Harmonic Capacity Calculation
Centralized governance
= 10,000 x U x √1 + THDR
SxK
THDI Formula
Note: The above formula is applicable for centralized treatment on the secondary side of the transformer.
Formula Parameter Introduction:
Transformer stable capacity: U: Transformer: actual stable voltage: 1: wave-making current: THDi: total harmonic distortion of current: K: load factor:
Transformer load factor, the range of values taken during transformer design is 0.6~0.85.
THDi is the variable in the above formula; its range depends on the industry and the load.
On-Site Treatment
The above formula is applicable for the centralized treatment of harmonics on the secondary side of a transformer. Here, it is recommended that designers conduct the treatment on the secondary side of the transformer.
If there is a high-power harmonic source load in the power distribution, it can also be locally treated at the input end of the load. The calculation can be performed using Formula 2 as follows.
th= IN x
THDi
(Formula 2)
h=KxIN x
THDi
(Formula 3)
√1+THD2
√1+THD/2
Among them, N represents the rated current of the equipment. The above formula only considers the operation of the load under full load conditions (K=NT). In the design, actual operation conditions should be taken into account.
The K value, as shown in Formula 3.
Estimation Formula
In everyday design, we can employ the estimation formula 4:
h=Calculate Current x THDi (Formula 4)
Note: As analyzed above, THDi is the primary variable to be determined; the selection of this value can refer to Table P15, "APF Selection Quick Lookup Table."
