).The K represents the load rate.
Formula explanation:
(1)?THDi select
As we can?see from the analysis above,?that THDi is the main variable value need to be confirmed, and then this value can be determined based on the harmonic analysis in Chapter.
(2) Quick model select
Quickly selected can according to formula _ 1-4?of the industry summary of various industry harmonics ,and then in Table 3.9 on page 14.
2.??Product select:
Refer to the harmonic current value calculated in Section 1.1 to determines the capacity to be installed according to the model of APF.The APF?installation capacity can be determined according to Formula 5,The?coefficient is to maintain the capacity reductant
Formula-5:
Among these, the IA presents the installation capacity of the APF.The IHR represents the harmonic current value.
See the product selection section in the product introduction in Chapter 4 for detailed?product selection.
3.??Dimension confirmation
After capacity determination and product selection?confirmed, the installation location and installation method can be selected according to the selected?APF to meet the requirements of the site.Recommended rack / vertical cabinet mounting methods for large mounting capacity.
4.??Drawing
After the capacity and size are determined, APF design can select the distribution system diagram.During APF installation, the following accessories are required: current transformer (CT), circuit breaker.The CT and circuit breakers need to be shown on the drawings.