NAME :
Dalton Brasil
COUNTRY :
Brasil
REGISTRATION NUMBER : 1774
GROUP REF. : SC C4
PREF. SUBJECT :PS1
QUESTION N° : 1.3
Is there any experience associated with installation of substantial number of cables, thus moving the resonance
points down in the frequency spectrum, and exacerbating harmonic voltage distortion on the system? Has there
been any other experience related to system technical performance issues other than harmonics associated with
the installation of long cables? Bearing in mind that continues technological developments in VSC HVDC
resulted in almost complete disappearance of harmonics injections at frequencies of the order given in C4112; is it therefore appropriate to impose harmonic distortion requirements and hence the provision of system
impedance loci at low harmonic orders in the case of VSC based HVDC schemes? Should the range of
harmonics be extended to cover higher frequencies?
Today in Brazil there is a large number of wind farms under integration into the electrical system. It is
expected that by 2015, plants with total installed capacity of about 7 GW will be in operation. Most of these
wind farms use FC (full-converter) or DFIG (Double-Fed Induction Generator) wind generators types, with VSC
technology in the conversion process. In order to approve the connection of these wind generators into the
system, power quality studies are required. These studies are carried out in order to assure that voltage harmonic
distortions, fluctuations and unbalances levels introduced by the power plant are below the individual limits
required in the Grid Code. Harmonic filters have been installed in many cases.
For these studies, wind farm manufacturers have to inform the levels of harmonic current that is injected
into the grid. Figure 1 illustrates a typical profile of the harmonic currents injected into grid (low voltage side of
transformer) that can be considered as representative for wind generators that are being installed in the Brazilian
electric system.
20
18
Current (A)
16
14
12
10
8
6
4
2
0
1
3
5
7
9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49
Harmonic
Figure 1 – Wind Power Plants – Typical Harmonic Currents
As observed in Figure 1, low order harmonic currents prevail in relation to higher order harmonic
currents. Thus, despite the possibility of reducing low order harmonic currents due to the use of VSC
technology, we have the opinion that the assessment of harmonic distortion for this frequency range should still
be performed in our case.