CN101577417B - Method for current differential protection of direct current electric transmission line - Google Patents

Abstract

The invention discloses a method for current differential protection of a direct current electric transmission line, which comprises the following steps: according to a distributed parameter model of the electric transmission line, using mode transformation in a time domain to transform sampling values of direct current and direct current voltage into a modulus; then using the mode voltage and thecurrent of two ends from two ends of a line respectively to calculate mode current of certain point of the line at each moment; and using the mode current to directly construct a current differential protection criterion, or synthesizing electrode current through electrode mode inverse transformation, and then constructing the current differential protection criterion according to the electrode c urrent. The method can improve the sensitivity and the reliability of direct current line protection, has good controllability and high security, has a complete setting theory, overcomes the defects of the conventional traveling-wave protection as the main protection of a high-voltage direct current line, and requires no recognition of a traveling-wave wave head; besides, the calculation is simple. The method is mainly used for the current differential protection of the direct current electric transmission line in an electric power system, in particular for the protection of an ultra/extra high-voltage direct current electric transmission line.

Description

Method for current differential protection of direct current electric transmission line

Technical field

The present invention relates to electric power system DC power transmission line relaying protection field, relate in particular to the current differential protection of ultra-high/extra-high voltage DC power transmission line.

Background technology

High voltage direct current (HVDC) transmission of electricity is big with its through-put power, the circuit cost is low, advantages such as control performance is good, in remote, high-power transmission of electricity, occupy more and more important position, world developed country is all its main means as big capacity, long distance electricity and asynchronous networking, China also becomes the focus of power construction because of " transferring electricity from the west to the east, north and south is confession mutually, national network ".Since direct current transportation was adopted in Ge Zhou Ba to Shanghai in 1989, China's DC transmission engineering quantity came out at the top in the world.

Generally as the interconnection of Da Qu networking, its fail safe and reliability not only are related to the stability of native system to HVDC (High Voltage Direct Current) transmission line, and will directly influence the stable operation of connected regional power grid even whole electrical network.Because DC line is long, the probability height that breaks down, the operation level that therefore improves the DC power transmission line relaying protection is significant to fail safe and the reliability that guarantees DC transmission system.Yet from existing DC transmission engineering ruuning situation; the DC line protective relaying device that puts into operation both at home and abroad exists theoretical incomplete; there is not the blanket principle of adjusting; adjusting only depends on simulation result problem such as adjust, thereby has caused the reliability of DC line protection not high.

The current differential protection function admirable is natural main protection in the transmission line of alternation current, yet for various reasons, it protects responsiveness slow in DC power transmission line, and performance is not good.Operating DC line many with traveling-wave protection as main protection, the traveling-wave protection quick action be not subjected to the influence of factors such as transition resistance, load, long line distributed capacitance, but reliability is not high, easy malfunction.Therefore, be necessary the differential protection of DC power transmission line is improved, its performance is promoted, in the hope of in the DC line fault overall process, all having good protective value.

Summary of the invention

The objective of the invention is to overcome above-mentioned prior art deficiency, a kind of method for current differential protection of direct current electric transmission line is provided, this method does not need to discern capable wave-wave head, only needs to calculate in real time current instantaneous value, and method is simple, quick action, reliability height.

In order to realize above-mentioned task, the present invention takes following technical solution:

The present invention proposes a kind of current differential protection method that is applicable to HVDC (High Voltage Direct Current) transmission line, the computational process of this method is based upon on the time domain distributed parameter model basis, and specific implementation comprises the following steps:

Step 1 in current conversion station, is carried out synchronized sampling with predetermined sampling rate, and offside direct current, direct voltage sampled instantaneous value is transferred to this side this side of DC line and direct current, the direct voltage of offside;

Step 2, (source: Automation of Electric Systems-2007.31 (24) .57-61), direct voltage, the direct current instantaneous value that sampling is obtained is converted to the instantaneous value of mode voltage, the mould magnitude of current according to formula (1), formula (2) respectively;

u _m＝S ^-1·u (1)

i _m＝S ^-1·i (2)

In the formula $S=\frac{\sqrt{2}}{2}\left[\begin{array}{cc}1& 1\\ -1& 1\end{array}\right],$ S ^-1=S ^T, be the decoupling zero matrix and the inverse matrix thereof of bipolarity DC power transmission line; u _m, i _mBe respectively mode voltage, mould current matrix; U, i are respectively in the current conversion station of bipolarity DC transmission system two ends, the direct voltage and the direct current instantaneous value that are collected through direct voltage transducer and DC current sensor.

Step 3, in distributed parameter model, according to formula (3) (source: Proceedings of the CSEE-2004.24 (3) .24-29), respectively with the direct voltage at the two ends that obtain of sampling, the mould current instantaneous value that the direct current instantaneous value calculates certain point on the local terminal DC line.

$i(x,t)=\frac{1}{2Z_c}\left(\frac{Z_c+\mathrm{rx}/4}{Z_c}\right)[u_M(t+\frac{x}{v})-i_M(t+\frac{x}{v})\·(Z_c+\mathrm{rx}/4)]-$

$\frac{1}{2Z_c}{\left(\frac{Z_c-\mathrm{rx}/4}{Z_c}\right)}^2[u_M(t-\frac{x}{v})+i_M(t-\frac{x}{v})\·(Z_c-\mathrm{rx}/4)]----\left(3\right)$

$\frac{1}{2Z_c}\frac{\mathrm{rx}}{2Z_c}[u_M\left(t\right)-i_M\left(t\right)\left(\frac{\mathrm{rx}}{4}\right)]$

(x is that t is constantly apart from the current value of local terminal protection installation place distance for the x place, Z t) to i in the following formula _cBe the characteristic impedance of circuit, r is the resistance of circuit unit length, u _M(t) for t constantly local terminal adopt magnitude of voltage, i _M(t) for t constantly local terminal adopt current value.

Step 4, when making differential protection with the mould electric current, this mould current instantaneous value sum that calculates according to two ends realizes that according to Kirchhoff's current law (KCL) current differential protection gets final product; When making differential protection, then need the mould electric current that calculates is carried out the electrode current that the mould inverse transformation is tried to achieve each utmost point according to formula (4), construct the electrode current differential protection of each utmost point again according to Kirchhoff's current law (KCL) with electrode current.

i＝S·i _m (4)

Step 5, the operating criterion of current differential protection is:

i _d＝|i _J(x，t)+i _K(l-x，t)|≥I _set (5)

i _dBe differential current, i _J(x, t) electric current, i apart from J end x place for calculating _K(l is a total track length, I for l-x, the t) electric current apart from K end l-x place for calculating _SetBe fixing threshold.

Be judged to be this polar region internal fault when satisfying formula (5), the fault order has been sent in the moving protection action of this extreme difference; Otherwise the moving protection of this extreme difference is failure to actuate.

The present invention adopts real-time calculating can overcome the weak point of existing DC line main protection (traveling-wave protection) effectively in time domain, as poor reliability, can only be used for the wave process of fault transient during, adjust theoretical incomplete, only rely on emulation to adjust etc.Current differential protection of the present invention has quick action, reliability height, can be used for the fault overall process, has the complete theory of adjusting, and can replace traveling-wave protection, as the main protection of DC line protection.

Description of drawings

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

Fig. 2 is the software flow pattern that constitutes the algorithm realization of current differential protection with the mould electric current.

Fig. 3 is the software flow pattern that constitutes the algorithm realization of current differential protection with electrode current.

Below in conjunction with accompanying drawing content of the present invention is described in further detail.

Embodiment

DC transmission system is by converting plant, and Inverter Station and DC power transmission line three parts constitute.Converting plant is transformed to direct current with alternating current, and transmission line is transferred to the Inverter Station of opposite end with direct current, and Inverter Station is transformed to alternating current with direct current.Core content of the present invention is to provide protection for DC power transmission line.

With reference to shown in Figure 1, by converting plant, Inverter Station and DC power transmission line three parts constitute.F is the fault point for DC line among the figure, u _Jp, i _JpBe respectively the direct voltage and the direct current of rectification side positive pole; u _Jn, i _JnBe the direct voltage and the direct current of rectification side negative pole; u _Kp, i _KpBe respectively the direct voltage and the direct current of inversion side positive pole; u _Kn, i _KnBe respectively the direct voltage and the direct current of inversion side negative pole; u _f, i _fIt is respectively the voltage and current of fault point; i _Jf, i _KfIt is respectively the electric current that calculates the both sides, fault point according to formula (3) with J end and K terminal voltage electric current.Because in calculating, need the data of opposite end, this can realize the transmission and the reception of two end datas by the remote communication system, and need to solve two ends data synchronization problem.

With reference to Fig. 2, shown in Figure 3, HVDC transmission line distance protecting method of the present invention is based upon on the time domain distributed parameter model basis, and the specific algorithm step is as follows:

1) in current conversion station, the local terminal of DC line and direct current, the direct voltage of opposite end are carried out synchronized sampling with predetermined sampling rate, and by modulus converter A/D direct voltage and the direct current of being gathered be converted to digital quantity at local terminal; Simultaneously, the direct voltage that the instantaneous value of opposite end direct current, direct voltage sampling is changed through the opposite end modulus converter A/D and the digital quantity of direct current are transferred to local terminal;

2) voltage, the current data that collect are carried out low-pass filtering with the filtering high fdrequency component, because energy mainly concentrates on low-frequency range, filter out high fdrequency component and not only can weaken of the influence of line parameter circuit value frequency dependent characteristic computational accuracy, and can weaken of the influence of various interference signals to computational accuracy, improved the accuracy of calculating; Respectively according to formula (1), formula (2), the electric current and voltage that records is converted to mode voltage, current instantaneous value then.

3) in distributed parameter model, according to formula (3), respectively with the two ends direct voltage of DC line, the mould current instantaneous value that direct current calculates certain point on the circuit.

4) for the mould current differential protection,,, be directly used in structure mould current differential protection criterion respectively by the mould current instantaneous value of circuit two ends mode voltage, electric current computational scheme point, and with the mould current instantaneous value that calculates according to formula (3).

5), need that then the mould current instantaneous value that calculates is carried out the utmost point-Mo inverse transformation according to formula (4) and try to achieve electrode current, and then construct the current differential protection criterion with electrode current for electrode current differential protection criterion.

6) operating criterion of current differential protection is:

i _d＝|i _J(x，t)+i _K(l-x，t)|≥I _set (5)

i _dBe differential current, i _J(x, t) electric current, i apart from J end x place for calculating _K(l is a total track length, I for l-x, the t) electric current apart from K end l-x place for calculating _SetBe fixing threshold.

If above-mentioned criterion satisfies, then be judged to be this polar region internal fault, the fault order has been sent in the moving protection action of this extreme difference; Otherwise the moving protection of this extreme difference is failure to actuate.

Claims (1)

1. a HVDC (High Voltage Direct Current) transmission line current differential protection method is characterized in that, this method is based upon on the time domain distributed parameter model basis, specifically comprises the following steps:

Step 1 in current conversion station, is carried out synchronized sampling with predetermined sampling rate, and by modulus converter A/D direct voltage and the direct current of being gathered is converted to digital quantity at local terminal the local terminal of DC line and direct current, the direct voltage of opposite end; Simultaneously, the direct voltage that the instantaneous value of opposite end direct current, direct voltage sampling is changed through the opposite end modulus converter A/D and the digital quantity of direct current are transferred to local terminal; Then respectively according to formula

u _m＝S ^-1·u (1)

i _m＝S ^-1·i (2)

In the formula S ^-1=S ^T, be the decoupling zero matrix and the inverse matrix thereof of bipolarity DC power transmission line; u _m, i _mBe respectively mode voltage, mould current matrix; U, i are respectively in the current conversion station of bipolarity DC transmission system two ends, the direct current that is collected through direct voltage transducer and DC current sensor, the instantaneous value of direct voltage sampling are converted to mode voltage, magnitude of current instantaneous value with the electric current and voltage that records;

Step 2, in distributed parameter model, according to formula (3),

$i(x,t)=\frac{1}{2Z_c}\left(\frac{Z_c+\mathrm{rx}/4}{Z_c}\right)[u_M(t+\frac{x}{v})-i_M(t+\frac{x}{v})\·(Z_c+\mathrm{rx}/4)]-$

$\frac{1}{2Z_c}{\left(\frac{Z_c-\mathrm{rx}/4}{Z_c}\right)}^2[u_M(t-\frac{x}{v})+i_M(t-\frac{x}{v})\·(Z_c-\mathrm{rx}/4)]----\left(3\right)$

$\frac{1}{2Z_c}\frac{\mathrm{rx}}{2Z_c}[u_M\left(t\right)-i_M\left(t\right)\left(\frac{\mathrm{rx}}{4}\right)]$

(x is that t is constantly apart from the current value of local terminal protection installation place distance for the x place, Z t) to i in the following formula _cBe the characteristic impedance of circuit, r is the resistance of circuit unit length, u _M(t) for t constantly local terminal adopt magnitude of voltage, i _M(t) for t constantly local terminal adopt current value, the mould current instantaneous value at certain some place on the instantaneous value calculating DC line of the direct current of being gathered with the DC line two ends, direct voltage sampling respectively;

Step 3 when making differential protection with the mould electric current, according to formula (3), respectively by the mould current instantaneous value of circuit two ends mode voltage, electric current computational scheme point, and with the mould current instantaneous value that calculates, is directly used in structure mould current differential protection criterion; When making differential protection with electrode current, the mould current instantaneous value that then needs to calculate is according to formula (4)

i＝S·i _m (4)

Carry out the utmost point-Mo inverse transformation and try to achieve electrode current, with electrode current structure current differential protection criterion;

Step 4, when the current differential protection criterion satisfies formula (5),

i _d＝|i _J(x，t)+i _K(l-x，t)|≥I _set (5)

i _dBe differential current, i _J(x, t) electric current, i apart from J end x place for calculating _K(l is a total track length, I for l-x, the t) electric current apart from K end l-x place for calculating _SetBe fixing threshold,

Then be judged to be this polar region internal fault, the fault order has been sent in the moving protection action of this extreme difference; Otherwise the moving protection of this extreme difference is failure to actuate.

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