CN104979808A - Penetration level calculation method for inverter power supply with longitudinal differential protection effect taken into account - Google Patents

Abstract

The invention relates to a penetration level calculation method for an inverter power supply with the longitudinal differential protection effect taken into account. The method comprises the steps of (1) setting a longitudinal differential protection device; (2) in the double-ended power supply system of a teed line inverter interfaced DG, the voltages of the grid-connected points of the DG and the voltages of the fault points of the DG can be obtained according to different voltage drop degrees of grid-connected points; (3) at a maximal phase-angle difference within the allowable range of the stable operation of the system, obtaining a single-phase short circuit current differential, figuring out inverter interfaced DGs of different capacities in the teed line based on an obtained according to different voltage drop degrees of grid-connected points via a maximal transition resistor at the voltage class of the inverter interfaced DG accessed to the power grid; obtaining the differential current during the occurrence of a single-phase grounding fault, and comparing the differential current with a protection setting value. If the differential current is equal to the protection setting value, the corresponding minimum capacity is just the maximum penetration level of the inverter interfaced DG. According to the technical scheme of the invention, the method is higher in guiding significance for engineering applications.

Description

A kind of inverter calculation of penetration level method taking into account longitudinal difference protection impact

Technical field

The present invention relates to field of relay protection in power, after relating to a kind of inverse distributed power T link, the calculation of penetration level method under longitudinal differential protection impact.

Background technology

Being incorporated into the power networks of a large amount of inverse distributed power (IIDG) creates impact to the reliability service of protection and control device original in electric power system.Determine the allowed capacity of IIDG, make the protective device in electric power system keep original harmony, most important to the safe and stable operation of electric power system.National policy help and technological progress promotion under, the grid connection capacity of IIDG is increasing, and grid-connected electric pressure is also more and more higher, and its network be incorporated to no longer is confined to radial low-voltage network." distributed power source access electric power network technique regulation " is pointed out, distributed power source, according to the power distribution network of the different electric pressure of capacity difference access, when capacity is at more than 15MW, accesses 35kV and 110kV electrical network.In addition " distribution network planning designing technique directive/guide " is pointed out in 110kV network, and DG can the mode that connects of T be connected to the grid.When IIDG access high-tension distributing line form T link time, use selectivity and the good longitudinal differential protection of quick-action to become preferred plan.Cannot DG obtained and under the prerequisite of the electric information of site, the method improving longitudinal differential protection setting value can only adopted, just can meet longitudinal differential protection optionally requirement.But, when the IIDG that T connects exceedes certain capacity, when being short-circuited fault in protection range inside through transition resistance, because differential current is less, longitudinal differential protection tripping may be caused.

The present invention gives the differential current calculating formula of Double-End Source system when transition resistance generation single-phase short circuit that T meets IIDG, propose the IIDG allowed capacity analytical method taking into account longitudinal differential protection impact.。

Summary of the invention

The object of the invention is to; known T connects the grid-connected position of IIDG; and under the prerequisite of the running status of IIDG and system operation mode the unknown; for ensureing the reliability of longitudinal differential protection action; a kind of computational methods of IIDG allowed capacity are provided; when the method is by comparing fault, the size of minimum differential current and longitudinal differential protection setting value, obtains the allowed capacity of IIDG.The present invention considers that abort situation, transition resistance, two side system phase angle differences are on the impact of differential current, and accurate and effective, has higher directive significance to engineer applied.

The present invention realizes by following technical scheme:

Take into account an inverter calculation of penetration level method for longitudinal difference protection impact, be made up of following steps:

(1) adjust to longitudinal differential protection device, setting value is:

I _unb＝0.1K _npK _samI _k.max+2I _N(1)

Wherein, I _k.maxfor maximum through current during longitudinal differential protection scope external fault, K _samfor being not more than the current transformer homotype coefficient of 1, K _npfor the influence coefficient of aperiodic component, value between 1.5 ~ 2, I _nfor the rated current of inverse distributed power;

(2) T connects in the Double-End Source system of inverse distributed power; circuit AB is longitudinal differential protection installation site; M point is the also site of inverse distributed power; when grid-connected point voltage drops in various degree; because the output characteristic of inverse distributed power is different; therefore it is also different that the differential current obtained calculates formula, when system is through transition resistance single phase ground fault, can obtain:

When grid-connected point voltage drops into 0.9U _ntime above

When grid-connected point voltage drops into 0.1-0.9U _nbetween time

When grid-connected point voltage drops into 0.1U _ntime following

Voltage Drop, to time in various degree, respectively by formula (2) ~ (4) and formula (5) simultaneous, can draw the grid-connected point voltage of DG with the voltage of fault point

And then the differential current of fault phase is when obtaining single-phase short circuit

$|{\stackrel{\·}{I}}_1+{\stackrel{\·}{I}}_2|=|\frac{{\stackrel{\·}{E}}_1-{\stackrel{\·}{U}}_{DG}}{Z_1}+\frac{{\stackrel{\·}{E}}_2-{\stackrel{\·}{U}}_f}{Z_{f2}}+\frac{2{\stackrel{\·}{U}}_f}{Z_3}|---\left(6\right)$

Wherein, U _nfor system nominal voltage, I _nfor inverse distributed power rated current, P is the power output of inverse distributed power, with be respectively the system equivalent electromotive force of circuit AB both sides, phase angle is δ, phase angle is 0 °; for inverse distributed power and the positive sequence voltage of site, its phase angle is for the positive sequence voltage of fault point, its phase angle is θ; The positive-negative sequence impedance of circuit AM is Z ₁, zero sequence impedance is Z ₁₀, and the positive-negative sequence impedance between site M to short circuit trouble point is Z _f1, resistance is R _f1, reactance is X _f1, zero sequence impedance is Z _f10, short circuit trouble point is Z to the positive-negative sequence impedance of bus B _f2, zero sequence impedance is Z _f20; Z ₃for Zhi Zu Pit such as faults in compound sequence network, its value is Z ₃=(Z ₁+ Z _f1) //Z _f2+ (Z ₁₀+ Z _f10) //Z _f20+ 3Z _d; R (x) is for getting real part computing, and im (x) is for getting imaginary-part operation;

(3) under the maximal phase angular difference of system stable operation permission; transition resistance maximum under inverse distributed power is connected to the grid electric pressure; according to the degree that grid-connected point voltage falls; select the corresponding computing formula by providing in step (2); the single-phase short circuit differential current obtained obtains the inverse distributed power that T connects different capabilities; differential current when diverse location single phase ground fault; and itself and the setting value protected are compared; when both are equal, corresponding minimum capacity is the allowed capacity of inverse distributed power.

The present invention has following advantage relative to existing technology:

First, the present invention is simply effective, and considers abort situation, transition resistance, two side system phase angle differences to the impact of differential current comprehensively, makes the computational methods of IIDG allowed capacity more accurately and reliably.Secondly, the present invention has taken into account the low voltage crossing output characteristic of IIDG, makes the calculating of differential current more meet engineering reality.Finally; the present invention has directive significance to the impact of circuit longitudinal differential protection and the configuration of protection after meeting IIDG to assessment T; when the IIDG capacity that T connects is less than calculation of penetration level value; only need to improve original longitudinal differential protection setting value; selectivity and the reliability of protection can be ensured; otherwise, need to use new protection scheme.

Accompanying drawing explanation

Fig. 1 is the NETWORK STRUCTURE PRESERVING POWER SYSTEM figure that T connects inverse distributed power;

Fig. 2 is the compound sequence network through transition resistance generation single-phase short circuit.

Embodiment

Be described in detail below in conjunction with embodiment and with reference to the technical scheme of accompanying drawing to this invention.

The present embodiment is for the structure chart shown in Fig. 1, in figure, circuit AB is the circuit that T connects inverse distributed power, system voltage grade is 110kV, the long 120km of circuit AB, the impedance of circuit positive-negative sequence is 0.21+j0.419 Ω/km, and zero sequence impedance is 0.63+j1.257 Ω/km, and inverse distributed power T is connected to the mid point of circuit AB.

Adopt the inverse distributed power calculation of penetration level method taking into account longitudinal differential protection impact of the present invention.Comprise the following steps:

(1) adjust to longitudinal differential protection device, setting value is:

I _unb＝0.1K _npK _samI _k.max+2I _N(1)

Wherein, I _k.maxfor maximum through current during longitudinal differential protection scope external fault, K _samfor being not more than the current transformer homotype coefficient of 1, K _npfor the influence coefficient of aperiodic component, general value is between 1.5 ~ 2.I _nfor the rated current of IIDG.

(2) under the maximal phase angular difference of system stable operation permission, transition resistance maximum under this electric pressure, during diverse location single phase ground fault, obtains the relational expression of differential current with IIDG volume change.

When f point in Fig. 1 is through transition resistance Z _dduring single phase ground fault, obtain compound sequence network as shown in Figure 2.In figure for IIDG and the positive sequence voltage of site, for the positive sequence voltage of fault point, with be respectively the system equivalent electromotive force of circuit AB both sides, M point is the also site of DG, and the positive-negative sequence impedance of circuit AM is Z ₁, zero sequence impedance is Z ₁₀, and the positive-negative sequence impedance between site M to short circuit trouble point is Z _f1, zero sequence impedance is Z _f10, short circuit trouble point is Z to the positive-negative sequence impedance of bus B _f2, zero sequence impedance is Z _f20.

Following relational expression can be obtained according to Fig. 2 and Kirchhoff's second law:

$\{\begin{array}{c}(\frac{1}{Z_1}+\frac{1}{Z_{f1}}){\stackrel{\·}{U}}_{DG}=\frac{{\stackrel{\·}{E}}_1}{Z_1}+{\stackrel{\·}{I}}_{DG}+\frac{{\stackrel{\·}{U}}_f}{Z_{f1}}\\ {\stackrel{\·}{I}}_{DG}=f\left({\stackrel{\·}{U}}_{DG}\right)\\ (\frac{1}{Z_{f1}}+\frac{1}{Z_3}+\frac{1}{Z_{f2}}){\stackrel{\·}{U}}_f=\frac{{\stackrel{\·}{U}}_{DG}}{Z_{f1}}+\frac{{\stackrel{\·}{E}}_2}{Z_{f2}}\end{array}---\left(2\right)$

Wherein, Z ₃be the Zhi Zu Pit such as the fault in compound sequence network shown in Fig. 2 in dotted line frame.Its value is Z ₃=(Z ₁+ Z _f1) //Z _f2+ (Z ₁₀+ Z _f10) //Z _f20+ 3Z _d. be the output characteristic of IIDG, access the technical stipulation of electric power system according to photo-voltaic power generation station and wind energy turbine set, obtain following output characteristic:

Wherein, P is the power output of IIDG, U _tfor the grid-connected point voltage of IIDG, U _nfor system nominal voltage.From above formula, when grid-connected point voltage is at 0.9U _ntime above, IIDG output current and voltage in phase, an active power of output; When Voltage Drop is to 0.9U _ntime following, the output current of IIDG and voltage phase difference 90 °, an output reactive power; When Voltage Drop is to 0.1U _ntime following, under the effect of current limliting link, IIDG output current is steady state value 2I _n.

Suppose formula (2) can be converted into scalar equation group.In equation group (2), the first two equation relates to the output characteristic of IIDG, and when between age at failure, grid-connected point voltage is different, its output characteristic also can change thereupon.

When grid-connected point voltage drops into 0.9U _ntime above, can obtain

When grid-connected point voltage drops into 0.1-0.9U _nbetween time, can obtain

When grid-connected point voltage drops into 0.1U _ntime following, can obtain

3rd equation of equation group (3) and grid-connected point voltage have nothing to do, and being converted into scalar equation is

When Voltage Drop is to time in various degree, formula (4)-(7) can be utilized to solve the grid-connected point voltage of DG with the voltage of fault point and then the differential current of fault phase is during known single-phase short circuit

$|{\stackrel{\·}{I}}_1+{\stackrel{\·}{I}}_2|=|\frac{{\stackrel{\·}{E}}_1-{\stackrel{\·}{U}}_{DG}}{Z_1}+\frac{{\stackrel{\·}{E}}_2-{\stackrel{\·}{U}}_f}{Z_{f2}}+\frac{2{\stackrel{\·}{U}}_f}{Z_3}|---\left(8\right)$

(3) maximum 60 ° allowed when both sides system equivalent electromotive force phase angle difference being set to stable operation, transition resistance is set to 110kV circuit maximum transition resistance 100 Ω.The single-phase short circuit differential current obtained in step (2) is utilized to calculate formula; obtain T and connect different capabilities inverse distributed power; differential current when diverse location breaks down; compare with the setting value of protection; when both are equal, corresponding minimum capacity 18MW is the allowed capacity of inverse distributed power.

Above content is only embodiments of the invention, and its object is not for the restriction to system and method proposed by the invention, and protection scope of the present invention is as the criterion with claim.Without departing from the spirit and scope of the present invention; those skilled in the art are not when departing from scope and spirit of the present invention, and all apparent amendment about form and details carry out it or change all should drop within protection scope of the present invention.

Claims (1)

1. take into account an inverter calculation of penetration level method for longitudinal difference protection impact, be made up of following steps:

(1) adjust to longitudinal differential protection device, setting value is:

I _unb＝0.1K _npK _samI _k.max+2I _N(1)

Wherein, I _k.maxfor maximum through current during longitudinal differential protection scope external fault, K _samfor being not more than the current transformer homotype coefficient of 1, K _npfor the influence coefficient of aperiodic component, value between 1.5 ~ 2, I _nfor the rated current of inverse distributed power;

(2) T connects in the Double-End Source system of inverse distributed power; circuit AB is longitudinal differential protection installation site; M point is the also site of inverse distributed power; when grid-connected point voltage drops in various degree; because the output characteristic of inverse distributed power is different; therefore it is also different that the differential current obtained calculates formula, when system is through transition resistance single phase ground fault, can obtain:

When grid-connected point voltage drops into 0.9U _ntime above

When grid-connected point voltage drops into 0.1-0.9U _nbetween time

When grid-connected point voltage drops into 0.1U _ntime following

Voltage Drop, to time in various degree, respectively by formula (2) ~ (4) and formula (5) simultaneous, can draw the grid-connected point voltage of DG with the voltage of fault point

And then the differential current of fault phase is when obtaining single-phase short circuit

$\left|{\stackrel{\·}{I}}_1+{\stackrel{\·}{I}}_2\right|=\left|\frac{{\stackrel{\·}{E}}_1-{\stackrel{\·}{U}}_{DG}}{Z_1}+\frac{{\stackrel{\·}{E}}_2-{\stackrel{\·}{U}}_f}{Z_{f2}}+\frac{2{\stackrel{\·}{U}}_f}{Z_3}\right|---\left(6\right)$

Wherein, U _nfor system nominal voltage, I _nfor inverse distributed power rated current, P is the power output of inverse distributed power, with be respectively the system equivalent electromotive force of circuit AB both sides, phase angle is δ, phase angle is 0 °; for inverse distributed power and the positive sequence voltage of site, its phase angle is for the positive sequence voltage of fault point, its phase angle is θ; The positive-negative sequence impedance of circuit AM is Z ₁, zero sequence impedance is Z ₁₀, and the positive-negative sequence impedance between site M to short circuit trouble point is Z _f1, resistance is R _f1, reactance is X _f1, zero sequence impedance is Z _f10, short circuit trouble point is Z to the positive-negative sequence impedance of bus B _f2, zero sequence impedance is Z _f20; Z ₃for Zhi Zu Pit such as faults in compound sequence network, its value is Z ₃=(Z ₁+ Z _f1) //Z _f2+ (Z ₁₀+ Z _f10) //Z _f20+ 3Z _d; R (x) is for getting real part computing, and im (x) is for getting imaginary-part operation;

(3) under the maximal phase angular difference of system stable operation permission; transition resistance maximum under inverse distributed power is connected to the grid electric pressure; according to the degree that grid-connected point voltage falls; select the corresponding computing formula by providing in step (2); the single-phase short circuit differential current obtained obtains the inverse distributed power that T connects different capabilities; differential current when diverse location single phase ground fault; and itself and the setting value protected are compared; when both are equal, corresponding minimum capacity is the allowed capacity of inverse distributed power.