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

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

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Publication number
CN101615784A
CN101615784A CN200910023481A CN200910023481A CN101615784A CN 101615784 A CN101615784 A CN 101615784A CN 200910023481 A CN200910023481 A CN 200910023481A CN 200910023481 A CN200910023481 A CN 200910023481A CN 101615784 A CN101615784 A CN 101615784A
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Prior art keywords
zero
protection
sequence
sequence current
neutral point
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索南加乐
粟小华
杜斌
张健康
胡勇
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Xian Jiaotong University
Northwest China Grid Co Ltd
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Xian Jiaotong University
Northwest China Grid Co Ltd
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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
Figure G2009100234817D00023
As declaring to foundation;
(2) when
Figure G2009100234817D00024
The time, satisfy the forward failure criterion, be judged to be forward earth fault; When
Figure G2009100234817D00025
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
Figure G2009100234817D00031
With the transformer neutral point zero-sequence current
Figure G2009100234817D00032
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
Figure G2009100234817D00033
As declaring (wherein to foundation
Figure G2009100234817D00034
Be the route protection residual voltage,
Figure G2009100234817D00035
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
Figure G2009100234817D00036
Too small.Because of the transformer neutral point zero-sequence current
Figure G2009100234817D00037
With the route protection residual voltage
Figure G2009100234817D00038
Constant phase difference is constant, and this sentences the transformer neutral point zero-sequence current Replace the route protection residual voltage
Figure G2009100234817D000310
With the route protection zero-sequence current
Figure G2009100234817D000311
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 ' ∑ h0With transformer high-voltage side zero sequence leakage reactance Z H0Series connection, transformer medium voltage side system zero sequence impedance Z ∑ m0With 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
Figure G2009100234817D00042
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 I · T 0 = - 3 I · j 0 Z Σm 0 + Z m 0 - ( n hm - 1 ) Z l 0 Z Σm 0 + Z m 0 + Z l 0
(2) at protection opposite direction k 2Earth fault takes place in point, the zero sequence net as shown in Figure 4, trouble power
Figure G2009100234817D00045
Be positioned at fault point k 2, transformer high-voltage side system zero sequence impedance Z ∑ h0With transformer high-voltage side zero sequence leakage reactance Z H0Series connection, transformer medium voltage side system zero sequence impedance Z ' ∑ m0With 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 I · T 0 = 3 I · j 0 n hm ( Z h 0 + Z Σh 0 ) + ( n hm - 1 ) Z l 0 Z l 0
Figure G2009100234817D00047
(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
3 I · T 0 3 I · j 0 = Z Σl 10 Z h 0 + Z Σ * Z Σm 0 + Z m 0 - ( n hm - 1 ) Z l 0 Z Σm 0 + Z m 0 + Z l 0
Wherein Z Σ = Z l 0 * ( Z Σm 0 + Z m 0 ) Z Σm 0 + Z m 0 + Z l 0
Figure G2009100234817D00053
Z wherein ∑ l10Be 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
Figure G2009100234817D00054
Criterion is during reverse direction failure
Figure G2009100234817D00055
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
Figure G2009100234817D00061
Step 4: relatively
Figure G2009100234817D00062
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
Figure A2009100234810002C1
With the protection zero-sequence current Phase difference
Figure A2009100234810002C3
As declaring to foundation;
(2) when
Figure A2009100234810002C4
The time, satisfy the forward failure criterion, be judged to be forward earth fault; When
Figure A2009100234810002C5
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.
CN200910023481A 2009-07-31 2009-07-31 Transmission line zero sequence longitudinal protection method based on the transformer neutral point zero-sequence current Pending CN101615784A (en)

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104076249A (en) * 2014-07-15 2014-10-01 国家电网公司 Three-phase three-winding transformer one-phase ground fault coverage diagnostic method
CN105207184A (en) * 2015-10-12 2015-12-30 国家电网公司 Zero-sequence directional element for neutral point via-resistance grounding system
CN105356427A (en) * 2015-11-09 2016-02-24 华中电网有限公司 Longitudinal zero sequence direction protection method of one-tower double-circuit parallel transmission line
CN110061481A (en) * 2019-03-28 2019-07-26 李晓明 A kind of zero-sequence voltage injection method and device
CN113466587A (en) * 2021-06-30 2021-10-01 南京国电南自电网自动化有限公司 Transformer air-drop fault discrimination method and system

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104076249A (en) * 2014-07-15 2014-10-01 国家电网公司 Three-phase three-winding transformer one-phase ground fault coverage diagnostic method
CN105207184A (en) * 2015-10-12 2015-12-30 国家电网公司 Zero-sequence directional element for neutral point via-resistance grounding system
CN105356427A (en) * 2015-11-09 2016-02-24 华中电网有限公司 Longitudinal zero sequence direction protection method of one-tower double-circuit parallel transmission line
CN105356427B (en) * 2015-11-09 2018-08-24 华中电网有限公司 The pilot zero sequence direction relay method of common-tower double-return transmission lines in parallel
CN110061481A (en) * 2019-03-28 2019-07-26 李晓明 A kind of zero-sequence voltage injection method and device
CN113466587A (en) * 2021-06-30 2021-10-01 南京国电南自电网自动化有限公司 Transformer air-drop fault discrimination method and system

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Open date: 20091230