CN104319734A - Large difference protection method based on second harmonic excitation surge current of converter transformer - Google Patents

Abstract

The invention relates to a large difference protection method based on second harmonic excitation surge current of a converter transformer. When a single-phase earth fault is generated in a valve side area of the converter transformer, second harmonic content in differential current in large difference protection, differential current in differential protection of a Yn/Y converter transformer and differential current in differential protection of a Yn/D converter transformer is adopted for comprehensive recognition to recognize excitation surge current, so that the resulting protection maloperation is effectively avoided. The method is simple and reliable to realize and lower in realization threshold, can be realized on the original protection device platform, and has a very high popularization value.

Description

A kind of large differential protection method shoved based on converter transformer secondary harmonic excitation

Technical field

The present invention relates to a kind of large differential protection method shoved based on converter transformer secondary harmonic excitation, belong to technical field of high-voltage direct.

Background technology

Converter transformer is one of key equipment in HVDC (High Voltage Direct Current) transmission system, current domestic high voltage direct current transmission project desired configuration is employing 12 pulse conversion device, configure 6 single-phase double winding converter transformers, form Yn/Y and Yn/D two Single Phase Transformer Set respectively, the source side winding mode of connection is star-connection, neutral-point solid ground, goes out line parallel incoming transport electrical network, and valve side winding is respectively the wiring of Y type and the wiring of D type.

At present; the large poor differential protection differential current of high voltage direct current transmission transformer adopts the change of current in 3/2 wiring alternating-current field to become relevant limit switching current, breaker in middle electric current, Yn/Y converter transformer valve side head end electric current and the Yn/D converter transformer valve side head end electric current of going here and there of lead-in wire; calculate four sides differential; for A phase differential protection, computing formula is as follows:

$I_{\mathrm{opA}}=|{\stackrel{\·}{I}}_{a1}+{\stackrel{\·}{I}}_{a2}+{\stackrel{\·}{I}}_{\mathrm{VD}1a}+{\stackrel{\·}{I}}_{\mathrm{VY}1a}|$ Formula 1

$I_{\mathrm{resA}}=\max \left\{\right|{\stackrel{\·}{I}}_{a1}|,|{\stackrel{\·}{I}}_{a2}|,|{\stackrel{\·}{I}}_{\mathrm{VD}1a}|,|{\stackrel{\·}{I}}_{\mathrm{VY}1a}\left|\right\}$ Formula 2

In formula: I _opAfor large poor A phase differential current;

I _resAfor large poor A phase stalling current;

for limit switch A phase current;

for breaker in middle A phase current;

for Yn/Y converter transformer valve side head end A phase current;

for Yn/D converter transformer valve side head end A phase current;

In the HVDC (High Voltage Direct Current) transmission system of reality, valve winding in converter transformer neutral point is all earth-free, when direct current system does not unlock and the trigger impulse of control system do not act on converter valve, valve group does not have conducting, converter transformer is the earth-free operational mode in valve side, when now there is single phase ground fault in converter transformer valve-side district, and non-faulty current; In direct current system running; converter transformer valve-side three-phase is communicated with the earth by the alternate conduction of converter valve; if now there is single phase ground fault in converter transformer valve lateral areas; to be broken down electric current; but fault current constantly changes along with the alternate conduction of converter valve; adopt large poor protection insufficient sensitivity when some scope generation single phase ground fault of formula 1 computational methods, easily cause large poor relay fail.Such as: when single phase ground fault occurs apart from neutral point 1% place converter transformer valve-side, differential current is almost nil.

At present, large poor protection adopts the secondary harmonic component in differential current to identify magnetizing inrush current usually, and discriminant equation is as follows:

I _op.2>K ₂* I _op.1formula 3

In formula: I _op.2for the second harmonic in large poor stream, I _op.1for the first-harmonic in large poor stream, K ₂for second harmonic coefficient.After satisfying condition, adopt "or" closedown mode, arbitrary locking large difference protection when meeting above-mentioned discrimination formula mutually.

The magnetizing inrush current of large poor protection is the magnetizing inrush current sum of star converter transformer, star angle converter transformer system side; if two converter transformers are because of remanent magnetism difference; the magnetizing inrush current produced differs greatly; cause the magnetizing inrush current symmetry of synthesis better; then in large difference protection, the second harmonic locking effect of differential current maximal phase was lost efficacy, and easily caused large poor false protection.

Summary of the invention

The object of this invention is to provide a kind of large differential protection method shoved based on converter transformer secondary harmonic excitation, when there is single phase ground fault in order to solve in converter transformer valve-side district, the problem of false protection.

For achieving the above object, the solution of the present invention is a kind of large differential protection method shoved based on converter transformer secondary harmonic excitation, and when there is single phase ground fault in converter transformer valve-side district, large differential protection method comprises the following steps:

1). arbitrary mutually in, when the secondary harmonic component of large poor protection is greater than the second harmonic coefficient of large poor protection, Blocking Differential Protection;

2). arbitrary mutually in, when the secondary harmonic component of large poor protection is less than or equal to the second harmonic coefficient of large poor protection, if when the second harmonic in Yn/Y converter transformer differential current is greater than the second harmonic coefficient of Yn/Y converter transformer, and the second harmonic in Yn/D converter transformer differential current is when being greater than the second harmonic coefficient of Yn/D converter transformer, Blocking Differential Protection;

3) if. 1) and 2) in differential protection all not lockings, large poor protection act.

Large poor protection determination methods also comprises that soft, the hard pressing plate of large poor protection drops into, large differential throwing countermands that value is 1, large differential starting component action, the differential input of TA abnormal obliteration; whether the differential input of TA abnormal obliteration is abnormal in order to detect TA; if TA is abnormal; send TA abnormal signal, and Blocking Differential Protection.

The invention has the beneficial effects as follows, the present invention, when producing symmetry magnetizing inrush current in converter transformer idle-loaded switching-on process, proposes a kind of new magnetizing inrush current locking criterion, effectively avoids large poor false protection.

Accompanying drawing explanation

Fig. 1 is star converter transformer magnetizing inrush current analysis chart;

Fig. 2 is star angle converter transformer magnetizing inrush current analysis chart;

Fig. 3 is the magnetizing inrush current analysis chart after star converter transformer and star angle converter transformer synthesize;

Fig. 4 is resultant current first-harmonic secondary harmonic component figure;

Fig. 5 is logic diagram of the present invention;

Fig. 6 is large poor protection TA installation site schematic diagram.

Embodiment

Below in conjunction with accompanying drawing, the present invention will be further described in detail.

When there is single phase ground fault in converter transformer valve-side district; large poor protection adopts the secondary harmonic component in large poor protection differential current, Yn/Y change of current transformer differential protection differential current and the protection of Yn/D change of current transformer differential in differential current to carry out comprehensive distinguishing; identify magnetizing inrush current, discriminant equation is as follows:

(1) when the secondary harmonic component of large poor protection is greater than the second harmonic coefficient of large poor protection

I _op.2>K ₂* I _op.1formula 6

In formula: I _op.2for the second harmonic in large poor stream, I _op.1for the first-harmonic in large poor stream, K ₂for large poor second harmonic coefficient.After satisfying condition, adopt "or" closedown mode, arbitrary locking large difference protection when meeting above-mentioned discriminant equation mutually.

(2) when the secondary harmonic component of large poor protection is less than or equal to the second harmonic coefficient of large poor protection, the secondary harmonic component in Yn/Y and Yn/D change of current transformer differential electric current is differentiated:

I _{op.2 (Y/Y)}>K _{2 (Y/Y)}* I _{op.1 (Y/Y)}formula 7

I _{op.2 (Y/D)}>K _{2 (Y/D)}* I _{op.1 (Y/D)}formula 8

In formula: I _{op.2 (Yn/Y)}for the second harmonic in Yn/Y change of current transformer differential electric current;

I _{op.1 (Yn/Y)}for the first-harmonic in Yn/Y change of current transformer differential electric current;

K _{2 (Yn/Y)}for the Yn/Y change of current becomes inrush current distinguishing second harmonic coefficient;

I _{op.2 (Yn/D)}for the second harmonic in Yn/D change of current transformer differential electric current;

I _{op.1 (Yn/D)}for the first-harmonic in Yn/D change of current transformer differential electric current;

K _{2 (Yn/D)}for the Yn/D change of current becomes inrush current distinguishing second harmonic coefficient.

Arbitrary identical time meet above two discrimination formula, i.e. the large difference protection of locking, effectively prevent the malfunction of large difference protection during converter transformer idle-loaded switching-on.

The present invention adopts excitation flow recognition method to judge large differential work, Fig. 1 is Yn/Y converter transformer magnetizing inrush current, Fig. 2 is Yn/D converter transformer magnetizing inrush current, Fig. 3 is the magnetizing inrush current after Yn/Y converter transformer and Yn/D converter transformer synthesize, and Fig. 4 is resultant current first-harmonic secondary harmonic component.As can be seen from Fig. 1 to Fig. 4, although resultant current secondary harmonic component is little, the secondary harmonic component of Yn/D converter transformer, Yn/Y converter transformer is all obvious.Therefore, in this case, the large difference protection of the second harmonic locking of Yn/D converter transformer, Yn/Y converter transformer is adopted to be feasible scheme.

Fig. 5 is large poor relay protective scheme block diagram of the present invention, and step is as follows:

1) judge soft, the hard pressing plate of large poor protection, whether control word drop into; If drop into, carry out 2);

2) the whether action of large differential starting component is judged; If action, carry out 3);

3) large poor difference element whether action; If action, carry out 4);

4) when the secondary harmonic component of large poor protection is greater than the second harmonic coefficient of large poor protection, Blocking Differential Protection;

5) when the secondary harmonic component of large poor protection is less than the second harmonic coefficient of large poor protection, 6 are carried out);

6) if when the second harmonic in Yn/Y no-load voltage ratio difference differential current is greater than the second harmonic coefficient of Yn/Y no-load voltage ratio difference, and when the second harmonic in Yn/D no-load voltage ratio difference differential current is greater than the second harmonic coefficient of Yn/D no-load voltage ratio difference, Blocking Differential Protection; If do not meet, carry out 7);

7) whether TA abnormal obliteration is differential drops into, if drop into, carries out 8);

8) carry out TA abnormality detection, if meet TA Anomaly criterion, send TA abnormal signal, and Blocking Differential Protection, otherwise carry out 9);

9) large poor protection act tripping operation.

By step 1)-9), the large difference protection of high-voltage commutation transformer can be realized.

The present invention calculates differential current by following methods; be illustrated in figure 6 large poor protection TA installation site schematic diagram; choose the half of Yn/Y converter transformer valve-side first and end electric current sum, the half of Yn/D converter transformer valve-side first and end electric current sum, limit switching current, the breaker in middle electric current of converter transformer lead-in wire make differential current, to point to converter transformer for positive direction.

For A phase differential protection, computing formula is as follows:

$I_{\mathrm{opA}}=|{\stackrel{\·}{I}}_{a1}+{\stackrel{\·}{I}}_{a2}+({\stackrel{\·}{I}}_{\mathrm{VD}1a}+{\stackrel{\·}{I}}_{\mathrm{VD}2a})/2+({\stackrel{\·}{I}}_{\mathrm{VY}1a}+{\stackrel{\·}{I}}_{\mathrm{VY}2a})/2|$

Formula 3

$I_{\mathrm{resA}}=\max \left\{\right|{\stackrel{\·}{I}}_{a1}|,|{\stackrel{\·}{I}}_{a2}|,|({\stackrel{\·}{I}}_{\mathrm{VD}1a}+{\stackrel{\·}{I}}_{\mathrm{VD}2a})/2|,|({\stackrel{\·}{I}}_{\mathrm{VY}1a}+{\stackrel{\·}{I}}_{\mathrm{VY}2a})/2\left|\right\}$

Formula 4

In formula: I _opAfor large poor A phase differential current;

I _resAfor large poor A phase stalling current;

for limit switch A phase current;

for breaker in middle A phase current;

for the Yn/Y change of current becomes A phase winding head end electric current;

for Yn/D converter transformer valve side A phase winding tail current;

for Yn/Y converter transformer valve side A phase winding head end electric current;

for Yn/Y converter transformer valve side A phase winding tail current.

Be presented above concrete execution mode, but the present invention is not limited to described execution mode.Basic ideas of the present invention are above-mentioned basic scheme, and for those of ordinary skill in the art, according to instruction of the present invention, designing the model of various distortion, formula, parameter does not need to spend creative work.The change carried out execution mode without departing from the principles and spirit of the present invention, amendment, replacement and modification still fall within the scope of protection of the present invention.

Claims (3)

1. based on the large differential protection method that converter transformer secondary harmonic excitation shoves, when there is single phase ground fault in converter transformer valve-side district, it is characterized in that, described large differential protection method comprises the following steps:

1). arbitrary mutually in, when the secondary harmonic component of large poor protection is greater than the second harmonic coefficient of large poor protection, Blocking Differential Protection;

2). arbitrary mutually in, when the secondary harmonic component of large poor protection is less than or equal to the second harmonic coefficient of large poor protection, if when the second harmonic in Yn/Y converter transformer differential current is greater than the second harmonic coefficient of Yn/Y converter transformer, and the second harmonic in Yn/D converter transformer differential current is when being greater than the second harmonic coefficient of Yn/D converter transformer, Blocking Differential Protection;

3) if. 1) and 2) in differential protection all not lockings, large poor protection act.

2. the large differential protection method shoved based on converter transformer secondary harmonic excitation according to claim 1; it is characterized in that, described large difference protection determination methods also comprises that soft, the hard pressing plate of large poor protection drops into, large differential throwing countermands that value is 1, large differential starting component action, the differential input of TA abnormal obliteration.

3. the large differential protection method shoved based on converter transformer secondary harmonic excitation according to claim 2; it is characterized in that, whether the differential input of described TA abnormal obliteration is abnormal in order to detect TA, if TA is abnormal; send TA abnormal signal, and Blocking Differential Protection.