Introduction to Electrical Power and Power Electronics

441Quality of Power

Solution:

Recall that the total effective rms value is the root-sum-squared (rss) value of the

(fundamental + harmonics), that is,

I IIII

T

th= ++++

1

2

3

2

5

2

7

2

25.... .

The table above gives the actual harmonic current ratios, from which we obtain

using Equation 16.12:

THD

i

=++++++0 173 0 108 0 041 0 032 0 021 0 015

222222

......00 011 0 009

0 212 21 2

22

..

..%.

+

= pu or

Similar calculations with theoretical values of I

h

= I

1

/h would give THD

i

= 28.7%,

which is significantly higher than the actual THD

i

found in practical converters.

As seen earlier, the harmonic current I

h

drawn by any nonlinear load on the bus

causes the harmonic distor