CN101615784A - Transmission line zero sequence longitudinal protection method based on the transformer neutral point zero-sequence current - Google Patents

Abstract

The invention discloses transmission line zero sequence longitudinal protection method based on the transformer neutral point zero-sequence current.The present invention is a benchmark with the zero-sequence current of transformer neutral point, with the transformer neutral point zero-sequence current with the protection zero-sequence current phase difference as declaring to foundation.Because of unfavorable with voltage accurate failure judgement direction just, thereby overcome the malfunction or the tripping problem of the protection that traditional zero-sequence direction component causes because of residual voltage is too small, improved the performance factor of longitudinal differential protection system, increase the reliability of protection.

Description

Transmission line zero sequence longitudinal protection method based on the transformer neutral point zero-sequence current

Technical field

The present invention relates to ultra-high-tension power transmission line pilot protection research field, be specially electric power line longitudinal coupling direction protection based on the transformer neutral point zero-sequence current.

Background technology

The vertical connection of zero sequence direction protection has the advantage that quick action, directivity clearly, are not loaded and system's concussion influences, and it is little influenced by transition resistance, does not have the voltage dead band.High-voltage fence neutral-point solid ground, zero-sequence fault network configuration are more fixing, so the vertical connection of zero sequence direction protection brought into play important effect in direction protection, generally can be used as the main protection of earth fault.

The residual voltage that the vertical connection of transmission line zero sequence direction protection records is actual to be zero sequence dividing potential drop on the transformer.Along with power system development, transformer capacity is increasing, and its zero sequence impedance is more and more littler, and the residual voltage of route protection is very little.When the circuit zero-sequence direction component carried out the fault direction differentiation, possibility was crossed low owing to residual voltage and is not satisfied the sensitivity requirement.Also repeatedly take place in the scene not satisfy malfunction and the tripping accident that the sensitivity requirement causes because of residual voltage.When adopt improving threshold value, under threshold value, during with the method for zero-sequenceprotection locking, may cause the protection tripping, thereby enlarge the power failure scope.And, as being subjected to secondary voltage circuit neutral ground or the loosening influence of earth point, residual voltage can't react real phase place, thereby cause the malfunction of zero-sequenceprotection.

At present, solve the vertical connection of circuit zero sequence direction protection and cause that because of residual voltage is too little the method for protection malfunction or tripping has a lot, but these methods all exist some defectives:

(1) method that residual voltage is compensated can only improve the forward fault sensitivity, has but reduced reverse fault sensitivity.

(2) though memory voltage extensive use in protection never has corresponding solution to zero-sequenceprotection.

(3) based on the zero-sequence direction component of fault type, must locking under heavy load and system's concussion situation, and must fail if select mutually based on the fault choosing mutually, the differentiation of fault direction also is false.

Need to seek the vertical connection of a kind of new zero sequence direction protection for this reason, solve tripping and malfunction problem that protection brings because of residual voltage is too for a short time, and reliable failure judgement generation direction.

Summary of the invention

The objective of the invention is to overcome the deficiencies in the prior art part, provide a kind of and can better solve the electric power line longitudinal coupling direction protection malfunction that causes because of residual voltage is too small or the method for tripping.This method principle is simple, reliable in action, stable.

Technical scheme of the present invention is achieved in that and may further comprise the steps:

(1) with the transformer neutral point zero-sequence current With the protection zero-sequence current Phase difference

As declaring to foundation;

(2) when

The time, satisfy the forward failure criterion, be judged to be forward earth fault; When

The time, satisfy the direction failure criterion, be judged to be reverse earth fault;

(3) if the protection of circuit two ends all is judged to forward earth fault, then fault is a troubles inside the sample space, two ends protection action; If end line protection is declared to being forward earth fault, other end route protection is declared to being reverse earth fault, and then fault is an external area error, and the two ends protection is failure to actuate.

The present invention has the following advantages:

(1) because of not adopting voltage, avoid protecting because of residual voltage does not satisfy protection or the tripping problem that the sensitivity requirement causes, improve the precision maneuver rate of protection;

(2) compare with voltage compensation method, this protects the sensitivity of forward and reverse fault all to be greatly improved;

(3) principle is simple, and reliable in action is rapid;

(4) because of utilizing zero-sequence component, not influenced by load, system oscillation, be subjected to transition resistance to influence little advantage so protection has.

Description of drawings

Fig. 1 is the hardware block diagram of circuit Microcomputer Protection;

Fig. 2 is both-end electric supply system figure;

Fig. 3 is k ₁Point earth fault zero sequence net figure;

Fig. 4 is k ₂Point earth fault zero sequence net figure;

Fig. 5 has two outlet system wiring figure for the transformer high-voltage side bus;

Fig. 6 is k ₃Point earth fault zero sequence net figure;

Fig. 7 is 750kV transmission line RTDS analogue system figure;

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

Embodiment

Referring to Fig. 1, the invention belongs to the circuit Microcomputer Protection, the circuit both sides all are equiped with uses protective device of the present invention.The input variable of protective device is the three-phase current of protection installation place and the zero-sequence current of transformer neutral point.They are recorded by the current transformer TA of protection.In Fig. 1 frame of broken lines is hardware block diagram of the present invention, is made of data acquisition system, microcomputer main system, input-output system three parts, and discriminating element core algorithm of the present invention is realized in microcomputer DSP main system by programming; Key algorithm of the present invention is realized in the DSP microsystem.Protection records A, B, C three-phase current i _Ja, i _Jb, i _JcWith transformer neutral point zero-sequence current i _T0The time domain discrete value, through sampling keep and the A/D conversion after, deliver to the microcomputer main system, calculate by respective algorithms and protect the installation place zero-sequence current

With the transformer neutral point zero-sequence current

Phase difference, and then failure judgement direction.

It is benchmark that the vertical connection of tradition transmission line zero sequence direction protection records residual voltage with protection, protection is recorded residual voltage and protection record zero-sequence current and carry out than mutually, with

As declaring (wherein to foundation

Be the route protection residual voltage,

Be route protection zero-sequence current, Z _R0Be simulated impedance).The reason that causes protection malfunction or tripping is exactly the route protection residual voltage

Too small.Because of the transformer neutral point zero-sequence current

With the route protection residual voltage

Constant phase difference is constant, and this sentences the transformer neutral point zero-sequence current Replace the route protection residual voltage

With the route protection zero-sequence current

Carry out than phase, Here it is based on the principle of transformer neutral point zero-sequence current electric power line longitudinal coupling protection.

With the system shown in Figure 2 is example derivation failure criterion.Wherein transformer is an autotransformer, circuit l ₁Two ends all are equiped with the vertical connection of circuit zero sequence direction protection, with circuit l ₁The vertical connection of right-hand member circuit zero sequence direction protection is a research object, and the forward earth fault is arranged on circuit l ₁Last k ₁Point, oppositely earth fault occurs in circuit l ₂Last k ₂The point; With circuit l ₁The protection of right-hand member zero sequence direction is research object, and wherein autotransformer adopts Y ₀/ Y ₀The wiring of/Δ, I is the high-pressure side, and II is a medium voltage side, and III is a low-pressure side.

(1) at protection positive direction k ₁Earth fault takes place in point, zero-sequence network figure as shown in Figure 3, wherein, trouble power Be positioned at fault point k ₁, transformer high-voltage side system zero sequence impedance Z ' _{∑ h0}With transformer high-voltage side zero sequence leakage reactance Z _H0Series connection, transformer medium voltage side system zero sequence impedance Z _{∑ m0}With transformer medium voltage side zero sequence leakage reactance Z _M0Series connection, step down side zero sequence leakage reactance Z _L0Earlier in parallel with the medium voltage side series arm, connect with the high-pressure side branch road then;

Wherein

Be respectively transformer high, medium and low voltage side zero-sequence current (the parameter reduction is to the high-pressure side).Through derive the transformer neutral point zero-sequence current

$3{\stackrel{\·}{I}}_{T0}=-3{\stackrel{\·}{I}}_{j0}\frac{Z_{\mathrm{\Σm}0}+Z_{m0}-(n_{\mathrm{hm}}-1)Z_{l0}}{Z_{\mathrm{\Σm}0}+Z_{m0}+Z_{l0}}$

(2) at protection opposite direction k ₂Earth fault takes place in point, the zero sequence net as shown in Figure 4, trouble power

Be positioned at fault point k ₂, transformer high-voltage side system zero sequence impedance Z _{∑ h0}With transformer high-voltage side zero sequence leakage reactance Z _H0Series connection, transformer medium voltage side system zero sequence impedance Z ' _{∑ m0}With transformer medium voltage side zero sequence leakage reactance Z _M0Series connection, step down side zero sequence leakage reactance Z _L0Earlier in parallel with the high-pressure side series arm, connect with the medium voltage side branch road then;

Can get the transformer neutral point zero-sequence current through deriving

$3{\stackrel{\·}{I}}_{T0}=3{\stackrel{\·}{I}}_{j0}\frac{n_{\mathrm{hm}}(Z_{h0}+Z_{\mathrm{\Σh}0})+(n_{\mathrm{hm}}-1)Z_{l0}}{Z_{l0}}$

(3) situation of two outlets is arranged for high-voltage side bus as shown in Figure 5, with circuit l ₁The vertical connection of right-hand member circuit zero sequence direction protection is a research object, works as l ₃Last k ₃Point during ground short circuit to l ₁Last protection is reverse external area error, and zero-sequence network figure as shown in Figure 6 at this moment.Can get through deriving by Fig. 6

$\frac{3{\stackrel{\·}{I}}_{T0}}{3{\stackrel{\·}{I}}_{j0}}=\frac{Z_{\mathrm{\Σl}10}}{Z_{h0}+Z_{\mathrm{\Σ}}}*\frac{Z_{\mathrm{\Σm}0}+Z_{m0}-(n_{\mathrm{hm}}-1)Z_{l0}}{Z_{\mathrm{\Σm}0}+Z_{m0}+Z_{l0}}$

Wherein $Z_{\mathrm{\Σ}}=\frac{Z_{l0}*(Z_{\mathrm{\Σm}0}+Z_{m0})}{Z_{\mathrm{\Σm}0}+Z_{m0}+Z_{l0}}$

Z wherein _{∑ l10}Be circuit l ₁Impedance and its system impedance sum, Z _L30For bus arrives circuit l ₃The impedance of last fault point;

Transformer neutral point zero-sequence current and protection zero-sequence current phase difference are about 180 ° when the forward earth fault as can be known by above analysis; when reverse earth fault, be about 0 °, have clear and definite directivity (this conclusion is equally applicable to the common transformer system) during forward and reverse fault.Consider the various factors influence, criterion is during based on transformer neutral point zero-sequence current direction component positive direction fault

Criterion is during reverse direction failure

During system generation earth fault, utilize transformer neutral point zero-sequence current and protection installation place zero-sequence current phase difference, can clear and definite failure judgement direction according to above criterion.If the protection of circuit two ends all is judged to the forward fault, then fault is a troubles inside the sample space, two ends protection action; If end line protection is declared to for just, other end route protection is declared to for negative, and then fault is an external area error, protects and reliably is failure to actuate.

In order to reach above-mentioned technical purpose, technical scheme of the present invention is achieved in that

When asymmetric earth fault took place transmission line, the protection starting component recorded zero-sequence current and surpasses threshold value, will protect input.

Step 1: protect installation place A, B, C three-phase current i after gathering fault _Ja, i _Jb, i _JcWith transformer neutral point zero-sequence current i _T0The time domain discrete value.

Step 2: will protect installation place A, B, C three-phase current i _Ja, i _Jb, i _JcThe centrifugal pump addition must be protected zero-sequence current centrifugal pump i _J0

Step 3: to i _J0, i _T0Carry out Fourier transform, get its fundametal compoment and be respectively

Step 4: relatively

Phase difference, and then failure judgement direction.

Step 5: if the protection of circuit two ends all is judged to the forward fault, then fault is a troubles inside the sample space, two ends protection action; If end line protection is declared to for just, other end route protection is declared to for negative, and then fault is an external area error, and two ends are protected and reliably are failure to actuate.

The RTDS analogue system as shown in Figure 7.Circuit l wherein ₁, l ₂Length is respectively 400km and 200km.The I of autotransformer, II, III side electric pressure are respectively 750kV, 330kV, 66kV.With l ₁Last protection is for investigating object, and the fault point is located at the k at 15% place in the forward region respectively ₁The k at point and 85% place ₂Point, reverse fault are located at circuit l ₂The k at 15% place ₃The k at point and 85% place ₄The point.Transition resistance be respectively 0 and this electric pressure under maximum transition resistance (being taken as 300 Ω and 400 Ω under 330kV and the 750kV respectively).Circuit and transformer parameter are as follows:

Circuit l ₁Parameter:

Z _pos＝(0.01305+0.25990i)Ω/km

Z _zero＝(0.23275+0.93422i)Ω/km

Z _zerocoup＝(0.21889+0.57875i)Ω/km

C _pos＝0.01418μF/km

C _zero＝0.00848μF/km

C _zerocoup＝0.00212μF/km

Circuit l ₂Parameter:

Z _pos＝(0.0218+0.25341i)Ω/km

Z _zero＝(0.1793+0.8085i)Ω/km

Z _zerocoup＝(0.0535+0.1510i)Ω/km

C _pos＝0.0146μF/km

C _zero＝0.0079μF/km

C _zerocoup＝7.7544e-009μF/km

750kV transformer T parameter:

Capacity: 2100/2100/699MVA (three-phase)

Voltage ratio: 765/345/63kV

Short-circuit reactance: senior middle school 18%; Height 56%; In low by 36%

Winding connection mode: YN/a0/d11

The transformer neutral point zero-sequence current is as shown in table 1 with protection zero-sequence current phase difference under the various failure conditions.

Transformer neutral point zero-sequence current and protection zero-sequence current phase difference under the various failure conditions of table 1

As can be seen from Table 1, during positive phase fault, transformer neutral point zero-sequence current and protection installation place zero-sequence current phase difference are near 180 °; During reverse fault, both phase differences are near 0 °, and forward and reverse fault has specific direction, and RTDS experimental data simulating, verifying has proved based on transformer neutral point zero-sequence current direction component to have superperformance.

Claims (1)

1, based on the transmission line zero sequence longitudinal protection method of transformer neutral point zero-sequence current, it is characterized in that:

(1) with the transformer neutral point zero-sequence current

With the protection zero-sequence current Phase difference

As declaring to foundation;

(2) when

The time, satisfy the forward failure criterion, be judged to be forward earth fault; When

The time, satisfy the direction failure criterion, be judged to be reverse earth fault;

(3) if the protection of circuit two ends all is judged to forward earth fault, then fault is a troubles inside the sample space, two ends protection action; If end line protection is declared to being forward earth fault, other end route protection is declared to being reverse earth fault, and then fault is an external area error, and the two ends protection is failure to actuate.

Images