SU505081A1 - Current Harmonic Filter - Google Patents

Description

LI is the reactor phase inductance of the direct sequence filter;

L2 - reactor inductance of the zero sequence filter chain at the frequency CO

FIG. Figure 1 shows the zero sequence current harmonics filter at a frequency lower than the direct sequence filter frequency; in fig. 2 is a zero sequence current harmonic filter at a direct sequence filter frequency and one lower frequency.

The harmonic current filter consists of a capacitor bank 1 and reactor 2 tuned to resonance at the frequency of the filtered harmonic I1. Resistor 3 shunts part of battery 1 and reactor 2, whose natural frequency is equal to the operating frequency. The filter is connected by a switch 4 to the high voltage switchgear assemblies 5. Between the neutral of the filter and the ground, a reactor 6 of a lower voltage class and a resistor 7 are connected, as well as a chain consisting of a series-connected capacitor 8, a reactor 9 and a resistor 10.

The appropriate choice of the ratio between the inductance of the reactor 6 and the parameters of elements 1 and 2 of the filter of the direct harmonic sequence with the frequency coi ensures that the entire filter is tuned to the zero-sequence current of the desired frequency, but not exceeding the frequency

If it is necessary to filter the zero sequence currents at the filter frequency of the direct sequence coj, you must additionally connect the capacitance and inductance tuned to resonance at the frequency coi and the appropriate choice of the ratio between the circuit parameters to ensure that the entire filter is tuned to compensate for the zero frequency of the desired frequency .

If the filter needs to be adjusted for a zero-sequence current of a higher frequency than wi, then instead of reactor 6, a capacitor should be switched between the neutral of the filter and the ground.

In transient conditions during short circuits in the AC network, free oscillations occur, making it difficult for the gates of the converter bridges to work stably. These oscillations usually contain

significant component of the zero sequence, which can be filtered by the proposed filter circuit, even if its frequency is not a multiple of the operating frequency of the alternating current. Resistors 7 and 10 are included in the reactor circuit 6 and the chains 8-9 for damping the filtered zero-sequence currents.

Formula inventions

1. A current harmonic filter containing a capacitor bank connected in series and a reactor tuned to resonance at the fundamental frequency of the filter, as well as damping resistors, characterized in that in order to further filter the zero-sequence current any more

low frequency, between the neutral of the filter and the ground included an additional reactor, the inductance is determined by the following ratio of parameters;

 -

LO

 one

where LO is the inductance of the additional reactor;

LI is the reactor phase inductance of the direct sequence filter;

(Oi is the setting frequency of the direct filter;

0) 0 is the frequency of setting the zero sequence filter.

2. The filter of claim 1, characterized in that, in order to maintain the filtering of the zero sequence current, a chain of a series-connected capacitor and a reactor is connected at the main filter frequency parallel to the additional reactor, tuned in resonance to the main filter frequency, and the inductance of all reactors These are as follows:

y / 2,.

Bo i 1

3L2 + i-i

VM-O

where 1.2 is the reactor inductance of the zero sequence filter chain at the fundamental frequency.

50 3. Filter on PP. 1 and 2, characterized in that, in order to damp the harmonics of the zero-sequence currents, resistors are connected in series with the additional reactors.

HI p