CN103474974A - Distribution network single-phase ground protection method based on zero-sequence current sudden change straight line fitting direction - Google Patents
Distribution network single-phase ground protection method based on zero-sequence current sudden change straight line fitting direction Download PDFInfo
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Abstract
The invention relates to a distribution network single-phase ground protection method based on zero-sequence current sudden change straight line fitting direction, belonging to the technical field of power system relay protection. For a resonant earthed system, when single-phase earth fault occurs on one feed line, firstly, a bus zero-sequence voltage in a short time window and zero-sequence currents of feed lines after the fault are intercepted and subjected to wavelet decomposition, and respectively extracted wavelet coefficients of a frequency band in which a power frequency is located; then the extracted wavelet coefficients are subjected to primary straight line fitting by using a least square method, and slope values of primary straight lines are solved; finally, the primary straight line slope value corresponding to the bus zero-sequence voltage is respectively multiplied by the primary straight line slope values corresponding to the feed line zero-sequence voltages; when the product is less than zero to determine positive-direction fault occurs on the feed line, a protective element acts; when the product is larger than zero to determine reverse-direction fault occurs on the feed line, and the protective element does not act. The distribution network single-phase ground protection method is low in using difficulty and high in protection reliability.
Description
Technical field
The present invention relates to a kind of distribution one-phase ground protection method based on zero-sequence current Sudden Changing Rate fitting a straight line direction, belong to the Relay Protection Technology in Power System field.
Background technology
The power distribution network broad covered area, and directly in the face of the user, for it, provide the electricity consumption service.Account for 80% of distribution network failure according to the statistics single phase ground fault.The power distribution network resonant earthed system is the neutral by arc extinction coil grounding system, belongs to small current neutral grounding system.Single-phase grounded malfunction in grounded system of low current can affect the healthy phases voltage to earth and cause its rising, and voltage raises and can produce and destroy the insulation of grid equipment; Intermittent arcing ground particularly, can cause arc overvoltage, this voltage is by destroying system insulation and then developing into alternate or multipoint earthing short circuit, cause system overvoltage, thereby damage equipment, destroy system safety operation, therefore must find accurately, fast faulty line and make in time faulty line and isolation of system.
The most original partition method is by manually faulty line being cut off after the route selection success.In recent years, some one-phase ground protection devices have obtained application in practice, and the safe operation of electrical network has been played to positive effect.But the practical manifestation of partial devices is also unsatisfactory, and the phenomenon of malfunction, tripping happens occasionally.Existing one-phase ground protection device based on principle be generally: zero-sequence current is than width method, zero-sequence current relative phase method and harmonic component method etc.Zero-sequence current has utilized the faulty line zero-sequence current to equal the characteristics of non-fault line capacitive earth current sum than width method; the selection of the introducing of cable line, the impact of transition resistance and operational mode all likely causes the capacitive earth current of certain circuit to be greater than the situation of other all line mutual-ground capacitor electric current sums, and this will cause protective device generation malfunction.The zero-sequence current relative phase method has utilized the characteristics that the faulty line zero-sequence current is contrary with non-fault line zero-sequence current flow direction, in the shorter zero-sequence current value of circuit hour, the impact of interference signal is more outstanding causes the judgement of direction comparatively difficult, after the resonant earthed system compensation process occurs, loses efficacy.The harmonic component method has still been utilized the colony amplitude comparison phase comparing method in essence, can not fundamentally solve the problem and shortage that above-mentioned two kinds of methods exist, the phenomenon of malfunction, tripping or often appearance.
Summary of the invention
The invention provides a kind of distribution one-phase ground protection method based on zero-sequence current Sudden Changing Rate fitting a straight line direction; with outstanding because of the little interference signal of zero-sequence current for solving existing one-phase ground protection principle; the impact of compensation process and non-fault line zero-sequence current are greater than All other routes zero-sequence current sum and cause the deficiency of protective device malfunction or tripping, to improve the reliability of protective device.
Technical scheme of the present invention is: a kind of distribution one-phase ground protection method based on zero-sequence current Sudden Changing Rate fitting a straight line direction, for resonant earthed system, when a feeder line generation single phase ground fault wherein, at first intercept the zero-sequence current of the bus residual voltage in short time-window and each feeder line after fault it is carried out to wavelet decomposition, and extract respectively the wavelet coefficient of power frequency place frequency band; Then utilize least square method to carry out fitting a straight line one time to the wavelet coefficient extracted, and solve the slope value of each straight line; Finally by the bus residual voltage slope value of a corresponding straight line respectively the slope value of a straight line corresponding with each feeder line zero-sequence current multiply each other; when being less than zero, product judges this feeder line generation forward fault; the protection component action; judge this feeder line generation reverse fault when product is greater than zero, protection component is failure to actuate.
Described one-phase ground protection method concrete steps are as follows:
A, when feeder line generation single phase ground fault, the bus residual voltage after the intercepting fault in short time-window and the zero-sequence current of each feeder line carry out wavelet decomposition to it, and extract respectively the wavelet coefficient of power frequency place frequency band;
B, utilize least square method respectively the wavelet coefficient of bus residual voltage and each feeder line zero-sequence current power frequency place frequency band to be carried out to fitting a straight line one time, and solve the slope value of each straight line;
C, by the bus residual voltage slope value of a corresponding straight line
a u0
the slope value of a straight line corresponding with each feeder line zero-sequence current respectively
a i0
(
j) multiply each other, product representation is:
S(
j)=
a u0
×
a i0
(
j) （1）
In formula:
j=1,2,3,
n,
nnumber for feeder line;
D, general
s(
j) with null value, compare, build following protection component operating criterion:
When
s(
j) 0 o'clock, be defined as
jbar feeder line generation positive direction fault, the protection component action, cut off this feeder line;
When
s(
j) 0 o'clock, be defined as
jbar feeder line generation reverse direction failure, protection component is failure to actuate.
After fault, the short time-window length of the zero-sequence current data cutout of bus residual voltage and each feeder line is 0.1ms.
Operation principle of the present invention is: after resonant earthed system generation single phase ground fault, bus residual voltage and each feeder line zero-sequence current can be undergone mutation, and fault feeder and perfect feeder line sudden change opposite direction.The sudden change direction difference of fault feeder zero-sequence current under positive and negative different fault initial phase, but the sudden change direction of fault feeder zero-sequence current all the time with the sudden change opposite direction that perfects feeder line zero-sequence current and bus residual voltage.Utilize this characteristic can build the protection component operating criterion.
After feeder line generation single phase ground fault, for fear of the impact of arc suppression coil compensation effect, intercepting bus residual voltage and each feeder line zero-sequence current data analysis in the short time-window after fault occurs before the arc suppression coil effect.If now the feeder line zero-sequence current is less; interference signal is particularly outstanding on the impact of characteristic signal; for making the guard method reliability higher; zero-sequence current to the bus residual voltage in short time-window and each feeder line carries out wavelet decomposition to it, and extracts respectively the object of the wavelet coefficient of power frequency place frequency band as further analysis.Because interference signal is generally high-frequency signal, power frequency place frequency band is low-frequency band, and the interference signal therefore decomposed on the power frequency band has obtained obvious weakening.
If discrete signal is
x(
n), under decomposition scale, it is carried out after small echo decomposed, the signal component institute inclusion information obtained as the formula (2),
In formula:
d j(
n) be the wavelet coefficient of signal high fdrequency component;
a j(
n) be the wavelet coefficient of signal low frequency component;
f s sample frequency for signal;
j=1,2,3,
m,
mfor maximum decomposition scale.Original signal sequence
x(
n) can be expressed as each component and, that is:
x(
n)=
D 1(
n)+
A 1(
n)=
D 1(
n)+
D 2(
n)+
A 2(
n)=…=
（3）
Wherein, power frequency place frequency band is the frequency band at 50Hz place;
Utilize least square method respectively the wavelet coefficient of bus residual voltage and each feeder line zero-sequence current power frequency place frequency band to be carried out to fitting a straight line one time, and solve the slope value of each straight line.The slope value of the straight line that the bus residual voltage is corresponding is labeled as
a u0
, the slope value of the straight line that each feeder line zero-sequence current is corresponding is labeled as
a i0
(
j),
j=1,2,3,
n,
nnumber for feeder line
nnumber for feeder line.
a u0
with
a i0
(
j) characterized respectively the sudden change direction of bus residual voltage and the sudden change direction of each feeder line zero-sequence current.
The principle of a fitting a straight line of least square method is: known point set
, intend obtaining function expression by matching
, make
minimum.Its specific implementation process is: establishing the linear equation that matching obtains is
y=
kx+
b, error expression is
, respectively to its about
kwith
bdifferentiate also makes it equal zero:
So,
,
.
If
,
,
,
.
Equation simplification becomes:
Solve
with
:
,
, wherein
kbe the slope value of a straight line after matching.
By the bus residual voltage slope value of a corresponding straight line respectively the slope value of a straight line corresponding with each feeder line zero-sequence current obtained product by multiplying each other:
s(
j)=
a u0
*
a i0
(
j), due to the sudden change direction of fault feeder zero-sequence current all the time with the sudden change opposite direction that perfects feeder line zero-sequence current and bus residual voltage, therefore work as
s(
j) 0 o'clock, can stipulate
jthe positive direction fault has occurred in feeder line, when
s(
j) 0 o'clock, can stipulate
jbar feeder line generation reverse direction failure.So build the protection component operating criterion, be: when
s(
j) 0 o'clock, be defined as
jbar feeder line generation positive direction fault, the protection component action, cut off this feeder line; When
s(
j) 0 o'clock, be defined as
jbar feeder line generation reverse direction failure, protection component is failure to actuate.
The invention has the beneficial effects as follows:
1, in the short time-window of this method after fault occurs, intercepting bus residual voltage and feeder line zero-sequence current data are as utilizing object, and now arc suppression coil is also to compensating system, so the method has been avoided the impact of arc suppression coil compensation effect.
2, the bus residual voltage of intercepting and feeder line zero-sequence current are decomposed to power frequency place frequency band by wavelet transformation is low-frequency band in the present invention, has effectively eliminated the impact of high-frequency interferencing signal, has improved the reliability of protection.
3, whether the action of this method protection component only depends on the sudden change direction of this feeder line zero-sequence current and the sudden change direction of bus residual voltage; do not rely on the relevant information of other feeder lines; avoid having used the colony amplitude comparison phase comparing method; be greater than the special circumstances of All other routes zero-sequence current sum for the non-fault line zero-sequence current, higher protection reliability is still arranged.
The accompanying drawing explanation
The resonant earthed system simulation model that Fig. 1 is the embodiment of the present invention 1 and embodiment 2;
Fig. 2 is bus residual voltage ripple and each feeder line zero-sequence current oscillogram in window during 0.1ms after the embodiment of the present invention 1 fault;
Fig. 3 is bus residual voltage ripple and the wavelet coefficient of each feeder line zero-sequence current on the frequency band of power frequency place in window during 0.1ms after the embodiment of the present invention 1 fault;
Fig. 4 is bus residual voltage ripple and each feeder line zero-sequence current oscillogram in window during 0.1ms after the embodiment of the present invention 2 faults;
Fig. 5 is bus residual voltage ripple and the wavelet coefficient of each feeder line zero-sequence current on the frequency band of power frequency place in window during 0.1ms after the embodiment of the present invention 2 faults.
Embodiment
Embodiment 1: be illustrated in figure 16 distributions that feed out the 35kV neutral by arc extinction coil grounding of circuit composition, the G in this electrical network is infinitely great power supply; T is main transformer, and no-load voltage ratio is 110 kV/35kV, and connection set is YN/d11; China's power distribution network main transformer distribution voltage side is generally delta connection, and there is not neutral point in system, and when system adopts the resonance grounding mode, need obtain can be for the neutral point of grounding through arc, and setting up grounding transformer is exactly best way, T herein
zit is the zigzag transformer for the special use of compensation network ground connection; L is arc suppression coil, the damping resistance that R is arc suppression coil.Circuit adopts overhead transmission line, overhead line-cable hybrid line and three kinds of circuits of cable line, and the numbering of six feeder lines is followed successively by
l 1,
l 2,
l 3...
l 6, wherein,
l 1for overhead wire, length is 15km;
l 2for cable, length is 6km;
l 3for overhead wire, length is 18km;
l 4for the cable joint line, cable length is 5km, and overhead wire length is 12 km;
l 5for overhead wire, length is 30km;
l 6for cable, length is 8km.Load is selected the firm power load model, wherein
p=800
kW,
q=140
kVar;
r 1,
r 2,
r 3...
r 6for protection component, the direction of its upward arrow is the positive direction that protection component is installed.
Now suppose feeder line
l 1apart from the bus 5km A of place, single phase ground fault occurs mutually, earth resistance 20 Ω, the fault angle is 90 °, sample frequency is 100kHz.After fault, the oscillogram of the bus residual voltage in window and each feeder line zero-sequence current is as shown in Figure 2 during 0.1ms.Utilize the db4 small echo to carry out 6 layers of wavelet decomposition to bus residual voltage and each feeder line zero-sequence current, while obtaining after fault 0.1ms, in window, bus residual voltage ripple and the wavelet coefficient of each feeder line zero-sequence current on the frequency band of power frequency place be as shown in Figure 3.Utilize least square method respectively the wavelet coefficient of bus residual voltage and each feeder line zero-sequence current power frequency place frequency band to be carried out to fitting a straight line one time, and it is as shown in table 1 to solve the slope value of each straight line.
According to the result of calculation of formula (1) and table 1, can try to achieve:
S(
j)=[-6.26×10
11 2.04×10
11 2.28×10
10 2.06×10
11 2.12×10
10 1.72×10
11]
Wherein,
s(1)=-6.26 * 10
11<0, protection component
r 1detect as positive direction fault, protection component
r 1start and disconnect feeder line
l 1.And
s(2),
s(3),
s(4),
s(5) and
s(6) all be greater than zero, protection component
r 2,
r 3...
r 6detect as negative direction fault, protection component
r 2,
r 3...
r 6be failure to actuate.The protection action is consistent with the hypothesis demand, and the protection action is correct.
Embodiment 2: the distribution network systems of neutral by arc extinction coil grounding as shown in Figure 1, system parameters is identical with embodiment 1.Now suppose feeder line
l 2apart from the bus 4km A of place, single phase ground fault occurs mutually, 90 °, the initial phase angle of fault, fault resistance is 20 Ω, sample frequency is 100kHz.After fault, the oscillogram of the bus residual voltage in window and each feeder line zero-sequence current is as shown in Figure 4 during 0.1ms.Utilize the db4 small echo to carry out 6 layers of wavelet decomposition to bus residual voltage and each feeder line zero-sequence current, while obtaining after fault 0.1ms, in window, bus residual voltage ripple and the wavelet coefficient of each feeder line zero-sequence current on the frequency band of power frequency place be as shown in Figure 5.Utilize least square method respectively the wavelet coefficient of bus residual voltage and each feeder line zero-sequence current power frequency place frequency band to be carried out to fitting a straight line one time, the slope value that solves each straight line is as shown in table 2.
According to the result of calculation of formula (1) and table 2, can try to achieve:
S(
j)=[ 1.83×10
11 -3.88×10
12 1.96×10
11 1.81×10
12 1.86×10
11 1.51×10
12 ]
Wherein,
s(2)=-3.88 * 10
12<0, protection component
r 2detect as positive direction fault, protection component
r 2start and disconnect feeder line
l 2.And
s(1),
s(3),
s(4),
s(5) and
s(6) all be greater than zero, protection component
r 1,
r 3...
r 6detect as negative direction fault, protection component
r 1,
r 3...
r 6be failure to actuate.The protection action is consistent with the hypothesis demand, and the protection action is correct.
The above is explained in detail the specific embodiment of the present invention by reference to the accompanying drawings, but the present invention is not limited to above-mentioned execution mode, in the ken possessed those of ordinary skills, can also under the prerequisite that does not break away from aim of the present invention, make various variations.
Claims (3)
1. the distribution one-phase ground protection method based on zero-sequence current Sudden Changing Rate fitting a straight line direction, it is characterized in that: for resonant earthed system, when a feeder line generation single phase ground fault wherein, at first intercept the zero-sequence current of the bus residual voltage in short time-window and each feeder line after fault it is carried out to wavelet decomposition, and extract respectively the wavelet coefficient of power frequency place frequency band; Then utilize least square method to carry out fitting a straight line one time to the wavelet coefficient extracted, and solve the slope value of each straight line; Finally by the bus residual voltage slope value of a corresponding straight line respectively the slope value of a straight line corresponding with each feeder line zero-sequence current multiply each other; when being less than zero, product judges this feeder line generation forward fault; the protection component action; judge this feeder line generation reverse fault when product is greater than zero, protection component is failure to actuate.
2. the distribution one-phase ground protection method based on zero-sequence current Sudden Changing Rate fitting a straight line direction according to claim 1, it is characterized in that: described one-phase ground protection method concrete steps are as follows:
A, when feeder line generation single phase ground fault, the bus residual voltage after the intercepting fault in short time-window and the zero-sequence current of each feeder line carry out wavelet decomposition to it, and extract respectively the wavelet coefficient of power frequency place frequency band;
B, utilize least square method respectively the wavelet coefficient of bus residual voltage and each feeder line zero-sequence current power frequency place frequency band to be carried out to fitting a straight line one time, and solve the slope value of each straight line;
C, by the bus residual voltage slope value of a corresponding straight line
a u0
the slope value of a straight line corresponding with each feeder line zero-sequence current respectively
a i0
(
j) multiply each other, product representation is:
S(
j)=
a u0
×
a i0
(
j) （1）
In formula:
j=1,2,3,
n,
nnumber for feeder line;
D, general
s(
j) with null value, compare, build following protection component operating criterion:
When
s(
j) 0 o'clock, be defined as
jbar feeder line generation positive direction fault, the protection component action, cut off this feeder line;
When
s(
j) 0 o'clock, be defined as
jbar feeder line generation reverse direction failure, protection component is failure to actuate.
3. the distribution one-phase ground protection method based on zero-sequence current Sudden Changing Rate fitting a straight line direction according to claim 1 and 2 is characterized in that: after fault, the short time-window length of the zero-sequence current data cutout of bus residual voltage and each feeder line is 0.1ms.
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Cited By (11)
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|---|---|---|---|---|
| CN103760461A (en) * | 2014-01-14 | 2014-04-30 | 昆明理工大学 | Bus protection method based on sudden-change direction of fault current containing power frequency bands |
| CN104393580A (en) * | 2014-11-05 | 2015-03-04 | 昆明理工大学 | T-connection power grid transient state quantity unit protection method utilizing voltage and current abrupt change quantity wavelet coefficient correlation analysis |
| CN107408812A (en) * | 2015-01-15 | 2017-11-28 | Nse股份公司 | Method and apparatus for identifying the earthing fault direction in three phase network |
| CN109283428A (en) * | 2018-08-22 | 2019-01-29 | 昆明理工大学 | A kind of feeder line exit single-phase earthing transient based protection method based on the transformation of zero-sequence component higher difference |
| CN110579672A (en) * | 2019-07-11 | 2019-12-17 | 国网江苏省电力有限公司徐州供电分公司 | Power transmission line fault detection system and method based on energy characteristic analysis |
| CN110879330A (en) * | 2019-12-02 | 2020-03-13 | 昆明理工大学 | Power distribution network single-phase earth fault development situation discrimination method based on zero sequence volt-ampere curve area |
| CN112649694A (en) * | 2019-10-12 | 2021-04-13 | 南京南瑞继保电气有限公司 | Method for judging single-phase earth fault of small-current grounding system |
| CN113567806A (en) * | 2021-07-02 | 2021-10-29 | 上海思源光电有限公司 | Small current fault line selection method, system, terminal and medium |
| CN113824095A (en) * | 2021-08-26 | 2021-12-21 | 西安理工大学 | Method for setting distance protection zero sequence current compensation coefficient of overhead-cable hybrid line |
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| CN103760461A (en) * | 2014-01-14 | 2014-04-30 | 昆明理工大学 | Bus protection method based on sudden-change direction of fault current containing power frequency bands |
| CN104393580A (en) * | 2014-11-05 | 2015-03-04 | 昆明理工大学 | T-connection power grid transient state quantity unit protection method utilizing voltage and current abrupt change quantity wavelet coefficient correlation analysis |
| CN104393580B (en) * | 2014-11-05 | 2017-06-13 | 昆明理工大学 | A kind of T of utilization voltage x current Sudden Changing Rate wavelet coefficient correlation analysis gets access to grid transient cell protection method |
| CN107408812A (en) * | 2015-01-15 | 2017-11-28 | Nse股份公司 | Method and apparatus for identifying the earthing fault direction in three phase network |
| CN107408812B (en) * | 2015-01-15 | 2018-12-07 | Nse股份公司 | The method and apparatus of earthing fault direction in three phase network for identification |
| CN109283428A (en) * | 2018-08-22 | 2019-01-29 | 昆明理工大学 | A kind of feeder line exit single-phase earthing transient based protection method based on the transformation of zero-sequence component higher difference |
| CN110579672A (en) * | 2019-07-11 | 2019-12-17 | 国网江苏省电力有限公司徐州供电分公司 | Power transmission line fault detection system and method based on energy characteristic analysis |
| CN112649694B (en) * | 2019-10-12 | 2023-11-17 | 南京南瑞继保电气有限公司 | Method for judging single-phase grounding fault of low-current grounding system |
| CN112649694A (en) * | 2019-10-12 | 2021-04-13 | 南京南瑞继保电气有限公司 | Method for judging single-phase earth fault of small-current grounding system |
| CN110879330A (en) * | 2019-12-02 | 2020-03-13 | 昆明理工大学 | Power distribution network single-phase earth fault development situation discrimination method based on zero sequence volt-ampere curve area |
| CN113567806A (en) * | 2021-07-02 | 2021-10-29 | 上海思源光电有限公司 | Small current fault line selection method, system, terminal and medium |
| CN113824095A (en) * | 2021-08-26 | 2021-12-21 | 西安理工大学 | Method for setting distance protection zero sequence current compensation coefficient of overhead-cable hybrid line |
| CN113824095B (en) * | 2021-08-26 | 2024-08-06 | 西安理工大学 | Method for setting distance protection zero-sequence current compensation coefficient of overhead-cable hybrid line |
| CN114268076A (en) * | 2021-12-08 | 2022-04-01 | 广东电网有限责任公司 | Zero sequence current protection method, zero sequence current protection system, electronic equipment and storage medium |
| CN114268076B (en) * | 2021-12-08 | 2024-01-19 | 广东电网有限责任公司 | Zero sequence current protection method, system, electronic equipment and storage medium |
| CN114725916A (en) * | 2022-05-16 | 2022-07-08 | 河北伟正电力技术有限公司 | Single-phase grounding flexible reverse automatic compensation system and control method thereof |
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