It is possible to
determine the K-factor needed when measurements can be obtained from the load.
To do this, measurements of the harmonic currents need to be taken. The
harmonic current at each harmonic needs to be found, which can easily be done
using a harmonic analyzer. If a current value is given for each harmonic,
simply divide that value by the total current value. This will yield a per unit
value for that given harmonic. If a percentage of the overall current is given,
multiply that number by 100, which will also give a per unit value. Then take
these values and plug them into the formula:
K = S [Ihn(pu)2(hn2)]
where Ihn(pu)2
is the value of the harmonic current squared (in the per unit form), hn2
is the order of the harmonic (3rd, 5th, 7th,
etc.) squared.
Multiply these two
numbers together for each harmonic order. The sum of these numbers gives the
K-factor rating. This procedure may look difficult, but it is actually pretty
simple. An example is demonstrated in Table 2. Column 1 shows the harmonic
orders present, column 2 shows the harmonic current on a per unit basis,
columns 3 and 4 show the square of the harmonic orders present and the harmonic
order respectively, and column 5 shows the product of columns 3 and 4. The
K-factor is found by summing all the numbers in column 5. A K-factor of 9.802
is formulated. This means that 9.802 times as much heat is produced by the
non-linear current than would have been produced by the same value of linear
current.
While K-factor shows how much more
heat is produced from a non-linear load, it doesn’t portray anything about
distortion of the sine wave.
