CN104865501A - Small current grounding line selection method - Google Patents
Small current grounding line selection method Download PDFInfo
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- CN104865501A CN104865501A CN201510334025.XA CN201510334025A CN104865501A CN 104865501 A CN104865501 A CN 104865501A CN 201510334025 A CN201510334025 A CN 201510334025A CN 104865501 A CN104865501 A CN 104865501A
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- current
- circuit
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- phase
- spill current
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Abstract
The invention provides a small current grounding line selection method and belongs to the field of power system relay protection and power dispatching and operation. The method comprises the following steps: S1, when grounding failure of lines occurs, judging grounding phases and types through busbar voltage of the lines; S2, after waiting for preset time, judging whether the grounding phenomenon disappears or not, if yes, shifting to the S5; otherwise, shifting to the S3; S3, obtaining differential current of each line by calculating; S4, selecting and comparing the differential current of each line to confirm the grounding line; S5, finishing.
Description
Technical field
The invention belongs to relay protection of power system and power scheduling runs field, be specifically related to a kind of small current earthing wire-selecting method.
Background technology
In Neutral point nonearthing system, during circuit generation ground connection, each outlet of this circuit place bus all can produce the very little zero-sequence current of amplitude, causes very large difficulty to faulty line location.
The technical method of current this problem of solution mainly contains two kinds, one injects harmonic high frequency wave source at bus place, circuit place, ground path is found by high-frequency harmonic electric current, but high-frequency harmonic makes the impedance component of voltage transformer (VT) increase, line-to-ground fault may make it saturated, and serious will burn out this equipment; Another kind is each line outlet installing residual voltage, current transformer, determines ground path by the zero-sequence current of more every bar circuit, however this technology to produce third harmonic resistivity to iron and steel impact load poor, may erroneous judgement be caused.All there is a significant problem in these two kinds of technology in addition, and namely Small Electric Current Earthing And Routing Device must be installed by transformer station.If not this device, according to " Shan Dongdi county electric power system dispatching control and management code " the 237th article regulation, what regulation and control personnel on duty can only carry out non-selectivity to all circuits of bus successively according to load importance draws road, has a strong impact on customer power supply reliability.
Summary of the invention
The object of the invention is to solve the difficult problem existed in above-mentioned prior art, a kind of small current earthing wire-selecting method is provided, in the impact avoiding high-frequency harmonic on voltage transformer (VT), while effective suppression iron and steel impact load third harmonic interference, realize transformer station and do not possessing ground path selecting properly in Small Electric Current Earthing And Routing Device situation.
The present invention is achieved by the following technical solutions:
A kind of small current earthing wire-selecting method, comprising:
S1, when ground connection occurs circuit, judges the separate and type of ground connection by circuit place busbar voltage;
S2, after waiting for the schedule time, judges whether grounding phenomenon disappears, if so, then proceeds to S5; If not, then S3 is proceeded to;
S3, asks for the spill current of every bar circuit;
S4, chooses and more each circuit spill current, determines ground path;
S5, terminates.
Described method is equipped with current acquisition element mutually the every of all circuits of Neutral point nonearthing system.
Described current acquisition element adopts current transformer, and its accuracy requirement is 0.5 grade.
Described S1 is achieved in that
Occur declining if circuit place bus A phase voltage is fallen, rising appears in B phase voltage and C phase voltage, and data value before isochrone voltage AB, BC, CA maintenance ground connection, be then judged as circuit A phase ground connection;
If rising appears in circuit place bus A phase voltage, declining appears in B phase voltage and C phase voltage, then ground connection when being judged as that circuit B, C are identical.
The described schedule time is 10 minutes.
Described S3 is achieved in that
Ask for the spill current of all circuits of reflection ground strap, specific as follows:
A B spill current is | I
nA-I
nB|;
B C spill current is | I
nB-I
nC|;
C A spill current is | I
nC-I
nA|;
Wherein, I
nAfor A phase current, I
nBfor B phase current, I
1Cfor C phase current, n is circuit number.
Described S4 is achieved in that
Access line spill current:
If A phase ground connection occurs circuit, then spill current gets AB spill current or CA spill current;
Ground connection when if circuit generation B, C is identical, then spill current gets AB spill current or AC spill current;
Compare the spill current of each circuit, find maximum spill current, the circuit that this maximum spill current is corresponding is ground path.
The described spill current to each circuit compares, and finds maximum spill current to be achieved in that
If the spill current of kth bar circuit meets the following conditions:
I
kdc＝max(I
1dc，I
2dc，…，I
kdc，…，I
ndc)，k＝1，2，…，n (1)
I
jdc＝|I
jgz-I
jfgz|，j＝1，2，…，n
In formula, I
kdcfor the spill current of kth bar circuit;
I
jdcfor the spill current of jth bar circuit;
I
jgzfor jth bar line fault phase current;
I
jfgzfor jth bar circuit healthy phases electric current.
Compared with prior art, the invention has the beneficial effects as follows:
(1) from technical feature, not only avoid the impact of high-frequency harmonic on voltage transformer (VT), and effectively suppress iron and steel impact load third harmonic interference.
(2) from applicable object, even if Small Electric Current Earthing And Routing Device is not installed by transformer station, regulation and control personnel on duty also can utilize this technology to carry out selectively drawing road, improve customer power supply reliability.
(3) implement from technology, this technology by the PAS system of regulation automatization or can be realized by the mode of manufacturing system plug-in unit, saves and installs Small Electric Current Earthing And Routing Device equipment cost and maintenance cost in transformer station.
Accompanying drawing explanation
The distribution of current during line-to-ground of Fig. 1 Neutral point nonearthing system
Voltage vector relation (dotted line is before ground connection, and solid line is after ground connection) before and after Fig. 2 a ground connection
Fig. 2 b ground path current phasor relation
The step block diagram of Fig. 3 the inventive method.
Embodiment
Below in conjunction with accompanying drawing, the present invention is described in further detail:
One, novel small current earthing wire-selecting method
Novel small current earthing wire-selecting method: require that all circuits of Neutral point nonearthing system are often equipped with current acquisition element mutually---current transformer (CT), according to Small Electric Current Earthing And Routing Device technical manual to zero-sequence current accuracy requirement, this method adopts 0.5 grade (measurement level) of same precision.The inventive method as shown in Figure 3, comprising:
1., when ground connection occurs circuit, judge the separate and type of ground connection by circuit place busbar voltage
During circuit A phase ground connection, this circuit place bus A phase voltage is fallen and is occurred that certain amplitude declines (if do not consider residual voltage, A phase voltage can become 0), corresponding B, C phase voltage occurs that certain amplitude rises (if do not consider A phase residual voltage, B, C phase voltage can rise to line voltage, i.e. 1.732 times of phase voltage before ground connection), isochrone voltage AB, BC, CA keep data value before ground connection substantially.When circuit B, C are identical during ground connection, place bus A phase voltage occurs that certain amplitude rises (if do not consider B, C phase residual voltage, A phase voltage can rise to line voltage, i.e. 1.732 times of phase voltage before ground connection), corresponding B, C phase voltage will occur that certain amplitude declines (if do not consider residual voltage, B, C phase voltage can become 0).Namely by busbar voltage change in place during ground connection, the separate and type of line-to-ground can be judged.
2., after waiting for 10 minutes, ask for the spill current of every bar circuit
In 10 minutes after there is ground connection, circuit impermanency earth fault may disappear automatically, simultaneously after ground connection line current reach relatively stable before have a temporal variations process, even if consider the current transformer also different qualities of identical type, now get line current and may there is comparatively big error, therefore need wait 10 minutes.(schedule regulation, when allowing Neutral point nonearthing system that ground connection occurs, failure operation 2 hours.)
Ask for the spill current of all circuits of reflection ground strap, list table 1:
| line name | a phase current | b phase current | c phase current | a B spill current | b C spill current | c A spill current |
| circuit 1 | i 1A | i 1B | i 1C | | I 1A-I 1B| | | I 1B-I 1C| | | I 1C-I 1A| |
| circuit 2 | i 2A | i 2B | i 2C | | I 2A-I 2B| | | I 2B-I 2C| | | I 2C-I 2A| |
| .。。 | ||||||
| circuit n | i nA | i nB | i nC | | I nA-I nB| | | I nB-I nC| | | I nC-I nA| |
Table 1
3. choose and more each circuit spill current
Access line spill current: if A phase ground connection occurs circuit, then spill current can get AB phase or CA phase spill current; Ground connection when if circuit generation BC is identical, then spill current can get AB phase or AC phase spill current.Namely the spill current chosen to meet wherein one for fault phase, another is healthy phases.
More each circuit spill current: if the spill current of certain circuit is the maximum spill current of all circuits, so this circuit is exactly ground path.
4. selection method criterion
Ground connection after reaching stable state is there is, if the current differential Ikd of kth bar circuit (faulted phase current-healthy phases electric current) meets the following conditions at Neutral point nonearthing system:
I
kdc＝max(I
1dc，I
2dc，…，I
kdc，…，I
ndc)，k＝1，2，…，n (1)
I
jdc＝|I
jgz-I
jfgz|，j＝1，2，…，n
In formula, I
kdcfor kth bar circuit spill current;
I
jdcfor jth bar circuit spill current;
I
jgzfor jth bar line fault phase current;
I
jfgzfor jth bar circuit healthy phases electric current.
Two, know-why
1. know-why
After ground connection occurs kth bar circuit, the equivalent capacity electric current of all circuits of place bus all can flow to this circuit by earth point, i.e. I
k0=I
10+ I
20+ ... + I
n0, as shown in Figure 1.Because ungrounded line capacitance electric current is much smaller than ground path capacitance current, the three-phase current change of current measurement device collection almost can be ignored.
From ground path angle, before not there is ground connection, the three-phase current of circuit current measurement device collection is load current I
aF, I
bF, I
cF.After there is A phase ground connection, just system voltage vector neutral point there occurs skew, not influential system line voltage, the therefore load current I of ground path
aF, I
bF, I
cFaffect limited by ground connection.In addition, after there is A phase ground connection, the equivalent capacity of all circuits of place bus sends capacitance current and is all collected to earth point, therefore kth bar line-to-ground electric current I
k0aobvious capacitive, as shown in Figure 2 a and 2 b.
According to operating experience, in Neutral point nonearthing system, ground current is usually much smaller than load current, and load current is almost 0 with measurement electric current angle theta, can show that the A phase current of this line current measuring sensor collection is I thus
a≈ I
aF+ I
o; And the electric current I of B, C current phasor measurement
b, I
caffect by ground connection hardly, can be similar to and think I
b=I
c=I
aF.Therefore, the ground current I of this circuit
o=I
a-I
bor I
a-I
c, i.e. faulted phase current and healthy phases difference between currents.
From ungrounded circuit angle, line capacitance electric current is much smaller than ground path capacitance current, and the three-phase current change of current measurement device collection almost can be ignored, therefore current differential I
dc≈ 0.
Conclusion below can be drawn: the maximum circuit of line current difference is ground path, namely meets formula (1) by above-mentioned analysis.
2. technical characterstic
(1) impact of high-frequency harmonic on voltage transformer (VT) is avoided
In whole method implementation process, any high-frequency harmonic is not injected to system, let alone the impact on voltage transformer (VT).
(2) iron and steel impact load third harmonic interference is suppressed
Iron and steel impact load triple harmonic current mathematic(al) representation is I
a3=√ 2I
m3cos (3* ω t); I
b3=√ 2I
m3cos (3* (ω t-120 °)); I
c3=√ 2I
m3cos (3* (ω t+120 °)), namely meets I
a3=I
b3=I
c3.(according to international standard, I
a3, I
b3, I
c3current phasor is represented) after overstriking.
Under third harmonic interference, line current vector expression becomes
I
1＝I
11+I
13，1＝A，B，C。(2) in formula, I
11represent fundametal compoment;
I
13represent third-harmonic component.
Need in the procedure of existing Small Electric Current Earthing And Routing Device to do vector, i.e. I to each phase current
0=I
a+ I
b+ I
ceven if when not having line-to-ground, circuit also can reflect larger ground current, i.e. I
0=3I
a3; And need in the process of small current earthing wire-selecting method proposed by the invention respectively to carry out spill current computing mutually to circuit, can by the public part I of A, B, C phase current
a3, I
b3, I
c3run cancellation by subtraction, therefore part impact load third harmonic interference can be suppressed.
Technique scheme is one embodiment of the present invention, for those skilled in the art, on the basis that the invention discloses application process and principle, be easy to make various types of improvement or distortion, and the method be not limited only to described by the above-mentioned embodiment of the present invention, therefore previously described mode is just preferred, and does not have restrictive meaning.
Claims (8)
1. a small current earthing wire-selecting method, is characterized in that: described method comprises:
S1, when ground connection occurs circuit, judges the separate and type of ground connection by circuit place busbar voltage;
S2, after waiting for the schedule time, judges whether grounding phenomenon disappears, if so, then proceeds to S5; If not, then S3 is proceeded to;
S3, asks for the spill current of every bar circuit;
S4, chooses and more each circuit spill current, determines ground path;
S5, terminates.
2. small current earthing wire-selecting method according to claim 1, is characterized in that: described method is equipped with current acquisition element mutually the every of all circuits of Neutral point nonearthing system.
3. small current earthing wire-selecting method according to claim 2, is characterized in that: described current acquisition element adopts current transformer, and its accuracy requirement is 0.5 grade.
4. small current earthing wire-selecting method according to claim 3, is characterized in that: described S1 is achieved in that
Occur declining if circuit place bus A phase voltage is fallen, rising appears in B phase voltage and C phase voltage, and data value before isochrone voltage AB, BC, CA maintenance ground connection, be then judged as circuit A phase ground connection;
If rising appears in circuit place bus A phase voltage, declining appears in B phase voltage and C phase voltage, then ground connection when being judged as that circuit B, C are identical.
5. small current earthing wire-selecting method according to claim 4, is characterized in that: the described schedule time is 10 minutes.
6. small current earthing wire-selecting method according to claim 5, is characterized in that: described S3 is achieved in that
Ask for the spill current of all circuits of reflection ground strap, specific as follows:
AB spill current is | I
nA-I
nB|;
BC spill current is | I
nB-I
nC|;
CA spill current is | I
nC-I
nA|;
Wherein, I
nAfor A phase current, I
nBfor B phase current, I
1Cfor C phase current, n is circuit number.
7. small current earthing wire-selecting method according to claim 6, is characterized in that: described S4 is achieved in that
Access line spill current:
If A phase ground connection occurs circuit, then spill current gets AB spill current or CA spill current;
Ground connection when if circuit generation B, C is identical, then spill current gets AB spill current or AC spill current;
Compare the spill current of each circuit, find maximum spill current, the circuit that this maximum spill current is corresponding is ground path.
8. small current earthing wire-selecting method according to claim 7, is characterized in that: the described spill current to each circuit compares, and finds maximum spill current to be achieved in that
If the spill current of kth bar circuit meets the following conditions:
I
kdc＝max(I
1dc,I
2dc,…,I
kdc,…,I
ndc),k＝1,2,…,n (1)
I
jdc＝|I
jgz-I
jfgz|,j＝1,2,…,n
In formula, I
kdcfor the spill current of kth bar circuit;
I
jdcfor the spill current of jth bar circuit;
I
jgzfor jth bar line fault phase current;
I
jfgzfor jth bar circuit healthy phases electric current.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201510334025.XA CN104865501A (en) | 2015-06-16 | 2015-06-16 | Small current grounding line selection method |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201510334025.XA CN104865501A (en) | 2015-06-16 | 2015-06-16 | Small current grounding line selection method |
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|---|---|
| CN104865501A true CN104865501A (en) | 2015-08-26 |
Family
ID=53911469
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|---|---|---|---|
| CN201510334025.XA Pending CN104865501A (en) | 2015-06-16 | 2015-06-16 | Small current grounding line selection method |
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|---|---|
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105425109A (en) * | 2015-11-27 | 2016-03-23 | 天津大学 | Single-phase ground line selection method with function of accuracy improvement for small-current grounding system |
| CN110535116A (en) * | 2019-09-10 | 2019-12-03 | 北京华电瑞通电力工程技术有限公司 | A kind of arc extinction cabinet and small current neutral grounding system |
| CN112485714A (en) * | 2020-11-30 | 2021-03-12 | 云南电网有限责任公司电力科学研究院 | High-sensitivity ground fault detection and identification method and device |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN112485714A (en) * | 2020-11-30 | 2021-03-12 | 云南电网有限责任公司电力科学研究院 | High-sensitivity ground fault detection and identification method and device |
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Application publication date: 20150826 |