CN102170114B - High-voltage direct-current transmission line low-voltage protective method - Google Patents

Abstract

The invention provides a direct-current transmission line low-voltage protective method built on the basis of a time domain distributed parameter model. The voltage value in the end of a protective range is obtained by utilizing a time domain calculating method of a line voltage according to the voltage and current measured values at a protection installation position, and a protection criterion is constructed by utilizing the voltage calculated value of the protective range end. When a line end voltage calculated value and the voltage calculated value at the protection installation position have opposite signs, a metallicity or low-transition resistor fault happens in a power transmission line area is judged, so that quick protection action is carried out; and when the line end calculated voltage amplitude is less than a set value, a high-transition resistor fault or an outside fault happens in the power transmission line area is judged, and selectivity is provided when in related protection coordination, so that at the moment, protection action can be realized after time is delayed. The method is realized in a time domain, so that a needed data window is short and calculating amount is low. The method is mainly used for the relay protection of the direct-current transmission line in an electrical power system.

Description

A kind of high-voltage direct-current transmission line low-voltage protective

Technical field:

The invention belongs to power system transmission line relaying protection field, relate to a kind of DC power transmission line method of undervoltage protection, especially a kind of method of undervoltage protection of HVDC (High Voltage Direct Current) transmission line.

Background technology:

Along with the high speed development of Chinese national economy, increasing to the demand of electric weight.High voltage direct current transmission has advantage at remote, large capacity transmission and asynchronous system on interconnected.High voltage direct current transmission has obtained development fast in China in recent years, has become the emphasis of China's power construction.The DC transmission engineering quantity of China comes out at the top in the world at present.

HVDC (High Voltage Direct Current) transmission line is as the interconnection of large regional grid, and its safety and reliability will affect the stable operation of interconnected network.The general distance of DC power transmission line is long, probability of malfunction is higher, and studies show that transmission line malfunction is the main cause that causes DC transmission system to be stopped transport.Therefore, high performance protection of direct current supply line is the assurance of DC transmission system safe and reliable operation.Be subjected to the effect of DC control system, it is obviously different that the fault signature of DC power transmission line and AC system have, therefore be necessary the protection philosophy of DC power transmission line is studied.Present HVDC (High Voltage Direct Current) transmission line mainly adopts traveling-wave protection as main protection, coordinates simultaneously under-voltage protection, transverse differential protection and current differential protection etc. to protect in support.Yet present DC minimum voltage protection lacks setting principle, poor performance, fails to fulfil well the effect of backup protection.

Summary of the invention:

The present invention is intended to overcome the deficiency of traditional under-voltage protection performance, and the under-voltage protection criterion that provides can quick and precisely be identified the metallicity fault in the transmission line district, and by coordinating high resistive fault in cog region with other protection.The method principle is simple, reliability is high, and protection range is stable, is not subjected to the impact of operational mode.Its specific implementation is to come the magnitude of voltage of computing electric power line end by voltage, the magnitude of current of protecting the installation place to measure, according to result of calculation establishing protective criterion.When line end voltage calculated value during with protection installation place voltage measuring value contrary sign, be judged to be generation metallicity or low transition resistance fault in the transmission line district, quick acting; When line end calculating voltage amplitude during less than set point, be judged to be high resistive fault or external area error in the transmission line district, need to could realize selectivity to the cooperation of relevant protection, protection this moment need to can be moved through the time-delay rear.

For realizing above-mentioned task, the present invention takes following technical solution:

Step 1 in the protection installation place, is sampled to direct current and the direct voltage instantaneous value of DC line local terminal; There is coupling between the DC bipolar circuit, in order to eliminate the impact of coupling, introduce following formula sampled data carried out decoupling zero, obtain the direct voltage of decoupling zero and direct current modulus value (source: Automation of Electric Systems-2007.31 (24) .57-61):

i _m＝S ^-1i (1)；

u _m＝S ^-1u (2)；

In formula:

S ^-1=S ^T, be decoupling zero matrix and the inverse matrix thereof of bipolar direct current transmission line, u _mAnd i _mBe respectively mode voltage and mould current matrix, u and i are respectively direct voltage and the direct current sampled values of local terminal bipolar direct current transmission system;

Step 2, in the Transmission Line Distributed Parameter model, according to following formula with the direct voltage of measurement point and direct current modulus value calculate direct voltage modulus value along the line (source: Proceedings of the CSEE-2004.24 (3) .24-29):

$u_{\mathrm{ym}}(x,t)=\frac{1}{2}{\left(\frac{Z_C+\mathrm{rx}/4}{Z_C}\right)}^2[u_m(t+\frac{x}{v})-i_m(t+\frac{x}{v})(Z_C+\frac{\mathrm{rx}}{4})]$

$+\frac{1}{2}{\left(\frac{Z_C-\mathrm{rx}/4}{Z_C}\right)}^2\·[u_m(t-\frac{x}{v})+i_m(t-\frac{x}{v})(Z_C-\frac{\mathrm{rx}}{4})]$

$-{\left(\frac{\mathrm{rx}/4}{Z_C}\right)}^2{u}_m\left(t\right)-\frac{\mathrm{rx}}{4}\left(\frac{Z_C+\mathrm{rx}/4}{Z_C}\right)\·\left(\frac{Z_C-\mathrm{rx}/4}{Z_C}\right)i_m\left(t\right)---\left(3\right);$

In formula: u _ym(x, t) is that the mode voltage instantaneous value at x place, Z are installed in t distance protection constantly _cBe the characteristic impedance of circuit, r is the resistance of circuit unit length, u _m(t) and i _m(t) be respectively t and constantly protect mode voltage and the mould electric current of installation place voltage and current value through obtaining after phase-model transformation;

Step 3, due to the pole tension establishing protective criterion of using the protection range end, therefore will be through the be protected pole tension instantaneous value of end-of-range of phase mould inverse transformation:

u(l _set，t)＝S·u _ym(l _set，t) (4)；

In formula: u (l _set, be t) l apart from local terminal constantly for t _setPlace's pole tension calculated value, u _ym(l _set, be t) l apart from local terminal constantly for t _setPlace's mode voltage calculated value, l _setBe the distance of DC minimum voltage protection end with the protection installation place;

Step 4 consists of the protection criterion with the protection range end pole tension instantaneous value that calculates and local terminal measuring voltage, and this protection criterion is comprised of quick acting criterion and deferred action criterion:

(1) quick acting criterion is:

u(t)·u(l _set，t)＜0 (5)；

In formula: carving copy side dc voltage measurement value when u (t) is t;

(2) deferred action criterion is:

$\left\{\begin{array}{c}u(l_{\mathrm{set}},t)<U_{\mathrm{th}}\\ t>\mathrm{\&Delta;t}\end{array}\right.---\left(6\right);$

In formula: u (l _set, t) be the pole tension calculated value of protection range end, U _thBe the threshold value of setting;

When satisfying formula (5), be judged to be metallicity or low transition resistance fault occur in the transmission line district, but the protection quick acting, and have absolute selectivity.In order to protect the reliability of action, can take the lasting satisfied strategy that can move of criterion in 5～10ms.When satisfying formula (6), be judged to be high transition Resistance Fault or external area error occur in the transmission line district, protect and can move after time-delay.Criterion or the action of time-delay criterion all will be judged to be the DC line troubles inside the sample space fast.

The present invention calculates in time domain, can utilize fault Whole frequency band information, quick action, good reliability, and can whole process drop into after fault, have complete setting principle, can identify fast and action message for metallicity fault and low resistance fault in the district, need through deferred action for high resistive fault in the district.

Description of drawings:

Fig. 1 is the system configuration sketch of bipolar direct current transmission line.

Embodiment:

Below in conjunction with accompanying drawing, the present invention is further elaborated.

DC transmission system is comprised of converting plant, Inverter Station and DC power transmission line three parts, as shown in Figure 1.Converting plant is direct current with exchange conversion, and transmission line is transferred to direct current energy the Inverter Station of opposite end, and Inverter Station is interchange with DC converting.Core content of the present invention is to provide under-voltage protection for DC power transmission line.

The under-voltage protection principle that the present invention proposes is based upon on the basis of Transmission Line Distributed Parameter model, is applicable to long transmission line.For realizing this protection philosophy; at first on the transmission line Bergeron model, by direct voltage, the dc current measurement value of protection installation place, calculate the direct voltage instantaneous value of protection range end; utilize afterwards this direct voltage calculated value establishing protective criterion, concrete steps are as follows:

In current conversion station, protect direct voltage, the direct current of installation place voltage divider and shunt when gathering fault, obtain the sampled value of direct voltage and direct current;

The direct voltage, the direct current data that collect are passed through the low pass filter filters out high fdrequency component, improve the reliability of calculating;

According to formula (1), formula (2), direct voltage, the current instantaneous value that measures is converted to mode voltage, mould current instantaneous value;

Calculate protection range end direct current mode voltage instantaneous value according to formula (3) again, convolution (4) carries out phase mould inverse transformation to result of calculation, the be protected pole tension instantaneous value of end-of-range, and consist of the protection criterion with the protection range end pole tension instantaneous value that calculates and local terminal measuring voltage;

The operating criterion of under-voltage protection comprises a quick acting criterion and a deferred action criterion:

(1) quick acting criterion is:

u(t)·u(l _set，t)＜0 (5)；

In formula: carving copy side dc voltage measurement value when u (t) is t, u (l _set, t) be the t pole tension calculated value of protection range end constantly;

(2) deferred action criterion is:

$\left\{\begin{array}{c}u(l_{\mathrm{set}},t)<U_{\mathrm{th}}\\ t>\mathrm{\&Delta;t}\end{array}\right.---\left(6\right);$

In formula: u (l _set, t) be the pole tension calculated value of protection range end, U _thFor setting threshold value;

When satisfying formula (5), be judged to be metallicity or low transition resistance fault occur in the transmission line district, but the protection quick acting, and have absolute selectivity.In order to protect the reliability of action, can take the lasting satisfied strategy that can move of criterion in 5～10ms.When satisfying formula (6), be judged to be high transition Resistance Fault or external area error occur in the transmission line district, protect and can move after time-delay.Criterion or the action of time-delay criterion all will be judged to be the DC line troubles inside the sample space fast.

Above content is in conjunction with concrete preferred implementation further description made for the present invention; can not assert that the specific embodiment of the present invention only limits to this; for the general technical staff of the technical field of the invention; without departing from the inventive concept of the premise; can also make some simple deduction or replace, all should be considered as belonging to claims that the present invention submits to and determine scope of patent protection.

Claims (1)

1. high-voltage direct-current transmission line low-voltage protective is characterized in that: the method utilizes single-end electrical quantity to consist of criterion in time domain based on distributed parameter model, to distinguishing interior metallicity or low transition resistance fault has absolute selectivity; To distinguishing interior high resistive fault, need to could realize selectivity to the cooperation of relevant protection; The specific implementation process comprises the following steps:

Step 1 in the protection installation place, is sampled to direct current, the direct voltage of DC line local terminal; Then according to following formula, sampled data is carried out decoupling zero:

i _m＝S ^-1i （1）；

u _m＝S ^-1u （2）；

In formula, $S=\frac{\sqrt{2}}{2}\left[\begin{array}{cc}1& 1\\ -1& 1\end{array}\right],$ S ^-1=S ^T, be decoupling zero matrix and the inverse matrix thereof of bipolar direct current transmission line, u _mAnd i _mBe respectively mode voltage and mould current matrix, u and i are respectively direct voltage and the direct current sampled values of local terminal bipolar direct current transmission system;

Step 2, in the Transmission Line Distributed Parameter model, calculate direct voltage modulus value along the line according to following formula:

$u_{\mathrm{ym}}(x,t)=\frac{1}{2}{\left(\frac{Z_C+\mathrm{rx}/4}{Z_C}\right)}^2\&lsqb;u_m(t+\frac{x}{v})-i_m(t+\frac{x}{v})(Z_C+\frac{\mathrm{rx}}{4})\&rsqb;$

$+\frac{1}{2}{\left(\frac{Z_C-\mathrm{rx}/4}{Z_C}\right)}^2.\&lsqb;u_m(t-\frac{x}{v})+i_m(t-\frac{x}{v})(Z_C-\frac{\mathrm{rx}}{4})\&rsqb;$

$-{\left(\frac{\mathrm{rx}/4}{Z_C}\right)}^2{u}_m\left(t\right)-\frac{\mathrm{rx}}{4}\left(\frac{Z_C+\mathrm{rx}/4}{Z_C}\right).\left(\frac{Z_C-\mathrm{rx}/4}{Z_C}\right)i_m\left(t\right)---\left(3\right);$

In formula, u _ym(x, t) is that the mode voltage instantaneous value at x place, Z are installed in t distance protection constantly _cBe the characteristic impedance of circuit, r is the resistance of circuit unit length, u _m(t) and i _m(t) be respectively mode voltage and the mould electric current of voltage and current value through obtaining after phase-model transformation that t protects the installation place sampling constantly;

Step 3, according to the be protected pole tension instantaneous value of end-of-range of phase mould inverse transformation formula:

u(l _set,t)＝S·u _ym(l _set,t) （4）；

In formula: u (l _set, be t) that t is constantly apart from local terminal l _setPlace's pole tension calculated value, u _ym(l _set, be t) that t is constantly apart from local terminal l _setPlace's mode voltage calculated value, l _setBe the distance of DC minimum voltage protection end with the protection installation place;

Step 4 consists of the protection criterion with the protection range end pole tension instantaneous value that calculates and local terminal measuring voltage, and this protection criterion is comprised of quick acting criterion and deferred action criterion;

(1) quick acting criterion is:

u(t)·u(l _set,t)<0 （5）；

In formula, carving copy side dc voltage measurement value when u (t) is t;

(2) deferred action criterion is:

$\left\{\begin{array}{c}u(l_{\mathrm{set}},t)<U_{\mathrm{th}}\\ t>\mathrm{\&Delta;t}\end{array}\right.---\left(6\right);$

In formula, u (l _set, t) be the pole tension calculated value of protection range end, U _thBe the threshold value of setting;

When satisfying formula (5), be judged to be metallicity or low transition resistance fault occur in the transmission line district, but the protection quick acting, and have absolute selectivity; In order to protect the reliability of action, take the lasting satisfied strategy that can move of criterion in 5～10ms; When satisfying formula (6), be judged to be high transition Resistance Fault or external area error occur in the transmission line district, protect and can move after time-delay; Criterion or the action of time-delay criterion all will be judged to be the DC line troubles inside the sample space fast.

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