A kind of earthing protecting method of small current neutral grounding system
Technical field
The present invention relates to a kind of earthing protecting method of small current neutral grounding system.
Background technology
One adopts isolated neutral mode, low resistance grounding mode or through the grounding through arc mode mesolow electrical network of China; when system's generation earth fault; characteristic quantities such as the zero-sequence current size of ground path and direction are influenced greatly by system operation mode; bring difficulty for the judgement of ground protection, seriously influenced the reliability of power supply.
Therefore, when small current neutral grounding system generation earth fault, how to select faulty line fast and accurately, great Practical significance is arranged.
Traditional earthing protecting method has following several:
1, residual voltage (electric current) method
Principle: when earth fault took place, fault was met and is produced residual voltage and zero-sequence current.The amplitude size of this method judgement residual voltage or zero-sequence current is distinguished faulty line and non-fault line.
Shortcoming: in small current neutral grounding system generation earth fault, non-fault line also has residual voltage and zero-sequence current; In the system of grounding through arc, because fault current is compensated, the zero-sequence current of faulty line may be also littler than the zero-sequence current of non-fault line.So this method can't realize selectivity.
2, zero-sequence current power direction method
Principle: when earth fault takes place, 90 ° of the leading residual voltages of the zero-sequence current of non-fault line, 90 ° of faulty line zero-sequence current hysteresis residual voltages.
Shortcoming: this method only is applicable to the high pressure long transmission line of isolated neutral system, for arc suppression coil earthing system, because the compensating action of arc suppression coil, no longer lag behind 90 ° of residual voltages of the zero-sequence current of faulty line, along with the difference of taking off humorous degree, the angle of hysteresis changes between 90 ° and 270 °; For low resistance grounding system and low pressure short-term road, the angle of faulty line zero-sequence current and residual voltage changes between 90 ° and 180 °.The criterion of this method is all inapplicable.
3, zero sequence real component method
Principle: through the circuit of arc suppression coil string and resistance, when earth fault takes place, provide the zero-sequence current active component to faulty line, non-fault line does not have active current.
Shortcoming: this method only is applicable to through the high-tension line of arc suppression coil string and resistance (insulation resistance is very big, and direct-to-ground capacitance plays a leading role).For isolated neutral system, faulty line, non-fault line all do not have the zero sequence active current; And the non-fault line of low pressure short-term road also has active current, and this method can't realize selectivity.
Summary of the invention
The objective of the invention is provides a kind of earthing protecting method that is applicable to small current neutral grounding system in order to overcome the defective of prior art.
Technical scheme of the present invention is: a kind of earthing protecting method of small current neutral grounding system, comprise image data, deal with data and analysis data step, wherein,
Described image data step comprises:
1. calculate the admittance of the zero sequence over the ground Y of circuit by single-phase earthing test or line parameter circuit value
0kd
2. gather the residual voltage U that protection inserts in real time
0, zero-sequence current I
0
Described deal with data step comprises:
1. calculate circuit zero sequence admittance Y
0k
2. calculate circuit zero sequence compensation admittance Y '
0k
3. calculate circuit zero sequence compensation admittance angle φ
k
4. preserve the zero sequence compensation admittance angle φ of N cycle
kSequence;
Described analysis data step comprises:
1. judge zero sequence compensation admittance Y '
0kAmplitude, if surpass to start threshold value, judge zero sequence compensation admittance angle φ
k
If 2. 100 °<φ
k≤ 280 °, then be judged to be faulty line;
If 3. 80 °<φ
k≤ 100 °, then carry out the following step 4.;
4. investigate the zero sequence compensation admittance angle φ of the N cycle of storage
kSequence was if 170 °<φ once occurred
k≤ 280 °, then be judged to be faulty line;
5. the involution of whole group is judged.
Principle of the present invention is:
In the small current neutral grounding system, under normal operation, the three-phase ground capacitance of every circuit is identical, and under the effect of phase voltage, every phase all has one to be ahead of in the capacitance current inflow place of 90 ° of phase voltages, and the three-phase current sum is zero.In certain bar circuit generation metallicity or behind the resistance single phase ground fault, residual voltage will appear in total system; Occur zero-sequence current on non-fault line, its numerical value equals this line mutual-ground capacitor electric current sum, and the direction of capacitive character reactive power is that bus flows to circuit; Also occur zero-sequence current on faulty line, its numerical value equals the non-fault element zero-sequence current of total system sum, and the direction of capacitive character reactive power is that line flows is to bus.
As seen from Figure 1, suppose L
kBe non-fault line, L
1Be faulty line; g
k, b
kBe respectively circuit L
kElectricity over the ground lead and hold; g
sAnd b
sThe electricity that is respectively arc suppression coil is led and is held.
Among the present invention, for non-fault line: zero sequence admittance Y
0k=g
k+ jb
k, the algorithm of zero sequence compensation admittance is Y '
0k=Y
0k-Y
0kd, under one situation, zero sequence admittance Y
0kWith line-to-ground zero sequence admittance Y
0kdEquate that Y ' is arranged
0k=0; Insulation level descends after system's operation is long-time, and admittance increases over the ground, and 0≤φ is arranged this moment
k≤ 90 °.
For arc suppression coil: zero sequence admittance Y
0s=g
s-jb
s
For faulty line: zero sequence compensation admittance Y
01=-(Y
0s+ ∑ Y
0k(the g of)=-
s+ ∑ g
k)-j (b
s+ ∑ b
k), so 90 °≤φ is arranged
1≤ 270 °.
As can be seen, during line single phase grounding failure, the zero sequence admittance offset angle of faulty line satisfies 90 °≤φ
k≤ 270 °, the zero sequence admittance offset angle of non-fault line satisfies 0≤φ
k≤ 90 °, can distinguish faulty line and non-fault line according to the phase place of zero sequence admittance offset angle.But in actual applications, because the influence of the sampling precision and the error of calculation has the confusion region near 90 °.
In the confusion region, for non-fault line, zero sequence admittance offset angle is by the decision of capacity current over the ground of circuit; And for faulty line, system entails is through arc suppression coil earthing system, and is operated in the overcompensation state.Because the electric current of inductance can not suddenly change, and is initial in fault according to first half-wave principle, inductive current can not be at once with the capacitive earth current full remuneration of fault point.It is a transient process that earth current becomes inductance current by capacity current, and in this process, because the character of residual voltage does not change, initial in fault, zero sequence compensation admittance angle is at third quadrant; After entering steady-state process, because the compensating action of inductive current, zero sequence compensation admittance angle enters second quadrant.
So 80 °<φ in the confusion region
k≤ 100 °, can utilize first half-wave principle to do further judgement.If before zero sequence admittance offset angle enters the confusion region, once be in third quadrant, then be the fault circuit, otherwise be exactly non-fault line.Consider the influence of sampling error and system accuracy, the criterion that we will once be in third quadrant is made as N cycle before the confusion region, 170 °<φ once occurs
k≤ 280 °.
According to above-mentioned analysis; the present invention is provided with the zero sequence admittance criterion, can select faulty line fast and accurately when system's generation single phase ground fault; and be not subjected to the influence of system operation mode, we define this kind ground protection scheme and are " self adaptation zero sequence node-pair method ".
This method is implemented simple, and physical significance is clear, can realize the ground protection in the small current neutral grounding system accurately and rapidly.
Description of drawings
Fig. 1 is system model figure of the present invention
Fig. 2 is the flow chart of the embodiment of the invention 1
Fig. 3 is and the embodiment of the invention 1 small current neutral grounding system ground protection logical flow chart
Embodiment
The present invention is used to realize the ground protection of small current neutral grounding system, is that example is described further below with the ground protection:
A kind of earthing protecting method of small current neutral grounding system comprises image data, deal with data and analysis data step, wherein,
The image data step comprises:
1. calculate the admittance of the zero sequence over the ground Y of circuit by single-phase earthing test or line parameter circuit value
0kd
2. gather the residual voltage U that protection inserts in real time
0, zero-sequence current I
0
The deal with data step comprises:
1. calculate circuit zero sequence admittance Y
0k
2. calculate circuit zero sequence compensation admittance Y '
0k
3. calculate circuit zero sequence compensation admittance angle φ
k
4. preserve the zero sequence compensation admittance angle φ of 10 cycles
kSequence;
The analysis data step comprises:
1. judge zero sequence compensation admittance Y '
0kAmplitude, if surpass to start threshold value, judge zero sequence compensation admittance angle φ
k
If 2. 100 °<φ
k≤ 280 °, then be judged to be faulty line;
If 3. 80 °<φ
k≤ 100 °, then carry out the following step 4.;
4. investigate the zero sequence compensation admittance angle φ of 10 cycles of storage
kSequence was if 170 °<φ once occurred
k≤ 280 °, then be judged to be faulty line;
5. the involution of whole group is judged.
Above-mentioned steps, we are defined as " self adaptation zero sequence node-pair method ".
Small current neutral grounding system ground protection logic is seen Fig. 3 in the present embodiment, comprising:
1. the initialization of ground(preference) relay;
2. the ground protection entry condition is judged: be to guarantee that protection is reliable to start, any one satisfies condition in greater than threshold value greater than threshold value, residual voltage when zero-sequence current, and then protection starts;
3. judge " self adaptation zero sequence node-pair method " element state, as this element action, then ground protection action;
4. the involution of the whole group of ground protection is judged.
Can know according to top description; according to " self adaptation zero sequence node-pair method ", can realize the ground protection function of small current neutral grounding system accurately and rapidly, reliably accomplish the correct quick acting of faulty line; not malfunction of non-fault line, and be not subjected to the influence of system operation mode.