04-10-2012, 10:24 AM
Reactive power and AC filters for HVDC
Reactive power.pdf (Size: 125.52 KB / Downloads: 31)
Conventional HVDC converters always have a demand for
reactive power. At normal operation, a converter consumes
reactive power in an amount that corresponds to approximately
50 % of the transmitted active power. The least costly way to
generate reactive power is in shunt connected capacitor banks.
Some of these capacitor banks can then be combined with
reactors and resistors to form filters providing low impedance
paths for the harmonics in order to limit them from entering into
the connected AC network.
AC filter types
A series resonance filter branch will give a very low impedance
and thereby efficient filtering in a narrow frequency band around
the tuning frequency. Such branches are therefore normally
used for the largest harmonics, i.e. the 11th and 13th. But often it
is advantageous to use a double-tuned filter for the 11th and
13th harmonics instead.
For the higher order harmonics, the
current levels are lower, but these
frequencies have the largest impact
on telephone interference.
Therefore they must also be
attenuated, but the filter impedance
can be larger than for the 11th and
13th harmonics. Thus, broadband
filters, normally of high-pass type,
are used to take care of all
harmonics from the 23rd and
upwards.